Download Science - Madhya Pradesh Textbook Corporation

SCIENCE
CLASS-10
Madhya Pradesh Rajya Shiksha Kendra, Bhopal
Year 2012
Price Rs. ............
I
Publication Year 2008
Reprint 2010, 2011, 2012
© Madhya Pradesh Rajya Shiksha Kendra, Bhopal
Direction
: Radheshyam Julania (I.A.S.), Commisioner, Rajya Shiksha Kendra, Bhopal
Guidance
: R.K. Jain, Addl. Mission Director, Rajya Shiksha Kendra, Bhopal.
: A.K. Dixit, Addl. Director, Rajya Shiksha Kendra,Bhopal
Coordination
: Shakuntala Shrivastava, Academic Coordinator, Rajya Shiksha Kendra,Bhopal
Subject Co-ordination : Brijesh Saxena, Rajya Shiksha Kendra,Bhopal
Co-Cordinator :
Physics : Brijesh Saxena, Rajya Shiksha Kendra, Bhopal.
Chemistry : Sanjay Chansoria, Lecturer, Rajya Shiksha Kendra, Bhopal
Biology : Ragini Uplopwar, Principal, Rajya Shiksha Kendra, Bhopal.
Writers and Moderators : Dr. S.M. Saxena, Retd. Professor (Biology), Bhopal, Dr. R.M. Shukla, Professor
(Biology) Govt. College Sarangpur (Rajgarh), Dr. Govind Ramani, Professor, L.B.S.
College, Harda, Dr. R.K. Shrivastava, Professor (Chemistry), Sarojini Naidu Girls College,
Bhopal, Amit Jain, Asst. Professor (Physics), M.L.B. College, Bhopal, R.S. Poddar,
Lecturer, Model Higher Secondary School, Bhopal, V.K. Jain, Principal, Govt. H.S.
School Khader (Vidisha), Dr. Subodh Saxena Lecturer (Physics) Govt. College of
education Bhopal, K.D. Shrivastava, Lecturer (Physics), Model H.S. School, Bhopal,
Madhusudan Chaubey, Vice-Principal (Retd.), Shivpuri, M.K. Jain, Dist. Education Officer
(Retd.), Ujjain, Dr. Shobha Chaturvedi Lecturer (Chemistry), Govt. Maharana Pratap
H.S. School Bhopal, Manju Rathi Lecturer (Chemistry), Govt. Excellence H.S. School
Vidisha, Rakesh Chaudhary, Lecturer (Chemistry), Govt. Excellence H.S. School, Tirla
(Dhar), J.C. Sharma, Lecturer (Chemistry), Govt. Girls H.S. School, Niwali (Badwani),
Dr. Rehana Siddiqui, Lecturer (Biology), St. Francis H.S. School, Bhopal, V.K. Sanodiya,
Lecturer (Biology), Maharishi Vidya Mandir, Bhopal, Asha Saxena, Lecturer, DIET. Bhopal,
Rajesh Sharma, Lecturer (Biology), Govt. Maharana Pratap H.S. School, Bhopal.
Editors :
Physics : Dr. Kapoormal Jain, Professor, College of Excellence, Bhopal.
Chemistry : Dr. D.D. Mishra, Principal, Govt. College, Udaipura (Raisen)
Biology : Dr. Suman Trivedi, Professor, Govt. MVM, Bhopal
Translators :
Physics : Dr. Praveen Kumar Sharma, Lecturer, BUIT- Barkatullah University, Bhopal
Chemistry : Reshma Lala, Lecturer, Govt. Hr. Sec. School, Dobi, Annu S. Mathew,
Lect. Govt. Hr. Sec. School, Deewanganj,
Biology : Dr. S.M. Saxena, Retd. Prof. Bhopal, Dr. Suman Trivedi, Prof. MVM, Bhopal,
Rakhi Nema, Lecturer, Maharshi Dayanad School, Bhopal, Ajra Asifm Lecturer Govt.
College of Eduction, Bhopal.
Review : Dr. V.G. Jadhav, Ret. Prof. NCERT, Radha Krishnan K.C. (Sen. Lect.) Govt.
H.Sec. School, Gunga, Anjali Khanna, (Sen.Lect.), Jawaharlal Nehru School, BHEL,
Bhopal.
Cover Page :
Vikash Malviya
Design & Graphics: Media Graphics & Computer, Bhopal
Gratitude :
Rajya Shiksha Kendra, Bhopal is thankful to all those persons, institution and publisher
who has given their valuable contribution in making this text-book. Lastly, we are grateful
to all the educationists and parents for their timely suggestions to improvise the book.
II
Approved by M.P. Textbook Standing
Committee
1.
Dr. Govind Sharma, Former Additional Director (Higher Education), Chairman
Government of Madhya Pradesh, Gwalior
2.
Dr. Umrao Singh Choudhary
Former Vice Chancellor, Devi Ahilya University, Indore
Member
3.
Prof. Uday Jain, Former Principal, Vaishnav College, Indore
Member
4.
Dr. Subhash Gupta, Dean (Student Welfare),
Devi Ahilya University, Indore
Member
5.
Dr. (Smt.) Binay Rajaram, Trustee Bharat Bhawan (literature)
Prof. and Head, Hindi Deptt., Shri Satya Sai College for Women
Bhopal
Member
6.
Prof. Sureshwar Sharma, Former Vice Chancellor
Rani Durgavati University, Jabalpur
Member
7.
Dr. Manmohan Upadhyay, Educationist and former Vice President, Member
M.P. Sanskrit Board, Bhopal
8.
Shri Bhagirath Kumrawat, Educationist
100/45, Shivaji Nagar, Bhopal
9.
Commissioner, Madhya Pradesh Rajya Shiksha Kendra
Bhopal
10.
Commissioner, Public Instruction Madhya Pradesh, Bhopal
Member
11.
Secretary, Board of Secondary Education, M.P. Bhopal
Member
12.
Managing Director, M.P. Textbook Corporation, Bhopal
Member
13.
National Council of Educational Research & Training,
(Any One Representative)
Member
14.
Navodaya Vidhyalay, (Any One Representative)
Member
15.
Dr. Prem Bharti, Educationist & member, Rajya Karyakarini
Sarva Shiksha Abhiyan, M.P.
III
Member
Member Secretary
Guest Member
PREFACE
Present textbook has been developed on the basis of the guidelines of
National Curriculum Framework 2005 and adopted by the Board of Secondary
Education, Madhya Pradesh, Bhopal. The subjects like Physics, Chemistry,
Biology and Environmental Studies are integrated in this textbook. Keeping
the continuity of learning in view the contents of the syllabus have been
rearranged to facilitate the smooth flow of learning of the subject.
Salient features of this textbook give a new dimension to its impact. The
contents of the chapters have been associated with daily life examples, ancient
scientific researches and the views of the researchers. The activities and
projects which can be easily done by students are also included at proper
places. This textbook is activity based so that students may acquire knowledge
by self learning. The thirst to know the unknown gives rise to science,
questions at the end of important topics provide them an opportunity to think
and find answers on their own and inspire them to carry forward their scientific
outlook.
Numerical examples are given to clarify the concepts wherever
necessary and the tough and challenging thoughts which could not be
included at this level are provided in the box as extra material. At the end of
each chapter, points to remember and questions are given which would enable
the students to test their subject knowledge.
Emphasis has been given to the concepts in place of definitions and
technical terms. It is expected that the students will develop a scientific
approach while reading the book.
This is an experimental edition of the textbook. Positive criticism is
always welcome for the enrichment of the textbook.
Commissioner
Rajya Shiksha Kendra
Bhopal
IV
Subject - Science
Class - 10th
Maximum Marks : 100
Theory : 75
Practical : 25
Unit. 1.
Max. Marks 05
Universe : The solar system, planets, asteroids, comets and meteorites, formation of the
earth, structure and development of the earth, stars, galaxies, Akash Ganga, Constellations,
structure and Theories of universe.
Space Exploration :- History of space exploration, basic knowledge of the history of space
satellites, artificial satellites and their orbits, use of artificial satellites in communication,
meteorological observations, remote sensing and space exploration, basic knowledge of
information technology.
Unit. 2.
Max. Marks 07
Light :- Nature of light, reflection of light, laws of reflection, reflection from plane and spherical
surfaces, plane mirror, concave and convex mirror, sign convention, mirror formula,
magnification.
Refraction of light : Laws of Refraction, refraction of light through rectangular slab, formation
of images through convex and concave lens, deduction of lens formula, sign convention,
power of lenses. some optical phenomena in Nature (twinkling of stars, mirage, defects of
vision and their correction)
Optical Instruments : Construction and working of compound microscope and astronomical
telescope.
Dispersion : Dispersion of white light by a prism, components of white light, colours of
objects, superposition of the primary colours of light.
Unit. 3.
Max. Marks 08
Electricity :- Electricity and its effects : Difference between electric potential and potential
difference, current electricity, Ohm's Law, electric resistance, combination of electric resistance
(Series and Parallel), Thermal effects of electric current and its uses, Electric power, SI unit
of electrical energy.
Chemical Effect of Current : Electrolysis, Faradays law of Electrolysis electroplating,
electrochemical cells, dry cell.
Magnetic Effect of Electric Current : Magnetic field due to a current in a straight conductor,
magnetic field due to a current in a circular loop and a current carrying solenoid, electromagnetic
induction, electric motor and generator (D.C.), Direct current and Alternating Current, domestic
electric circuits, safety precautions while using electricity.
Unit. 4.
Max. Marks 05
Sources of Energy :- Renewable and non-renewable energy sources : Sun as a source of
renewable energy (solar cooker, solar water heater, solar cells) wind energy, hydro energy
(Tidal, Ocean, Ocean Thermal energy, Hydro-electricity), Mangal Turbine (fuel less turbine),
wind energy, geothermal, wood, biogas, hydrogen and alcohol.
V
Non renewable Sources : Fossils fuels (coal, petroleum and natural gas) combustion calorific
value of a fuel, selection of a good fuel, characteristics of a good fuel, nuclear fusion and
nuclear fission, nuclear chain reaction, nuclear reactor (basic principle and safety measures)
Advantages and Disadvantages of Nuclear Power, Judicious use of Energy.
Unit. 5.
Max. Marks 6
Rate of chemical and Chemical equilibrium :- Elementary idea of rate of chemical reaction,
slow and fast chemical reactions; reversible and irreversible reactions, chemical equilibrium
dynamic nature only. acids and bases. pH scale, Thermal changes in chemical reaction.
Some important chemical compounds :- Method of preparation / manufacture (only outline),
properties and using of washing soda, baking soda, bleaching powder and plaster of paris.
Manufacture of some important building materials lime, cement, glass and steel.
Unit. 6. Natural Resources
Marks - 9
Metals and non-metals :- Ores and minerals, metallurgy, enrichment of ores, extraction of
metal from ores, refinement and purification of metal with reference to Iron and aluminium,
activity series of metals, general properties and corrosion of metals, alloys, components,
properties and uses of steel; stainless steel, brass, magnesium. alloys of gold.
Non-metals :- Importance and general properties, method of preparation of hydrogen,
properties and its uses. Manufacturing of ammonia (Only reactions), its properties and uses,
sulphur - occurrence, extraction, properties (allotropy and effect of heat) and uses. Properties
and use / uses of Sulphur dioxide. Manufacture of sulphuric acid (Only reactions), its properties
and uses.
Unit.7. Carbon Compounds
Marks - 8
Functional groups (only oxygen containing) Alcohols - preparation, properties and uses,
preparation methods, properties and uses of formaldehyde, Acetone and Acetic acid. Some
common synthetic polymers, soaps and detergents.
Unit 8. Living world :Marks 6
Life Processes :Nutrition, Modes of nutrition : Autotrophic, heterotrophic, Parasitic and saprophytis.
Nutrition of plants : - Photosynthesis factors affecting the photosynthesis:
Nutrition in animals : Amoeba grasshopper, digestive system of human.
Respiration :- Respiration and breathing. Respiration in plants and animals, types of
respiration: aerobic and anerobic respiration; respiration through skin, gills, trachea lungs.
(earthworm, fishes, grasshopper and human). Knowledge of structure and function of
respiratory system of human.
Unit 9. Transportation, Excretion
Marks - 8
Transportation :- Transportation in plants and animals. (Water, minerals, food). Transportation
in human, composition and function of blood, clotting of blood, blood groups. Transfusion of
blood, heart, structure and functions of blood vessel (elementary knowledge). Lymphatic
system.
Excretion :- Excretion in animals (Amoeba and earth worm), excretion in humans,
VI
Osmoregulation.
Control and co-ordination :- coordination, plants and animals. Nervous system and
hormones in humans, reflex action.
Unit.10. Reproduction, growth, Heredity and Evolution
Marks - 5
Reproduction and growth :- Types of reproduction
Asexual : Fission budding, regeneration vegetative propagation in plants, cutting, grafting
and layering, Pathenogenesis. Sexual reproduction and it significance Reproductive parts of
plants, pollination and fertilization. Human reproductive system, Mental and physical change
during human development.
Heredity and Evolution :Heredity and variations, physical basis of heredity - chromosomes; D.N.A. (elementary
knowledge), genes, sex determination. Elementary knowledge of evolution.
Unit.11. Environment
Marks - 8
Environment and Environmental Problems :- Causes, prevention and control of environmental
problems, land, water, air, noise pollution and accumulation of waste materials. Biodegradable
and non biodegradable materials, interaction, between biotic and non biotic component of
ecosystem. Ecological balance, efforts and measures for conservation of environment.
Process of water management and conservation :- Rain water harvesting ground water
recharging, conservation of forests; Land management and conservation, public awareness
for environmental protection, Green house effect, global warming, ozone layer depletion,
acid rain.
Morphological study of medicinal plants. Their classification on the basis of their use and
life span. Study of botanical names and medicinal use of the following plants.
Seasonal plants Malkangni, Ashwaganda, Ginger, Turmeric, Garlic, Fenugreek, Touch me
not, Soya, Shatawar, Sarpgandha, Isabgol, Dioscorea, Mustard, Cumin, Fennel, Ajwayin,
Marua, Tulsi, Vacha, Adusa, Giloy, Harjor, Bryophytum, Bhui Aonla, Castor.
Trees and perennial plants Harad, Baheda, Aonla, Nirgundi, Babool, Oak, Neem, Sheesham,
Catechu, Karanj, Sweet Neem, Molshree, Kachnar, Peepal, Harshinagar, Amaltash,
Pomegranate, Sandal, Nuxvom, Paras peepal, Arjuna, Eucalyptus, Bel, Apamargh, Bhringraj,
Kaner.
VII
SCIENCE PRACTICAL
Marks - 25, Time - 2 Hours
LIST
1.
2.
3.
4.
5.
6.
7.
8.
9.
OF PRACTICALS:
Preparation of C02 in the laboratory and study its properties.
To study the reaction of metals with dilute acids.
To compare the foaming capacity of different samples of soaps / detergents.
To study two physical and two chemical properties of acetic acid.
To prepare a model of Solar Cooker (Project).
To make a model of wind mill and demonstrate the production of wind energy.
To identify bleaching powder in the given samples of chemicals.
To make a temporary mount, slide of stomata.
To study the reaction of bases with.
(1). Litmus Paper. (2). Metals. (3). Hydrochloric Acid.
10. To verify reflection of light using plane mirror.
11. To determine the focal length of concave mirror by one pin method.
12. To trace the path of a ray of light passing through a rectangular glass slab and draw the
refracted ray and emergent ray.
13. To determine the focal length of convex lens by two pin method.
14. To draw the incident ray, refracted ray and emergent ray for a ray of light incident on a
glass prism.
15. To show magnetic lines of forces with the help of a bar magnet.
16. To verify Ohm's Law in the laboratary.
17. To find out the resultant resistance of two resistors connected in.
(I). Series and (II). Parallel.
18. To show that CO2 is produced during respiration .
19. To show endosmosis in raisins (Kismis).
20. To prove that oxygen is released as a by-product of photosynthesis.
21. To find the rate of heart beat per minute / “pulse rate” by the student.
22. To observe the different components of blood with the help of microscope.
23. To study the different parts of a flower.’
24. To study the strucutre of living organism in the given samples.
25. To construct through diagrams new model of food chains.
26. To complete the missing links in the given mineral cycles.
(a) Study of Nitrogen Cycle in nature.
(b). Study of Water Cycle in nature.
(c). Study of Carbon Cycle in nature.
SUGGESTED INVESTIGATORY PROJECTS
1.
To prepare a model of artifical geo-satellite or rocket launching station.
2.
To measure the variation in temperature each day in a month , tabulate it and study the
effect of temperature on the weather. (maximum and minimum)
VIII
3.
To tabulate the daily diet and calories obtained from it and compare it with the balanced
diet.
4.
Systematic collection of cuttings and news from Old magazines and news papers, related
to pollution of water, forest, soil and air.
Accoroding to this scheme it is compulsory to perform one practical.
Marks distribution will be as follows.
Marks
1.
Practical Exercise (Any One)
12
2.
Viva Voce
03
3.
Practical Record.
05
4.
Project (Work done during the session ).
05
Total 25
Break up of 12 marks of Practical Exercise will be as follows:
1.
On writing, materials required.
2.
Basic principle and formula.
3.
Labelled diagram.
4.
Calculation, obsevation and tabulation.
5.
Result and precautions
Marks
01
02
02
05
02
Total 12
Break up of 05 marks for Practical Record will be as follows :1.
Indexing.
2.
Recording of experiments.
3.
Regularity in submitting.
4.
Neatness.
Marks
01
02
01
01
Total 05
IX
CONTENTS
No.
Chapter
Page No.
1.
Universe
1
2.
Space Exploration
17
3.
Light : Nature, Reflection and Refraction
23
4.
Optical Instrument
46
5.
Electricity and its effects
54
6.
Magnetic Effect of Electric Current
72
7.
Non Renewable Energy Sources
89
8.
Renewable Energy Sources
101
9.
Rate of Chemical Reaction and Chemical Equilibrium
109
10.
Some Important Chemical Compounds
128
11.
Metals and Non metals
145
12.
Organic Compounds
167
13.
Nutrition
195
14.
Respiration
206
15.
Circulation
217
16.
Excretion and Osmoregulation
229
17.
Control and Coordination
238
18.
Reproduction and Growth
249
19.
Genetics
260
20.
Organic Evolution
269
21.
Environment and Environmental Problems
276
22.
Medicinal Plants
297
X
Chapter - 1
UNIVERSE
Brightness of the sun and its energy, twinkling stars
and their groups and the different phases of the moon have
been a great attraction for man since ages.
The mysteries of space have always attracted man
from ancient times and this attraction has encouraged man
to explore space and universe. There are evidences which
show that people had the knowledge of Uttrayan and
Dakshinayan sun in Mahabharat era. History of our ancient
Saints like Aryabhatta provides evidences that Indian saints
had discovered the orbital motion of planets. In the year
499 B.C., Aryabhatta just at the age of 23, mentioned this
fact in his book “Aryabhattiya” in chapter 3
We will study
1.1
Solar System
1.2
Earth
1.3
Stars
1.4
Constellations
1.5
Galaxy
1.6
Milky way
1.7
Structure and
Theories of
Universe
UNIVERSE
∑§ˇÿʬ˝ÁÃ◊á«U‹ªÊ ÷flÁãà ‚fl¸ ª˝„UÊ— SfløÊ⁄UáÊ–
◊ãŒÊëøÊŒŸÈ‹Ê◊¢ ¬˝ÁËÊ◊¢ øÒfl ‡ÊËÉÊ˝ÊëøÊØH
Meaning :- The rotation of all the planets from its
farthest point is slow and from the lowest (nearest) point is
fast. Aryabhatta assumed that sun is stationary and earth
rotates around the sun on its axis. About 1000 years later
Copernicus also said the same thing and brought a
revolution in Space science. Let us know about our Solar
System, Stars, Planets and Universe.
1.1 Solar System
Among many galaxies present in the universe, one is
our “Milky way”. Our Sun and its family also belongs to one
such galaxy, whose Indian name is “Akash Ganga”. Sun is
one of the stars amongst many which are present in
Akashganga. Planets revolve around sun. Earth is one
among the planets which are revolving in spherical orbits
around the sun. There are eight planets in the Solar System.
The natural satellites revolving around the planets are called
moons. Earth has only one satellite (Natural) i.e. moon. Apart
from satellites there are a number of asteroids, comets and
meteors in a galaxy. Due to the gravitational pull of the sun
all the planets and other heavenly bodies revolve around
the sun. Sun and its nine planets, different satellites and
numberless heavenly bodies like asteroids, comets etc.
together constitute the Solar System. The size of the Solar
1
System is approx. 105 AU. (1 AU = 1.496x1011m)
Let us now discuss about some of the members of
the Solar System.
Chromosphere
Sun : The sun is the head of our Solar Family. As
compared to millions of stars, the sun is a medium sized
star of average brightness. The sun appears to be larger
and brighter because of its distance from the earth which
is the shortest in comparison to the other stars. The sun
accounts for almost 99.9% of the total mass of the Solar
System. It is the main source of energy of the Solar
System. Our earth receives all the energy, visible and
invisible light and heat from the Sun. We are lucky that
earth receives only that part of the energy from the sun
which is sufficient to sustain life. The diameter of the sun
is almost 100 times than that of the earth while its mass
is about 10 lakh times than that of the earth. The sun is
not a solid body but a lump of hot gases. It consists mostly
of hydrogen gas. The centre of the sun is called the core
(nucleus). The temperature of the nucleus is about two
crore kelvin (1.56x107K) whereas its pressure is around
2x1016 Pascal. At such a high pressure and temperature
nuclear fusion reaction takes place and produces a
tremendous amount of energy in the form of heat and
light.
Photosphere
Sun
2.0×10 K
7
Let’s Know
Some important facts about
Sun (estimated)
1.
Age - 4.6x109 years
2.
Diameter - 1.4x106 km
3.
Mass - 1.989x1030 kg
4.
Distance from the earth 150×106 km.
5.
Density of the nucleus There is a visible layer of the gases ranging from
104kg/m3
800 km to 1600 km. above the core of the Sun. This layer
6.
Rotation period about its
is called Photosphere. Its temperature is about 6000K.
own axis - 25 days 9 hours
The sun does not end at the photosphere. Just above
and 7 minutes.
the photosphere lies the chromosphere which is also
called Corona. The meaning of this Latin word in English
is Crown. Though the temperature of these regions is very high, they give out very little light in
comparison to photosphere and so remains invisible. This region becomes visible only during a
total solar eclipse and looks like a bright crown.
Planets : After the sun, the most important members of the Solar System are the planets.
They are the heavenly bodies which revolve around the sun, in a closed elliptical orbit. Planets
have no light of their own but appear to shine due to reflected light of the sun. Due to some
features in common these planets are divided into two groups.
Terrestrial Planets : The four innermost planets Mercury, Venus, Earth and Mars have
some features in common with the earth and hence they are called Terrestrial Planets. These
are also called surface planets. The common features of terrestrial planets are2
SCIENCE 10
(a)
They have a thin and rocky crust.
(b)
They have a mantle rich in iron and magnesium.
(c)
They have a core of molten metals.
(d)
They have thin atmosphere.
(e)
They have very few or no natural satellites (or moons) or no satellites.
Jovian Planets :The planets which are situated outside the orbit of Mars are called Jovian Planets. Their
structure is similar to that of Jupiter, Saturn, Uranus and Neptune. The common features of
Jovian Planets are :(a)
They all are gaseous bodies.
(b)
They have ring systems around them.
(c)
They have a large number of natural satellites.
Let us now study Planets in detail in the increasing order of their distances from the sun.
1.
Mercury : It is the first and the smallest planet in the Solar System and is closest to the
sun. Because of its closeness to the sun it is the hottest planet in the Solar System. It has
no atmosphere and no water vapours. Most of the time Mercary remains hidden in the
bright background of sun, and it is difficult to see it. Still it can be observed on the horizon
just before sunrise or just after sunset.
2.
Venus : This planet is very close to the earth. Except the moon it outshines all the other
heavenly bodies at night. It is visible in the early morning in the eastern sky or early in the
evening in the western sky. That’s why it is also known as the ‘Morning Star’. Venus
appears bright because it reflects about 75% of the sunlight falling on it. The planet venus
has excessive carbon dioxide in its atmosphere so it gets heated excessively due to
green house effect and hence there are no possibilities of life on Venus. There are no
clues of water on Venus till date.
3.
Earth : When viewed from the outer space, the earth appears blue and green due to the
presence of water and greenery. The earth is the only planet in our Solar System which
has water in large quantity. The temperature of the earth is neither too low nor too high. It
has an atmosphere which contains nitrogen, oxygen, carbondioxide, water vapours and
some quantity of ozone. Suitable conditions of temperature, oxygen and water makes the
earth a unique planet on which life is possible. The atmosphere of the earth plays a vital
role in flourishing and nourishing life on the earth.
4.
Mars : Next to Venus, Mars is the planet which is closest to the earth. The day here is 24
hrs long. It is far away from the sun hence remains cool. It’s atmosphere contains traces
of carbon dioxide, nitrogen and oxygen but there are no traces of water on Mars. Thus the
UNIVERSE
3
conditions of Mars are not suitable for life. Since Mars is a small planet, it has a small
gravitational field. The soil of Mars contains oxides of iron (around 16%) due to which its
surface is red and so it is also called the ‘Red planet’.
5.
Jupiter : This is the first planet in Jovian category. It is made up of mainly hydrogen and
helium. When seen through the telescope, it appears to be colourful. Jupiter has a very
dense atmosphere. Jupiter has some rings around it but they are extremely thin. The
atmosphere of Jupiter consists of hydrogen, helium, methane and ammonia. The most
distinguishing feature of Jupiter is “ The Great Red Spot’ in its atmosphere. The great red
spot of Jupiter is believed to be a complex storm in its atmosphere which is long lived and
will be there for hundreds of years. The temperature of its surface is 1500C. It is the
biggest planet of the Solar System. Its mass is more than any other planet in the solar
system. Because of its extremely large mass, Jupiter exerts a very strong gravitational
pull on other objects which pass by it. Its
gravitational pull is so strong that a comet passing
close to jupiter often gets deflected from its
original path, some of the comets even break up
into pieces on coming close to jupiter. In 1994,
the comet called ‘Shoemaker-Levy’ broke into
Saturn
several pieces when it came too close to Jupiter,
the pieces of this comet then collided with Jupiter.
6.
Saturn : Saturn is the second biggest planet of
the Solar System. Like Jupiter, Saturn is also
Saturn ring
made up of mainly hydrogen and helium. Saturn
is surrounded by hundreds of narrow rings. In
fact, saturn has the most visible and beautiful system of rings around it. Saturn is an
extremely cold planet. It’s temperature is about –1800 C.
7.
Uranus : This is the first planet to be discovered through telescope. After Jupiter and
Saturn, Uranus is the third biggest planet of the Solar System. Uranus is made up mainly
of hydrogen and helium. It also has some rings around it. It looks like a green ball. It is also
known as Indra.
8.
Neptune : Neptune is similar in size and constitution to Uranus and it is the last planet in
Jovian group. It’s surface has a temperature less than –200°C.
4
SCIENCE 10
Some facts related to planets of Solar System.
S. Name of the
Distance
No. Planet
from Sun
(in increasing order
(in Km)
of the their distance
from Sun)
1.
2.
3.
Mercury
Venus
Earth
58x106
108x106
150x106
4.
Mars
228x106
5.
6.
7.
8.
Jupiter
778x106
Saturn
Uranus
Neptune
1427x106
Rotation
Period
around
Sun
Rotation Period Diameter
on its own
of Planets
axis
(in Km)
88 days
58 days
225 days
243 days
(365 days (23 hr. 56 min.
5 hr. 58 min.
4 sec.)
46 sec.)
about
----24 hr.
1
365 4 days
687 days
24 hr.
11
3
4
1
2
years
9 hr. 50 min.
29 years 10 hr. 14 min.
2870x106 84 years 10 hr. 49 min.
4504x106 165 years 15 hr. 48 min.
Mass of No. of
Planets Natural
(Kg.)
satellites
(Moons) of
planets.
4880
12100
12760
0.335x1024
4.870x1024
5.980x1024
None
None
1
6780
0.639x1024
2
142800
1.901x1027
28
120000
50800
48600
5.693x1026
30
21
8
8.73x1025
1.028x1026
Activity
Aim : To study the change in the relative position of earth with respect to the Sun.
Task : Choose a place from where the east horizon of the sky is clearly visible. Now
choose a tree, tower etc as a symbol exactly behind which the sun lies. Repeat the same
process next week with some other symbol. The process needs to be repeated for many weeks.
During the process you will find that from the longest day i.e. 21 June, Sun starts shifting
towards South. This is called Dakshinayan. It continues till the shortest day i.e. 22 Dec. After 22
Dec Sun starts shifting towards North which is called Uttarayan.
Conclusion :
1.
Direction of sunrise changes every day i.e. the Sun does not rise from the
same location exactly in the east everyday.
2.
Position of the earth relatively changes with respect to the sun.
Answer these questions :
1.
Which nuclear reaction is responsible for the high temperature in the core of
the sun?
2.
Why corona is clearly visible on complete solar eclipse?
UNIVERSE
5
Asteroids :
Asteroids are very small bodies of rock and metal which revolve round the sun mainly in
between the orbits of Mars and Jupiter. Actually, asteroids are a belt of a kind of debris which
some how failed to assemble into a planet and keep revolving in between the orbits of mars and
jupiter. There may be as many as 100,000 asteroids. The name of the biggest asteroid is ‘Ceres’.
Its diameter is about 800 km. The smallest asteroid may be as small as a pebble (small stone).
Some experts believe that there was a planet between Mars and Jupiter which went closer to
Jupiter and was broken up by its gravitational pull. Others think that they are the part of a ring of
separate pieces of matter and were formed at the same time as the rest of the planets. Sometimes
asteroids collide with the earth. Though the collision of an asteroid with the earth happens very
rarely, even then a careful watch is kept on the motion of asteroids by the astronomers. This is
because the collision of an asteroid with the earth can cause a lot of damage to life and property
on the earth.
It is believed that, the extinction of dinosaurs from the earth which occured about 65
millions years ago, was caused by the collisions of some asteroids with the earth. When an
asteroid collides with the earth a huge crater forms on the surface of the earth.
Apart from planets and asteroids, small pieces of rocks travel through the space. These
rocks are fragments from asteroids, comets, moon etc. These
are called meteoroids. Sometime a meteoroid travelling towards
Do you know?
the earth, enters the atmosphere of the earth . In the
atmosphere, air friction produces so much heat that quite often
Scientist named Halley
the meteoroid vaporizes completely. The hot vapours give off
studied a comet which
light before cooling down, causing a streak of light seen in the
appears in the sky after
sky at night this streak of light caused by a vaporizing meteroid
every 76 years. This
is called a meteor or a Shooting star. A meteoroid that hits the
comet is also known as
ground and forms a crater is called a meteorite. One such
Halley’s comet. It was last
crater formed the Lonar Lake near Aurangabad in Maharastra.
seen in 1986.
Comets : Comets are the objects
which move in highly elongated orbits
around the sun. Their central part is solid
while outer part is made up of frozen gases
like ammonia, Methane, water vapours etc.
However it is not a star. Comets are
heavenly bodies which revolve around the
sun in highly elliptical path. Usually
comets come no closer than a few million
km to the sun. Their mass is very less.
They may be even millionth part of the mass
6
Know More
The study of the tail of the comets has shown the
existence of molecules of carbon, oxygen,
hydrogen and nitrogen. For example it has atoms
of carbon monoxide (CO), Methane (CH4) and
Hydrogen cyanide (HCN) etc. in its tail. These
molecules helps to form complex molecules
necessary for the origin of life. Some scientists
have suggested that the seeds of life on earth
were brought by comets from the outer space.
SCIENCE 10
of earth. So far only 1000 comets could be seen. It is believed that they may be more than 100
Arab in number. Most of the comets revolve much beyond the orbit of its outer most planet.
Thus, generally, they are not visible from the earth. Normally when they are away from the sun,
they are neither visible nor they have a tail. As they come close to the sun, the frozen gases
vaporize and start glowing. As the distance from the sun reduces, the vaporisation increases
and hence the length of the tail increases. Due to the presence of this tail, it is also called a
“Puchchal Tara”. We can see comets when they are closer to the sun because in this position
they are closest to the earth too.
Answer these questions :
1.
Name the two planets between which the orbit of Ceres lies?
1.2
2.
Where do we find Asteroids?
3.
What are Meteors?
4.
Why Meteors flash across the sky?
5.
Write one difference between ‘Stars’ and ‘Shooting Stars.
Earth :
It is a planet on which we live. Its mountains, rivers, forest, deserts, etc. are of great
attraction. Since we live on the planet earth, we like to know about its origin and formation. Let’s
know more about our planet.
1.
Evolution of Earth : In the beginning, the whole earth was a huge collection of cold rocks
on being separated from the sun. The rocks of the earth contained radioactive materials
like uranium, thorium and potassium-40. The natural disintegration of radioactive materials
like uranium, thorium and potassium 40 produced a lot of heat energy. The enormous heat
energy thus produced alongwith the heat produced by gravitational compression, heated
the earth to an extent that it melted to form a liquid. The melting of the planet earth happened
about 800 million years after the existence of basic earth that came into being..
2.
Development (Formation) : When the earth melted, the molten material present in it
began to reorganize itself under the influence of gravity. The molten iron, being the heaviest
material fell in to the centre of the earth and formed the core of the earth. The lighter
constituents which were earlier present in the core, came up and formed the crust of the
earth. The reorganization of molten earth into various layers having different densities is
called differentiation. As a result of differentiation, the earth is divided into three major
layers : crust, mantle and core. The crust is the lightest and the core is densest. It was
during the differentiation process that the water vapours and atoms of the gases present
in the rocks of the earth were released. This water formed the oceans on the earth
whereas the gases formed the atmosphere.
UNIVERSE
7
Structure of the Earth :
The earth is made up of many layers. However, the earth can be broadly classified into
three major layers. These are :
1. Crust 2. Mantle 3. Core.
Now, let’s study these layers in detail.
1.
The Crust : Earth appears to be a huge spherical ball, when observed from the space.
The Earth’s crust can be compared to a skin around the orange. It is a thin solidified layer
formed during the cooling of the molten lava. The rocks of crust are rich in aluminium
silicate. The crust of the earth has a low density of about 3 g/cm3. The thickness of the
earth is not uniform throughout. Under the continents (land masses), the thickness of
earth’s crust can be upto 40 kilometre The thickness of earth’s crust under the oceans is
very less. It is only about 10 kilometre three quarters of the earth crust is covered with
water. There is atmosphere and ionosphere above the earth’s crust upto an altitutde of
1600 Km. which supports life.
2.
Mantle : The region between the crust and the core of the Earth is called the Mantle. It
extends from the base of the crust downwards to a depth of 2900 Km. Though direct
observations of this layer cannot be made but we can know its contents by some other
means. It is rich in iron and magnesium silicates.
The pressure inside the mantle increases with the depth. Even under high pressure in the
mantle, the rocks are usually in the solid state. There is high pressure and temperature
under the bottom layer of the mantle (near the core of the earth). Under extreme pressures
and temperatures, however some of the rocks tend to flow like coal-tar. The density of
mantle increases slowly as we go deep. In the beginning of the mantle, the density is
about 4 g/cm3 which is 6 g/cm3 at the bottom. Here, the mantle ends and a sudden increase
in density occurs.
3.
Core : The innermost (central) part of the earth is called its core. The core of earth has a
radius of about 3400 km and it is extremely hot. It is mainly made up of iron. The temperature
of its central part is more than the melting point of iron but still it is made up of solid iron.
The reason for this is high pressure. The Excess pressure is equal to the atmospheric
pressure. So although the temperature is quite high (more than its melting point) iron in the
inner core remains solid. Since the pressure is comparatively low in the outer core, therefore,
iron remains in the molten form (liquid form) in the outer part of the core of earth. Thus iron
is in the liquid form from the upper surface of the earth down to 1600 km. The density in
core varies from about 10 g/cm3 to 16 g /cm3. from outer to inner. The density of the
innermost part of the core is 18 g/cm3.
1.3 STARS :
Stars are the heavenly bodies that are extremely hot and have brightness of their own. In
ancient times, people used to depend on stars for finding directions. The ancient people also
8
SCIENCE 10
used the positions of stars in the night sky to estimate time. The ancient people could predict the
arrival of monsoons with the help of stars. For example when certain stars appeared in the night
sky, people would guess that the rains were about to arrive.
Every star is made up of large clouds of hydrogen gas, some helium and dust. In all the
stars, hydrogen is continuously being converted into helium and a large amount of nuclear
energy in the form of heat and light is released in this process. Thus a star is a hydrogen nuclear
furnace. The stars are classified according to their physical characteristics like size, colour,
brightness and temperature. The stars do not last for ever. The stars are born, mature, grow old
and finally die. However, the age of stars has been estimated to be billions of years. Since the
changes which takes place in the stars are very slow as compared to our own life time. (75 or
80 yrs.) they appear to be permanent objects in the sky which do not change at all.
Birth and Evolution of Stars :
The life cycle of a star begins with the condensation of hydrogen and helium gas present
in the galaxies, to form dense clouds of these gases having temperature of about 173°C. The
stars were then formed by the gravitational collapse of these over-dense clouds of gases in the
galaxy. Due to large gravitational force, the gas clouds started contracting. This is called collision
of clouds. Ultimately, the gases were compressed so much that they formed a highly condensed
object called a protostar.
The process of contraction of protostar continued for about a million years during which
the inner temperature in the protostar increased from a mere 173°C in the beginning to about
107 0C. At this extremely high temperature nuclear fusion reaction of hydrogen takes place to
form helium and a tremendous amount of energy is produced in the form of heat and light. This
further raises the temperature and pressure inside. The protostar thus begins to glow and
becomes a star.
Core
Outer shell
(A) A huge cloud of
contracting hydrogen
gas
(B) A
protostar
(C) A star is formed
as hydrogen converts
into helium through
nuclear fusion.
Fig. 1.3
UNIVERSE
9
The increased pressure from within the star stops the gaseous matter from collapsing
further. The star is now in delicate equilibrium under two opposite forces. One is gravitational
attraction which tries to compress and ignite the fusion reaction while the second is the internal
pressure generated by the energy released by nuclear fusion. All the while the fusion reaction
continues to liberate energy. Our sun is now in this balanced stage of development. It was
formed some 4.6x109 years ago and will continue to radiate energy for about same length of
time in the future.
The declining phase of a star’s life
Nuclear fusion reaction in star continues in the interior and more and more of hydrogen is
converted into helium. When fusion reaction ceases the star begins to contract under its own
weight. This process transfers enough heat to the material around the core which enough still
contains hydrogen to start a new series
of fusion reaction. This burning of the
outer core hydrogen (shell) causes the Core
star’s outer envelope to expand and
Core shrinks
cool. The temperature drop changes the
colour from white to red and the star
Outer shell expands
becomes a red giant or a supergiant.
The energy emitted from a Red
Red giant star
Normal Star
Giant Star gradually decreases. Our
sun will eventually become Red Giant
Fig. 1.4 Transition of normal star to red-giant star.
after about 5,000 million years from
now. The fate of a star after reaching
Red Giant phase depends on its initial mass.
l
If the mass of a star is less than 1.4 times the solar mass Ms then the core continues to
contract till a certain stage when it stops. The size of star is very small say, about the size
of the earth but its mass is very high. It is now called White Dwarf. The star at this stage
is dead with its nuclear furnace off.
The limit on the mass of the white dwarf (1.4Ms) is called Chandrashekhar limit. It is worth
noticing that famous scientist S.
Core
outer shell
Chandrashekhar (1910-1995) of
Indian origin found this limit.
Stars that have mass greater
than about 1.4 times that of our
sun dies with much fun fare. The
carbon oxygen core formed at
the red giant phase has so much
mass that gravity shrinks the
10
outershell is lost
white
dwarf star
core shrinks
Fig. 1.5 Formation of white dwarf star
SCIENCE 10
core further, causing its temperature to become very high. As there is high temperatures,
nuclear reactions fuse carbon and oxygen to successively heavier elements like Neon,
Silicon and finally iron. The enormous energy released in these reactions cause the outer
layers explode like a massive bomb. Such an exploding star is called a supernova. A
supernova emits the same amount of energy in one second that the sun radiates in about
100 years.
Core
Outer shell
l
If the mass of a star is more than
1.4 Ms but less than 5 Ms then
the core continues to contract
Supernova explosion
(shrink) under the tremendous
outer shell explodes
force of gravitation and ultimately
Neutron
star
forms an extremely dense lump
of matter. This extremely dense
lump of matter is called a
Red giant star
Fig.
1.6
Formation
of neutron than that star through supernova
Neutron Star. A neutron star,
explosion
contains matter that is denser
than that is found in white dwarf stars. A spinning neutron star emits radio waves and is
called a Pulsar.
l
The future of a Neutron star depends on its mass. If the neutron star is very heavy (>20Ms),
then due to enormous gravitational attraction, it would continue to contract indefinitely and
the vast amount of matter present in a neutron star would be ultimately packed into a mere
point object. Such an infinitely dense object is called a BLACK HOLE. The neutron stars
shrink so much and become so dense that the resulting black holes do not allow anything
to escape, not even light. Since even light cannot escape from black holes, the, black
holes are invisible i.e. they cannot be seen. But, if we see a star moving in a circle with no
other visible star in the centre, we imagine that there is a black hole at the centre. One
possible location for a black hole is in the cygnus constellation.
Let’s know some difference between a star and a planet.
Stars
1. A star has its own light and hence
self luminous.
2. Stars twinkle thus their light increases
and decreases continuously.
3. Stars are countless in number.
Planet
1. A planet has no light of its own. It shines
because it reflects light received from the sun.
2. Planets do not twinkle at all.
Their present number is 8. Previously included
Pluto is not a planet now.
4. Generally, Stars are comparatively
4. Planets are very small in size as compared
bigger than planets.
to stars.
5. A star is a huge mass of extremely hot 5. A planet is made of rocks and metal and its
gases and its temperature is about
temperature depends on its distance from
7
10 °C
the sun.
UNIVERSE
3.
11
1.4 Constellation
Group of stars which seems to be arranged in beautiful patterns and make up identifiable
shapes are called constellations. About 88 constellations are known so far. Distance between
different stars in a constellation varies. Constellations provide suitable location point for various
heavenly bodies. It is easier to recognize constellations with the shape resembling to animals,
human being or some other object. Our ancestors named these constellations after familiar
animals, gods etc. Following are the names of such constellations.
1.
Ursa major or Big Bear (Saptarishi)
2.
Orion (Mriga)
3.
Aries (Mesh)
4.
Taurus (Vrish)
5.
Gemini (Mithun)
6.
Cancer (Karka)
7.
Leo (Simha)
8. Virgo (Kanya)
9.
Libra (Tula)
10. Scorpio (Vrashchik)
11. Sagittarius (Dhanu)
12. Caparicorn (Makar)
13. Aqurarius (Kumbh)
14. Pisces (Meen)
Let’s now recognise some constellations
1.
2.
3.
Ursa Major (Saptarishi) : The
arrangement of stars in ursa major
constellation
or
great
bear
constellations is shown in fig 1.7 (a)
Every star in this constellation is
belongs to a Rishi hence is called
Saptarishi. The stars marked 1, 2, 3 and
4 are supposed to form the head of the
bear whereas the stars marked 5, 6 and
7 form the tail of the bear. Thus it is also
called the Big Bear.
Orion (Mriga) : Orion constellation also
consists of seven prominent stars.
Orion means hunter. The stars marked
1 and 2 in fig 1.7 (b) are supposed to
form the shoulders of the hunter
whereas stars marked 6 and 7 are
imagined to form the feet of the hunter.
The three stars in the middle i.e. 3, 4,
and 5 represent the waist of the hunter.
Libra (Tula ) : Libra means ‘simple
balance’, or scales which is called ‘tula’
12
(a) Saptarishi
(b) Orion
(c) Libra
SCIENCE 10
or ‘tarazu’ in Hindi. So, the
arrangement of stars in Libra
constellation is supposed to
resembles the shape of a simple
balance. The stars marked 1 and 2
is figure 1.7 (c) are supposed to
represents the arms of a simple
balance whereas the stars marked
3 and 4 are thought to represent the
two pans of the simple balance.
4.
(d) Taurus
Taurus (Vrish) : Taurus
Fig. 1.7
constellation is shown in figure 1.7
(d) Vrish (Bull) means Taurus in English. The arrangement of stars in the taurus
constellation is imagined to resemble the shape of a bull. The stars marked 1 and 2 in
figure 1.7 (d) are imagined to represent the horns of the bull whereas the stars marked 3,
4, 5, 6 and 7 are imagined to represent the face of the bull and rest of the stars are
supposed to form the other half of the body.
1.5 Galaxy
There are billions of stars in this
universe but they are not distributed
uniformly in space. These stars occur
in huge bunches or clusters. Each
cluster consists of billions of star. Apart
from the stars, these cluster contains
a large number of gas clouds mainly
of hydrogen gas and dust. Such a big
cluster of stars is called a galaxy.
Galaxies appear in different shapes
and sizes. On the basis of their shapes
Fig. 1.8
they are called spiral, elliptical or
irregular galaxies. Such type of galaxy is a vast system of billions of stars which contains a
large number of clouds mainly of hydrogen gas and dust particles. Actually, galaxies are the
building blocks of this universe. There are about 1011 galaxies. So, the total number of stars in
this universe has on an average 1022 stars. Though galaxies contains clouds of different gases
and dust particles but stars are the most interesting ones.
1.6 Milky Way
The galaxy to which our solar system belongs is called the milky way. It is a spiral type of
galaxy. Its diameter is about 100,000 light years. Like other galaxies, milky way is also made up
UNIVERSE
13
of shrinking overdense clouds of hydrogen gas and
dust. As mentioned above this also contains about
10 11 stars. When observed from the space it
appears like a flattened disc-like structure. The stars
are not uniformly distributed throughout the disc but
are arranged in spiral arms emerging from the
nucleus of the galaxy. The milky way galaxy is
rotating slowly about its centre. The stars in the milky
way galaxy are slowly rotating about its centre. The
sun along with the solar system rotates around the
centre of the milky way galaxy. It takes about 250
Fig. 1.9 : Milkyway
million years to complete one revolution. People on
the earth get an end on view of the milky way galaxy since our earth is also a part of the milky
way galaxy. Stars at the centre of the galaxy are more dense. Our sun along with other planets
are located on one side of this disc-like structure at a distance of 30,000 light years from the
central region of the galaxy. Thus the sun is far away from the centre of the milky way galaxy.
If the sky is clear, then the milky way galaxy appears as a wide band of stars whitening the sky
from north to south on a dark night. This is why it is called Akash Ganga.
Answer these questions :
1. What is Chandrashekhar limit?
2.
Can a white dwarf star become a neutron star?
3.
What is the distance of the sun from the centre of our galaxy?
1.7 Structure and theories of the Universe
Structure of the Universe : We know that
the galaxies are the building blocks of the
universe. An astronomer Edwin Hubble observed
in 1920 from the Mount Wilson observatoty in
California (USA), that galaxies are not stationary
in the universe. All the galaxies are travelling
away from one another at a great speed. The
speed with which the galaxies run away from one
another is directly proportional to the distance
between them. Thus, larger the distance between
two galaxies, the faster they run away from one
another. The farthest galaxies observed are
travelling at more than 1.5 lakh km/sec. This
means that our universe is expanding. Now, the
the question arises, that where these galaxies
came from.
14
Activity
To understand the expansion of
the Universe, take a balloon and
mark galaxies with marker pen
as points on it. When the balloon
is inflated, its surface expands
three dimensionally in space
and the distance between these
points increases. In the same
moving way galaxies are apart
from each other.
SCIENCE 10
Theories of the structure of universe1.
Big Bang Theory : This theory explains the formation of heavenly bodies like galaxies,
stars and planets. According to this theory all the matter in the universe was originally
concentrated at one point in one lump called primeval atom. About 15x109 years ago this
superdense and extremely hot primeval atom exploded and the matter started flying in all
the directions through space and eventvally formed galaxies moving away from each
other in all directions.
2.
The steady State Theory : According to this theory, the universe was always like the
one we have now and will always be so. It does not change. It appears the same at all
points. The universe did not have a beginning and it will not have an end.
In the recent years many experimental evidences have been arranged in support of BigBang theory. It is to be noted that in the year 2006, Nobel prize (Physics) was given to
Mather and Smute for their research work, done on the satellite ‘Kobe’ in this regard. Thus
evidences suggests that from the above mentioned two opposing theories of universe,
Big Bang theory is more preferred theory of the formation of the universe.
Answer these questions :
1.
What is the relation between the distance between two galaxies and the speed
with which they are moving away from each other?
2.
What is the estimated age of the universe at present?
3.
Which one of the two theories, the Big-Bang theory and the steady state theory
is more persuasive one?
Points to remember l
The solar system consists of the sun, its planets and their satellites (or moons)
and thousands of other heavenly bodies such as asteroids, comets and
meteors.
l
Sun is also a star.
l
The diameter of sun is about 100 times the diameter of the earth.
l
The temperature of the nucleus of sun is about 2x107K.
l
Corona appears bright on total solar eclipse.
l
Terrestrial planets are those with structure similar to that of earth.
l
Planets with structure similar to Jupiter are called Jovian planets.
l
A great red spot has been observed on Jupiter’s surface.
l
Jupiter is the biggest planet in the solar system.
l
Mercury is the smallest and the nearest planet to the sun of the solar system.
UNIVERSE
15
l
The existence of rings makes Saturn unique amongst all the other planets.
l
The comets which shows its appearance after a period of 76 years is Halley’s
Comet.
l
Earth is believed to evolve by the cooling of the material separated from the
sun.
l
There are three layers of the earth : (1) Crust (2) Mantle (3) Core
l
Conversion of a red giant star into white dwarf star or Neutron star depends
on its mass.
l
There are about 1022 stars in the universe.
EXERCISES
Very short answer type questions.
1.
Who wrote ‘Aryabhattiya’?
2.
Which layer of the sun appears brightest on a total solar eclipse?
3.
What is the name of the central region of the earth?
4.
Write the name of the planet on which the great red spot is seen.
Short answer type questions.
1.
Why does sun appear brighter and bigger in comparison to other planets?
2.
Which force makes all the planets revolve around the sun?
3.
Write any three characteristics of terrestrial planets.
4.
Write any three characteristics of Jovian planets.
5.
How is energy created inside the sun?
6.
What is a galaxy?
Long answer type questions.
1.
Explain the different parts of the sun.
2.
Discuss the construction of the earth under the following heads.
(a) Crust (b) Mantle (c) Core.
3.
Explain the evolution of a protostar?
4.
What is called the Red Giant star? How is it formed?
5.
What is the Black Hole? How can it be felt when it is not at all visible?
16
SCIENCE 10
Chapter-2
SPACE EXPLORATION
The limitless region beyond the earth’s atmosphere is
known as the outer space or just space in brief. This outer
space contains stars, planets, meteorites, comets,
asteroids, dust, gases and radiations. The collection of
information about these objects is known as Space
Exploration. In fact, it has always been a dream of mankind
to know the mysteries of the outer space and its objects.
It has been a longing desire of all the scientists
throughout the world to unveil the mysteries of the moon
and their constant efforts enabled man to reach the moon.
2.1 Brief History of Space Exploration
The history of space exploration began in the year
1957 when Russia (The erstwhile Soviet Union) launched
the, first artificial satellite named ‘Sputnik-1’ into space on
October 4, which was followed by America’s successfully
launched artificial satellitite called ‘Explorer-1’ just a few
month later from the former. Since then many countries
including India have established hundreds of satellites in
space for various purposes.
Apart from the artificial satellites spaceships called
‘space probes’ are also being used for space exploration.
These spaceships can travel distant planets beyond the
earth’s gravitational area. These artificial satellites and
spaceships are mainly divided into 3 groups on the basis of
their utility.
1.
For technological development of the earth and
fulfilling the needs of mankind.
2.
For space launching
3.
To travel other planets in spaceships.
We will study :
2.1 Brief history of
space exploration
2.2 Space programme
in India
2.3 Artificial Satelllite
2.4 Information
Technoloy
SPACE EXPLORATION
Appliances or instruments of the artificial satellite need
electrical energy for their functioning. This energy is
provided by the solar panel of the satellite. Solar panel
transforms solar energy into electrical energy.
17
2.2 Space programme in India
India is a land of geographical diversities. A big part of India is surrounded by the sea. For
the development of all the parts of India, there is a need of a good communication system. India
is agriculture based hence prior information of impending rain fall, snowfall, cyclone, floods or
even drought conditions are of great importance.
Artificial satellites play an important role in transfer
Let’s Recall
of information. Keeping all these things in view, India
The United States of America
is running a very important space programme since
last 30 years. Today, India is one among six has created a special agency which
countries which are self dependent in making and controls and coordinates all the space
launching ar tificial satellites as per their activities. NASA has played a very
important role in space exploration.
requirements.
Because of its effor ts men have
In India, many scientists and engineers of
attained success to land on moon. It
ISRO have worked hard and achieved success in
has sent a series of probes to planets
establishing many artificial satellites in their orbits
even to comets. The data gathered by
according to our needs.
the various probes sent by NASA has
It is to be noted here that the Satellite Launch brought about a revolution in our
Vehicles (SLV) required to send artificial satellites knowledge of the solar system and its
in their orbits are also indigenously built and evolution. The agency responsible for
developed by ISRO and now we are also using them the development of space science
commercially.
programmes in India is ‘Indian Space
Some of the important achievements of ISRO Research Organistation’ (ISRO). It has
persued a very active space
are.
programme to travel the moon.
1.
Development of the Indian National Satellite
Probably by 2012, India will succeed
series INSAT-1, INSAT-2, INSAT-3 for
in landing on moon.
Telecommunication and weather monitoring
purposes.
2.
Development of Indian Remote Sensing satellite for collecting information about far off
places.
3.
Development of METSAT satellite specially for the collection and forecasting the data
regarding weather condition.
4.
Development of ROHINI series artifical satellite for astronomical observations.
5.
Polar satellite launch vehicle (PSLV) were developed and tested successfully. It can launch
1,000 to 2000 kg class of remote sensing satellites.
6.
Geosynchronous satellite launching vehicle has also been tested successfully.
7.
Development of EDUSAT for spreading education in farflung areas.
18
SCIENCE 10
Let’s know about Artificial Satellites.
2.3 Artificial Satellite
A man-made spacecraft that orbits the earth or a planet is called an artificial satellite.
Spacecrafts which orbit around the earth are Geo-stationary satellites. Some examples are
INSAT, IRS and ROHINI Series. These satellites orbit around the earth in an elliptical orbit
beyond the earth’s atmosphere due to earth’s gravitational pull. Artificial satellites are launched
at speed ranging from 3 km/s to about 8 km/sec which is achieved by powerful launch vehicles.
To set these satellites in desired orbit it needs to be pushed enough to gain the required height
and speed for which more than one rockets are used one after the other.
Rocket is a kind of a launching/carrying vehicle. When a rocket is fired, it discharge gases
from its nozzle at a very high speed and thus forward force acts on the rocket as per the
Newton’s third law of motion. It requires a special type of fuel which is a mixture of liquid hydrogen
and liquid oxygen or kerosene and liquid oxygen. The fuels used in rockets are called
propellants.
Characteristics of Rocket fuel.
1.
It should burn rapidly.
2.
It must emit large volume of gas at very high speed, pressure and temperature.
3.
No smoke or residue should be left after its combustion.
Two types of fuels are used in rockets
(i) Solid fuel
(ii) Liquid fuel.
To carry out different functions many devices are put in artificial satellites which increase
its weight. The instruments carried along with satellites are called PAYLOAD. Such satellites
have to be lifted with more than one rocket fired one after the other. The system so formed is
called a multi-stage launch vehicle.
Types of artificial satellitesThese satellites can be classified into 3 groups on the basis of their applications.
(1) Telecommunication Satellite
The process of sending radio or television messages / broadcast through satellites stationed
in outer space inside or outside the country by Tele satellite is called Tele communication. Mainly
Geo-stationary satellites are used for Tele communication. The period of revolution in the orbit of
Geo-stationary satellite and direction is the same as that of the earth i.e. 24 hours. The
communication satellites in geo-stationary orbits have a device called transponder. The
transponders receive audio or video signals from broadcasting station on the earth. After receiving
these electromagnetic signals, they transmit them in various directions towards earth.
SPACE EXPLORATION
19
2. Weather Monitoring Satellite (MET SAT)
Weather monitoring and weather forecasting is done through geostationary satellites.
Using the information sent by satellites, scientists can make better weather forecasts.
With information of earlier arrival of hurricanes, clouds, rains, storms and about air temperature
and pressure preventive measures can be taken and damage to life can be minimised.
Remote sensing means collecting all the relevant information about an object without
actually touching it or coming close to it. A remote sensing satellite is one whose orbit is Sun
Synchronous. “The orbit of a satellite is said to be sun-synchronous if the satellite passes over
a particular latitude at approximately the same local time. Therefore, a remote sensing satellite
can take photographs of a particular region of earth with nearly the same illumination due to
sunlight, everytime it passes over that region. Remote sensing helps us in conducting repeated
surveys of vast and inaccessible areas in a very short time.
The Indian Remote sensing satellites IRS-I and IRS-II have been used for remote sensing.
The pictures and data obtained from these satellites are used for many practical purposes like(1) Ground water survey
(2) Forestry
(3) Maps of wasteland
(4) Assessing drought conditions
(5) Estimating rainfall
(6) detecting crop diseases
(7) Underground surveys for detecting and locating areas rich in coal, oil and ores
(8) Surveys of potential fishing zones in sea.
Collecting information about planets and Natural satellites
Landing space probes directly on planets or sending probes such that they pass as close
as possible to the planets, has helped the astronomers a great deal to know about their physical
features. Voyager spacecrafts launched by USA took pictures of the planet from a close range
and transmitted them to the earth. The voyager spacecrafts have discovered new rings and
new moons of saturn. Before its discovery only two moons of Neptune were known. But now it
found four new moons of Neptune. The data collected from voyager and other spacecrafts have
enabled scientists to have a better understanding about origin of the solar system and the
composition of the planets in detail. Now many space stations have a number of laboratories
established to study all aspects of outer space.
From the continuous data flowing from various space probes man has evolved a better
idea about the formation of the solar system and universe.
Our country has developed a series of artifical satellites named Rohini. Indian scientists
are consistently studying and analysing the data being sent by these satellites.
Though, our knowledge about universe has increased but it is still negligible in comparison
to the knowledge of the vast space around.
20
SCIENCE 10
Answer these questions :
1.
Name the orbit of the satellitite used for sending television signals.
2.
Name the Indian satellite used in remote sensing.
3.
Which scientific achievement made it easier to study weather.
2.4 Information technology
Today we are able to transform the whole world into a Global Village by means of information
technology. This has become possible with the help of artificial satellites.
Development of super computer and the establishment of artificial satellite space exploration
gave birth to modern information technology. Its efforts gave rise to the internet service, mobile
service, Global positioning system, remote sensing, tele-conferencing tele medicine etc. These
services have brought unbelievable/unimagined changes in our working ability and working
system. Today no area is left untouched or left unhelped by information technology like education,
weather forecasting, disaster management, medicine transportation, geological surveys and
administration etc.
It has now become very easy and cost effective to contact anyone living anywhere just
by sitting at home. The Global positioning system which is working very efficiently in many parts
of the world has helped and increased availability and reduced uncertainity by starting ‘City Link
Service’ in the cities like Bhopal and Indore in Madhya Pradesh.
Scientist of MP council of research and technology have conducted a geological survey
of Madhya Pradesh by using the data provided by remote sensing satellites and written golden
lines of success in evaluating water, forest and natural resources.
Points to Remember
l
The collection and study of details of known or unknown heavenly bodies in outer
space is called space exploration.
l
History of space exploration starts from 1957 when erstwhile USSR launched
SPUTNIK-I.
l
Indian artificial satellites are mainly used for the following purposes1.
Satellite communication.
2.
Weather monitoring
3.
Preparing maps of the areas rich in minerals.
4.
Space study and space launching.
5.
Geo-stationary satellites are used for sending. T.V., Phone, Fax signals etc.
6.
A Natural satellite of a planet is known as the moon of that planet while artificial
satellites are called ‘Satellite’.
SPACE EXPLORATION
21
EXERCISE
Very short Answer type Question1.
What is the common name of Indian Space Research Organisation?
2.
What is the name of the American Space Agency.
3.
Name the vehicle used to launch and establish a satellite in its orbit.
4.
What is the name of the technique used to collect data relating underground areas
through satellites?
5.
Name the satellite used to study weather.
Short answer type Questions1.
Write down the main objective behind launching Rohini Satellite.
2.
Write any four achievements of ISRO.
3.
Where are the data collected by the Indian IRS-I and IRS-II utilised?
4.
Write the full name of INSAT.
5.
What are Geo-stationary satellites?
Long Answer Type Questions1.
What are communication satellites and how do they work?
2.
What is a weather monitoring satellite and how does it work?
3.
What is a remote sensing satellite? Write its main function.
22
SCIENCE 10
Chapter - 3
LIGHT : NATURE, REFLECTION AND REFRACTION
3.1 Nature of light
We see many things around us. Have you ever
wondered why we can’t see things in dark? We can see
only in the presence of light. This shows that light is an
important medium to see things. Twinkling stars, shining
objects, rainbow during rainy season, Mirage in deserts are
some of the phenomenon associated with light. On the basis
of these phenomenon we’ll try to understand nature and
characteristics of light.
We will Study
3.1
Nature of light
3.2
Reflection of light
3.3
Reflection at plane
and curved surfaces
3.4
Sign convention for
mirror
3.5
Mirror formula
3.6
Refraction of light
3.7
Lens
3.8
Sign convention for
lens
3.9
Lens formula
3.10 Power of lens
3.11 Defects of vision.
In ancient India, nature and natural phenomenon have
been deeply studied by Rishis. Information related to physics
is available in specialised epics of that times.
Maharishi Bharadwaj was an eminent scientist in the
field of study of nature of light. He has mentioned apparatus
like spectrometer to measure the wavelengths of different
colours in the regions like, visible, ultra-violet and infra-red
in his work. We are fascinated by the fact that all these
researches have been done long ago in our country when
there was no air of science in the west.
Newton and Huygens paid a lot of interest in studying
the nature of light. Newton gave the idea that light is made
up of particles while Huygens considered it to be like sound
waves. Young and Fresnel established wave nature of light
through various experiments. Maxwell further explained that
light waves are actually electromagnetic waves. This
suggested scientists to study other characteristics light of
like, reflection and refraction.
Let us now study some of the important characteristics
of light like reflection and refraction.
LIGHT : NATURE, REFLECTION & REFRACTION
23
3.2 Reflection of light The process of sending back the light rays
which falls on a polished surface is called reflection
of light.
Example - We can see the flash of light
when light rays fall on a bright surface or a mirror.
Some Definitions Related to ReflectionPoint of Incidence - The point on the mirror
where an incident ray strikes is called point of
incidence.
Fig. 3.1
Incident Ray - A ray of light which strikes the mirror is called incident ray.
Normal - The perpendicular drawn at the point of incidence, to the surface of the mirror is
called normal.
Reflected Ray : A Ray of light which bounces off the surface of a mirror, is called reflected
ray.
Angle of Incidence : The angle made by the incident ray and the normal is called angle of
incidence.
Angle of Reflection - The angle made by the reflected ray and the normal is called angle
of reflection.
3.2.1 Laws of Reflections :1.
The angle of reflection is always equal to the angle of incidence.
2.
The incident ray, reflected ray, and the normal (at the point of incidence), all lie in the same
plane.
Laws of Reflection are applicable to all type of surfaces spherical, plane, curved, smooth
and rough.
Answer these questions :Q. 1
What happens when a ray of light- falls ‘normally’ on the surface of a mirror?
Q. 2
Name the form of energy which enables us to see the objects?
Q. 3
What is meant by ‘reflection of light’?
Q. 4
A ray of light is incident on a plane mirror at an angle of 30°, what is the angle
of reflection?
24
SCIENCE 10
Image :- An optical image of a point is the point of intersection (real or virtual) of all the
reflected rays of light, originating from an object point.
Important Facts : To locate the position of image any two rays are sufficient to consider.
3.3 Reflection at Plane and spherical surfaces.
Reflection at Plane Surfaces :In the case of reflection by a plane mirror
the image formed has the following
characteristics:
1.
The image is always virtual.
2.
The image forms on the backside
of the mirror.
3.
The size of the image is equal to
the size of the object.
4.
The distance of image from the
reflecting surface is always the
same as the distance of the object
from the reflecting surface.
Fig. 3.2 The formation of virtual Image
of a point object by a plane mirror.
Reflection at Curved Surfaces :-
The size and position of the images
formed by the curved mirrors or spherical mirrors are quite different from those formed by the
plane mirrors because the normals at different points of incident do not have the same direction.
We will first define the spherical mirrors and then study the reflection of light from these spherical
mirrors.
You must have seen your image on the curved smooth surface of a glass or a metal plate.
These surfaces are either spherical or curved. That’s why images formed on these surfaces are
different from those formed by plane mirror. The spherical surface is one whose reflecting surface
is spherical.
Generally we use spherical mirrors for the study of spherical surfaces. The spherical
mirrors are of two types :(1) Concave Mirror and (2)
Convex Mirror.
1. Concave Mirror :- The
Centre of
Curvature
concave mirror is a type of spherical
mirror in which the inner surface is
Centre of
Curvature
polished but outer surface is painted.
2. Convex Mirror :- The
LIGHT : NATURE, REFLECTION & REFRACTION
25
convex mirror is one whose inner surface is painted and reflection takes place from the outer
surface.
Some Definitions Related to Spherical Mirrors :Centre of Curvature :- The centre of the sphere of which the spherical mirror is a part, is
called centre of curvature. It is denoted by the letter C.
Radius of Curvature :- The radius of curvature of the sphere of which the mirror is a part,
is called the radius of curvature. It is denoted by the letter R.
Pole :- The centre point of the reflecting mirror is called the pole. It is denoted by the
letter P.
Principal axis :- An imaginary line passing through the pole and the centre of curvature of
a spherical mirror is called the principal axis.
Principal Focus :- It is a point on principal axis where parallel beam of light after reflection,
either actually meets or appears to meet. It is denoted by the letter F.
In the case of concave mirror principal focus is in front of it but in the case of convex
mirror it lies behind the mirror.
Aperture :- The periphery or the part of the mirror which can be exposed to incident light
is called aperture.
3.3.2 Rules for obtaining images formed by spherical mirror.
Any two rules out of following are used for locating the position images by a spherical
mirror:(a)
Rays which are incident parallel to the principal axis always pass through the principal
focus of the mirror (Concave mirror) or appears to come through principal focus
(convex mirror).
(b)
A ray which is incident on the mirror passing through the centre of curvature follow
the same path afther reflection.
(c)
A ray that passes through the principal focus goes parallel to the principal axis after
reflection from the mirror.
Formation of different Types of Images by Concave Mirror.
Centre of
Curvature
26
SCIENCE 10
Fig. 3.3 Graphical construction of images in concave mirrors.
Summary of images formed by the spherical concave mirror.
No. Position of
the object
Position of
the image
(a)
(b)
at Focus F
In between F and C
(c)
(d)
(e)
(f)
At Infinity
beyond the centre
of curvature (C)
At the centre of
curvature (C)
Between F and C
At Focus F
Between pole P
and focus F
size of
image
highly diminished
Smaller then the
size of the object
At the centre of
Same size of
curvature
object.
Between infinity and Magnified
centre of curvature
At infinity
Highly enlarged
Behind the mirror
Enlarged
Nature of
image
Real and inverted
Real and inverted.
Real and inverted.
Real and inverted.
Real and inverted
Virtual and erect.
Formation of Different Types of Images by convex mirror :S.No. Position of object
Position of image
Size of image
Nature of image
(a)
At Infinity
Between infinity
and the pole
Very small,
point image
Smaller than
object
Virtual, erect
(b)
At F, behind
the mirror
between the focus
and the pole
LIGHT : NATURE, REFLECTION & REFRACTION
Virtual, erect.
27
Focal lenght
Fig. 3.4 Image Formation by Convex Mirror
3.3.3 Relation between focal length and radius of curvature of a spherical mirror:Consider a spherical mirror, such that ‘P’ is its pole.
AB is a ray of light, incident at point B and is travelling parallel
to principal axis, C is the centre of curvature of the mirror,
CB will be the normal to the mirror at B. After reflection,
reflected ray BD passes throughs the focus F. If R is the
radius of curvature and f is the focal length than we can
show the relation between them by following formula.
f =
1
R
2
D
Fig. 3.5
Thus, we can show that focal length of a spherical mirror is half of its radius of curvature.
This relation is true for convex mirrors also.
Important fact : Focal length of plane mirror is infinity.
Experiment :Object :- To know the type (concave or convex) of mirror without touching it.
Material required : Pencil, concave, convex and plane mirror.
Experiment (a) : If on placing the pencil in front of the mirror anywhere, the image
formed in the mirror is erect, virtual and of the same size as that of the pencil then
the mirror is plane mirror.
(b) If on placing the pencil at different distances from the mirror, the image formed in
the mirror is erect, always shorter than the object and also virtual then the type of
the mirror is convex mirror.
(c)
If on keeping the pencil close to the mirror the image formed is virtual, erect and
bigger than the object but on sliding the pencil away the image formed is real,
inverted and smaller than the object (pencil) then it is a concave mirror.
Conclusion : We can identify the mirror type on the basis of the image formed in it.
28
SCIENCE 10
3.4 Sign conventions : Following new cartesian sign
conventions are generally used for
measuring the size and distances
of focus, object and image in
spherical mirrors.
1.
The object by convention, is
always placed to the left of the
mirror, and hence light rays
are always considered to be
travelling from left to right.
2.
All distances are measured from the pole of a spherical mirror.
3.
Distances measured in the same direction as that of the incident light are taken as positive
and the distances measured against the direction of incident light are taken as negative.
4.
Heights or distances measured upwards and perpendicular to the principal axis are
considered positive whereas heights or distances measured downwards and perpendicular
to the principal axis are considered negative.
3.5 Derivation of Mirror Formula :
A relationship between the distance of object from the pole (u), the distance of image from
the pole (v) and the focal length of spherical mirror (f) is called mirror formula.
It is shown in following ray diagram that if an object is placed beyond the centre of curvature
of a concave mirror then its image is formed in between principal focus and centre of curvature.
Figure (3.7) shows a concave mirror DPE, whose pole is P, focus F and centre of curvature
C. An object AB is placed in front of a concave mirror and its image is formed at A’B’. DM is the
normal on principal axis.
According to sign conventionDistance of object from pole (PA) = –u
Distance of image from pole (PA’) = –v
Focal lenght of mirror (PF) = –f
Radius of curvature of mirror (PC) = –R
Now ∆ABC and ∆A’CB’ are similar Triangles.
Therefore
AB
CA
=
------ (1)
A' B' A' C
∆FA’ B and ∆FMD are also similar triangles.
LIGHT : NATURE, REFLECTION & REFRACTION
29
Therefore :
MD MF
=
Assuming the aperture of the mirror to be small,
A' B' FA'
we have. MD = AB.
So
AB MF
=
----(2)
A' B' FA'
Comparing equations (1) and (2)
CA MF
=
A' C FA'
If point D is very close to the pole P then we can say that
MF = PF (approximately)
CA
PF
=
A' C FA'
or
PA − PC
PF
=
PC − PA' PA' − PF
or
−f
−u − (−R)
=
−R − (−v) −v − (−f )
or
(u - R
= f
(R - v
v -f
or
uv – uf – vR + fR = fR – vf
or
uv = uf + vR – vf
We know that R = 2f
so
uv = uf + v x 2f - vf
or
uv = uf + vf
Now, dividing both the sides by uvf, we get-
1 1 1
= +
f v u
or
v+u 1
=
uv
f
f=
uv
( u + v)
Magnification :
30
SCIENCE 10
We know that the size of image formed by
a spherical mirror depends on the position of an
object with respect to the mirror. If heights of
object and image are measured perpendicular
to principal axis than the ratio of the height of
image (I) to the height of object (O) is known as
linear magnification. It is denoted by m.
Magnification (m) =
=
Height of image
Height of object
Commit to memory
In the above equation the values
of u, v and f are written by using
sign convention. The values of u
and f for concave mirror is always
negative. For real image the value
of v is negative and for virtual
image it is positive.
A' B' I
=
AB O
Here we have considered the height of object (AB) as positive and according to the sign
convention the height of real and inverted image (A’B’) is negative so the magnification is always
negative in this case.
(But, if the image is virtual and erect then the height of image will be positive according to
the sign convention and the magnification has a plus sign.)
Magnification is also related to distance of object (u)
and image (v) from the mirror. (see fig. 3.8)
So, Magnification
m=
− I −( − v )
v
=−
=
( − u)
O
u
Magnification is a relative quantity. Its magnitude
shows how many times is the size of image as compared
to that of the object.
Answer these question :
1.
What is focal length of a concave mirror whose radius of curvature is 1m?
2.
What is the radius of curvature of concave mirror whose focal length is 25 cm.
3.
If on placing an object at a distance of 20 cm from the concave mirror, the image of
that object forms at the same point then what is the focal length of the mirror?
4.
A magnified image of an object is formed by a concave mirror. If the length of the
object is 1 m and magnification is 2 then what is the length of the image?
Uses of Spherical Mirrors :
LIGHT : NATURE, REFLECTION & REFRACTION
31
l
When an object is placed between focus (F) and pole (P) of a concave mirror it forms a
virtual, erect and enlarged image. Thus, by using this kind of mirror we can have a proper
magnified shape. E.N.T. doctors use it to focus light on the internal parts of ear, nose and
eye for proper examination.
l
Convex Mirrors are widely used as rear-view mirrors in cars, scooters, motorcycles etc.
It produces an erect image that is smaller in size than the object. Therefore, a wide view of
the traffic behind the vehicle can be seen in a small mirror. It is also used as a reflector in
street light bulbs.
3.6 Refraction of Light :
Generally when light rays coming from the source of light, enters from one medium to
another then,
(a)
Some part of incident light is reflected back to the same medium.
(b)
Remaining part of incident light is propagated into another medium.
The phenomenon, due to which a ray of light deviates from its original path, while travelling
from one optical medium to another optical medium is called refraction.
When a ray of light travels from optically rarer medium to optically denser medium it always
bends towards the normal and when a ray of light travels from optically denser medium to
optically rarer medium it always bends away from the normal (see fig. 3.9). Except when ray is
incident normally on the surface of second medium.
In Fig 3.9, Let interface boundary of two optical mediums is AB, incident ray PO, incident
angle ∠ NOP = ∠ i and angle of refraction ∠ MOQ = ∠ r. It is clear in figure that when a ray of light
travels from rarer medium to denser medium. The angle of incident ∠ i is always greater than the
angle of refraction ∠ r and when, ray of light travels from denser medium to rarer medium, the
angle of incident ∠ i is always smaller than the angle of refraction ∠ r.
Fig. 3.9
32
SCIENCE 10
So, it is clear that angle of deviation δ = i–r
3.6.1 Refraction of light through a rectangular slab
Now let’s understand the refraction of light when light enters from air into glass or from
glass into air with the help of a rectangular glass slab PQRS.
A ray of light AO travelling in air is incident on the surface of glass slab (PQ) at a point O
and refracted ray OB travelling in denser medium bends toward the normal OM.
This refracted ray OB again gets refracted at the surface SR at a point B and comes out
in the direction BC and known as
the emergent ray which bends
away from the normal as it goes
from denser medium (glass) to
rarer medium (air). The angle
which the emergent ray (BC)
makes with the normal (DE) is
called the angle of emergence
(∠EBC).
Since the incident ray AO
and the emergent ray BC are
parallel to one another, so the
angle of emergence (∠EBC) is
equal to the angle of incident
∠AON.
3.6.2 Laws of Refraction(i)
The incident ray, the refracted ray and the normal at the point of incidence are in the same
plane.
(ii)
For a particular wavelength (or colour) of light the ratio of sine of the angle of incidence to
the sine of angle of refraction is constant for a given pair of medium and it is called refractive
index of medium 2 with respect of medium 1 and usually denoted by the symbol n21.
If angle of incidence is i and angle of refraction is r then
sin i
= n21 (Constant)
sin r
(Snell’s law)
Refractive Index - The refractive index is a pure ratio of two similar quantities. It has no
unit. This law is valid for refraction at plane and spherical surfaces.
LIGHT : NATURE, REFLECTION & REFRACTION
33
3.6.3 Relation between refractive index and speed of light
As we have seen in the case of ractangular glass slab that ray of light bends toward
normal when it moves from rarer medium (air) to denser medium (glass). Actually the bending
of light rays depends on the relativs velocity of light (V2) in second medium. If the volocity of light
in first medium is (V1) then
Velocity of light in first medium (V1)
Refractive index n21 =
Velocity of light in second medium (V2)
Where n21 is a constant. When the incident ray is travelling from vacuum (or air) to the
other medium the value of refractive index so obtained is known as absolute refractive index i.e.
refractive index of medium with respect to vaccuum. But when ray of light travels in two different
optical media then refractive index of medium (second) relative to medium (first) is known as
relative refractive index.
Absolute Refractive Index of some media
Medium
Refractive Index
Air
1.0003
Medium
Refractive Index
Quartz
1.46
Water
1.33
Crown glass
1.52
Ice
1.31
Rock salt
1.54
Kerosene
1.44
Flint glass
1.65
Turpentine oil
1.47
Ruby
1.71
Diamond
2.42
Important Fact l When an incident ray strikes normally
at the point of incidence, it does not
deviate from its path.
l Since the incident ray goes along the
normal to the surface. The angle of
incidence in this case is zero so Sin i =
O and there is no bending of the ray of
light and it goes straight.
34
SCIENCE 10
3.7 Lens :
A lens may be defined as a portion of
transparent medium bounded by two spherical
surfaces or by one spherical surface and other
plane surface.
Spherical lenses are mainly of two types :(1) Convex lens :- A convex lens is thick at
Fig. 3.11
the centre but thinner at the edges. Figure 3.11 (a)
shows a convex lens in which the two surfaces are convex or bulging out at the centre.
(2) Concave lens :- A concave lens is thin in the middle but thicker at the edges
(Fig. 3.11 (b).
A convex lens is also known as a converging lens because it converges a parallel beam
of light rays at a point. But on the contrary, a concave lens diverges a parallel beam of light rays.
So it is known as diverging lens.
Definitions of terms related to lenses :1. Principal axis :- The straight line passing through the centre of curvature of the surfaces
of the lens is called the principal axis.
2. Optical centre :- The optical centre of a lens is the point on the principal axis, such that
rays passing through it do not suffer any change in direction.
Fig. 3.12
(3) First Focus F1 : The first principal focus is that point on the principal axis of the lens,
from which rays diverge or appear to converge become parallel to the principal axis, after
refraction.
>
>
>
>
>
>
Fig. 3.13
LIGHT : NATURE, REFLECTION & REFRACTION
>
>
>
>
35
(4) Second Focus F2 :- The second principal focus is that point on the principal axis at
which the incident rays travelling parallel to the principal axis of the lens, either converge or
appear to diverge.
Fig. 3.14
3.71. Rules for obtaining images formed by lenses :There are three rules for obtaining images formed by lenses.
1.
A ray of light which is travelling parallel to the principal axis, after refraction through
the convex lens passes through second focus (F2) of the lens and in a concave
lens, after refraction appears to diverge through its second focus.
2.
A ray of light which passes through the optical centre of a lens does not suffer any
deviation.
3.
A ray of light which passes through first focus (F1) of the convex lens or seems to
converge at first focus (F1) of the concave lens, after refraction travels parallel to
the principal axis.
3.7.2 Formation of images by a convex lens.
36
SCIENCE 10
Fig. 3.15
Position and nature of images formed by convex lens at different positions of object :S.No. Position of object Position of image
a.
b.
c.
d.
e.
f.
At infinity
Nature of image
At focus (Other side of lens)
Real, smaller than the object
and inverted (highly diminished).
Beyond 2 F
Between (F) and (2F) on the Smaller than the object,
other side of the lens, between real and inverted.
focus and centre of curvature.
At 2F
At 2F, other side of the lens
Same size as of the object Real
and inverted
Between F and
Beyond 2F, other side of
Enlarged than the object,
2F
the lens
real and inverted.
At Focus
At infinity
Highly enlarged, real and
inverted
Between Focus
On the same side of the
Enlarged, erect and virtual.
and optical centre lens as the object
3.7.3 Formation of images by a concave lens.
No matter where the object in placed in front of a concave lens, the concave lens always
forms virtual, erect and diminished image of the object. When an object is placed at the distance
of focal length in front of a concave lens, the image of object formed is virtual, erect and smaller
than the object.
Fig. 3.16 Nature of image formed by concave lens.
LIGHT : NATURE, REFLECTION & REFRACTION
37
S.No. Position of object
Position of Image
Nature of Image
1.
At Focus
Virtual, erect and highly
At infinity
diminished
2.
Between infinity and
Between optical
Virtual, erect and
optical centre
centre and focus
diminished
3.8 Sign convention for lenses :-
Fig. 3.17
Same sign convention which are used for spherical mirrors are applicable to lenses. All
the distances are measured from the optical centre of the lens. According to the sign convention,
the focal distance of convex lens is taken as positive and focal distance of concave lens is
taken as negative.
3.9 Lens Formula :An object AB is placed on the principal axis of a convex lens. A ray of light BC parallel to
the principal axis, passes through the second focus F2 after refraction through the lens. The
second ray of light BO passes through the optical centre. (see fig 3.18). Both these refracted
rays actually meet at point B’. So B’ is the real image of point B of the object. Thus A’B’ is the real
image of the object AB.
From figure it is clear that
∆AOB and ∆A’OB’ are similar.
So
AB AO
=
---- (1)
A' B' AO
Similarly ∆COF2 and ∆B’A’F2 are similar.
So
38
OC
OF2
=
A' B' F2 A' But, AB = OC
Fig. 3.18
SCIENCE 10
AB OF2
=
A' B' F2A' ----(2)
From equation (1) and (2)
OA OF2
=
OA' F2 A'
According to the sign convention AO = u (Negative)
OF2 = f (positive) OA’ = v (positive)
F2A’ = OA’–OF2 = (v–f) (positive)
−u
f
=
v
v−f
or - uv + uf = vf
dividing uvf both sides, we get
1 1 1
− =
v u f
or f =
uv
( u − v)
3.10 Power of lens :A convex lens converges the light rays towards the principal axis whereas a concave
lens diverges the light rays away from the principal axis. In this way a lens bends the light rays.
It is observed that a lens of shorter focal length bends the light rays more, and said to have
greater power. Power (P) of a lens is defined as the reciprocal of its focal length (f) in metres.
Power of lens =
1
focal length of the lens (in metres)
P=
1
f (in metres)
The S.I. Unit of the power of a lens is dioptre, which is denoted by the letter D.
1 Dioptres = 1 m–1
The power of a convex lens is positive and the power of concave lens is negative.
Some examples of refraction in daily life :1. Twinkling of stars :- Densities of air gradually decrease as we go up above the
LIGHT : NATURE, REFLECTION & REFRACTION
39
surface of earth. At the same time, due to variation of temperature on earth and motion of air
particles, densities of different layers are changed. Thus light rays coming from stars continuously
changes their paths, (bends towards normal some time more and some times less), due to
which the number of rays reaching an observer’s eye on earth continuosly change. Thus stars
appears to twinkle.
Know more :(a) When the incident ray travels from a denser medium to a rarer medium it bends
away from the normal [see figure (a)]
(b) If we gradually increase the angle of incidence in a denser medium then at a
certain stage angle of refraction in rarer medium becomes 900 . At this stage the
angle of incidence is called critical angle for denser medium relative to rarer medium.
Thus, the angle of incidence for which the corresponding angle of refraction
is 900, is called the critical angle for the two given media.
(c) When a ray of light travelings from a denser medium into a rarer medium, is
incident at an angle greater than the critical angle, the ray is totally reflected
back into the same medium. (See figure (c)). This phenomenon is called total
internal reflection.
(2) Mirage in Desert :
In deserts, some times we see the inverted images of trees which creates illusion of
water lake. During day the land of desert becomes very hot. The hot sand, in turn, heats the air
in contact with it. In this way, the layers of air in contact with the ground becomes very hot and
expand, and hence becomes optically rarer. The cooler air (layers) up in the atmosphere behave
as optically denser medium.
Now consider a ray of light starting from a top of tree, moving from denser medium into
rarer medium it bends away from the normal. While travelling down, it is continuosly passing
40
SCIENCE 10
through different regions and at some stage the
angle of incidence becomes greater than critical
angle. At this total internal reflection of light takes
place. Due to total internal reflection, the ray of
light passes from hotter to colder air that is from
rarer medium to denser medium and bends
Medium
Medium
towards normal and inverted image of tree is
seen by the observer. This image also keeps
moving due to movement of air and creats an
illusion of water in a lake In summer similar effect
can be seen on hot roads.
Defects of Vision :-
Fig. 3.19
One of the most important sense organs
is our eye. You are very well familiar with the construction of a human eye. Our eyes behaves
like an optical instrument. The real images are formed at Retina of our eye and due to sensation
of vision we can see the objects. But with growing age or some other reasons, eye lens grows
hard and muscles becomes weaker. This results in the defects of vision.
There are four main defects of vision :(1)
Near sightedness or myopia
(2)
Far sightedness or Hypermetropia
(3)
Presbyopia
(4)
Astigmatism
3.11.1 Near sightedness or Myopia :A person suffering from this defect can see nearer objects clearly, but cannot see far off
objects clearly.
Causes of Myopia :One of the following causes are responsible for this defect.
(1)
Sometimes the eye ball gets elongated and therefore the image of the far off objects
is formed in front of the retina.
(2)
The curvature of lens surfaces increases i.e. lens becomes thicker due to which
focal length reduces.
LIGHT : NATURE, REFLECTION & REFRACTION
41
Correction of near sightedness
or Myopia
To correct this defect such a lens
should be used which reduces the
converging capacity of eye. Thus concave
(diverging) lens is used to correct Myopia.
The Myopic eye
3.11.2 Far sightedness or
Hypermetropia
A man suffering from hypermetropia
or far sightedness can see distant objects
clearly but cannot see near objects lying
within a certain point.
Fig. 3.20 Correction of Myopia
Reasons (causes) of HypermetropiaOne of the following may cause Hypermetropia(i)
The distance between lens and retina reduces and the eye ball contracts.
(ii)
Due to some disease or age, the ciliary muscles become stiff and hence, they do not
relax. Thus they are unable to exert sufficient inward pressure on the crystalline lens, with
the result that the focal length of the crystalline lens does not decrease as and when
required.
Correction of far sightednessIn this defect the focal length of
the lens increases due to which eye
lens become less convergent.
Therefore such a lens should be used
which makes it converging. Thus
convex lens (convergent) lens of
proper focal length is used.
Presbyopia
In this defect, the eye can see
neither the nearer nor the far off
objects clearly. This defect can be
overcome by using combination of
glasses. Bifocal lens can be used to
correct presbyopia. Lower half is
made convex lens to see nearer
objects and the upper half is made
concave lens to see far off objects.
42
The hypermetropic eye
Fig. 3.21 Correction of Hypermetropic
SCIENCE 10
Astigmatism :
Sometimes the surfaces of the crystalline lens of the eye become uneven. A person
suffering from this defect does not see clearly objects or their parts which are at a particular
inclination ‘Cylindrical’ glasses (lens) are used to correct Astigmatism.
Points to remember
l
When a ray of light falling on a body is sent back to the same medium it is called
reflection of light.
There are two laws of reflection
(1) angle of incidence = angle of reflection.
∠i = ∠r
(2) Incident ray, normal at the point of incidence and reflected ray, all three lie in the
same plane.
l
The spherical mirrors are of two types - Concave mirrors and convex mirrors. The
reflection of light takes place at the concave surface (or bent in surface) in concave
mirrors and it takes place from convex surface (or bulging out surface) in convex
mirrors .
l
The focal length of a spherical mirror is equal to half of its radius of curvature
f=
R
2
l
The focal length and radius of curvature of a plane mirror is infinity.
l
The mirror Formula for spherical mirror is
1 1 1
= +
f v u
l
For an object situated anywhere in front of the convex mirror, the image is always.
virtual, erect and diminished.
l
The change in direction of ray of light when it passes from one medium to another
medium is called refraction of light.
l
When a ray of light goes from a rarer medium to a denser medium, it bends towards
the normal and when it goes from denser medium to rarer medium, bends away
from normal.
l
There are two laws of refractions(1) Incident ray, normal and refracted ray all lie in the same plane.
(2) The ratio of sine of the angle of incident and sine of the angle of refraction is a
constant. It is known as refractive index and denoted by n21. It is also defined by
the ratio of the velocites of light in the two media.
LIGHT : NATURE, REFLECTION & REFRACTION
43
l
Refractive index has no unit.
l
Lens is a transparent medium bounded by two spherical surfaces.
l
A convex lens is thick at the centre but thin at the edges whereas concave lens is
thicker at the edges and thiner at the centre.
Lens formula for the refraction by thin lens is
1 1 1
– =
v u f
l
Magnification by lens (m) =
=
I (Height of image)
O (Height of object)
m=
l
–v
I
=
O
u
Human eye can have following defects of visionNear sightedness, far sightedness, Presbyopia and Astigmatism.
l
If a man can see near objects but cannot see distinctly far off objects then it is
called short sightedness. It is corrected by using concave lens.
l
If a man can see distinctly distant objects but cannot see distinctly near objects
then it is called far sightedness. It is corrected by using a convex lens.
EXERCISE
Very short answer type questions :1. What is meant by ‘reflection of light”?
2. What is the importance of reflection?
3. State the laws of reflection?
4. What is a spherical mirror?
5. Write down two uses of each type of spherical mirror.
6. How do we identify the nature of mirrors?
7. What is refraction of light?
8. State the laws of refraction.
9. What type of mirror & (side mirror) is used in automobiles for viewing of rear side?
10. What is the focal length of plane mirror?
Short answer type questions :1. What is the difference between real and imaginary (virtual) images?
44
SCIENCE 10
2. Explain the terms converging and diverging nature of lenses.
3. What is the power of lens? Write its unit.
4. State the sign convention for lenses.
5. The focal length of a convex lens and concave lens is 50 cm, what is its power?
6. Where in front of a concave mirror, an object should be placed so that it produces
enlarged and erect image?
7. How far from the concave mirror should an object be placed so as to form its real,
inverted and magnified image. (show the diagram)
8. Why do the trunks of trees and roads appear shaking during summer?
9. Why do stars twinkle?
Long answer type questions1. Describe with the help of diagrams, the formation of images when object is placed in front of
a concave mirror.
2. If an object is placed at the distances of 8 cm from the concave mirror, where will the image
form? Draw the ray diagram (Focal length of mirror is 10 cm.)
3. The magnification of a concave mirror is found to be 4 times when the object was fixed at 15
cm from the mirror find the focal length of the mirror.
4. How far an object from a concave mirror be placed so that its real image is formed which is
double in size of that of the object (Focal length = 10 cm.)?
5. Derive the relation between u, v and f for a concave mirror.
6. Derive the lens formula for a convex lens.
7. Explain with the help of a labelled ray diagram, the defect of myopia and how it is corrected.
8. Explain with the help of a labelled ray diagram, the defect of Hypermetropia and how it is
corrected.
Project :To produce the images by a big metallic spoon having smooth surface and then compare
them.
1. Try to see your face in the curved surfaces of the spoon.
2. Are you able to see the image? if yes then what is the size of the image, it’s big or small?
3. What happens to the image if you increase the distance between the face and the spoon?
4. Now turn the spoon and repeat the same process. Infer what can you say about the spoon?
In the same way, observe and compare the images formed by the spoon at different
positions.
LIGHT : NATURE, REFLECTION & REFRACTION
45
Chapter - 4
OPTICAL INSTRUMENT
The optical instruments are mainly classified into two
main categories : Image forming and Analytical devices.
Image forming instruments like microscope, telescope
etc. are used to see magnified images of objects and also used
for the study of apparent size of the object. Essential element
of these instruments are lens or mirror.
Analysing devices like spectrometer, interferometer etc
are used for the study of the nature of light along with optical
nature of the objects. Essential elements of these instruments
are Prism, Grating and Mirror.
We will study
Let’s know more about optical instruments and see how
4.1 Microscope
they can be useful to us.
4.2 Telescope
4.1 Microscope :
4.3 Dispersion of light
4.4 Superposition of
primary colours.
4.5 Colours and
pigments of objects.
It is an instrument which makes a big and clear image of
small objects. We have already studied that when an object is
placed within the focus of a convex lens, a magnified virtual
and erect image is produced. But magnification can be achieved
by convex lens only upto a certain limit. Thus, when we have
to see very small objects clearly, we increase the magnification
by using a combination of two lenses. There are two types of
microscopes.
(a) Simple microscope (b) Compound Microscope
4.1.1 Simple Microscope :
Simple microscope consists of a convex lens of short
focal length fitted in with a handle.
Principle of working : A simple microscope works on
the principle that when an object is placed between the focus
and optical centre of a convex lens, a magnified, virtual and
erect image is produced. Here, convex lens acts as a magnifier.
46
SCIENCE 10
Activity :
Making (constructing) a simple
microscope with the help of a fuse
bulb.
Remove the black cap of a fuse
bulb carefully and partially fill it with
water. Now try to read the bold
letters of a book with the help of
the same. Note down your
observations and try to find out the
reason.
(Warning : Perform this activity
under supervision)
Fig. 4.1 Simple Microscope
4.1.2 Compound Microscope :
The device used to
achieve greater magnification by
the combination of two lenses
which makes minute things
clearly visible is known as a
compound microscope.
Construction :- The
convex lens L1 is mounted at
one end of a cylindrical tube, It
Fig. 4.2 Formation of image through compound
is called the objective lens. This
microscope
tube contains another movable
cylindrical tube at the other end.
The lens L2 is fitted at the end of this movable cylindrical tube. The observer looks through this
and so it is called eye lens. A crown wire is arranged at a finite distance of eye lens. The
combination is known as eye-piece. The eye piece can slide in the wider tube by rack and pinion
arrangement. So that we can change the distance between objective lens and eye piece.
Let, the focal length of objective lens is = fo
and focal length of eye lens is = fe
The first focus of objective is Fo and first focus of eye lens is Fe.
Working :- When AB be a small object placed just beyond the first focus of the objective
lens L1. Its real, inverted and magnified image A’B’ is formed on the other side of lens L1 but
infront of eye lens L2.
OPTICAL INSTRUMENT
47
Now both these lenses are moved in such a way that the image A’B’ of the object AB
formed by objective L1, lies within Focus of eye lence L2. (Image A’B’ is formed between optical
centre of eye lens O2 and its first focus of Fe)
Image A’B’ acts as an object for the eye lens L2.
Image A”B” is the image of object A’B’ formed by eye lens which is highly magnified and
gives virtual image of object AB.
4.2 Telescope :A telescope is used to see a clear and magnified image of an object situated at a very
large distance from the observer. There are two types of Telescopes :(1) Astronomical Telescope
(2) Terrestrial Telescope.
An astronomical telescope is used to see the celestial bodies. It produces virtual, inverted
and magnified image. A telescope used for observing objects situated on earth is called terrestrial
telescope. A terrestrial telescope produces an erect image.
4.2.1 Construction of Astronomical Telescope
This telescope consists
of a long hollow metallic tube
fitted with a convex lens Lo at
A
coming
one end which faces the object
(heavenly body). It is known
as object (objective) lens.
B
There is one more
hollow tube fitted inside the first
tube on the other end. These
tubes can slide into one
another. The second tube is
Fig 4.3 Formation of image through an astronomical telescope.
fitted with one more convex
lens Le at the outer end which
Important Fact :
is known as eye lens or Eye
l
In a compound microscope the focal length of eye
lens is slightly greater than the focal length of the
object lens.
l
In a telescope focal length of object lens is large
while the focal length of eye lens is comparatively
small.
piece.
48
SCIENCE 10
Working of Astronomical Telescope :
The parallel rays coming from very very far-off object forms a real, inverted and diminished
image A’B’ at the focus of objective lens Lo. This image A’B’ acts as an object for the eye piece
lens Le. Now the eye lens Le is so adjusted that the image A’B’ formed by the objective falls
between the focus and the optical centre of the eye-piece. In that case, the final image A”B” is
virtual, magnified and inverted.
Answer these questions.
Q. 1
Which type of lens is used in a simple microscope?
Q. 2
Name the lenses which are used in a compound microscope?
Q. 3
Which lens has shorter focal length in compound microscope?
Q. 4
What is the difference between, compound microscope and telescope?
Q. 5
What are the different types of telescopes? Write down their names and uses.
4.3 Dispersion of Light :
You must have seen a
rainbow during rainy season.
Do you know why do we see
different colours in a rainbow?
In the year 1665,
Newton discovered this
phenomenon. Newton found
that if a beam of white light is
passed through a prism, the
white light splits to form a band
of seven colours on a white
screen.
Fig. 4.4 A glass prism splits the white light into seven colours.
When a beam of a white light is passed through a glass prism a band of seven colours
forms on a white screen, called spectrum of white light. The order of seven colours of the spectrum
are as follows :
(1)
Voilet
(5)
Yellow
(2)
Indigo
(6)
Orange
(3)
Blue
(7)
Red.
(4)
Green
These seven colours of spectrum can be memorised by the word VIBGYOR. The splitting
up of white light into seven colours is called dispersion of light.
It is clear from the figure that in the white light spectrum the maximum deviation is produced
in the violet colour so violet colour appears at the bottom and least deviation is produced in the
OPTICAL INSTRUMENT
49
red colour so red colour appears at the top of the
spectrum, on the screen.
The formation of spectrum produced by a prism
shows that white light is made up of seven different
colours mixed together. We can obtain white light
again by keeping another prism inverted near the
first one because it will nullify the deviation produced
by the first one. Now you can answer why we can’t
obtain a spectrum through a glass slab.
Do you know?
The colour of a light ray depends on
its wavelength. Different coloured
rays have different wavelengths.
Red colour has the maximum
wavelength while voilet has the
minimum.
4.4 Superposition of primary colours of light :Red, green and blue colours are called primary colours of light because all the other
colours can be obtained by mixing these three colours in suitable proportions which are known
as composite colours. Magenta, peacock blue and yellow colours are known as composite
colours. The following composite colours are obtained by mixing primary colours.
Red + Green = Yellow (y)
Red + Blue = Magenta (m)
Green + Blue = Peacock blue (c)
Complementary colour : Any two colours which when mixed produce white light are
called complementray colours.
For Example
Yellow + Blue = White
Peacock Blue + Red = White
Magenta + Green = White
It is clear from the diagram (Fig. 4.5), yellow blue, peacock blue - red, and magenta - green are
complimentry colours. A mixture of these colours
produces white light. When a colour absorbs white light
then its complementry colour appears. For ExampleWhite - Red = Peacock Blue (Green + Blue)
White - Blue = Yellow (Green + Red)
White - Green = Magenta (Red + Blue)
4.5 Colour of objects and pigment
Fig. 4.5
We observe different coloured objects around us. Some of them are luminous and some
are non-luminous. Non-luminous objects are either transparent or transluscent.
50
SCIENCE 10
The transparent body allows light of certain colours to pass through it and rest of the
colours are absorbed. The colour of a transparent body depends upon the colour it transmits.
Have you ever thought why things appear coloured? The colour of a non-transparent body is
the colour of light which it reflects out of the seven colours of white light falling on it. Most of the
colours of the white light are absorbed by the object while only one colour is reflected back.
So, when white light falls on an object, following three cases may arise :
1.
An object appears white when it absorbs none of the colours of white light and
reflects all of them.
2.
An object appears black when, it absorbs all the colours of white light and reflects
none.
3.
When only one colour is reflected, while all others are absorbed, the object appears
coloured (having the colour of reflected light).
A white rose appears white because it reflects all the colours of white light. A red rose
appears red, because if absorbs all the colours of white light except the red.
The colour of an opaque object depends on the colour of light which it reflects. But the
colour of a transparent object depends on the colour of light which it transmits.
An illuminating body emits light on its own. The light emitted by illuminating body may
be studied by prism and grating.
Pigments : The coloured substances which are used in paints are called pigments. The
paints which are used on our doors and windows
and the paints which are used to make paintings in
our drawing note books and the poster colours are
all pigments.
A special method is used for the preparation of
different colours of pigments. The primary colours of
pigments are different from the primary colours of
light. They are megenta, yellow and cyan. The painters
consider them as red, yellow and blue respectively.
Magenta (Red + Blue) - Red colour
Yellow (Red + Green) - Yellow colour
Cyan (Blue + Green) - Blue Colour
A painter mixes yellow and blue pigment to
make green colour. While studying light we have
known that yellow and blue are complementary
OPTICAL INSTRUMENT
51
colours which make white light together.
Blue pigment reflects violet, blue and green
colour and absorbs yellow and red colours. While
yellow pigment reflects green and yellow colours
and absorbs blue and violet colour.
This shows that the mixture of both
pigments can only reflect green colour.
Answer these questions.
1.
What is a spectrum?
2.
Why do objects look of different colours? Explain.
3.
What is a pigment?
4.
Name the primary colours of white light.
5.
What are the primary colours of pigments?
Points to remember
l
Simple microscope produces virtual, erect and enlarged image of an object.
l
Simple microscope consists of a convex lens of short focal length.
l
Compound microscope produces virtual, inverted and enlarged image of an object.
l
In a compound microscope, focal length of objective lens is comparatively small
than eye lens.
l
Telescope is an optical instrument which forms a magnified and clear image of
far-off objects situated on earth or in sky for the eye of the observer.
l
Astronomical telescope produces virtual, inverted and magnified image of an
object.
l
Red, green and blue are primary colours. The mixture of these colours is called
composite colour.
l
The coloured materials which are mixed in paint are known as pigments.
EXERCISE
Very short answer type questions.
(1)
Which instrument (device) is used to see the celestial bodies?
(2)
How many primary colours are present in white light?
(3)
Which colour deviates most in the spectrum of white light?
(4)
Which lens is used in a simple microscope?
52
SCIENCE 10
(5)
Write the name of the lens used in a compound microscope near object and near
eye?
(6)
What is a telescope?
Short answer type questions.
(1)
Why do things appear coloured? Explain.
(2)
Write the names of those three primary colours which when mixed in suitable ratios
produces white light?
(3)
What is a microscope?
(4)
Out of two convex lenses with focal lengths 5 cm and 10 cm, which one will be used
as an objective lens and which one as an eye lens?
(5)
Explain the position, nature and type of the image formed by a compound microscope
and by an astronomical telescope.
Long answer type questions
1.
Explain the construction and working of a compound microscope with the help of a ray
diagram.
2.
Explain the construction and working of an astronomical telescope through a ray diagram.
3.
Draw the diagram for dispersion of light through prism and show the position of different
colours of light obtained on screen.
4.
Explain the formation of different colours from the three primary colours (red, green and
blue) with the help of a diagram.
OPTICAL INSTRUMENT
53
Chapter - 5
ELECTRICITY AND ITS EFFECTS
We have seen lightning in the sky during the rainy
season. Probably our ancestors had first encounter with
electricity in the form of lightening.
Our ancestors had knowledge of electricity as it is
mentioned in the Atharva Ved. The Agastya Samhita
illustrates the formation of electric cell. The book named
‘Bright Tradition of Science in India’ mentions all the above
facts and shows that the primary Indian knowledge of
electricity spread all over the world and became an
inspiration for different experiments related to electricity.
5.1 Electric Potential :
We will study
5.1 Electric Potential
5.2 Concept of
Potential
Difference
5.3 Electric current
5.4 Ohm’s Law
5.5 Combination of
resistance
5.6 Thermal effect of
electric current
5.7 Electric power
5.8 Chemical effect of
electric current
5.9 Faraday’s law of
electrolysis
5.10 Electroplating
5.11 Electro chemical
cell
54
Water always flows from a higher level to a lower level
Heat flows from body at a higher temperature to body at a
lower temperature. The temperature of a body rises by
transfer of heat, similarly the potential of a body increases
by the transfer of charge. It should be mentioned here that
the word potential in electricity is used in the same sense
as temperature is used with heat and surface level of a
liquid in a vessel.
When two bodies of different potentials are connected
by a conducting wire then the flow of positive charge takes
place from higher potential to lower potential and it continues
to flow till the potential of those two bodies becomes the
same.
Thus, electric potential determines the direction of the
flow of charge from one conductor to another conductor.
Measurement of Potential :
When a test charge +q0 is brought from infinity to any
point in the electric field of a charge +q, some work has to
be done by test charge + q0against the repulsive force of
+q. Suppose work done to bring a charge +q0 from infinity
to a point A against the repulsion force is W.
SCIENCE 10
+q0
A
+q
O
W is the work done by the test charge +q0,
then the work done by a unit positive charge will
Infinity
W
be q
0
.
The measure of the work done by unit
positive charge is called the potential. Electric
potential is denoted by “V”. Thus the electric
potential at a point A in an electric field is given
by
Fig. 5.1 Direction of positive Charge flow
W
V= q
0
The potential at any point is defined as
the work done in bringing a unit positive
charge from infinity to that point.
If the work done in bringing a unit positive
charge from infinity to a point in electric field is 1
Joule then the potential of that point in the electric
field will be 1 volt.
Fig. 5.2 Test charge will feel repulsive
force due to electric field produced by
positive charge
Did you know?
l
Therefore, 1 volt = 1 joule/1coulomb.
S.I. unit of charge is Coulomb.
5.2 Concept of potential difference :
Potential difference is the difference
of potential between any two points in an
electric field.
Let a +q charge placed at the point
O, then if work done in bringing a unit
positive charge from infinity to the points
A and B are W1 and W2 respectively in the
electric field, then the work done in bringing
a unit positive charge from point B to A in
electric field is denoted by W = W1–W2
The potential of a charged particle is
measured by assuming the earth’s
potential zero. If the potential of an
object is more than the potential of
the earth then it has a positive
potential and if its potential is lessthan the potential of the earth then it
is said to have a negative potential.
Remember
l
A small charge which on kleeping in
an electric field doesn’t alter the
intensity of the field is called a test
charge.
According to the definition of
potential
W = V A –V B = Difference of
potentials at two points = Potential
difference.
Fig. 5.3
ELECTRICITY AND ITS EFFECTS
55
Where VA is the potential at point A and VB is the potential at point B.
The amount of work done in moving a unit positive charge from one point to another
point in an electric field is called the potential difference between those two points.
Since work is a scalar quantity, thus potential difference is also a scalar quantity.
S.I. unit of potential difference is volt V.
Following formula is used to calculate potential difference (P.D.) between two points
Potential difference =
Amount of work done in moving a test charge from one point to another
magnitude of test charge
W
P.D. = q
0
Where W = work done in moving a test charge from one point to another in an electric field
and q0 = magnitude of test charge
Numerical Example : What amount of work is done in moving a charge of 4 coulombs
from a point at 220 volt to a point at 230 volt?
Know more
Solution : We know that
Voltmeter is a device which is used to
Work done
measure the potential difference.
Potential difference =
Amount of charge
Voltmeter is joined parallel between the
W
two points whose potential difference
P.D. =
--------(1)
q
is to be measured as shown in figure.
Given :
P.D. = (230 volt – 220 volt) = 10 volt
Charge = 4 coulomb
Work done W = ?
Substituting these value in equation (1)
We get, 10 =
W
4
Fig. 5.4
W = 10 x 4 = 40 joule, So, work done is 40 joule.
Answer these questions
Q. 1 What do you mean by the potential of a conductor?
Q. 2 Potential at a point is 1 volt, what is the meaning of this statement?
Q. 3 Define potential difference and write down its SI unit.
Q. 4 Write down the difference between electric potential and potential difference.
Q. 5 If 5 joule work is done in bringing 0.5 coulomb charge from one point to another, find
the potential difference between the two points.
56
SCIENCE 10
5.3 Current Electricity :
To light a bulb or a tube light at home we need to turn on the switch like we need to do to
light a torch. Why does an electric bulb or a torch bulb produce light when switches are turned
on? Let’s do an activity to know this phenomenon.
A bulb, battery, key and conducting wires, all are connected according to the figure (5.5)
Terminal ends of a cell are marked with
+ve and –ve sign. Potential of +ve terminal end
is greater than the potential of -ve terminal of a
cell.
When switch (key) is pressed, then the
potential difference across the ends of the cell,
causes the current to flow in the wire and the
bulb. Due to this the bulb glows. When switch
(key) is released, the flow of charge breaks
down and the torch bulb extinguishes. Thus it is
clear that the existence of electricity in the
conducting wire depends on the flow of charge
in the wire.
Fig. 5.5
We can define electric current as “the amount of charge flowing through any conductor in
unit time” or in other words “rate of flow of charge is known as electric current.”
If a charge of Q coulomb flows through a conductor for t second, then the magnitude I of
the electric current flowing through it is given by
Current, I =
Q
t
The S.I. unit of electric current is ampere which is denoted by the letter A. Electric current
is a scalar quantity. Electric current through a conductor is said to be 1 ampere if one coulomb
charge flows through any conductor for one second.
5.4 Ohm’s Law
Current starts flowing in a conducting wire when conductors of different potentials are
connected. Similarly, when a cell is connected in an electric circuit the current starts flowing
due to potential difference between +ve and -ve terminal of the cell. It is clear that, there is some
relation between the potential difference and electric current of a conductor. Lets do an activity
to understand this.
ELECTRICITY AND ITS EFFECTS
57
Activity :
Object : To find the relationship between potential
difference and electric current.
Material required : 1/2 m long iron or nichrome
wire, Ammeter, Voltmeter and four cells of 1.5 V.
Method : Arrange the circuit as shown in the
Fig. 5.6
figure. First connect a cell and note down the
reading in Ammeter and Voltmeter in the following table. Subsquently increases the number
of cells to 1, 2, 3 and 4 and again note down the readings of Ammeter and Voltmeter.
S.No.
No of cells connected
in the circuit
1.
2.
3.
4.
Reading of Ammeter
in ampere (I)
Voltmeter reading
in volt (V)
1 (one)
2 (two)
3 (three)
4 (four)
V
for each observation.
I
l Draw the graph between V and I
l Calculate
Analysis : The values of
V
comes out to be nearly same for every observation.
I
The graph between V and I is a straight line.
Conclusion : There is a constant ratio between P.D. (V) and Current (I).
A German scientist G.S. Ohm in 1827, studied the relationship between electric current (I)
and potential difference and states that the electric current flowing in a conductor is directly
proportional to the potential difference across the ends of the conductor, provided the physical
conditions of the conductor remains the same.
If I is the current flowing through a conductor and V is the potential difference across its
ends then according to Ohm’s Law V ∝ I
or
V = RI ⇒ R =
V
I
Where R is a constant called resistance of the conductor and It’s Unit is ohm, which is
denoted by the symbol omega (Ω).
The resistance of any conductor depends on the following factors.
1. Nature of conductor : Two wires of same length and same size made of different
materials have different resistance at the same temperature. For example, a gold wire having
the same length and size as a silver wire, offers different resistances at room temperature.
Thus, resistance of a conductor depends upon the nature of the conducting material.
58
SCIENCE 10
2. Length of the wire : The resistance of a uniform conducting wire is directly proportional
to its length. i.e. R α l -----(1)
Where R is the resistance of wire and l is the length of wire.
3. Cross-section of the wire : The resistances of two wires of same conducting material
having same length but different thickness is also different. The resistance of thin wire is more
than thick wire. Thus
Rα
1
A
-------(2)
Where A - area of cross- section of wire.
4. Temperature of wire : Resistance of a metallic wire of uniform thickness increases
with the increase of temperature and decreases with the decrease in temperature.
Combining (1) and (2) we get
Rα
l
A
or
R=ρ
l
A
Where, ρ is a constant, called the specific resistance of conducting material.
If l = 1 m and A = 1m2
Then we get R = ρ
Thus, specific resistance of a conductor may be defined as the resistance offered by the
conductor whose length is one meter and area of cross-section is one square meter. The specific
resistance of all the wires made from same material would be same. It depends only on the
nature of the substance. The S.I. Unit of specific resistance is ohm metre. The specific resistance
of copper and aluminium is 1.69 x 10–8 ohm-metre and 2.63x10–8 ohm- metre respectively.
Read carefully
l
The continuous path formed by joining conducting wires and other resistances like
bulb etc. across of a cell through which the current flows is called electric circuit.
l
Some symbols (signs) used for denoting some elements used in electrical circuits
are as follows :
Element
Cell
Battery Open key
more than
one cell
Closed key
Electric
bulb
Sign
or
Ammeter
Volt
meter
A
V
Resistance
or
When two charged bodies are connected with a
metallic wire then electric current flows from
higher potential to lower potential while the flow
of electrons in wire is opposite to the direction of
flow of electric current (see Fig 5.7)
Fig. 5.7
ELECTRICITY AND ITS EFFECTS
59
5.5 Combination of Resistance :The resistances can be combined in two ways.
(i) In series and (ii) In parallel
(1) Resistances connected in series : When a number of resistances are connected
end to end such a way that the tail end of one resistance is connected to the initial end of the
other resistance so as to form a closed circuit, then such a circuit is called the series circuit.
Let R1, R2, R3 be the resistances of the various conductors joined in series and I ampere
be the current flowing through them. If. V1, V2 and V3 be the potential difference developed
across the ends of these conductors, then the total potential difference, (V) across the
combinations is given by
V = V1 + V2 + V3 .............. (1)
Now by Ohms law, we have V = IR
(Where R in total resistance of the
combination and I is the current flowing
through the circuit) and then
V1 = IR1, V2 = IR2 and V3 = IR3
Substituting these values in equation (1)
Fig. 5.8 Combination of Resistances in Series
We get
IR = IR1 + IR2 + IR3
Or,
R = R1 + R2 +R3
Thus, the total resistance of the circuit is equal to the sum of the resistances of the individual
conductors joined in series.
Numerical Example 2. : A resistance of 6 ohm is connected in series with another
resistance of 4 ohm. A potential difference of 20 volt is applied across the combination. Calculate
the current flowing through the circuit and potential difference developed across the ends of 6
ohm resistance.
Solution : (i) Let R is the total resistance of series combination.
Then by the formula of series combination
R = R1 + R2
Where R1 = 6 Ω and R2 = 4 Ω
R = 6 + 4 = 10 ohm.
According to Ohm’s law V = RI
or I = V/R
Given : V = 20 volt and R = 10 ohm
So, current flowing in the circuit is
60
Fig. 5.9
SCIENCE 10
I=
V 20
=
= 2 ampere.
R 10
(ii) We know that the current flowing through the 6 ohm resistance is 2 ampere. Now
potential difference across this resistance is calculated by using Ohm’s Law.
V1 = IR1
V1 = 2 x 6 = 12 volt.
Numerical Example 3. Potential difference between two points of a wire carrying 2 ampere
current is 0.1 volt. Calculate the resistance between these points.
Solution : According to Ohms Law
V = IR or R =
V
I
(Given : Potential difference V = 0.1 volt and current I = 2 ampere)
R=
01
.
= 0.05 ohm.
2
Thus, the resistance between the two ends of conductor will be 0.05 Ω
(ii) Parallel combination of resistances :
Two or more resistances are said to be connected in parallel if one end of each resistance
is connected at one common point and the other end is connected at other common point.
Let R1, R2 and R3 be the resistances of the three conductors joined, in parallel according
to the Fig 5.10. The two ends of all the conductors are joined together at A and B and a potential
difference of V is applied by means of a cell. Thus, the potential difference accross the two ends
of the combination is V.
Suppose the total current following in the circuit is I, then it is divided into three parts I1 (in
resistance R1), I2 (in resistance R2) and I3 (in Resistance R3) at point A.
It is obvious that
Total current I = I1 + I2 + I3 .............. (1)
Suppose the resultant resistance of this parallel combination is R. Then by applying Ohms
Law to the whole circuit, we get I =
V
R
by applying Ohms Law to each resistance
separately we get
I1 =
V
V
V
, I2 =
, I3 =
R3
R2
R1
Now, Putting the values of I1, I2 and I3 in
equation (1) we get
ELECTRICITY AND ITS EFFECTS
Fig. 5.10 Combination of Resistances in Parallel
61
V V V V
=
+
+
R R1 R2 R3
1 1
1
1
= +
+
R R1 R2 R3
Or
Thus, when three resistances are connected in parallel the reciprocal of the combined
resistance is equal to the sum of the reciprocals of the individual resistances.
Numberical Example 4. Calculate the resultant resistance when three resistances of 3Ω
are connected in parallel.
Solution : Suppose R is the total resistance of parallel combination then it is given by
1 1
1
1
= +
+
R R1 R2 R3
Given - R1 = R2 = R3 = 3Ω
or
1 1 1 1 3
= + + = =1
R 3 3 3 3
Thus R = 1 Ohm.
Fig. 5.11
Numerical 5. : Calculate the total resistance of the circuit shown in Fig. 5.12
Resistances 3Ω and 6Ω are connected in parallel.
Let R’ be their combined resistance.
R1 = 3Ω
1 1
1
=
+
R' R1 R2
R3 =
(Given R1 = 3Ω, R2 = 6Ω)
So
1 1 1 2 +1 3 1
= + =
= =
R' 3 6
6
6 2
2Ω
R2 =
6Ω
Fig. 5.12
Or R’ = 2Ω
Now R1 is in series with the resistance of 2Ω If R is
the total resistance of this circuit, then R = 2Ω+2Ω = 4Ω
Fig. 5.13
Thus, total resistance of this combination of resistances will be 4Ω
Answer these questions.
Q. 1
Q. 2
Q. 3
62
If two conductors at same potential are joined by a wire then, will the current
flow through the wire? Explain by giving reason.
If 6 Coulomb current flows through a conducting wire in 3 second, what will be
the value of electric current flowing through the wire?
Out of the two copper wires of the same length but different cross-section,
which one will have less resistance?
SCIENCE 10
5.6 Thermal Effect of Electric Current :
Important Facts.
It is by our experience we can say that when
electric current is passed through an electric bulb it glows
and becomes hot after some time. In the same way when
current flows in high resistance wire like nichrome it
becomes red hot and gives out heat. This is known as
the heating effect of current. This principle is used for
making appliances like electric iron, electric heater, and
electric kettle etc.
l
Some part of the total energy
suplied to an electrical
appliance is used to do work
while the rest is wasted in
the form of heat. This is the
reason that if electric fans,
T.V.s, radios etc. work for a
long time they get heated up.
Suppose a current I flows through a resistance R
for t seconds and a potential difference V is applied across
its ends. Then the flow of charge in wire in t seconds, is
given by
l
In the thermal effect of the
electric current, electrical
energy is transformed into
thermal energy.
Charge = current x time
or q = I x t ............. (1)
Now when an electric charge q moves
against a potential difference V, the amount of
work done is given by
W = qV
From eq (1) q = It
Then W = VIt ............ (2)
This work done is equal to heat (H)
produced in the conductor.
i.e. H = VIt
Fig. 5.14
Using Ohms law
V = IR
∴ Heat produced, H = I2Rt .......... (3)
This is known as Joules law of heating.
Equation (3) gives us the heat produced in joule when a current of I ampere flows in a wire
of resistance R ohm for t second.
According to this law
1.
The amount of heat produced in a conductor is directly proportional to the square of the
electric current flowing through it i.e. Hα I2
2.
The amount of heat produced in a conductor is directly proportional to the resistance of
the conductor i.e. H α R
3.
The amount of heat produced in a conductor is directly proportional to the time for which
current flows i.e. Hα t.
ELECTRICITY AND ITS EFFECTS
63
Numerical Example 6. : A potential difference of 250 volt is applied across a resistance
of 500 ohm in an electric iron. Calculate (1) the current and (2) heat energy produced in 10
seconds.
Solution : (i) Calculation of current flowing in elecric iron.
According to Ohm’s Law
Current (I) =
Potential difference (V) 250
=
= 0.5 ampere
500
Resistance (R)
Thus the current flowing in the electric iron is 0.5 ampere.
Calculation of Heat energy produced in electric iron :
Given : R = 500 ohm, t = 10 second
according to Joule’s law H = I2Rt
H = (0.5)2 x 500 x 10
= 1250 joule
Thus heat energy produced in electric iron is 1250 joule.
Applications of the heating effect of current :
Some of the important applications of the heating effect of electric current are given below:
1.
The heating effect of current is utilized in the electrical heating appliances like electric iron,
electric heaters etc. All these heating appliances contain coils of high resistance wire
made of alloy of nichrome. When these appliances are connected to power supply by
insulated copper wires, a large amount of heat is produced in the heating coils.
2.
The heating effect of electric current is utilized in electric bulbs for producing light. When
electric current passes through a thin, high resistant tungsten filament of an electric bulb,
the filament becomes white hot and emits light. Please note that the same current flowing
through the tungsten filament of an electric bulb produces enormous heat but almost
negligible heat is produced in the connecting wires of copper. This is because of the fact
that the fine tungsten has very high resistance, whereas copper connecting wires have
very low resistance.
3.
An electric fuse is an important application of the heating effect of current. When the
amount of current in a domestic electric circuit rises beyond a certain limit the fuse wire
gets heated up and melts and thus breaks the circuit. This prevents the circuit from catching
fire and protects electrical appliances, from passage of high current.
5.7 Electric Power :
When an electric current flows through a conductor, electric energy is used in doing work.
We know that the rate of doing work is called power. So “Electric power is defined as the amount
of electric work done in one second. Electric energy is consumed by electrical appliances for
doing work and so energy loss takes place in this process. Thus the rate at which electric
energy is dissipated, is also called “electric power”.
64
SCIENCE 10
When curent I is flowing in a circuit under a potential difference V for t second, then
electric energy loss is given by W = VIt
So electric energy loss in 1 second. =
W
= V.I
t
It is called electric power (P).
P=
W
= VI
t
S.I. unit of electric power is watt.
Electric power of 1 watt is defined as the rate of energy loss of 1 joule per second.
So 1 watt =
1 joule
1 sec ond
Watt is small unit of electric power, bigger unit known as kilowatt or megawatt are also
used.
1 kilowatt = 1000 watt = 103 watt
1 megawatt = 106 watt
Practical unit of power is horse power (h.p.)
1 horse power (h.p.) = 746 watt
We know that the electrical energy is the product of power and time. So, the unit of electrical
energy is watt hour (Wh). The energy consumed in an electric circuit is one watt hour if power of
one watt is used for one hour.
In practice a bigger unit known as the kilo-watt hour (kWH) is used. It is also known as
‘unit’ in common language.
1 kWH (or 1 unit)
= 1 kilo watt x 1 hour
= 1000 watt x 3600 second
= 3.6 ×106 J
Numerical Example 7. : An electric bulb is rated 200 V - 100 W. Find the resistance of the
bulb.
Solution : Given : Power of bulb = 100 watt.
and potential difference V = 200 volt
Resistance of bulb R = ?
We know that power P = VI and by Ohm’s law I =
So, P =
V
R
V2
(200)2
watt or R =
= 400 ohms.
R
100
ELECTRICITY AND ITS EFFECTS
65
Numerical Example 8. : An electric bulb is rated 20 watt 15 V. Find out how much
electrical energy will be consumed at 12 volts.
Solution : Given : P = 20 watt and V = 15 volt
V2
We know that electric power P =
R
V2 (15)2 225 45
=
=
=
R=
ohm
P
20
20
4
Thus, resistance of a given bulb is 45/4 ohm.
Now electric power consumed at 12 volts is
V2
P’ =
R
P' =
(12)2 144 4 576
=
×
=
= 12.8 watt.
45 / 4
1
45 45
5.8 Chemical Effects of Current
Electrolysis : A conducting wire becomes hot when electric current is passed through it.
Have you ever thought what will happen on passing electric current through a liquid?
Following three cases may arise when electric current is passed through a liquid.
(i)
The curret does not pass through the liquid. Such a liquid is called non conducting
for example- distilled water
(ii)
Current passes through the liquid but does not affect the structure of liquid. Such a
liquid is called conducting liquid for example mercury.
(iii)
Electric current passes through the liquid but changes the structure of the liquid
Such a liquid is called an electrolyte for example - Acidic water.
In the third case the atoms of liquid decompose into positive and negative ions. On applying
electric field (or potential difference) these ions start moving. Positive ions move towards the
cathodes while negative ions moves towards the anode. This process is known as electrolysis.
The positive ions moving towards the cathode are called cations and negatively charged ion
moving towards the anode are called anion.
The phenomenon by virtue of which a substance in aqueous solution (or molten state)
decompose into their constituentions is called chemical effects of current.
5.9 Faraday’s laws of Electrolysis :
In 1883, Michael Faraday studied the effects of electrolysis and stated two laws of
electrolysis.
66
SCIENCE 10
First law : The mass of any substance liberated at an electrode is directly proportional to
the charge flowing through the electrolyte.
i.e. m ∝ Q, where ‘m’ represent the mass and “Q” the charge transferred
Second law : If same amount of charge flows through different electrolytes, the masses
of substances liberated or deposited at electrodes are directly proportional to their chemical
equivalents (E).
mα E
i.e.
[Chemical equivalent = Molecular weight/Valency]
If m1 and m2 be the masses of copper and silver deposited on the electrodes when same
current is passed for electrolysis of CuSO4 and AgNO3 respectively for the same time
According to second Law
m1 E1
=
m 2 E2
The containers, which are used for electrolysis of copper sulphate and silver nitrate are
called copper voltameter and silver voltameter respectively.
(Chemical equivalent of copper
E1 =
63
= 31.5
2
Fig 5.15
and chemical equivalent of Silver
E2 =
108
= 108)
1
5.10 Electroplating :
To prevent the containers made of iron from corrosion, they are plated by a layer of chromium
or nickel to make their surface smooth and shiny. Similarly silver or other metallic jewellery are
plated with a layer of gold to give them golden lustre. In the past history of India, people were
aware of the process of plating. The process of plating one metal on the other metal by chemical
effect of electric current is known as electroplating. It is based on the principle of electrolysis.
ELECTRICITY AND ITS EFFECTS
67
The metal article on which electroplating
is to be done is made the negative electrode i.e.
cathode the metal to be deposited or plated is
made the positive electrode by hanging its rod
or plate at the place of anode.
When electricity is passed through
electrolytic solution then the metal from anode
gets transferred to the metal at cathode.
The arrangement used for copper plating
is shown in fig 5.16. Here an iron vase is to be
plated with copper.
Fig. 5.16
Following table shows the name of the electrolytic solution (electrolyte) to be used for
plating a particular metal on the other.
Name of the element which
is to be plated
Electrolyte
1.
Copper
Copper sulphate solution
2.
Silver
Silver Nitrate Solution
3.
Gold
Gold and Potassium cyanide solution.
4.
Nickel
Nickel ammonium sulphate Solution.
5.11 Electro Chemical Cell
You must have seen a small bulb in a torch
producing light. The bulb acquires energy from
the cell inside the torch and produces light. Now
the question arises, from where does the cell
get the energy?
Cell acquires energy from the chemical
subtance present inside the cell.
Thus an Electro chemical cell is a device
which converts chemical energy into electrical
energy.
Now, Let us know about voltaic cell which
was first made in the year 1800 by Volta.
Fig. 5.17
It consists of a vessel containing dilute sulphuric acid (H2SO4) as an electrolyte. Copper
and Zinc rods are dipped in the electrolyte. These rods act as electrodes. Electrodes are
connected to a bulb by a conducting wire as shown in the figure 5.17
68
SCIENCE 10
This was invented by a scientist, named Volta hence it is called voltaic cell. When sulphuric
acid is dissolved in water, it decomposes into hydrogen ions and sulphate ions. The negative
charge on zinc plate and the positive charge on the copper rods builds up a potential difference
accross these rods. This potential difference causes flow of electrons from zinc rod to copper
rod through the wire connecting these rods and lights the bulb. The flow of electrons from zinc
rod to the copper rod constitutes electric current. The direction of electric current is from positive
electrode to the negative electrode through the wire while the flow of electrons is from negative
electrode to positive electrode, in the wire.
Dry CellGenerally we use dry cells in torch, transistor, radio and in toys.
The chemicals used in dry cell are not in liquid form (as in a voltaic cell) but are in the form
of compact paste. They are easily transportable.
A dry cell Consists of a cylindrical container made of Zinc. This contains the paste of
ammonium chloride and zinc chloride mixed with manganese dioxide and powdered carbon
which act as a catalyst.
This container is covered and sealed by wax from the top.
The Carbon rod acts as anode (+ve electrode) and cylindrical vessel made of zinc acts
as cathode (-ve electrode). A brass cap is mounted on carbon rod.
When dry cell is connected by a conducting wire to complete the circuit, the electrolyte
(Ammonium Chloride) decomposes into ammonium ions (NH 4 + ) and chloride ions
(Cl–). The chloride ions (Cl–) moves to the zinc vessel and ammonium ions (NH4+) moves to the
carbon rod which produces a negative charge on vessel and positive charge on carbon rod
NH4Cl →
NH+4
Cl–
+
(on cathode) (on anode)
When the electrons reach the carbon cathode they are combined with the ammonium ions
present in the electrolyte to form ammonia and hydrogen gas at the cathode. This hydrogen gas
forms a layer around the positive carbon electrode and gets accumulated opposing the flow of
electric current. However to prevent this, the dry cell is filled with powdered managnese dioxides
which reacts with hydrogen and oxidise it. In this way
mangazene dioxides works as a depolariser in cell.
+
2NH4 +2e– → 2NH3 + H2 ↑
2MnO2
+
H2
→ Mn2O3 + H2O
(Manganese dioxide) (Hydrogen)
(Water)
A small hole is made in a dry cell for ammonia gas to
escape. On connecting dry cell in circuit 0.25 Ampere
current is obtained at 1.5 Volt.
ELECTRICITY AND ITS EFFECTS
69
Points to remember
l
Mercury conducts electricity but does not decompose into ions when current
passes through it.
l
Distilled water is a bad conductor of electricity.
l
Substances in molten state or in aqueous solution which allow large amount of
electric current to pass through them and completely decompose to give ions are
called electrolytes. eg. CuSO4, AgNO3, NaCl etc.
l
On passing the current through electrolytes, cations deposit on cathode and anions
deposit on anodes. The phenomenon is called electrolysis and the effect is called
chemical effect of current.
l
To polish gold on a metal, Gold and Potasium Cyanide solution are used as
electrolytes
l
Voltaic cell and dry cell are called electro chemical cell. Chemical energy is
transformed into electrical energy in these cells.
l
Dry cells are easy to use as they are portable and so they are used mainly in
most of the appliances used in daily life like watches, torch, toys etc.
EXERCISE
Very short answer type questions.
(i)
What is potential? Write its S.I. Unit
(ii)
Write the difference between potential and potential difference.
(iii)
What do you understand by the thermal effect of electric current?
(iv)
Write any three appliances used in daily life based on thermal effect of electric current.
(v)
Define Electric Power.
(vi)
Define the unit ‘Watt’ of electric power and write the relation between watt and kilowatt.
(vii) Pick out electrolyes from the following.
(i) Distilled water
(ii) Acidic Water
(iii) Mercury
(iv) Copper Sulphate
(v) Ammonium Chloride
(vi) Silver Nitrate
(vii) Sodium Chloride
(viii) Molten Silver.
Short answer type questions.
(1)
State Ohm’s Law.
(2)
In electroplating, the vessel or jewellery to be plated is kept at cathode or anode?
(3)
what is the function of a Carbon Rod in a dry cell?
70
SCIENCE 10
(4)
What are the factors responsible for resistance of a conductor?
(5)
Draw a labelled diagram of a dry cell.
Long answer type questions.
(1)
Write Faraday’s laws of electrolysis.
(2)
How will you polish zinc on an iron vase. Explain with diagram.
(3)
Define electric resistance. What are the factors affecting electrical resistance?
(4)
Draw a well labelled diagram of dry celll and explain its construction.
Project 1 :
In the following circuit join wires of iron and aluminium etc. (as many material you can
collect) of same length between the two points X and Y. Note down the readings of
Ammeter and Voltmeter and record the values in the following observation table.
Project 2 :
Next join two pieces of wires of same material in series and then in parallel one by one
and tabulate your observations.
+
x
y
Observation table 1.
S.No.
1.
2.
Material of
Reading of
Reading of
Resistance
wire
Voltmeter (V)
Ammeter (A)
R=
Reading in
Reading of
Resistance
Voltmeter (V)
Ammeter (A)
R=
Aluminium
Iron
Observation table 2.
S.No. Type of
combination
1.
2.
V
I
V
I
Series
Parallel
ELECTRICITY AND ITS EFFECTS
71
Chapter - 6
MAGNETIC EFFECT OF ELECTRIC CURRENT
We have studied the heating and chemical effects of
electric current in the previous chapter. But do you know that
there is one more effect of electric current which is called the
magnetic effect of electric current and is very useful in our
daily life. Let us discuss more about this effect.
In the year 1820, The famous scientist Hans Christian
Oersted of Denmark found that when an electric current is
passed through a conducting wire, the magnetic needle kept
near it shows the deflection. On increasing the electric current
the deflection in the needle increases and on changing its
direction the direction of deflection also changes.
We will study
6.1
Magnetic field due
to straight current
carrying conductor
6.2
Magnetic field due
to current carrying
coil and solenoid
6.3
Electromagnetic
Induction.
On the basis of the experiment, Oersted concluded that
when electric current is passed through a conducting wire, a
magnetic field is produced around it.
Fig 6.1 Magnetic field produced due to electric current
In this way, the phenomenon of occurence of a magnetic
field around a current carrying wire is known as magnetic effect
of electric current.
6.4
Electric Motor
6.5
D.C. generator
6.6
Direct and
alternating current.
6.1 Magnetic field due to a straight current carrying
conductor
6.7
Domestic
electrical circuit
6.8
Precautions in
using electricity.
Connect a long straight copper wire with two or more
dry cells and a key as shown in the Fig. 6.2. A magnetic needle
is placed under the copper wire such that the needle is parallel
to the wire.
72
l
Now pass the current in the circuit by pressing the plug.
SCIENCE 10
Note down the deflection of the north
pole of the needle.
l
Now take the magnetic needle away
from the copper wire. We will see that,
on increasing the distance of the
magnetic field from the copper wire,
the deflection in the magnetic needle
comparatively decreases and it further
reduces with the increasing distance.
Now increase the number of cells in
the circuit and place the magnetic
needle under the copper wire as
earlier. You will see that the deflection
in the magnetic needle is comparatively larger than before.
Following conclusions can be drawn from
the above experiment.
1.
When current is passed through a
conducting wire, a magnetic field is
produced around it whose direction
depends upon the direction of current in
the wire.
2.
The magnitude of the magnetic field
produced by a current carrying wire
decreases with the increasing distance
from the wire.
3.
Greater the current in the wire stronger
will be the magnetic field produced.
N
S
M agnetic needle
Connecting wire
W ooden board
Plug key
Cell
W
Deflection
Current
N
N
S
S
N
S
M agnetic needle
M
W
S
N
S
M agnetic needle
Fig 6.2
N
N
l
Copper wire
Now change the poles of the cells in
the circuit so that the direction of flow
of current in the wire is reversed. Now
on passing the current in the circuit
you will find that the deflection of the
north pole of the magnetic needle is
reversed.
S
l
De flection
M
Know more
The space surrounding a magnet in
which magnetic force is exerted is called a
magnetic field. The magnetic lines of force
are the lines drawn in a magnetic field along
which a north magnetic pole of magnetic
needle would move.
Magnetic lines of force produced by
a bar magnet is shown in the figure.
The magnetic field produced on passing
current through a conducting wire can be
understood by the following activity.
MAGNETIC EFFECT OF ELECTRIC CURRENT
73
Activity
Aim : To see the magnetic field pattern due to
straight current carrying conductor.
Materials required- 12 V battery, rheostat,
ammeter of range 0-3 ampere, Iron filings, a plug
key, a thick and straight copper wire and a piece
of rectangular card board.
Procedure- Paste a white sheet of paper on the
rectangular card board.
l Pass the straight vertical wire through a hole
in the middle of the card board as shown in the
figure.
l Now connect a battery, ammeter, rheostat and
plug key in series between the two points X
and Y as shown in the figure.
l Now sprinkle iron filings around the wire on the
Fig 6.4 Magnetic field pattern
obtained in iron filings
card board uniformly.
l Now pass the current in the circuit by pressing the plug.
l Tap the cardboard gently and observe the motion (movement) of iron filings carefully.
l The iron filings arrange themselves in the form of concentric circles as shown in the
figure.
l Analysis- A magnetic field is produced around a wire on passing current through it due
to which iron filing on the card board arrange themselves in concentric circles.
l Conclusion - The magnetic lines of force round a straight conductor (wire) carrying
current form concentric circles.
The direction of magnetic field produced
by current carrying conductor can be obtained
by using following rules1. Right hand thumb ruleImagine that you are holding the current
carrying wire in your right hand so that your
thumb points in the direction of current, then
the direction in which your fingers encircle the
wire will give the direction of magnetic lines of
force around the wire.
74
Fig. 6.5 To know the direction of
magnetic lines of force
SCIENCE 10
2. Maxwell’s cork screw ruleMagnetic field
If a cork screw is driven in the direction of
current passing through the wire, then the motion of
the thumb shows the direction of the magnetic field.
(Fig. 6.6)
Answer these questions.
Electric current
Q. 1 What do you understand by the magnetic
effect of electric current?
Q. 2 State “Right Hand Thumb Rule” and
explain. What is its use?
Fig. 6.6
Q. 3 Draw the magnetic lines of forces of the
magnetic field produced around a straight
vertical current carrying conducting wire.
6.2 Magnetic field due to circular coil carrying
current and solenoid.
We have seen the magnetic lines of force of
magnetic field produced around a conducting wire
on passing current. What will be the shape of
magnetic lines of force of the magnetic field produced
on passing current through a thick copper loop. Let
us see through an activity.
Learn More-
Did you know.
The earth’s magnetic field
is supposed to arise from
electric currents, in the molten,
iron rich outer core surrounding
the solid inner core of earth.
Presence of magnetic field
in human body : Weak ionic
currents that flow along the
nerve cells produces magnetic
field in our body. The Magnetic
Resonance Imaging (MRI)
technique in Medical Science
which is used to scan inner
human body parts is based on
the magnetic field present inside
the body.
Fig. 6.7 A conductucting wire in the form of a
circle is called a loop.
MAGNETIC EFFECT OF ELECTRIC CURRENT
75
ActivityAim- To see the magnetic lines of force
of the magnetic field produced arround
current carrying loop (coil)
Materials required- Thick insulated
copper wire, piece of card board, battery,
key, rheostat, magnetic needle and pencil.
Procedurel
Make 10 to 15 loop of thick insulated
copper wire by turning it round.
l
Complete the circuit by joining loop
with rheostat, key and battery as
shown in the figure.
l
Pass the current in the circuit.
l
Now place the magnetic needle near the hole A on the card as shown in the figure
board and mark a point on the card board where the north pole of the needle points.
l
Now place the centre of the needle on the point marked above and again put a dot on
the cardboard at the north pole of the magnetic needle. Repeat this process until you
get points all around the conducting wire and then join all the points.
l
You will obtain a circle. Show the direction of the motion of north pole of the magnet on
the circumference of this circle by making arrow heads. The figure so obtained is called
magnetic lines of force of magnetic field around the loop.
l
Draw magnetic lines of force by keeping the magnetic needle at different positions
around the point A.
l
Now repeat the same process as above to draw magnetic lines of force around the
point B.
Fig. 6.8 Magnetic field produced due to
current carrying loop
Conclusion 1.
The lines of force are circular at points A and B.
2. The direction of motion of north pole of the magnetic needle near the points A and B are
opposite due to the direction of flow of current in the coil. The lines of force become
straight and parallel at the centre of the coil. This shows that as the distance of the point
from the coil increases the intensity of the magnetic field at that point decreases.
The lines of force at the centre of the circular coil appears or becomes a straight line.
If we have a circular coil having n turns of wire then the magnitude of the magnetic field
76
SCIENCE 10
would be n times than that in the first case.
The reason is that the flow (direction) of current
in each turn is same due to which the
magnetic field produced by each turn gets
added.
A circular current carrying loop behaves
like a thin disc-magnet whose axis is
pependicular to the axis of the coil depending
to the direction of current. The poles in a coil
are identified as per the figure 6.9 and 6.10.
Answer these questions.
Q. 1 Which surface of the current carrying
coil behaves like a south pole?
Q. 2 What magnetic pole is produced at the
face of the coil in which current flow
anticlockwise?
Magnetic field due to current flowing
Solenoid.
The solenoid is a long coil containing a
large number of close turns of insulated
copper wire. A solenoid is made of an insulated
copper wire wound on a hollow cylindrical tube
of non conducting material like card baord,
clay etc.
When the electric current is passed
through the solenoid, it produces a magnetic
field around it as shown in Fig. 6.11. The
direction of magnetic field inside a solenoid is
parallel to the axis of the solenoid. The end of
the solenoid where the direction of flow of
current is anticlockwise behaves like a north
pole and the other end where the flow of
current is clockwise acts like a south pole.
Intensity of magnetic field near the middle of
the axis of solenoid is uniform. Solenoids are
MAGNETIC EFFECT OF ELECTRIC CURRENT
Face of the coil where
current flows anticlockwise
acts as a noth pole
Face of the coil where
current flows clockwise
acts as a south pole
Fig. 6.9
Fig. 6.11 Magnetic lines of force for a
current carrying solenoid
77
used to make strong magnets if a soft iron rod is placed inside a solenoid then strength of the
magnetic field becomes very large because the iron core gets magnetised by induction. This
combination of a solenoid and a soft iron core is called electromagnet.
Answer these questions.
Q. 1 What is a solenoid?
Q. 2 Which end of a solenoid acts as a south pole when current is passed through
it?
Force on a conductor carrying current in a magnetic field.
A French scientist Andre Ampere (17751836) suggested that when current is passed
in a conductor kept in a magnetic field then a
magnetic force acts on it. This can be
understood by the following experiment.
l
A thick copper wire is suspended
horizontally from a support by means of
a soft conducting spring which is
attached to a hard support and a battery.
l
A horse-shoe magnet NS is placed in
such a way that the wire PQ remains
perpendicular to the magnetic lines of
force as shown in figure.
l
On passing the current in wire PQ by the
battery it rises upwards and the spring
appears to contract.
l
If the direction of current in the wire is
changed then the wire goes downwards
and the spring expands.
Fig. 6.12 force experienced by a current
carrying rod PQ perpendicular to its own
length and magnetic field as well
In this experiment the direction of flow of current in the wire (copper) is perpendicular to
the direction of magnetic field of the horse shoe magnet. In such situation the force exerted on
the conducting wire is perpendicular to both these directions.
The direction of the force exerted on a conducting wire in a magnetic field can be known
easily by Fleming’s left hand rule.
78
SCIENCE 10
Fleming’s left hand ruleStretch the fore finger, the middle finger and
the thumb in such a manner that all three are
perpendicular to each other. If the fore finger points
the direction of magnetic field and the central finger
shows in the direction of current then the thumb will
point the direction in which the conductor will move.
Electric generators, electric motors etc. works
on the principle of electro-magnetic Induction.
Answer these questions.
Q. 1 What happens when current is passed in a
conducting wire placed in a magnetic field?
Q. 2 Write Fleming’s left hand rule.
6.3 Electromagnetic Induction
We have learnt that when a current carrying conductor is placed in a magnetic field, a
force is exerted on it which can make the conductor move. But is the converse of this effect
possible? That is, if a conductor is moved in a magnetic field then will an electric current be
produced in the conductor?
Yes, it is possible. The device used to produce electricity, named “Generator’ uses this
effect. A coil of insulated wire is moved in a magnetic field which produces electricity (current) in
the wire.
In the year 1831, Michael Faraday succeded in producing current in a coil kept in the
magnetic field of a moving magnet. Let us do the
following experiment to understand this property.
1.
Connect a current measuring instrument
(Galvanometer) between the two ends of a coil
of insulated copper wires. Fig. 6.14 (a)
2.
Bring the north pole N of a bar magnet near one
end of the coil. A little deflection in the
galvanometer would be seen. Note this direction
of deflection Fig. (b)
MAGNETIC EFFECT OF ELECTRIC CURRENT
79
3.
Now keeping the magnet stationary bring the
coil close to the north pole of the magnet.
Galvanometer will show a deflection in the
same direction Fig. (c)
4.
There is no deflection in the galvanometer
when both the magnets and coil are stationary.
5.
Now move the north pole of the bar magnet
away from the coil. The galvanometer shows
a deflection in the opposite direction than in
step (2) and (3) Fig. (e). The same effect
occurs when coil is taken away from magnet.
You can see that if the south pole of the magnet
is brought near the coil then the deflection in the
galvanometer will be opposite to that in step 2 & 3.
Fig 6.14
When a magnet is in a relative motion to a coil attached with a galvanometer, induced
electric current is set up in the coil. This process of producing electric current is
called electromagnetic induction.
When there is a relative motion between the magnet and the coil, the number of magnetic
lines of force passing through the coil changes which induces an e.m.f. between the ends of the
coil. This induced e.m.f. produces the current known as induced current. When a magnet is
moved towards the coil, more and more magnetic lines of force pass through the coil. When a
magnet is moved away from the coil, the number of magnetic lines of force passing through the
coil decreases.
We know that when electric current is
passed through a coil, a magnetic field is
produced around it. Thus if a coil is placed near
a current carrying coil and induced current is
set up in the second coil then the galvanometer
connected between the two ends of this second
coil shows a deflection.
80
secondry coil
Faraday’s law of electromagnetic induction states that the magnitude of the induced e.m.f.
produced in the coil is directly proportional to the rate of change in the number of magnetic lines
of force in the coil.
Fig 6.15
SCIENCE 10
The coil in which the electric current is passed is called the primary coil and the one in
which the electric current is induced is called the secondary coil.
When the magnitude of the electric current passing through the primary coil changes, the
magnitude of the magnetic field produced around it also changes accordingly due to which
induced electric current is produced in the secondary coil.
Answer these questions.
Q. 1 What do you understand by electromagnetic induction?
Q. 2 What is the reason of the electric current obtained in a coil when there is a
relative motion between coil and magnet?
6.4 Electric motor
It is a device which converts electrical energy into mechanical energy. Electric motor is
used in electric fans, washing machines, mixer and grinder, tape recorder, cassette player, CD
players etc. Generally, there are two types of electric motors.
1. Motors using current from cell or batteries.
2. Motors using electricity supplied by power stations.
Principle of a motor
It works on the principle that when current flows through the coil placed in a strong magnetic
field then by Fleming’s left hand rule, each arm of the coil experiences a force equal in magnitude
and opposite in direction. These forces makes the coil rotate around its axis.
ABCD = current carrying coil
NS = direction of magnetic field.
F1, F2 = Forces acting on the arms
of the coil due to current flowing in the coil
which are equal in magnitude but opposite
in direction.
XX’ - axis
As the coil completes a half turn in
Fig 6.16
the direction of the arrow as shown in the
figure the arm AB comes in place of CD and vice-versa. Now the direction of current in the two
arms is opposite the forces acting on them are also opposite. It makes the coil to rotate in
opposite direction. Thus it cannot complete one rotation. To avoid this problem the two ends of
the coil are soldered to the two half metallic rings which rotates with the coil. These half rings
enable to reverse the direction of current flowing through the coil after each half turn this enables
the coil to rotate in one direction.
MAGNETIC EFFECT OF ELECTRIC CURRENT
81
Main parts of an Electric Motor1.
Field Magnet NS- This is a permanent magnet whose
poles are concave as shown in the figure. Commonly
electro magnets are used in place of field magnets.
2.
Coil or Armature- It consists of a large number of turns of
insulated copper wire wound on soft iron core which
rotates on an axis.
3.
Commutator (Split rings)- It consists of two halves of a
metallic ring. The two ends of the armature coil are
connected to these two halves of the ring.
4.
Fig 6.17 Electric Motor
Brush (B1B2)- Two carbon brushes B1 and B2 press
against the commutator. A battery is connected across the carbon brushes. This battery
supplies the current to the armature coil.
WorkingSuppose that initially the coil ABCD is parallel to the magnetic field and in the horizontal
position. In this position the split ring S1 is in contact with brush B1 and the split ring S2 is in
contact with brush B2. When current flows through the coil, according to fleming’s left hand rule
a couple force acts on the coil which rotates the coil in anticlockwise direction until the coil is in
the vertical position. Beyond this position, the contacts of commulator and brushes gets reversed
and so the direction of the current in arms AB and CD is also reversed. The force acting on arm
AB is in the down ward direction and the force acting on the arm CD is in upward direction.
These two equal and opposite force again constitute a couple which makes the coil move again
in anticlockwise direction. Thus the coil completes one rotation and it continues to rotate in the
same direction on passing the electric current.
Answer these questions.
Q. 1 Why does the coil start rotating on passing electric current in the electric motor.
Q. 2 Explain the working or the use of split rings in the electric motor.
Fleming’s Right Hand RuleStretch the right hand such as the
fore finger, the central finger and the thumb
are mutually perpendicular to each other. If
the fore finger points along the direction of
the magnetic field and the thumb points
along the direction of motion of the
conductor, then the direction of induced
current is given by the direction of the
central finger.
82
Fig. 6.18 Fleming’s right hand rule.
SCIENCE 10
6.5 D.C. Generator (Dynamo)
A device which produces direct current as
is obtained from a cell or a battery is called D.C.
Generator or Dynamo.
Principle- When a coil rotates in a magnetic
field, an induced e.m.f. is produced in the coil.
The direction of the electric current produced
in the coil changes after every half revolution
according to Fleming’s right hand rule. Thus two
split rings S1, and S2 are used in D.C. generator to
obtain electricity in the same direction.
Main parts of a D.C. generator- Like an
electric motor, D.C. generator has following parts which are described earlier.
1. Field magnet 2. Armature or coil 3. Split rings (commutator) 4. Brush.
Working When armature rotates between the poles of field magnet NS an induced current is produced
in the coil ABCD. In the first half rotation the direction of induced current is ABCD as shown in
the figure and the brush B1 is in contact with S1 while B2 is in contact with S2. Thus current flows
from B1 to B2 in outer circuit.
In the second half rotation the brush B1 comes in contact with S2 and B2 come in with
contact with S1 due to which the flow of current is DCBA in coil. But the flow of current in the
outer circuit is again from B1 to B2. Thus a DC generator supplies a current in one direction in the
outer circuit.
Answer these questions.
Q. 1 Write any two sources of D.C. current.
Q. 2 Write the principle of Electric Motor.
Q. 3 Write the names of the main parts of a D.C. generator.
6.6. Direct and Alternating current
We know that rate of flow of electric charge is
called electric current. There are two types of electric
current.
1. Direct current 2. Alternating current.
1. Direct current- The current whose direction
of flow remains same with time i.e. it does not
changes direction is called direct current. The
current obtained from a D.C. generator changes but
MAGNETIC EFFECT OF ELECTRIC CURRENT
83
always remains positive [say in +y axis see Fig. 20 (a)]. The current which we get from a cell or
a battery is direct current because it always flows in the same direction and remains almost
constant.
2. Alternating current- The current
which changes direction after equal intervals
of time, is called alternating current, e.g.
electricity obtained from alternating generator
is alternating current. The electricity supplied
in our houses is also alternating current.
Answers these questions.
Q. 1 What type of current is used by fans
and fridge etc.?
Q. 2 Write the difference between
alternating current and direct current.
6.7 Domestic electric circuits
Connect three bulbs (220V) of 40
watt in series as shown in the figure.
Now pass the current in these
bulbs through an alternating current
source of 220V and switch on the key.
All the three bulbs will glow.
Now connect all the three bulbs
in parallel as shown in the figure and
pass the current. The bulbs will glow
brightly this time than in the series
connection.
When the three bulbs are
connected in series with an alternating source of current of
e.m.f. 220V then the potential difference on each bulb is not
220V but less than that so that the sum of the potential
difference applied on three bulbs is equal to 220V. While in
the case of parallel connection a potential difference of 220V
is exists on each of the three bulbs.
Please Note : Generally the
potential difference of
domestic alternate current
(AC) is 220 V and frequency
is 50 oscillation/second.
Therefore the bulbs connected in series give less light
while in parallel they glow brightly.
84
SCIENCE 10
Thus it is clear from this experiment that
domestic appliances like fan, mixer, tube light, bulbs
etc would work efficiently when they are connected
with alternating current source in parallel. This is the
reason that all the appliances in domestic electric
circuits are connected in parallel with an alternating
source of current.
Electricity is brought to our homes by
conducting wires fixed over tall electric poles outside
our houses. These wires are called main wires or
‘mains’. One of the wires having red plastic insulation
is called live wire or positive wire. The other one
having black rubber covering is called neutral wire
or negative wire. There is 220V potential difference
between the live wire and the neutral wire. The two
insulated wires coming from the electric pole enter
the electricity meter by main fuse. The two wires
coming out of the meter are connected to a main
switch and then connected to the line fitted inside
the house. The wires of the electrical wiring are
connected to all the electrical appliances like bulbs,
tube light, C.F.L., fans, cooler, fridge etc. in parallel
across the live wire and the neutral wire.
There is one more wire in electric wiring having
a green plastic insulation called the earth wire.
This wire along with the other wires i.e. live wire
and neutral wire enter our rooms where we use an
electric bulb, a fan etc. One end of the earth wire is
Read Carefully
What is short circuit?
Sometimes the plastic insulation of the
live wire and neutral wire gets torn, then
the two wires may touch each other.
Since the resistance is very small, the
current flowing through the wires
becomes very large and heats the wire
to a dangerously high temperature and
may cause the wires to catch fire. Thus
a sudden flow of electric current due
to touching of the live wire and nuetral
wire is called short circuiting.
What is overloading?
When extremely large current flows in
domestic electrical circuits, it is called
overloading. Due to overloading
resistance of the circuit may burn and
household wiring may catch fire.
What is fuse wire?
To prevent electrical circuits from
damage which may be caused by
short circuit or overloading, domestic
electrical device is protected by a
device called fuse wire having high
resistance and low melting point.
Whenever large current flows through
the fuse wire, it melts and breaks the
circuit and the flow of current in the
circuit stops.
Earth wire
MAGNETIC EFFECT OF ELECTRIC CURRENT
85
is buried in the earth and connected to a metallic plate. The earth wire is connected to the
appliances having metallic body like iron, water heater, room cooler etc. so that if by chance the
live wire touches the metal case, the current passes directly to the earth. Thus we earth the
metallic body of an electric appliance to save ourselves from electric shocks.
Answer these questions.
Q. 1 All the electrical appliances in our house are connected in parallel in domestic electric
circuit. Why?
Q. 2 What is the use of using earth wire in domestic electric circuit?
6.8 Precautions in using electricity
In case, we touch a live wire in domestic electric circuit of 220 V, a very high current flows
through our body and we get an electric shock. Therefore to avoid the hazards like electric
shocks or electric fires, we should observe following precautions in the use of electricity.
1.
All the electrical appliances should be given earth connections.
2.
The electric wire, plug, socket and holders used in domestic circuits should be of quality/
standard.
3.
High power electrical appliances like geysers, air conditioners, coolers etc. should be
fitted with plug, socket and switch of 15 A current rating.
4.
To avoid the damage caused by overloading and short circuit, high quality fuse should be
used in the circuit.
5.
We should not touch the switches with wet hands.
6.
While using the electrical appliances like electric iron, mixer etc. rubber gloves must be
put on and we should stand on a dry wooden board.
7.
Electrical appliances should be properly checked and maintained for reducing the electricity
consumption due to sparking.
8.
Electricity should be used reasonably i.e. unnecessary use of electricity should be avoided.
9.
All the wire connections with switches, sockets and plugs should be tight and all the wire
joints should be covered with insulated adhesive tape.
10.
We should promote the use of high quality electrical appliances based on the new technique.
Answer these questions.
Q. 1 Write the potential difference and frequency of the electricity used in domestic electric
circuits.
Q. 2 What precautions should be taken while using electricity? Write any five.
86
SCIENCE 10
Points to remember :
l
A magnetic field is produced around a conducting wire carrying current.
l
Magnetic field can be felt by using magnetic needle.
l
A solenoid acts as a bar-magnet on passing current through it.
l
When there is a relative motion between a magnet and coil induced current is
produced in the coil. This effect is known as electromagnetic induction.
l
An electric motor converts electrical energy into mechanical energy.
l
A device that converts mechanical energy into electrical energy is called electric
generator.
l
D.C. generator is a device that converts mechanical energy into direct current.
l
Currents are of two types1. Direct current 2. Alternating current.
l
All the electrical appliances in domestic electric circuit are connected in parallel.
l
Earth wire connected to electical appliances protects us from electric shock etc.
l
Electricity or electrical appliances should be used carefully and with safety because
we may get electric shock if our body comes in contact with some naked wire.
l
Electricity should be used reasonably because production of electricity at a large
scale harms the enviroment directly or indirectly.
EXERCISE
Very short answer type questions.
1
Write the names of any two electrical appliances which use electro magnet.
2
What is a magnetic field?
3
Define the following terms(a) Electromagnetic induction
(b) Induced current.
4
Write Fleming’s left hand rule.
5
Make a list of appliances based on electromagnetic induction.
6
What are the different types of electric generators?
7
What precautions should be taken while using electricity?
8
Write Maxwell’s cork-screw law.
9
Write the difference between alternating current and direct current.
MAGNETIC EFFECT OF ELECTRIC CURRENT
87
Short answer type questions 1
Write Faraday’s law of electromagnetic induction.
2
Write the main components of electric motor and explain each one of them in brief.
3
Draw a well labelled diagram of DC generator.
4
What do you understand by current carrying coil?
Long answer type questions1
Describe an electric motor under the following heads.
(a) Labelled diagram
(b) Main parts of electric motor
(c) Working.
2
Describe a DC electric generator under the following heads.
(a) labelled diagram
(b) Main parts of generator
(c) Working.
3
Draw a labelled diagram of domestic electric circuit.
Projectl
Draw magnetic lines of force of a magnetic field produced by a straight current carrying
conductor of many turns with the help of magnetic needle.
l
Prepare a list of those electrical appliances around you, which use electric motor.
l
Prepare a solenoid by winding insulated copper wires on a hollow card board cyclinder.
Now pass the current through the solenoid with the help of cell and identify the north pole
and south pole of solenoid with the help of magnetic needle.
88
SCIENCE 10
Chapter - 7
NON RENEWABLE ENERGY SOURCES
We will study
7.1 Fossil Fuel
Our every day activities need energy to work, for
example we need heat energy to cook food, chemical
energy to run motor, car, scooter etc., electrical energy to
run machines in factories etc. These are the different forms
of energy. We know that energy can neither be created
nor be destroyed but it can be transformed from one form
to another. Since centuries, we have been using different
sources of energy. Some of the common sources are man,
animals, wood, hydro electricity, heat energy, fossil fuels
etc. These are called conventional sources of energy. After
industrial revolution, fossil fuels i.e. coal, deisel, petrol etc.
are also being commericially used. Now to keep in pace
with the process of development and industrialisation, need
and demand of these energies have increased. That is why
apart from conventional sources of energy, we need to
depend on non-conventional sources like, solar energy,
wind energy, hydro energy etc.
7.2 Combustion and its
conditions
Renewable and Non-renewable sources of energy
7.3 Calorific value of fuel
1. Non-renewable sources - Those sources of
energy which have accumulated in nature over a very,
very long time and when exhuasted by continuous use
cannot be quickly replaced are called non-renewable
(which are in exhaustible) sources of energy. Example coal,
natural gas, petroleum etc. These energy sources are on
the verge of extinction because of continuous use.
7.4 Selection of a good
fuel
7.5 Nuclear energy
7.6 Nuclear reactor
7.7 Energy Utilisation
Sources of energy are divided into two parts
2. Renewable sources of energy - Those sources
of energy which are being produced continuously in nature
and are inexhaustible, are called renewable sources of
energy. Example wind energy, solar energy, sea-waves
energy, Geothermal energy etc. An important thing about
these sources is that nature itself reproduce these energy
continuously.
NON RENEWABLE ENERGY SOURCES
89
Let us know about some sources of energy
Sources of Energy
↓
Renewable
Non-renewable
→ Solar energy
→ Hydro energy
→ Coal
→ → Wave energy
→ Natural gas
→ Tidal energy
→ Fossil Fuels
→ Wind energy
→ Ocean thermal energy
→ Bio-mass as Fuel
→ Geo-thermal energy
→ Hydro electricity
→ Bio-gas
→ Mangal Turbine
→ Nuclear energy
→ Wood
→ Hydrogen
→ Alcohol
7.1 Fossil Fuel :
Fossils are the remains of the prehistoric animals or plants, buried under the earth, millions
of years ago. The plants and animals which died millions of years ago, were buried deep in the
earth and got covered with sediments like mud and sand, devoid of oxygen. Due to cover of
sediments neither oxidation nor reduction takes place. But due to the weight of sediments it
remained whereas water and other vapourable substances got separated. Thus, fossil fuels are
energy-rich compounds of carbon which were originally made of plants and animals with the
help of solar energy. Examples of fossil fuels are-coal, petroleum, natural gas etc. Now you can
understand that the fossil fuels took millions of years to form. The rate of using fossil fuels is
more than the rate of their production. If the rate of consuming these fuels is more than the rate
of their production, the possibility of getting them completely exhausted will increase.
Let us study some fossil fuels7.1.1 Coal : Coal is the remains of those trees which grew in swamps about 300 crore
years ago. With the passage of time, thick forests of fern trees were buried under the crust of the
earth. With the passage of time, the thickness of the soil and rocks over these buried trees
increased. Thus the pressure increased due to which water and gases were driven off and
converted into coal in the absence of oxygen. Now we use coal as a fuel extracted from these
huge deposits of coal. Coal is mainly found in Bihar, Orissa, Madhya Pradesh and West Bengal
in India.
Coal is a mixture of mainly carbon and compounds of carbon containing oxygen, hydrogen
and some amount of sulphur. It is found in 3 types, lignite, bituminous coal and anthracite. The
different varieties of coal differ in their carbon content, volatile matter and moisture. For example.
90
SCIENCE 10
Lignite contains 38% carbon, 19% voltile matter and 43% moisture while Anthracite contains
96% carbon, 1% volatile matter and 3% moisture. Bitumin has 65% carbon.
7.1.2 Petroleum
Petroleum is the main product of the
remains of animals buried deep in the earth
millons of years ago. After death, animals and
other mammals were buried deep under the crust
of the earth and got covered by thick layers of
sand and sediments. Over a period of millions
of years the bacterial decomposition of these
remains of animals and plants took place in the
absence of air and under high temperature and
pressure below the surface of the sea. As a result
of this bacterial decomposition of the remains of
the animals and plants, petroleum so formed was
trapped by impervious rocks forming an oil trap.
This is how the oil traps are formed. Petroleum
is obtained by drilling a hole in the earth’s crust
and inserting the pipes in this hole upto the oil
trap. Petroleum exists in the rocks of the earth
in a crude state. This crude oil is a mixture of
Bubble
gaseous, liquid and solid hydrocarbons. Thus,
caps
various hydrocarbons present in petroleum need
to be separated and purified because it cannot
be used directly. It needs to be purified and
processed. The process of separating and
purifying various hydrocarbons into its
constituents by fractional distillation (taking into
advantage their different boiling points) is called
refining of petroleum. The process of distillation
is based on the fact that its constituents have
different boiling points. Thus its constituents are
separated by means of a huge fractionating
column. The crude oil is heated in a spiral pipe at 4000C. At this temperature all the components
except asphalt is vapourised which rises up and enter the upper compartment through the
holes covered with caps known as bubble caps. The vapours enter the first compartment whose
temperature is less than the bottom compartment. So the components whose boiling point is
more than the temperature of the first compartment are liquified in this compartment. These
components in the liquid form are drained off through a pipe. On the other hand the components
NON RENEWABLE ENERGY SOURCES
91
whose boiling point is less than the temperature of the first compartment remain in vapour form.
These vapours rise up and enter the second compartment through the holes of this compartment.
Exactly the same process takes place in other higher compartments. Hence various components
of the crude oil are separated as shown in the figure. The products of fractional distillation of
crude oil or petroleum and their uses are given in the following table :Products of Fractional Distillation of Petroleum
Name of the component
Boiling range
Uses
Petroleum gas
Petroleum ether
Petrol/Gasoline
Kerosene
Fuel oil or Deisel oil
Lubricating oil
Petroleum wax
Petroleum Coke
(Solid remains)
below 30oC
30oC-90oC
70oC-200oC
175oC-275oC
250oC-400oC
Above 350oC
-
Gaseous fuel
Dry cleaning etc.
Fuel for automobiles
Jet engine fuel and domestic fuel.
Diesel engines and factories
In the form of grease,
wax and fuel.
Fuel in electrical
industry.
7.1.3 Petroleum Gas
Petroleum gas is a mixture of three hydrocarbons i.e. butane, propane and ethane. However,
the main component is butane. All these constituents of petroleum gas are in gaseous state at
room temperature. They burn easily and hence act as a source of heat energy. Out of these
gases, butane can be easily liquified at room temperature. Petroleum gas is liquified under high
pressure and filled in cylinders as liquified petroleum gas (LPG). When we turn on the knob of
the gas cylinder, the pressure is released and highly volatile LPG gets converted into gas. This
gas goes into the burner of our cooking stove and burns with a blue flame. It produces 50 kJ
energy/g.
LPG should be used carefully because any leakage may result in explosion. If excess
of LPG is inhaled, it is quite harmful and can even cause death. A strong smelling
substance called ethyl mercaptan is added to LPG cylinders to help in the detection of
gas leakage. If we smell gas leakage on entering kitchen, then the door and windows
should be opened at once to allow the gas to escape. In the case of gas leakage don’t
turn on/off any electrical switches. The rubber pipe connecting the gas cylinder to gas
stove should be checked periodically for any wear and tear.
7.1.4 Natural Gas
The main component of natural gas is methane. Some wells dug into the earth produce
only natural gas. It is a good alternative to petrol and diesel and it is used as Compressed
Natural Gas(CNG). Natural gas burns easily and produces a lot of heat. Natural gas is also
used as a domestic and industrial fuel. It is a good source of hydrogen. Hydrogen obtained from
natural gas is used in the production of ammonia and fertilizers.
92
SCIENCE 10
7.2 Combustion
Burning in the presence of oxygen is called combustion which produces heat. Thus
combustion is an exothermic process. Oxygen is necessary for combustion to take place. You
must have observed that the burners of the gas stove are perforated so that oxygen present in
the air can mix with gas and can burn. When wood is burnt, gaps are left between various logs
of wood. These gaps are left for the air to enter. In a sigri, which is used to burn coal, an iron
grate made of iron bars and having spaces in between is used so that coal can get adequate air
for combustion from these holes.
A substance starts burning at a specific temperature which is different for different
substances. The minimum temperature at which a substance catches fire and starts burning is
known as its ignition temperature.
The heat produced by burning a unit mass of a fuel is called the calorific value of the fuel.
Following are the calorific values of some fuels.
Fuel
Charcoal
Coal
Kerosene
Alcohol
Hydrogen
Methane
Butane
Biogas
Calorific value
kJ/g
kWH/kg
33
25.33
48
150
150
55
55
35-40
9.17
6.94-9.17
13.33
41.66
41.66
15.28
15.28
9.72-11.11
7.4 Selection of a good fuel
Sometimes we need to select a fuel which is most appropriate for domestic and industrial
purposes. Some points can be kept in mind while selecting a fuel, like physical state of fuel,
calorific value, rate of combustion etc.
Characteristics of a good fuel are :
1. High calorific value.
2. Proper ignition temperatue.
3. Balanced rate of combustion.
4. Low percentage of non-combustible materials.
5. Absence of poisonous substance 6. Easily available.
after combustion.
8. Easy to store and safe to transport.
7. Cheap
Following are some of the questions that may help in selecting a good fuel.
1. Does it burn easily?
2. Does it burn constantly?
NON RENEWABLE ENERGY SOURCES
93
3. Does it release sufficient heat (energy)?
4. Is it adequately available?
5. Is the storage safe and easy?
6. Is it easy and safe to transport?
7. Does it pollute air on combustion?
8. Does it leave ash after burning?
9. Is it expensive?
If the answers of first six questions is ‘Yes’ and last three questions is ‘No’ then the fuel is
good.
7.5 Nuclear energy
Production of electricity from nuclear
energy does not release carbondioxide. Some
atoms have huge amount of nuclear energy
stored in their nucleus which is known as
nuclear energy. This energy is released by two
reactions.
(1) Nuclear fusion (2) Nuclear fission.
Nuclear fusion :- When two nuclei of light
atoms combines to form a heavier nucleus the
process is called nuclear fusion. The loss of
mass in this process is released in the form of
energy.
Eg :- Heavy nuclei hydrogen (deuterium)
atoms combine to form a heavier nucleus of
helium. This fusion process can be shown as
below
2
1H
(Deuterium)
→
2
1H
+
(Deuterium)
1H
Do you know?
Hydrogen bomb was first made by American
scientist in the year 1952. This is based on
nuclear fusion reaction. To make a hydrogen
bomb, first an atom bomb is made based on
nuclear fission which is surrounded by heavy
isotopes of hydrogen called deuterium and
tritium alongwith an element Lithium-6 when
the atom bomb is exploded, its fission reaction
produces a lot of heat and pressure This
raises the temperature of deuterium and
tritium so that fusion of deuterium can take
place producing an enormous amount of
energy in a very short time. Hydrogen bomb
is more destructive than atom bomb.
3
1
1H
+
(Tritium)
+
4Mev
(Proton)
Nuclei of Tritium and deuterum combine to form nuclei of Helium and neutron.
3
1H
(Tritium)
+
1H
2
(Deuterium)
→
4
2He
(Helium)
+
On
1
+ 7.6 Mev.
(Neutron)
In this way 21.6 MeV (Million Electron Volt) energy is released in the process.
Nuclear fusion is a typical process which cannot be carried out at room temperature.
When positively charged nuclei come closer to combine, they repel each other. So the nuclei
94
SCIENCE 10
should have suffiently high kinetic energy to overcome this repulsion and undergo fusion to
form a bigger nucleus. This requires very high temperature and pressure.
These conditions of temperature and pressure are not readily available in nature.
Temperature and pressure conditions required for nuclear fusion process exist in stars and sun.
That is why nuclear fusion process which takes place continuously in the sun releases a huge
amount of energy.
Nuclear Fission.
When a heavy nucleus is bombarded with neutrons, it splits into two lighter nuclei. This
process is called nuclear fission.
The loss of mass during the process in small nuclei is converted into energy released as
given by the relation E = mc2.
In the year 1938, German Scientists Atto Hann and Strassman bombarded Uranium
(92U235) nucleus with slow moving neutrons, These are absorbed by the nucleus of Uranium
and in turn becomes highly unstable. Thus heavy uranium nucleus breaks up to produce two
medium weight atoms.
Fig. 7.4
This process releases 3 neutrons and a large amount of energy. This processs can be
explained by the following equation :
92
U
235
+
(Uranium)
0
n
1
(Neutron)
236
U
92
(Unstable nucleus)
56
Ba
139
Barium
+
94
Kr
36
Krypton
1
+ 3 n + Energy
0
Neutron.
The energy released in this process is about 200 MeV.
Answer these questions.
Q. 1 What is the reason that nuclear fusion process doesnot place at room
temperature and pressure?
Q. 2 What happens when the nucleus of Uranium-235 is bombarded with slow
moving neutrons? Explain by giving an equation.
NON RENEWABLE ENERGY SOURCES
95
Chain reaction : When a Uranium235 atom is bombarded with a neutron, its gets fissioned
to produce two light nuclei also a huge amount of energy is released along with three neutrons.
These 3 neutrons in turn, cause the fission of other uranium atoms and produce a lot of energy.
In this way the process goes on like an unending chain of fission reactions which if once starts,
ends up till all the uranium atoms are fissioned. This repeated process of nuclear fission is
called chain reaction. Chain reactions are of two types.
1. Uncontrolled chain reactions.
2. Controlled chain reactions.
Uncontrolled chain reaction :
In this reaction, neutrons produced during fission again cause fission of other uranium
nuclei. As a result, the production of more neutrons and release of more and more of energy
goes on multiplying endlessly. This process takes place very rapidly and within a few seconds
whole substance is fissioned. The release of tremendous amount of energy leads to an explosion.
This reaction is used in an atom bomb.
Controlled chain reaction :
In this type of reaction such an
arrangement is made that out of three
emitted neutrons only one neutron is
allowed to cause further fission and so
constant amount of energy is released.
In this way rate of nuclear fission process
is controlled and it takes place very
slowly. The energy released in the
controlled chain reaction is used for
constructive and peaceful purposes.
Nuclear reactor uses this kind of reaction.
7.6 Nuclear Reactor This is a device working on the
principle of controlled nuclear fission. The
energy obtained by a nuclear reactor is
very useful. Following are the
components of nuclear reactor.
(1) Nuclear Fuel : The fissionable material
used in nuclear reactors is called nuclear fuel.
Generally rods of enriched uranium–235 are
used as nuclear fuel in nuclear reactors. To keep
these rods from oxidation they are covered with
an aluminium layer.
96
Enriched Uranium : Naturally occuring
uranium has very less fissionable uranium.
To increase the percentage of fissionable
uranium-235 it needs to be processed. The
processing is called enrichment and the
uranium so obtained is called enriched
uranium.
SCIENCE 10
(2) Moderator : In order to carry out the
Do you know
fission of uranium-235 nuclei more effectively the
1. Naturally occuring uranium contains
speed of neutrons must be slowed down. A
two types of atoms 92U235 and 92U238.
substance which is used to slow down the speed
This contains 99.3% of U-238 and
of neutrons in the nuclear reactor is called a
0.7% of U-235. It is found from
moderator. Graphite and heavy water are used as
experiments that U-238 is fissioned by
moderators in nuclear reactors.
fast moving (1MeV) neutrons while U(3) Controller: In order, that the nuclear fission
235 fissions by slow neutrons.
reaction go on smoothly in a controlled manner, an
2. The uranium-238 present in nuclear
arrangement in mechanism is made that excess
reactor is not fissioned but it absorbs
neutrons are absorbed by the rods of Boron and
a neutron and makes Plutonium-239.
Cadmium. These rods are kept in the cylindrical
In comparison to U235, Pu239 is good
holes made in the walls of nuclear reactors and the
fissionable substance. The size of
chain reaction can be controlled. By inserting rods
Pu239 is smaller than U235, so it is
inside or taking out changes the rate of the reaction
cheaper than U235 Pu239 is used in
as and when required.
reactors and atom bombs.
(4) Coolant- The substance which is used
to absorb the heat produced as a result of chain
reaction is called coolant. In general liquid sodium
metal is used as the coolant. In some reactors,
however, carbondioxide gas and even water are
used as coolant.
(5) Shield - The whole arrangement of reactor
core and the vessel surrounding is covered with a
thick and strong concrete wall known as sheild. This
prevents the harmful radiations to come out of the
nuclear reactor emmitted during nuclear fission.
Fig. 7.6 Nuclear reactor
Uses of Nuclear reactor 1. Producing electrical energy
2. Producing plutonium
3. Emmission of fast moving neutrons
4. In the production of radioactive isotopes.
Difference between Nuclear Fusion & Fission
Nuclear Fusion
1. In this reaction two nuclei combine to
form a heavy nucleus.
2. This requires very high temperature.
3. They are not radioactive.
4. This reaction is hard to control.
5. Hydrogen bombs are made on the
basis of uncontrolled fusion reaction.
NON RENEWABLE ENERGY SOURCES
Nuclear Fission
In this reaction one heavy nucleus
spilits into two lighter nuclei.
This process is possible at room
temperature.
Fissionable materials are radioactive.
This reaction can be controlled.
Atom bombs are made on the principle
of uncontrolled fission reaction.
97
Uses of nuclear energy
1.
Production of electricity and as a fuel for
submarines etc.
2.
Treatment of diseases like cancer.
3.
In areas of agriculture and industry.
Disadvantages of Nuclear energy1.
In the process of nuclear fission to produce
electricity, radioactive materials like Barium139 and Krypton-94 are obtained as byproducts which are harmful for us. A person
affected by radioactive radiations can suffer
with dangerous diseases like cancer.
2.
The dangerous nuclear radiations can enter
into environment by leakage from nuclear
reactors. Two major accidents in reactors
have already taken place in threemile island
and chernobyl.
3.
Disposal of nuclear wastes obtained in
different steps of nuclear energy production
is a threat to vegetation and human life.
4.
Person affected by nuclear radiation may
suffer by genetic effects which leads to the
malformation of future generations.
5.
The highly destructive atom bomb is based
on the nuclear fission reactions.
Why nuclear energy is good.
1. It does not produce gases which
increase ‘Global Warming’.
2. Comparatively less space is required
to produce electricity from nuclear
energy.
3. Nuclear fission of 1 gram Uranium235 produces ample amount of
energy (about 5.21x1022 MeV) while
tons of coal is required to produce
this amount of energy.
Why nuclear radiations are harmful?
The high energy nuclear radiations
convert the molecules of living cells into
charged particles called ions. These
ions are chemically very reactive and
dirupt cell membranes reducing
effectiveness of enzymes or even
disrupt genes and chromosomes, there
by causing serious illness like cancer.
Let’s know :
In the year 1969, ‘Nuclear Power
Corporation’ have established first
nuclear power station in India called
‘Tarapur nuclear power station’ near
Mumbai. A numer of nuclear power plant
have been established to meet the
energy requirements in agriculture and
other fields.
During the second world war, America
dropped an atom bomb on the city of Hiroshima and another in Nagasaki. Both these
bombs caused a great loss to human life and almost major part of these cities were
destroyed.
7.7 Utilisation of Energy
Energy is the fundamental need of the present world. By the rate at which energy sources
are being used, it seems that within a short span of time they will be exhausted. We depends on
the conventional sources of energy for our energy requirement. We should keep following things
in our mind for the utilisation of energy.
98
SCIENCE 10
1.
Alternative sources of energy should be promoted.
2.
Conventional sources of energy should be used
reasonably and only when required.
Just Think!
Today, the world is struggling
with the energy crisis. Through
huge amount of nuclear energy
is available we have met
accidents like chernobyl which
are scary. So, there is a need
to use them carefully and in
balanced manner.
3.
Appliances based on solar energy, like, solar cooker,
solar water heater, solar panel etc. should be used.
4.
To reduce the consumption of electricity C.F.L’s
should be used in houses in place of bulb. Use of
electrical appliances like A.C., microwave etc.
should be minimised. Use of electricity in functions
like marriage and processions etc should be
minimised.
5.
Biomass fuels like gobar gas, wind energy and fossil fuels based technique and appliances
should be used.
6.
Fossil fuels like kerosene, petrol, deisel etc should be used economically and efficiently.
Answer these questions.
Q. 1
When and where was the first nuclear power plant established in India?
Q. 2
Write the advantages and disadvantages of nuclear energy.
Q. 3
How are the nuclear radiations harmful for human beings?
Points to rememberl
The process of combining two light nuclei to form a heavy nucleus is called nuclear
fusion in which an enormous amount of heat energy is liberated.
l
When a heavy nucleus is bombarded with slow neutrons, it splits into two light
nuclei and huge amount of energy is released. This process is called nuclear
fission.
l
Atom bombs are made using uncontrolled fission chain reaction.
l
Nuclear reactors are the devices based on the principle of controlled nuclear
chain reaction in which energy produced by nuclear fission is used for constructive
purposes.
l
Nuclear reactors are used- (i) To make plutonium (ii) Emission of fast moving
neutrons (iii) Producing electrical energy (iv) Producing radioactive isotopes.
l
Production of nuclear energy does not emits or form carbon dioxide.
l
Nuclear energy production emits radioactive radiations which may cause genetic
defects on a person.
l
Energy is a basic requirment of mankind. Thus we must conserve energy and
their sources.
NON RENEWABLE ENERGY SOURCES
99
EXERCISE
Very short answer type questions.
1.
What do you understand by non-renewable sources of energy?
2.
What are fossil fuels?
3.
Write the names of the elements obtained from refining of petroleum.
4.
What is the name of gas used in kitchens for cooking purpose?
Short answer type questions.
1.
What is combustion?
2.
What is nuclear fusion?
3.
What is nuclear fission?
4.
What do you mean by chain reaction?
Long answer type questions.
1.
What are fossil fuels. What are their types? Explain each in brief.
2.
Discuss fractional distillation method of petroleum refining.
3.
What precautions should be taken while using Liquified Petroleum Gas (LPG)?
4.
What measures should be taken in the case of leakage of gas in kitchen?
5.
In the era of energy crisis, nuclear energy is an alternate; Comment on the statement.
6.
Write the main components of nuclear reactor and explain them in brief.
7.
Write the advantages and disadvantages of nuclear reactor.
8.
Explain the ways to select a good fuel.
Project :
Is Nuclear energy appropriate for environment or not? Find out the facts based on the
topic from textbook and write a detailed answer to the question. Also write your
conclusion.
100
SCIENCE 10
Chapter - 8
RENEWABLE ENERGY SOURCES
Increasing population, growing industries and
immense use of conventional sources of energy is leading
to a hike in their price on one hand and decrease in their
availability on the other. Fast depleting sources make us
to look for alternate sources of energy.
Let’s know about these alternate sources of
energy.
8.1 Solar Energy
We will study
8.1 Solar Energy
8.2 Hydro Energy
8.3 Wind Energy
8.4 Geo-Thermal Energy
8.5 Bio-Gas
8.6 Hydrogen Energy
8.7 Alcohol
8.8 Wood
The sun is a huge source of energy. It is radiating
energy since around 4.6x109 years continuously and will
continue to do the same for the same period. The radiations
coming out of the sun include all the electro-magnetic
radiations from infrared to γ (gama) rays. The γ rays ionise
air and forms ionosphere. This makes life possible on
earth. It is the primary source of all the sources of energy
on earth. It facilitates all the life activities of living creatures
on earth. All the natural phenomenon like flowing of wind,
cyclones, water-cycle, photosynthesis etc. are possible
only due to solar energy.
The location of India on the globe helps us to gain
solar energy most of the time during the year. On an
average we receive about 5x108 million kWH solar energy
every year. The amount of solar energy received per
square metre per second on the surface of the earth is
called solar constant and it is approx imately. 1.4 (kJ/
m2s). Only 47% of the solar energy of the atmosphere
reaches the surface of the earth while rest is reflected
back in to the space. X-rays, Ultra violet rays and
Gamma rays are absorbed by the atmosphere, while only
remaining radiations reaches the surface of the earth.
The formation of energy in the sun is due to nuclear
fusion. Four hydrogen nuclei combines to form a nucleus
of Helium under high temperature and pressure. This
RENEWABLE ENERGY SOURCES
101
process releases large amount of energy.
8.1.1 Principle of solar heating devices
All solar heating devices work on the principle
of absorbing more and more solar energy. Since
black surfaces are good absorbers as well as good
heat radiators, a black strip kept in the sun can be
considered a simple heating device. But this kind
of black strip also radiates the absorbed heat
continuously which causes loss of heat and thus
its temperature doesn’t rise further beyond a certain
limit.
Thus a suitable measure should be used to
make it a useful heating device. We know that the
loss of heat takes place through conduction,
convection and radiation. To stop the heat loss due
to conduction and convection the black strip is kept
in an insulated box whose upper surface is covered
by a glass-plate. Walls of the box are painted black
from inside so that maximum heat can be absorbed
and heat loss due to reflection can be reduced.
When such a device is kept in sun, then its inner
surfaces gets heated due to absorption of heat. Hot
surfaces themselves start radiating heat but the
glass plate on the upper surface checks the flow
of heat out and thus the total heat absorbed remains
inside the box.
Do you know?
what is Million Electron Volt [MeV]?
It is a bigger unit of Energy.
1 Mev = 106ev (Electron volt)
When an electron is accelerated in a
field of 1 V potential difference then
the energy gained (stored) by the
electron is called 1 electron volt (ev)
1ev= 1.6×10–19 Joule
Fig 8.1 Solar heating device
The glass plate allows the transmission of
visible part of light of solar light but it does not allow to pass those infra-red radiations which are
emitted from a hot surface. We may note that hotter the object is, lesser is the wavelength of the
rays emitted from it. As the temperature inside the box is very less than that of the sun. Thus the
wavelength of the infra-red rays emitted from inside the box is larger than wavelengths of the
infra-red radiations received from the sun. In this way most of the heat remains inside the box
only.
This property of glass and absorption of heat (infra-red rays) by a black surface is used in
making solar cooker and solar water heater.
8.1.2 Solar Cooker- A solar cooker consists of a rectangular wooden box, which is lined
from inside with some insulating material to minimize the heat loss by conduction and radiation.
102
SCIENCE 10
The walls of the box are painted black from
inside. On the upper part of the box there is a
lid of two parallel plane glass sheets which
allows the light to penetrate. A plane mirror
(adjustable) reflector is used to reflect the sun
rays is attached to the box.
The food to be cooked is placed in metal
containers painted black from outside.
Depending on the weather, the sun-rays get
trapped in the black-box, due to which the
temperature in the box rises upto 1000C to
1400C in two to three hours. This type of solar
cooker is used to cook those food materials
which requires slow heating.
Note : Students may prepare a list of
food-items which can be cooked in such solar
cookers.
8.1.3 Solar Water Heater
It consists of a rectangular, insulated
metallic box which is painted black from inside
and in which copper tube is fitted in the form of
a coil. One end of this coil is connected with a source of cold water while the other end supplies
hot water. This device is fitted on the roof of a house or a building at a place where more of the
sunlight falls on it. When the sun shines, the radiant heat energy is absorbed by water present in
copper pipes. Water on getting hot expands and pushes itself in the insulated storage tank
through pipe. Whenever hot water is required, it is taken out from the hot water outlet. Fig 8.3
shows the construction of a solar water heater.
This is an ideal device to heat water. This can heat water upto 800C. This can reduce
consumption and expenditure of electricity. It is
used at places which require hot water
continuously like house, hotel, hospital etc.
8.1.4 Solar Cell
It is a device which converts solar energy
into electrical energy. It is made up of semi
conductor Silicon. The potential difference
produced by a single solar cell is between 0.4
to 0.5 V and about 0.7 W electrical energy can
be produced.
RENEWABLE ENERGY SOURCES
Electric
Motor
Fig. 8.4 Irrigation by means of solar panel
103
The group of solar cells connected in a specific pattern to produce desired potential
difference and magnitude of electrical energy is called solar panel. Solar cells produces D.C.
current. Since these cells work only in sunlight, the electrical energy produced by these cells
are stored in storage battery so that it can be used when required.
Solar cells are used for providing electricity for street lights and operating T.V., radio etc. in
the areas where direct supply of electricity is either not possible or not available . All the artificial
satellites and space probes like Mars Orbitores mainly depend upon electricity generated by
solar cells. Solar cells are used to provide electricity to dig offshore oil wells and electric poles.
8.2 Hydro Energy
Water flowing in the river or water stored in a dam are the sources of hydro energy. The
kinetic energy of water flowing through rivers has been used for rotating the wheels of watermills
which are still operating in remote hilly areas.
The simple and the best method to use hydro energy is to convert it into electrical energy.
The water flowing in river is collected in the dam. Water turbine located near the bottom of the
dam and the shaft of water turbine is connected to electric generator. When the water turbine
rotates, the armature of generator also rotates rapidly.
8.2.1 Generation of hydro electricity
Generation of electricity on a large scale has helped in the growth of Industrial and
technological development. There are two
main parts of Hydro Electricity Generator1. Turbine 2. Generator
Generator has two main parts. One
which remains fixed is called stator. Other
one rotates on an axis called rotor.
Axis of the rotor is joined to the axis
of the turbine. Many pieces of powerful
magnets are joined to form rotor. Stator is
made up of many coils inside a hollow
cylinder.
Fig. 8.5 Turbine and Generator
The turbine is coupled to a generator.
When the coils of the armature of the generator rotates rapidly in the magnetic field, electric
energy is produced in the coils. The electric energy so produced is fed to step-up transformer
and then supplied to distant places through high tension wires. In India, one fourth of the total
energy requirement is fulfilled by hydro electricity.
104
SCIENCE 10
8.2.2 Mangal Turbine
Mangal turbine is such a machine which
can work by the kinetic energy of a small dam.
Its working principle is like an electric generator.
It is connected with engine to obtain electrical
energy. This turbine was made by an Indian
named Mangal Singh and so it is named ‘Mangal
Turbine’. It is used for small irrigation projects
and domestic electrification.
8.2.3 Tidal Energy
Fig. 8. 6 Mangal Turbine
The water level of the ocean rises or falls
because the gravitational pull of the moon exerted on the rotating earth. This is known as a tide.
We obtain tidal energy from the rise or fall of water level during Tides. The position of tide
continuously moves or shifts in a sea. We can harness this energy constructing a dam on
narrow bays. With the help of turbine on the gate of the dam, the tidal energy can be converted
into electrical energy.
8.2.4 Ocean Wave Energy
Kinetic energy of huge waves on the shores can be used to produce electricity. The place
where high kinetic energy waves comes the surface of the ocean can be used to produce
electrical energy. With the help of different devices, wave energy can be used to rotate the
turbine to produce electricity.
8.2.5 Oceanic Thermal Energy
The water on the surface of the oceans gets heated while it remains comparatively cool in
the depth. The difference in the temperature is used to obtain electricity in Oceanic Thermal
Energy Conversion plant or OTEC. OTEC generators work or function only when the difference
between the temperature of water on the surface and water under the depth of 2 km from the
surface is 200C.
The capacity of oceans to produce
energy is very large but its commercial and
effecient use has many practical problems.
8.3 Wind Energy
We know that the wind blows due to
difference in the temperature of water sources
and land. Since centuries, man is using this wind
energy to row their sail boats in the desired
direction. Now the kinectic energy of wind is
used for electrical energy or for mechanical
RENEWABLE ENERGY SOURCES
105
energy.
Wind mill is a source of electrical energy
in which a turbine functions with the help of wind.
Turbine activates the electrical dynamo which
produces electricity. The electricity obtained
from a single wind mill cannot be used
commercially because it is quite small. Thus
many wind mills are set together over a vast
area to generate a large amount of energy
which is known as wind energy farm. These
wind energy farms are generally established
only at places where most of the days in a year
experience strong winds because to maintain
the speed of the turbine, the kinetic energy of
wind should be at least 15 km/hr. Such kind of
farms are working in some states of India
including Madhya Pradesh. There is a wind
energy farm of 6.25 MW capacity at Phalsodi
of Dewas District in Madhya Pradesh.
Did you know?
Denmark is called ‘country of wind’.
More than 25% of electricity requirement
is fulfilled by generating electricity from
a huge network of wind turbines.
Germany is also a lead producer of
wind energy while India ranks at 5th
position in generating electicity using
wind energy. The wind potential of our
country is estimated to be about 45,000
MW. A large wind energy farm has been
established near Kanyakumari in
Tamilnadu which can generate 380 MW
electricity. In Dewas district of Madhya
Pradesh also, one such wind energy
farm is established.
8.4 Geo-Thermal Energy
Many changes are taking place continuously in the core of the earth. Some rocks inside
the earth are very-very hot. The high temperature is caused by the fission of radioactive material
present in these rocks. The areas where very hot rocks occur are called hot spots. When water
present inside the earth comes in contact with these rocks, it is converted into vapours and
gets accumulated between these rocks. When a big amount of water vapour gets compressed
between two rocks, it exerts high pressure. When such rocks are drilled and with the help of
pipes, the steam comes out with a great speed which is used to rotate the blades of turbine and
thus electricity is generated.
8.5 Bio-gas
In India, agriculture and animal husbandry are of great importance. Due to a large number
of animals, gobar (cow-dung) is easily available. In rural areas people use the cow-dung cakes
to produce energy by burning them directly.
But in this process a big part of the energy is lost in nature and it also harms the environment.
Now it is used to produce the gas fuel which is known as Bio-gas.
Biogas is a mixture of gases such as methane (75%), carbon dioxide, hydrogen, hydrogen
sulphide etc. which is obtained by the decomposition of animal and plant wastes like animal
dung etc., with the help of micro-organisms in the presence of water. It is used as fuel in gas106
SCIENCE 10
stoves these days especially in rural areas.
It can also be used for lighting streets and for
running engines.
There are two commonly used designs
of Bio-gas plants in India.
(i) Fixed dome type
(ii) Floating gas holder type.
Fresh cattle dung and water forms
slurry which is introduced in the inlet chamber.
The biogas collected in the dome is taken out
through the outlet pipe by opening the gas
valve and is made available to consumers.
Fresh slurry is required to be added to the
mixing tank and fed to the digestor for the
regular supply of biogas. Human excreta can
also be used in a biogas plant. In some cities
human excreta is disposed off in bio-gas
generator which otherwise creates air pollution
and water pollution, if dumped into water.
Biogas burns without smoke, producing
large amount of heat. Biogas is an excellent
Fig. 8.9 Flating gas holder type Biogas plant
fuel for domestic purpose. The slurry left
behind in digestor is a good manure because it is rich in plant nutrients i.e. rich in nitrogenous
and phosphorus compounds.
8.6 Hydrogen energy
To meet the increasing demand of energy of the modern life, efforts are being made to
develop the unconventional sources of energy. Hydrogen is a good source of energy because
it does not create pollution and produces maximum energy on burning. Hydrogen can be easily
produced by electrolysis of water and is also obtained as a by product in many industrial process.
Using Hydrogen gas as basic fuel, cells and hydrogen power plants are being made.
There are many technical constraints in using hydrogen as a source of energy for domestic and
industrial purpose. But it is used in space probes and for producing flame of high temperature.
8.7 Alcohol
Alcohol has many commercial and medicinal purposes. It can also be used for producing
energy. Alcohol is easily combustible and releases a large amount of heat. Alcohol can be
obtained while making sugar from sugarcane. Thus it a very cheap source of energy. Mixture of
petrol and alcohol is being used as a fuel in automobiles these days. This mixture is called
‘Gasohol’
RENEWABLE ENERGY SOURCES
107
8.8 Wood
Wood is an ancient and traditional source of energy. It is mainly a mixture of many
carbohydrate compounds. These compounds contain atoms of oxygen with carbon and hydrogen.
It is used to cook food. It pollutes air also. It leads to deforestation which may give rise to the
nature imbalance. Thus this source of energy should be totally stopped or minimised.
Points to remember :
l Energy is required to do work.
l There are two types of sources of energy Renewable and Non-renewable.
l Sun, water, wind etc are renewable sources of energy.
l The source of sun’s energy is nuclear fusion.
l The temperature inside the solar cooker can rise upto 100–1400C when kept in sun.
l Solar cooker, solar heater, solar panel etc. work on Solar energy.
l Kinetic energy of water flowing with great speed can be used to produce electricity.
l The main component of Bio-gas is methane (CH4).
EXERCISE
Very short answer type questions.
(1) Write the names of renewable and non-renewable sources of energy.
(2) What type of rays are emitted by sun’s radiation?
(3) What is the principle of the solar water heater?
(4) Why are the inner walls of the solar cooker painted black?
(5) Which type of radiations provide heat energy?
(6) What is the main constituent element of Bio gas generator?
Short answer type questions.
(1) What are the renewable sources of energy? Explain with examples.
(2) Draw a well labelled diagram of a solar cooker.
(3) What are the benefits of using a solar cooker?
(4) What are the uses of wind energy and how is it used? Explain.
Long answer type questions.
(1) Explain tidal energy and wind energy in brief.
(2) Where can solar cells be used?
(3) What are the benefits of using a solar water heater?
(4) Why is Biogas considered as an appropriate fuel?
(5) Discuss a Biogas generator.
(6) Explain the production of Hydro Electricity with diagram.
(7) What is Geo thermal energy?
Project :- Try to make a solar cooker by using cheap and easily available materials and
find out the maximum temperature achieved?
108
SCIENCE 10
Chapter - 9
RATE OF CHEMICAL REACTION AND
CHEMICAL EQUILIBRIUM
In different activities of our daily life we come across
with many physical and chemical changes. Some peculiar
events taking place around us are the results of some
chemical reactions. Have you ever thought about the reason
behind setting of cement, shining of glow worm, burning of
crackers, medicines kept in coloured bottles etc? Perhaps
not at all. All these changes are chemical reactions taking
place at different rates. In chemical reactions energy is either
absorbed or evolved in the form of heat, light etc.
We will study here
9.1 Slow and Fast Chemical
reactions.
9.2 Rate of a Chemical
reaction.
9.3 Energy changes during
Chemical reactions
9.4 Reversible and
Irreversible reactions
9.5 Chemical equilibrium
9.6 Ionis ation of
electrolytes
Strong and
electrolytes.
9.7 Acids and Bases
9.8 pH scale.
Weak
We observe that rusting of iron takes place when it is
left open in moist air, this is a slow reaction, but in the
laboratory when dilute sulphuric acid is added to Barium
chloride solution, white precipitate of barium sulphate is
formed instantly. On the basis of chemical reactions many
substances like soap, detergents, medicines, plastics and
fibres are manufactured.
A chemical reaction is generally represented by an
arrow in between the products and the reactants eg. in a
chemical reaction where A and B are the reactants while C
and D are the products, this chemical reaction be represented
as
A+B
C+D
There are certain chemical reactions in which the
products formed combine with themselves to form the initial
reactants, these reactions are called Reversible reactions.
These reaction are represented by
between reactant and product.
sign, placed in
Reversible reactions proceed in the forward as well
as in the backward direction. When the rate of the forward
and backward reaction becomes equal then an equlibrium
is established. This is known as Chemical equilibrium.
Equilibrium can be established in physical processes
also. For example, the concept of vapours pressure of a liquid
at a given temperature is a equilibrium process.
RATE OF CHEMICAL REACTION AND CHEMICAL EQUILIBRIUM
109
Do you know : The branch of Physical chemistry which deals with rate of chemical
reaction and its mechanism is known as Chemical Kinetics.
9.1 Slow and Fast Chemical Reactions
Chemical reactions can be mainly divided into two groups on the basis of the rate of
reactions(1) Fast chemical reactions (ii) Slow chemical reactions.
(1) Fast Chemical reactions :- Those reactions which takes place quickly or
instantaneously are called fast chemical reactions. For example1. When a solution of Silver nitrate (AgNO3) is added to a solution of Sodium chloride
(NaCl), a white precipitate of silver chloride (AgCl) is formed immediately (precipitation reaction).
AgNO3
+
→
NaCl
Silver nitrate Sodium chloride
AgCl ↓
+
Silver chloride
(White precipitate)
NaNO3
Sodium nitrate
2. The formation of salt and water by acid and base (neutralisation reaction)
NaOH
+
HCl
Sodium hydroxide Hydrochloric acid
→
NaCl
+
Sodium Chloride (salt)
H2O
Water
3. When Magnesium wire is heated in the flame of a burner it immediately catches fire and
a white powder of Magnesium oxide is formed with a sparkle (combination reaction).
2Mg +
O2
Magnesium
Oxygen
→
2MgO
Magnesium oxide
4. Like reaction (i) the mutual reaction of barium chloride and sulphuric acid
BaCl2 +
H2SO4 →
Barium chloride Sulphuric acid
BaSO4 ↓
Barium sulphate
2HCl
Hydrochloric acid
Slow Chemical Reactions
Those reactions which do not occur immediately but takes place slowly are called slow
reactions. For example –
1.
Decomposition of potassium chlorate
2KClO3
2.
→
2KCl + 3O2
Rusting of iron.
4 Fe
+ 3O2 +
Iron
Air
X H2O
Moisture
→
2Fe2O3 × XH2O
Hydrated iron oxide (Rust)
(Where, X = No of water molecules)
110
SCIENCE 10
3.
Fermentation is also a slow chemical reaction
[ Zymase enzyme ]
4.
C6H12O6
2C2H5OH + 2CO2 ↑
Glucose
Ethyl alcohol
Other Example of slow reactions :
Formation of biogas, setting of cement and burning of a candle are also examples of Slow
reactions.
Activity
1.
Take two test tubes. Pour BaCl2 solution to one of the test tubes and dilute H2SO4
in the other test tube. Now add H2SO4 solution to the first test tube slowly.
2.
Take a clean piece of iron (without rust). Dip the iron piece in water and leave it
open in air.
Observation : In the first experiment white precipitate of BaSO4 is formed immediately
hence it is a fast reaction. Whereas in the second experiment, some change is
observed after a very long time, hence it is a slow reaction.
Differentiate the following into fast and slow reactions : 1.
Rusting of iron.
2.
Burning of magnesium wire
3.
Setting of cement
4.
Reaction between aqueous solution of barium chloride and sulphuric acid.
5.
Formation of coal.
6.
Mixing of sodium chloride to silver nitrate solution.
7.
Fading of the colour of clothes.
9.2 Rate of chemical reaction.
In the initiation of any chemical reaction, only reactants are present in the reacting container.
As the reaction proceeds the concentration of the reactants decreases while the concentration
of product/products goes on increasing. The rate of change of concentration of a particular
reactants or products in a definite time interval is known as the Rate of a Chemical reaction.
The rate of a chemical reaction is defined as the change in concentration of
reactants or products per unit time.
Rate of reaction =
Change in concentration of reactants or poducts
Time taken to cause the change
Suppose in a Chemical reaction A + B → C + D, the concentration of the reacting
substance i.e. A and B decreases with the passage of time while the concentration of the products
C and D increases.
*Fermantation has been described in Chapter 12 in this book.
RATE OF CHEMICAL REACTION AND CHEMICAL EQUILIBRIUM
111
Then Rate of reaction
=
Decrease in concentration of A or B or both
Time taken
Also rate
=
Increase in concentration of C or D or both
Time taken
Note : Decrease in concentration of reactants dcreases with time,
[Change in concentration of Reactant]
Rate of reaction = –
Time taken
In terms of reactants while concentration of products increases, hence it is represented
by + (plus) sign
Change in concentration of Products
Rate of reaction =
Time taken
{
}
In terms of products Mathematically, it is denoted as
Rate of reaction =
Ä [x]
Ät
=
d[x]
dt
Here ∆ [x] in change in molar concentration in a definite time interval ∆t and d (x) is the
change in concentration in very small interval dt.
Note : Molarity or Molar concentration of reactants or products is expressed in
bracket [ ]
Number of moles of the solute present in 1 litre of a solution is known as
Molarity or Molar concentration of the solution.
consider a reaction 2A + B
3C + D
In the above reaction, twice the amount of A is used as compared with B Hence, while
denoting the rate of reaction, molar concentration of A is divided by 2. Thrice the amount of C is
formed as compared to D, hence molar concentration of C is divided by 3.
Therefore,
Rate of the reaction for the above reaction is = −
Ä[B] 1 Ä[C] Ä[D]
1 Ä[A]
=−
=
=
2 Ät
3 Ät
Ät
Ät
Example - Let’s see a Chemical reaction (Habers’ process) for manufacture of Amonia
N2 + 3H2 → 2NH3
Mathematically, the rate of the above reaction
 Ä[N 2 ] 
 1 Ä[H 2 ]  1 Ä[NH 3 ]
=
 = −
 Ät 
3 Ä t  2 Ä t
Rate of reaction = − 
112
SCIENCE 10
Rate of reaction =
Concentration change of reactant or product
=
Time taken
Mole/Litre
sec or min.
Hence Unit for rate of reaction = mole/litre/sec (mole L–1s–1)
or
= mole/litre/min (mole L–1 m–1)
Measurement of Reaction Rate
The rate of reaction is measured by determining the change in concentration of reactants
or products during a certain time period.
For example in an experiment the reaction of its Dichlore diamine platinum (II) (NH3 )2 Cl2
with water as follows :-
Time (in min)
0
concentration of
0.0100
20
0.0097
40
0.0094
80
0.0088
(initial concentration)
The rate of reaction for the above reading can be calculated as
Given here : concentration at 0 minute =
0.0100 mole/L
concentration at 40 minute
0.0094 mole/L
=
During the time interval (0 to 40 minute) change in concentration
= 0.0094–0.0100
=
– 0.0006 mole/L
Time taken for the change
=
∆t = 40–0 = 40 minute
Rate of reaction
=
—
=
Thus rate of reaction
 (A) 

Ät
(−0.006)
40
mole L–1 min–1
=
1.5x10–5 mole L–1 min–1
=
1.5x10–5 mole L–1 min–1
*Cis - dichloro diamine platinum is used for treatment of cancer.
RATE OF CHEMICAL REACTION AND CHEMICAL EQUILIBRIUM
113
Graphical Representation of Rate of Reaction
The
change
in
concentration of reactants
and products with passage
of time can be understood
by plotting a graph. (Fig.
9.1) the decrease /increase
in concentration of reactant
and the product against
time interval.
Average Rate and Instantaneous Rate of reaction
The rate of a reaction calculated with considerable time interval is called average rate of
reaction. The concentration of the reacting molecules keeps on decreasing. The rate of reaction
calculated in an infinitesimally small interval of time is called Instantaneous rate.
Lets see a Chemical reaction reaction A + B → C + D
Average rate of reaction =
∆ [C]
∆t
and instantaneous rate of reaction =
d[C]
dt *
Factors affecting the rate of a Chemical reaction
The factors which influence the rate of a chemical reaction are as follows1.
Concentration of the reactants
2.
Temperature
3. Pressure
4. Nature of the reactants
5.
Catalyst
6. Surface area
7. Exposure to radiation.
Above factors are discussed briefly one by one as follows.
I.
Concentration- Rate of reaction increases with increase in concentration of the reactants.
II.
Temperature- In general the rate of reaction increases at higher temperature as increasing
the temperature, the kinetic energy of molecules increases and it increases the number of
collosion in between molecules, hence, the rate of reaction increases.
III.
Catalyst - A catalyst is a substance which alters (influences) the rate of the reaction
without taking part in the reaction.
* If there is an infinitesimally change in concentration, It is denoted by d (delta) instead of ∆
114
SCIENCE 10
Positive catalyst increases the rate of a reaction while Negative catalyst decrease the
rate of reaction called Inhibitors.
Example - In the Manufacture of Ammonia gas Iron is used as a catalyst.
[Fe]
N2 + 3H2
IV.
2NH3 + Heat
Pressure - Rate of a reaction increases, as soon as the pressure increases (whenever
all the reactants and products are gaseous in state).
V.
Nature of the reactants - Rate of a reaction depends on the nature of the reactants. Ionic
substances react rapidly whereas the rate of reaction for covalent compounds is
comparatively slow.
VI.
Surface Area- On increasing the surface area, the rate of reaction increases. Hence, if
the powdered reactant particles are used the rate of reaction will be higher. This primanily
is the reason that powdered coal burns fasteras compaired lumps of coal.
VII
Exposure to radiation- Certain reactions take place faster in the presence of light. For
example Photosynthesis takes place faster during noon time as compared to morning
and evening because during noon time sunlight is available in abundant quantity.
Answer these questions.
Q. 1
What is the unit of rate of reaction?
Q. 2
What do you mean by instantaneous rate of a reaction?
Q. 3
Write the main difference between average and instantaneous rate of reaction.
Q. 4
State the effect of temperature and pressure on the rate of a reaction?
Q. 5
What is a catalyst? How does it effect the rate of a reaction?
9.3 Thermal Changes in Chemical Reaction (Energy changes in a Chemical reaction)
Generally, energy is evolved during a chemical reaction but in certain reactions energy is
absorbed also. The energy is evolved or absorbed in the form of heat or light. Chemical reactions
are mainly of three types on the basis energy change(1) Exothermic Reactions.
(2) Endothermic Reactions.
(3) Photo Chemical Reactions.
RATE OF CHEMICAL REACTION AND CHEMICAL EQUILIBRIUM
115
1. Exothermic reactions- “The chemical reactions which release heat as they occur, are
called Exothermic Reactions.
Example- (i) In our daily life we use coal, Liquified Petroleum gas (LPG), kerosene etc as
a fuel. Heat is evolved during combustion of these fuel. Combustion of natural gas, (methane) is
represented by the following chemical reaction, which is regarded as a food fuil.
CH4 + 2O2
Methane Oxygen
→
CO2
+
Carbon dioxide
2H2O + Heat
Water
(ii) During thermite reaction Iron and aluminuim oxide is formed with evolution of large
amount of heat
Fe2O3
+ 2Al
→
2Fe
Ferric (III) oxide Aluminium
+
Iron
Al2O3
+
Heat
Aluminium oxide
(iii) Reaction of quicklime (CaO) with water. During preparation of lime for whitewashing.
the container gets heated up.
CAUTION
CaO
+ H2 O →
Ca(OH)2 + Heat
Be careful ! while making
Calcium oxide water
Calcium hydroxide
lime. Prepare the solution in
In this reaction calcium oxide reacts vigoursly
a strong container with the
evolution of large amount of heat. This reaction is known
help of brush to avoid any
as slaking of lime.
type of untoward accident.
(iv) During burning of crackers heat is evolved along
with light and sound.
2. Endothermic Reaction - A
reaction in which heat is absorbed is
called Endothermic reaction.
Example - (i) When Nitrogen and
Oxygen is heated to a high temperature,
they combine to form NO (Ntric oxide).
In this reaction large amount of heat is
absorbed.
N2
+
O2
→
Nitrogen Oxygen
2NO – Heat
Nitric oxide
(ii) When ice is kept in a container
it changes into water after some time.
This shows that changing of ice into
water involves absorption of heat.
116
Do you know?
THE WONDER WORLD OF CRACKERS
The technique of manufacture and use of
firework is known as pyrotechnic. Fuels like Dextrin,
Charcoal, Redgum, Aluminium, Magnesium etc. are
generally used. Potassuim chlorate, Ammonium
perchlorate etc. are used as oxidising agents. The
outer covering of a cracker is mainly made of gun
powder which is a mixture of Potassuim nitrate,
sulphur and charcoal. On ignition the cracker at high
temperature, the fuel reacts with the oxidising agent
and produce sound. To make firework colourful many
chemical are added to it for example strontium
carbonate for red colour, Aluminium for white,
Sodium for yellow, Copper for blue and Barium for
green while compounds of Iron for orange colour
are mixed.
SCIENCE 10
Ice + heat
→
Water
(iii) When aqueous solution of Potassuim nitrate is formed the container gets cooled.
Activity
(I)
Take water in a beaker and touch it from
nc.
Co
outside. Now add concentrated H 2 SO 4
slowly along the wall of the beaker. This must
be done carefully. Experience the change in
temperature by touching the beaker from
outside.
(II) Take solid KNO3 in an another beaker and
touch it. Mix water to it slowly, experience the
change in temprature by touching the beaker.
Fig. 9.2. (A)
Observation : In the first experiment the beaker gets heated up hence it is an exothermic
reaction, while in the second experiment the beaker gets cool hence it is an
endothermic reaction.
Photochemical Reactions
Medicine Bottles are coloured!
Those Chemical reactions which take
place in the presence of light are called
Photochemical reactions. In these
reactions absorption of light energy takes
place for example(i)
Chlorination of methane
Sunlight
CH4 + Cl2
(ii)
→
CH3Cl + HCl
Almost all the bottles of medicines you might
have seen written “Store in a cool and dark
place” Why?
Generally most of medicines contain
chemicals which get decomposed by heat and
light and form harmful compounds. To prevent
this process it is advised to store medicines in
a cool and dark place. Dark coloured bottles
help medicines to isolate from the contact and
prevent with sunlight.
Photosynthesis
Sunlight
6CO2 + 6H2O
→
Chlorophyll
(iii)
C6H12O6 + 6O2 ↑
glucose
Photochemical reaction takes place in Photography also. Photographic film used in
camera is coated with a film of Silver bromide. In the presence of light following
reaction takes place
Sunlight
2AgBr
Silver Bromide
→
2Ag + Br2
Silver
Bromine
RATE OF CHEMICAL REACTION AND CHEMICAL EQUILIBRIUM
117
Activity
l
Take about 1 gm silver chloride in a china dish. Note
the colour of the substance. Keep the china dish in
the sunlight for some time.
l
Observe the colour of silver chloride after some time.
l
Observation & Conclusion- In the presence of
sunlight white silver chloride turns into black. It is
because decomposition of silver chloride to silver and
chlorine takes place in the presence of sunlight.
Sunlight
2AgCl (s)
→
2Ag(s) + Cl2(g) ↑
Answer these question
Q.1 Why is heat produced on adding water to
quicklime?
Q.2 Give any two examples of Photo chemical
reactions.
Why does Glow worm shine?
The formation of light in glow worm
is due to a complex chemical
process called bio illumination.The
Q.3 Classify the following Chemical reactions as
main substance responsible for the
exothermic, endothermic and photo chemical
shining of glow worm is Luciferrin.
reactions.
Luciferrin reacts with oxygen during
(i) Combustion of Methane
respiration and produce shining.
(ii) Preperation of food by plants
(photosynthesis)
(iii) Photography
(iv) Formation of ammonia
(v) Changing of ice into water.
9.4 Reversible and Irreversible Reaction
Chemical reactions are mainly of two types(i) Reversible reaction
(ii) Irreversible reaction.
Reversible Reactions - Those reactions in which reactants combine to form products
and under some conditions products formed react with themselves to produce reactants, known
as Reversible reactions.
118
SCIENCE 10
Example : When steam is passed over red hot Iron, Iron oxide is formed and hydrogen
gas is evolved. When hydrogen gas is passed over Iron oxide at the same condition formation
of iron and water takes place. These reactions never come to a state of completion. In these
) is used instead of arrow (→)
reactions sign of reversibility (
forward reaction
3Fe +
4H2O
Red hot iron Water vapour
Fe3O4 + 4H2
backward reaction Iron (II) oxide
Hydrogen
Other examples of reversible reactions
Catalyst
(i)
N2
+ 3H2
Nitrogen Hydrogen
(ii)
H2 +
Hydrogen
(iii)
N2 + O2
Nitrogen Oxygen
I2
Iodine
2NH3
Ammonia
2HI
Hydrogen Iodide
2NO
Nitric Oxide
Irreversible Reaction : Those reactions in which reactants combine to form products but
under similiar conditions products do not react with themselves to produce reactants, are called
Irreversible reaction. Irreversible reaction takes place uni-directionally. In this type of reaction
reactants converted into products completely.
Example : Barium chloride reacts with sulphuric acid (H2SO4) to form barium sulphate
and hydrochloric acid, whereas under similar condition barium sulphate does not react with
hydrochloric acid.
BaCl2
Barium chloride
+
H2SO4
Sulphuric acid
BaSO4
+
2HCl
Barium sulphate Hydrochloric acid
Other Example :
(i)
(ii)
Zn +
H2SO4
Zinc Sulphuric acid
+
2NaOH
H2SO4
Sulphuric acid
Sodium hydroxide
ZnSO4
+ H2
Zinc sulphate Hydrogen
Na2SO4
+
Sodium sulphate
2H2O
water
Answer these question.
1. Differentiate between reversible and Irreversible reaction.
2. What sign is used to represent reversible reactions?
RATE OF CHEMICAL REACTION AND CHEMICAL EQUILIBRIUM
119
9.5 Chemical Equilibrium
When any reversible reaction is allowed to take place in a closed manner then initially the
rate of the forward reaction is greater but slowly as the reaction proceeds the rate of the backward
reaction increases and the rate of forward reaction decreases, until eventually a condition is
reached where the rate of the forward and the backward reactions becomes equal. At this point
Chemical equilibrium is established. At this stage the rate at which the products are formed is
similiar to the rate at which it changes into reactants. Hence, Chemical Equilibrium is dynamic,
because at this stage reaction takes place continuously. At the equilibrium, the concentration of
the reactants and the products remain constant. Equilibrium can be shifted by a change in
temperature, pressure or concentration.
The state of a reversible chemical reaction in where the concentration of
the reactants and products remain constant is known as Chemical
Equilibrium.
In a chemical equilibrium
Rate of forward reaction = Rate
of backward reaction
Example- In a closed container
when Hydrogen and Iodine reacts to
form Hydrogen iodide, it is a reversible
reaction.
H2 + I2
2HI. At 4440C HI
decomposes into H2 and I2. The results
obtained by experiments show that at
constant temperature during equilibrium
the container contains 80% HI and 20%
each of H 2 and I 2 which does not
change with time. This happens
because the rate at which H2 and I2
reacts to form HI is equal to the rate at which
HI decomposes to H2 and I2. As the rate of
the forward reaction and the backward
reaction is equal, Chemical Equilibrium is
established.
If the reaction is related to change in physical state only then it is called, Physical
Equilibrium for example change of ice into water and vis-versa
ice
solid
120
water
liquid
SCIENCE 10
Dynamic Nature of Equilibrium State
Chemical equilibrium is dynamic in
nature Dynamic means “Continuously
reactive”. A dynamic equilibrium is that state
in which two opposite reaction takes place
continuously at the same rate. At equilibrium
the reactions are not static but forward and
backward reaction goes on (simultaneously)
with the same speed.
Hauze
Example : A water pump is fitted in a
Fig. 9.5 Dynamic Nature of Equilibrium
hauze (tank). The hauze is filled with water
in such a manner that the pump draws water from the hauze and pours back it. In the process,
sucking of water from the tank and pouring back into it are two opposite processes taking place
at the same velocity simultaneously. At this stage no change in The water level is observed.
It seems that no activity has taken place but actually two opposite activities at the same rate
takes place, simultaneously.
Important aspects of Chemical Equilibrium
l
Equilibrium can be attained only when a reaction is carried out in a closed manner.
l
At equlibrium the reaction does not stop but the rate of the forward and the backward
reaction becomes equal.
l
At equilibrium the concentration of the reactants and products remains constant.
l
Equilibrium may be changed by changing temperature, pressure and concentration,
equilibrium may be shifted on either side through changes in these three factors.
l
Catalysts do not alter the equilibrium but help to attain equilibrium at the earliest.
Answer these questions.
Q. 1 “At equilibrium reactions do not stop”, explain the statement.
Q. 2 Can we attain equilibrium in a physical process? Explain, giving an example.
Q. 3 What is the nature of chemical equilibrium?
Q. 4 How does a catalyst effect the equilibrium?
Q. 5 Write two important aspects of equilibrium?
9.6 Electrolytes and Non - Electrolytes
Substances (compounds) which conduct electricity through them in their molten state or
in aquous solution are called Electrolytes. Whereas those substances whose melten state or
aqueous solution do not conduct electricity are called non electrolytes.
RATE OF CHEMICAL REACTION AND CHEMICAL EQUILIBRIUM
121
Electrolytes - Sodium hydroxide, Sodium chloride, Copper sulphate etc.
Non electrolytes - Sugar, Glucose, Urea, Alcohol, Benzene etc.
Sodium chloride is an ionic compound formed with sodium (Na+) and chloride (Cl-) ions. In
a solid crystal of sodium chloride, the sodium and chloride ions are strongly bound together with
electrostatic force of attraction. Although in solid Sodium chloride there exist sodium and chloride
ions but it is not conductor of electricity because in solid state the ions have no freedom of
motion. When Sodium chloride is dissolved in water the electrostatic force of attraction breaks
are weakened and Sodium and Chloride ions are free to move in this aqueous solution and in
this way electric current passed through them. This process by which any electrolyte provides
free mobile ions is called Ionisation.
When sodium chloride solid sample is heated, the thermal energy overcomes the electrostatic
forces of attraction between the ions and a certain point be again set free mobile ions.
HCl gas (Polar covalent compound) when dissolved in water also breaks up into H+ and
Cl– ions. e.g. HCl → H+ + Cl–
H+ ion does not exist in an independent state and combine with water molecule to form
Hydronium ion (H3O+).
H+ + H2O → H3O+ (Hydronium ion), H3O+ is a single motion of H+(ag)
Strong and Weak Electrolyte
Electrolytes are of two types
(1) Strong Electrolyte (2) Weak Electrolyte
Those substances which are completely ionised into ions when dissolved in water (in
solution) are called Strong Electrolytes eg. Conc. HCl, H2SO4 etc. Substances which do not
ionise completely in solution are called weak electrolytes eg CH3COOH, Ca(OH)2 etc.
Table 9.1
Strong Electrolytes
Weak Electrolytes
Sodium chloride
NaCl
Water
H2O
Sodium hydroxide
NaOH
Acetic acid
CH 3COOH
Copper sulphate
CuSO4
Carbonic acid
H 2CO 3
Silver nitrate
AgNO3
Ammonium hydroxide
NH 4OH
Hydrochloric acid
HCl
Calcium Hydrauxide
Ca(OH)2
Nitric acid
HNO 3
Hydrogen sulphide
H2S
Sulphuric acid
H 2SO 4
122
SCIENCE 10
9.7 Acids and Bases
General properties of Acids
l
Acids are sour in taste.
l
Acids turn blue litmus* paper into red.
l
Reacts with metal carbonates/bicarbonates and evolve CO2 gas.
l
Neutralize bases.
General Properties of Bases
l
Have a soapy touch.
l
Have a bitter taste.
l
Turn red litmus blue.
l
Neutralize acids.
In 1884 Arrhenius put forward the theory about electrolytes. According to this theory Acid
is a substance which when dissolved in water gives H+ ions while base gives hydroxy ion
(OH–). for example HCl is an acid because it ionise to give H+ ion. NaOH is a base because it
ionise to give OH– ion
NaOH
→
Na+ + OH–
Arrhenius theory explains nature of acid and bases at aqueous solution only. It does not
explain acidic and basic properties in non aqueous solvents, hence, Lowry and Bronsted
proposed a new definition for acid and base, according to which Acid is a proton donor where as
a base is a proton acceptor.
NH3
Proton acceptor
(Base)
+
HCl
→
Proton donor
(Acid )
NH4+
Ammonium ion
+
Cl–
Chloride ion
In the above example Ammonia is a proton acceptor hence it is a base whereas HCl is a
proton donor therefore it is an acid.
Some substances even in the absence of solvent exhibit acidic and basic properties.
These properties can be understood on the basis of exchange of lone pair of electron.
Lewis proposed a new definition of acid and base according to which Acid accepts an
electron pair while base accepts the same e.g.
* Ltmus paper is a dye of purple colour which is extracted from a plant called lichen. It is used as an indicator.
RATE OF CHEMICAL REACTION AND CHEMICAL EQUILIBRIUM
123
CaO: : ++ CO2
l
HCl
Hydrochloric acid
H2SO4
Sulphuric acid
HNO3
etc.
Nitric acid
Weak acid- Those acids which do not donate (H+ion) proton easily, are called weak acids.
CH 3COOH
Acetic acid
l
CaCO3
Strong acid - Those acids which donate H+ion (proton) easily, are called strong acids.
e.g.
l
→
H2CO3
Carbonic Acid
H2SO3
etc.
Sulphurous acid
Strong bases - Those bases which easily accept proton or produce hydroxyl ion (OH–)
easily, are called strong base.
eg. NaOH (Sodium hydroxide) KOH (Potassuim
hydroxide)
l
Weak Bases - Those bases which do not accept
proton easily or do not produce hydroxyl ion easily
are called weak bases. for eg. NH4OH (Ammonium
hydroxide).
Important facts
All alkalies are base but all
bases are not alkali.
Answer these question.
1. What is the difference between electrolytes and non electrolytes?
2. Write name of any two water soluble alkalies.
3. Write name of any two strong acid and two weak acid.
4. Define acid and base according to Arrhenius theory..
Let us know about some of the daily used acids.
Source/substance
Name of the Acid present
i.
Vinegar
Acetic acid
ii.
Orange, Lemon
Citric acid
iii.
Tamarind
Tartaric acid
iv.
Tomato
Oxalic acid
v.
Curd
Lactic acid
vi.
Sting of ant
Formic acid
124
SCIENCE 10
9.8 pH scale
The acidic and basic character of an aqueous solution
is described in terms of concentration of hydrogen ion
present in it. Sorensen (in1909) defined a scale for measuring
hydrogen ion concentration in a solution and is, called pH
scale.
In pH, p stands for potenz
[(it means power (in German
Language)]. H is the symbol
of hydrogen.
(Increase in OH– ion concentration)
(Increase in H+ ion concentration)
pH is defined as - “pH value of a solution is the negative logarithm of the hydrogen ion
concentration”.
pH = – log (H+)
Above is a pH scale [having 0-14 marking].
pH should be thought as simply a number which indicates the acidic or basic nature of a
solution.
Pure water is neutral hence its pH value is 7. Values less than 7 on a pH scale represent
an acidic solution and values greater than 7 represent a basic solution. In pure water, the product
[(H+)] [(OH–)] is always constant at a giver temperature and the idea of pH is linked with it.
Numerical Problem In a solution the concentration of hydrogen ion is 2x10–4 mol/litre. Find the pH value of the
solution. Will the solution be acidic or basic in nature? [log 2 = 0.3010]
Solution : Here given H+
because pH
= 2x10–4
--------(1)
= –log10 H+ --------(2)
Putting values of eqn (1) in eqn (2)
pH
= log 10 [2x10–4]
= [–log102 + log1010–4]
= –[log2 – 4 log10]
[ as log10 = 1]
= –[0.3010–4]
= –[–3.6990]
= + 3.6990
RATE OF CHEMICAL REACTION AND CHEMICAL EQUILIBRIUM
125
Conclusion = As pH value is less than 7 the solution is acidic in nature.
Importance of pH.
1. In Agriculture - By knowing the pH value of the soil, the variety of crops to be cultivated
and the type of fertiliser to be used can be ascertained..
2. pH of the digestive system - Our stomach produces hydrochloric acid. It helps in
digestion of food. During indigestion the stomach produces too much acid and this causes pain
and irritation (burning). This is called acidity. To get rid off this pain bases antacids used on
acids are used. Our blood has a fixed pH value
3. pH change causes tooth decay
Tooth decay starts when the pH of the saliva of the mouth becomes less than 5.5. Tooth
enamel is made up of basic calcium phosphate Ca5 (PO4)3 OH and is insoluable in water. When
pH value in the mouth is below. 5.5, enamel gets corroded. Bacteria present in the mouth produce
acids by degradation of residual sugar and food particles remaining in the mouth after eating
decays the teeth. To prevent tooth decay regular cleaning of teeth and mouth after every eating
is a must.
Points to remember
l
The branch of Physical chemistry which deals with the rate of chemical reaction
and the mechanism of Chemical reaction is known as Chemical kinetics.
l
Those reactions which take place rapidly on mixing of reactants are called fast
reaction while those which take place at slow speed (slowly) are called slow
reactions.
l
Rusting of Iron, setting of cement are examples of slow reaction.
l
Rate of reaction is the rate of change of concentration of reactants or products
with unit time interval.
l
Rate of reaction is always positive.
l
The unit of rate of reaction is mole per litre per second (mole L–1 S–1)
l
Those reactions in which heat is evolved are called exothermic reactions.
l
Those reactions in which heat is absorbed are called endothermic reactions.
l
These chemical reactions which takes place in presence of light are called Photo
Chemical reactions.
l
Photosynthesis, Photography etc. are example of Photo chemical reactions.
l
Rate of reaction increase by increasing the concentration of the reactants.
l
Generally, rate of the reaction increases on increasing the temperature.
l
Those substances which alter the rate of the chemical reaction without undergoing
change in themselves are called Catalysts.
l
In gaseous reactants the rate of the reaction increases by increasing the pressure.
l
Those reactions in which reactants combine to form products and products reunite
to form reactants are called reversible reactions.
126
SCIENCE 10
l
If in a reversible chemical reaction when there is no change in concentration of
the reactants or the products occur, such state is called Chemical equilibrium.
l
Chemical equilibruim can be attained in closed system only.
l
The equilibrium may be shifted by change in temperature, pressure or concentration.
l
Substances which conduct electricity in aqueous solution or molten state are
called electrolytes.
l
According to Arrhenius, Acids give H+ ion while bases give OH– ions.
l
HCl, H2SO4, HNO3 etc are strong acids while NaOH (is a strong base).
l
According to Bronsted and Lowry, acids are proton donors while base are proton
acceptors.
l
The pH value of a solution is the negative logarithm of the H+ ion concentration pH
Value of pure water is 7.
EXERCISES
Very short answer type questions.
1.
Give examples of oxidation reactions.
2.
Define the rate of a chemical reaction.
3.
What is the pH value of pure water?
4.
Write units of rate of a reaction.
Short answer type questions.
1.
What is the difference between exothermic and endothermic reactions?
2.
Write the basic principle of the photography.
3.
Write two factors which increase the rate of a reaction.
4.
Explain three factors affecting rate of a reaction.
Long answer type questions.
1.
What are fast and slow reactions. Give two example of each of them.
2.
Differentiate the average rate of reaction from instantaneous rate of a reaction.
3.
Name the factors that affect the rate of a reaction. Explain in detail.
4.
Explain reversible and irreversible reactions. Write their characteristics.
5.
What is a chemical equilibrium stage. Give any five characteristics of chemical equilibruim.
6.
What are Electrolytes and Non electrolytes? Explain the difference between strong
electrolytes and weak electrolytes.
7.
How are acids and bases defined in different ways.
8.
What do you mean by pH value? Explain the importance of pH.
RATE OF CHEMICAL REACTION AND CHEMICAL EQUILIBRIUM
127
Chapter - 10
SOME IMPORTANT CHEMICAL COMPOUNDS
Have you observed carefully the use of baking soda in
the kitchen during the preparation of Sev, Namkeen etc. You
may also recall that baking soda is also used in making cakes,
bread etc.
We will study l
Method of
preparation,
Properties and
uses of following
compounds
10.1 Washing soda
10.2 Baking soda
10.3 Bleaching powder
10.4 Plaster of paris
l
Manufacture of
substances those
are used in
making buildings
as building
materials
10.5 Quick lime
You need not worry if there is a crack or other damage
or injury in the bone, as it will regain it’s original form in a few
days by applying plaster of paris. In our daily life, besides
baking soda, washing soda, plaster of paris, there are other
chemical compounds such as cement, steel, glass, quick lime
etc, which we use in one or the other way but we are not
much familiar with their nature and structure. In this chapter
we will study some of such chemical compounds.
10.1 Washing SodaCommon name : Washing soda
Chemical name : Sodium carbonate Decahydrate*
Chemical formula : Na2CO3.10H2O
Nature : White crystalline
Soda Ash
Common name : Soda Ash
Chemical name : Sodium Carbonate
Chemical formula : Na2CO3
Nature : White anhydrous (dry/waterless)
Washing soda is Na2CO3 (Sodium carbonate) including
ten molecules of crystalline water. Sodium carbonate,
does not have any water of crystallisation in it is called
anhydrous (waterless) sodium carbonate (Na2CO3). Dry
sodium carbonate is commonly known as Soda Ash.
Deposites of Sodium Carbonate are found in the lakes of
desert situated in East Africa, Egypt, America etc. In India it is
found mostly in Dehradun, Mathura, Jaunpur, Varanasi etc.
10.6 Cement
10.7 Glass
*Deca means ten (10)
10.8 Steel.
128
SCIENCE 10
Manufacture of Sodium CarbonateImportant Facts
The Industrial preparation of
sodium carbonate is carried out by
following methodsl
The number of fixed molecule of water present
in a unit structure of a substance is called
crystalline water on water of crystallisation.
Solvay Method or Ammonia
Soda Method
l
Le Banc Method.
l
Electrolytic Method
Example : there are five molecules of crystal
line water in Copper sulphate (CuSO4.5H2O)
Solvay MethodErnst Solvay was the first to use this method for preparing sodium carbonate in 1864. The
main advantage of this method is that no harmful fumes/vapours are released. The method is
described below.
(1) Raw material CaCO3
(Calcium carbonate)
NH3 and
saturated solution of NaCl
Carbon dioxide is prepared by heating Calcium carbonate in hot furnance.
*
CaCO3
CaO + CO2 ↑
2. Ammonia Saturating Tank- In this tank brine is saturated with ammonia gas.
3. Filter - Impurities are removed from the ammonical brine by filtering.
4. Cooling pipe - The temparature of this solution is reduced in the cooling pipes, as
excessive amount of heat is produced by the reaction of ammonia and Sodium chloride solution.
5. Carbonating Tower - In this tower, ammoniated brine is dropped from above and the
CO2 gas obtained from hot furnace is released from below. Sodium hydrogen carbonate
(NaHCO3) is obtained as a result of the chemical reaction.
NaCl + NH3
+
H2 O
+
CO 2
→
NaHCO3 ↓
+
NH4Cl
Ammonium
Sodium
chloride
hydrogen carbonate
(Precipitated)
The Sodium hydrogen carbonate obtained by the above reaction is precipitated which is
then filtered, washed and dried. It is then heated to form dry anhydrous Sodium carbonate.
Sodium chloride + Ammonia + Water
Ammoniated brine
2NaHCO3
∆∗
Sodium hydrogen carbonate
∗∆ is a symbol of heating.
Na2CO3 + CO2 ↑ + H2O
Sodium Carbonate
(Soda Ash)
SOME IMPORTANT CHEMICAL COMPOUNDS
129
To obtain washing soda, the soda ash is dissolved in water and then recrystallized.
→
Na2CO3 + 10H2O
Na2CO3.10H2O
Washing soda
6. Ammonia recovery tower- Ammonia is recovered by reaction of Calcium hydroxide
and Ammonium chloride. Calcium hydroxide is prepared by using Calcium oxide obtained from
the hot furnace.
CaO + H2O
Ca(OH)2 + 2NH4Cl
→ Ca (OH)2
→ 2NH3 + 2H2O + CaCl2
Properties1.
It is a white crystalline solid.
2.
It is soluble in water. Its aquous solution is alkaline as NaOH (Sodium hydroxide) which is
formed in this reaction is a strong base, where as H2CO3 is a weak acid so that the
resulting solution is alkaline
Na2CO3 + H2O
3.
→
NaOH
+ H2CO3
Strong base
Weak acid
Reaction with air - On keeping in open air, it loses 9 molecules of crystalline water and
forms Sodium carbonate monohydrate which appears as white powder on the surface of
washing powder crystals. This process is called Efflorescence.
open air
Na2CO3.10H2O
Washing soda
Na2CO3.H2O
Efflorescence
+
9H2O
Sodium Carbonate Monohydrate
The loss of crystalline water on keeping a hydrated salt in open air is called
Efflorescence
4.
Effect of heat- On heating it forms dry salt at 7500C while it melts at 8520C
7500C
Na2CO3.10H2O
Wasing soda
5.
Reaction with acids - CO2 gas is formed
Na2CO3 + 2HCl
6.
–10H2O
Na2CO3
Sodium carbonate
2NaCl + H2O + CO2 ↑
Detergent or Cleansing propertiesWashing soda has cleansing properties. It can remove dirt, grease etc from dirty clothes.
130
SCIENCE 10
Uses 1.
In the manufacturing of glass, caustic
soda, soap, borax etc.
2.
As a detergent and a cleansing agent.
3.
As a laboratory reagant.
4.
In textile and glass industry.
An Important Fact
On melting Sodium carbonate
with silica (SiO2), Sodium silicate
(Na 2SiO 3 ) is formed which is
known as Water glass.
Answer these questions
1.
What is Efflorescence? Name a compound that shows efflorescence.
2.
The aqueous solution of washing soda is acidic or alkaline in nature give reson?
3.
Write the chemical formula of(1) Soda Ash (2) Washing Soda.
10.2 Baking SodaCommon Name : Baking Soda.
Chemical Name : Sodium hydrogen carbonate (Sodium bicarbonate)
Chemical Formula : NaHCO3.
Laboratory Method : Sodium hydrogen carbonate is made by saturating an aquous
solution of Sodium Carbonate with carbon dioxide.
Na2CO3 + H2O + CO2
→
2NaHCO3
Manufacture : It is obtained as a bye
product in solvay method.
Properties -
Do you know?
1.
It is a white crystalline solid
Why is baking powder used in
2.
It is soluble in water
making cake, bread etc.?
3.
It’s aqueous solution is alkaline in nature. On
heating it decomposes to form CO2 gas.
Baking powder is a mixture of baking
Heat
2NaHCO3
→
soda and tartaric acid or citric acid.
When baking powder is mixed in the
Na2CO3 + H2O + CO2 ↑
flour of the cake and heated, the
Uses -
baking soda (NaHCO3) present in it
1.
In preparation of baking powder.
generates CO2 gas. This CO2 gas
2.
In making cold drinks.
comes out in the form of bubbles,
3.
As a laboratory reagant.
leaving holes in cakes and making
4.
In manufacture of fire extinguishers.
them light and fluffy. If we do not mix
5.
It is used as an antacid to decrease the
acidity of stomach. Due to its alkaline nature
it neutralizes the extra acid present in the
the baking powder in making cakes,
SOME IMPORTANT CHEMICAL COMPOUNDS
the cake became comparatively
harder and smaller in size.
131
stomach.
Activity Let’s prepare a Fire Extinguisher.
l
In the laboratory, soda acid fire extinguisher can be prepared in the following way-
l
Take 20 ml of Sodium hydrogen carbonate (NaHCO3) solution in washing bottle (Fig.
10.2 (a)
l
Place an ignition tube filled with diluted
Sulphuric acid in the washing bottle.
l
Close the lid of the washing bottle.
l
Bend the washing bottle in such a way so
that the acid of the ignition tube mixes with
the Sodium hydrogen carbonate solution.
l
You will see that a gas comes out in the
form of bubbles from the nozzle.
l
Bring this gas towards a lighted candle. See
what happens? The candle blows out(stops
burning) Fig. 10.2 (b)
Conclusion : Due to the releasing of CO2, the
candle blows out which explains the
mechanism of a fire extinguisher.
Answer these questions
1. What’s happen, when Baking soda does not
mixed in the Cake mixture?
2. Which of these is used as an antacid in
medicines- NaHCO3 or Na2CO3? Why and
How?
132
Let’s Know
How does fire extinguisher work?
In soda acid type
of fire extinguishing
apparatus,
NaHCO 3
and
H2SO4 are kept in
s e p a r a t e
containers. When
this apparatus is
turned
upside
down, CO2 gas is
produced as a result of reaction between
H 2 SO 4 and NaHCO 3 . Due to the
pressure of CO 2, the liquid of this
apparatus oozes out. CO2 gas which
comes alongwith the liquid forms a layer
all around the burning substance,
inhibiting the intake of oxygen and thus
preventing burning.
SCIENCE 10
10.3.
Bleaching Powder-
Common Name - Bleaching Powder
Chemical Formula - CaOCl2 (Though this formula is generally assigned to bleaching
powder, actually it is a mixture)
Chemical Name - Calcium Oxychloride
Manufacture- It is manufactured by passing chlorine gas on dry slaked lime.
Ca(OH)2 + Cl2
→
Slaked lime Chlorine
CaOCl2
+
Bleaching Powder
H2 O
Water
It is manufactured in following two type of apparatusl Hasenclever Plant
Hasenclever Plantl
This apparatus contains
many
hollow
Iron
spherical cylinders which
have blades along with
shafts. (Fig. 10.3)
l
Slaked lime is passed
with the help of hopper in
the spherical cylinders.
l
Chorine gas is passed
through the lowest
cylinder.
l
The slaked lime dropped
from the hopper in the
upper cylinder passes
Fig. 10.3 Hasenclever plant
downward with the help
of the blades in the shaft and comes in contact with the chlorine gas coming upwards.
l
The slaked lime reacts with chlorine gas to form bleaching powder which is removed
outside from the outlet of the lowest cylinder.
Properties 1.
It is a yellowish white powder with a pungent smell like chlorine.
2.
It is soluble in cold water but does not form a clear solution due to the presence of lime.
3.
When it is exposed to open air, it reacts with CO2 of the atmosphere and releases chlorine
gas.
CO2
CaCO3 +
Cl2 ↑
Bleaching Carbon dioxide
powder (Present in atmosphere)
Calcium
carbonate
Chlorine
CaOCl2
+
SOME IMPORTANT CHEMICAL COMPOUNDS
133
4.
It releases chlorine gas on reacting with
dilute HCl or dilute H2SO4. The chlorine
released in this way is known as Available
Chlorine. The more the quantity of available
chlorine, the better will be the quality of
bleaching powder. A good quality sample of
bleaching powder contains 35-38% of
Available chlorine approximately.
CaOCl2 + H2SO4
CaOCl2 + 2HCl
→ CaSO4 + Cl2 + H2O
→
Available Chlorine
CaCl2 + Cl2 + H2O
Do you know?
What is bleaching?
The chlorine gas released from bleaching
powder reacts with water to form Nascent
oxygen. This Nascent Oxygens converts
coloured substance to colourless
substances, which is know as bleaching
Cl2 + H2O → 2HCl + [O] Nascent
Oxygen
Coloured + [O] → Colourless
substance
substance
Uses 1.
In textile industry.
2.
In paper industry for bleaching timber pulp.
3.
As a disinfectant for purifying water.
4.
In making (shrinking less) wool.
5.
As an oxidant in chemical industry.
6.
For removing toxic acidic gases from the atmosphere.
Note - Teacher may explain the functioning of bleaching powder in the water
purification process.
Answer these questions
1.
What is the chemical name of bleaching powder? How is it prepared?
2.
What happens when bleaching powder is exposed to open air?
10.4 Plaster of Paris
Common Name : Plaster of Paris
Chemical Name : Calcium sulphate hemihydrate (CaSO4)1/2 H2O
Chemical Formula : CaSO4, 1/2 H2O
It was first prepared by heating Gypsum (CaSO4 2H2O). It
is found mostly in Paris, the capital of France. It is so that it is also
known as P.O.P.
Preparation : Plaster of Paris is formed by heating gypsum
(CaSO4.2H2O) at 1000C .
1000C
CaSO4.2H2O
Gypsum
134
→
1
2
CaSO4. 1/2 H2O +1 H2O
Plaster of Paris
Important Fact
Only half molecule of
water is present as
crystalline water in
Plaster of Paris. This
means that two units of
CaSO 4 share one
molecule of water.
Water
SCIENCE 10
On heating above 1000C, it loses all it’s crystalline water and anhydrous Calcium sulphate
is formed which is called Dead burnt plaster.
Properties - It is white in colour. On mixing with an adequate quantity of water for half an
hour, if forms a plastic mass that sets into a hard solid.
CaSO4.1/2H2O + 1.5 H2O
Plaster of Paris
→
Water
CaSO4 . 2H2O
Gypsum (Hard and Solid)
The setting of Plaster of Paris leads to its volume change. Due to this property it is used
for making statues and toys etc.
Uses - 1. In making plasters to mend bones.
2.
In making casts of teeth in dentistry.
3.
In making toys, Jewellery, Chalk, Statues etc.
4.
As a fire proof substance.
5.
In making some laboratory apparatus.
6.
In making decorative designs.
Answer these questions.
1.
What is the commercial name of calcium sulphate hemihydrate?
2.
What will happen if Gypsum is heated at 1000C.
3.
Write two important uses of Plaster of Paris?
10.5 Quick Lime
Common Name : Quick lime or lime
Chemical Name : Calcium Oxide
Chemical Formula : CaO.
Manufacture - It is prepared on a commercial scale by heating limestone (CaCO3) in a
rotary Klin at 10000C, a special type of furnace having burners on the right and left side of the
base, so that the ash of the fuel does not mix with the lime so that pure lime is obtained. Calcium
carbonate is dropped from the hopper in the furnace and fuel is burnt in the burners. The hot
gases obtained by burning fuel, reduce Calcium carbonate to Calcium oxide and Carbon dioxide.
Carbon dioxide gas is released out and lime is collected at the bottom. (Fig 10.4)
∆
CaCO3 →
CaO + CO2 ↑
Properties :
1.
It is a white amorphous solid.
2.
Its melting point is 20000C (approx.).
SOME IMPORTANT CHEMICAL COMPOUNDS
135
3.
On heating in Oxyhydrogen flame it gives
bright white light, which is known as Lime
Light fire.
4.
Reaction with water : It reacts with water
to form slaked lime. Heat is produced in
this reaction.
CaO + H2O
→
Ca(OH)2 + Heat
A hissing sound is produced when water
is added slowly to quick lime. So much heat is
produced in this reaction that some part of water
is converted into vapour and the lump of lime
breaks on heating to form powder. This process
is called Slaking of lime and the substance
obtained is called Slaked lime. Slaked lime
(Ca(OH)2) is a white powder which is sparingly
soluble in water. The aqueous solution of
Calcium hydroxide [(Ca(OH)2] is known as
Lime water and a suspension of slaked lime in water is known as Milk of lime. These materials
have the chemical formula Ca (OH)2
Uses :
1.
For makeing lime light.
2.
For white washing of walls.
3.
In manufacturing glass, cement, mortar,
calcium hydroxide i.e. lime water.
l
Lime Stone- is Calcium
carbonate (CaCO3)
4.
For removing temporary hardness of
water.
l
Quick Lime- is Calcium oxide
(CaO)
5.
For making bleaching powder, caustic
soda, calcium carbide etc.
l
6.
As a flux.
Slaked lime - is Calcium
hydroxide Ca(OH)2
7.
To remove acidity of soil.
l
Lime Water - is the aqueous
solution of Calcium hydroxide
in water is called lime water. It
is used in laboratory for testing
CO2 gas.
l
Milk of Lime - is suspension
of Slaked lime in water.
Do you Know?
Answer these questions.
1. What happens when calcium carbonate
is heated rapidly?
2. Write the name and formula of slaked
lime?
136
SCIENCE 10
10.6 CementCement is an important building material. It was first introduced in England in 1824 by
Joseph Aspdin. He observed that if a mixture of Calcium carbonate (lime stone) and Clay is
heated strongly and left for 2-3 hours after mixing it with some water, it sets into a hard mass
which resembles the natural hard limestone quarried in the Isle of portland, England. That is why
it is also known as Portland Cement.
In India, the major Cement manufacturing factories are situated in Gujarat, Orissa,
Rajasthan, Madhya Pradesh and Tamil Nadu States.
The common composition of Portland Cement is -
Important Facts
CaO (Calcium oxide) = 60-70%
SiO2 (Silica) = 20-25%
l
If the quantity of lime in cement
is less than that required, it will
set easily and quickly but it will
be less hard / strong. On the
other hand if the quantity of lime
is more, cracks will be formed
after setting of cement.
l
Gypsum is added only to slow
down the process of setting of
cement so that it gets
sufficiently hardened.
l
Cement is mainly a mixture of
Calcium and Aluminuim
silicates which have the
property of setting on mixing
with water.
Al2O3 (Alumina) = 5-10%
Fe2O3 (Iron oxide) = 2-3%
Gypsum (CaSO4.2H2O) = 2% Approx.
Manufacture of CementThe following raw materials are used in the
manufacture of Cement1.
Lime stone- CaCO 3 which produces
CaO (Calcium oxide)
2.
Clay- It provides Silica (SiO2) Alumina
(Al2O3) and Iron oxide (Fe2O3) etc. Some
types of clay do not provide Fe2O3.
3.
Gypsum- CaSO4.2H2O
Process
Lime stone and clay mixture are put in a rotary Klin with the help of the hopper. This special
type furnace, Klin is a long and bent downwards and rotates continuously. (fig. 10.5) Hot air is
blown from bottom to top in this furnace. At this high temperature, clay and lime fuse and react
to form small pieces of Cement klinker.
15000C
Calcium Carbonate + Clay
Cement + CO2 + H2O
Cement clinker is cooled and mixed with 2-5% gypsum. The mixture of clinker and gypsum
is grinded to get fine powder of portland cement which is stored in a big structures vessel called
Silos and then packed in air tight bags for sale. In the process and tri silicates and tri Calcium
SOME IMPORTANT CHEMICAL COMPOUNDS
137
aluminate are the major products, formed. All these ingredients of cement when mixed with
water, set to give a hard mass.
Uses - Cement is an important building material used in following various forms1.
Mortar- It is used for joining bricks in plastering etc. It is prepared by mixing 1 part cement
and 3 parts sand with adequate amount of water.
2.
Concrete - When cement, thick sand and water are mixed with small pieces of stone
(gravel/pebbles) the mixture obtained is called concrete. It becomes extremely hard on
setting. It is used in making floors and roofs of houses, roads, bridges, dams, rail tracks
etc.
3.
Reinforced Concrete Cement (R.C.C.)- When concrete is filled inside Iron rod and allowed
to set, it is called Reinforced Concrete Cement. It is used in the construction of building’s
roofs, tunnels, dam etc.
Answer these questions.
1.
Why is Cement known as Portland Cement?
2.
What is Mortar? Give it’s one use.
3.
Name the raw materials used in making cement.
4.
Why is lime stone used in making cement?
5.
Why is gypsum mixed in cement?
10.7 Glass
Glass is an amorphous transparent or opaque substance which is a mixture of sodium
silicate (Na2SiO3), Calcium silicate (CaSiO3) and Silica (SiO2)
In India, glass is manufactured mostly in Bangalore, Baroda, Mumbai, Kolkata, Firozabad
and Delhi. It’s constitutional formula may be written approximately as Na2SiO3.CaSiO3.4SiO2 or
Na2O.CaO.6SiO2.
138
SCIENCE 10
ManufactureThe following raw materials are used to make ordinary glass or soda glassSodium carbonate (Na2CO3), calcium Carbonate (CaCO3) and Sand (SiO2)
Process of Manufacturing
A fine mixture of soda ask, lime
stone and sand (which is called Batch)
is mixed with glass pieces (called cullet)
and kept in tank furnace. The melting of
the mixture becomes easy by adding
cullet. The tank furnace is heated by
burning fuel gases which generate
temperature upto 14000 C in the furnace
(fig 10.6). At this temperature the raw
materials react with one an other to form
Fig. 10.6 Tank Furnance for Glass manufacture
melted glass which on cooling forms solid
glass. Before cooling the melted glass can be put in different cast to make items of desirable
shape. To obtain the desired properties of glass such as hardness, heat resistant power, colour
etc some other substances are also mixed in it.
Annealing of glassIf a hot glass substance is cooled immediately, it becomes fragile and cracks easily. If
cooling is done very slowly the glass becomes opaque. Thus hot glass substances should be
neither cooled immediately nor very slowly. After casting the glass in the desired shape, it is
cooled gently to prevent it from becoming fragile. The process by which the prepared glass
materials are cooled gently with a uniform speed is called annealing.
Various types of glasses and their usesVarious types of glasses are required for various works. For example the glass used in
making laboratory tools has the property of resisting high temperature whereas mirror is made
up of ordinary glass (soft glass).
The various types of glass and their uses are depicted in the following tableS. No. Type of Glass
Uses
1.
Soda glass (soft glass)
Crockery, bottles, mirror, window glass,
light bulbs etc.
2.
Potash glass (Hard glass)
In making laboratory tools.
3.
Pyrex glass (Heat resistant glass)
Laboratory tools, Injections, some utensils.
SOME IMPORTANT CHEMICAL COMPOUNDS
139
4.
Optical glass
Spectacles, lenses of optical
instruments, prism etc.
5.
Lead crystal glass
For making decorative items.
6.
Safety glass
7.
Photochromatic glass
For making air proof curtains of trains,
aero planes, car, bus, truck etc.
For making sun glasses, camera etc.
8.
Coloured glass
9.
Glass Fibre
Medical instruments, refrigerators etc.
10.
Crookes glass
It prevents harmful ultraviolet rays hence
used in making lenses of spectacles.
For making artificial jewellery, gems,
window
glass etc.
Different coloured glasses are formed in following waysS. No.
Compound mixed in glass
Colour of the glass
1.
Cadmium sulphide
Yellow
2.
Ferric oxide
Brown
3.
Cobalt oxide
Blue
4.
Chromium oxide
Green
5.
Cuprous oxide
Red
6.
Maganese dioxide
Violet
Answer these questions
1.
Write the constitutional formula of glass.
2.
Write the names of the raw material used for making ordinary glass?
3.
What is meant by annealing of glass?
10.8 Steel
It is a mixture of iron and carbon. Pure Iron is shock proof and ductile but it is not durable
and strong. If a small amount of carbon is added to pure Iron it’s strength increases and the Iron
including carbon in it is called steel. It contains .1-1.5% of carbon in it.
Manufacture
Steel is manufactured from raw Iron. Raw Iron contains carbon (C), sulphur (S), manganese
140
SCIENCE 10
(Mn), silicon (Si) and phosphorous (P minutely) in
the form of impurities.
The process for manufacture of steel is carried
out in the Bessemer converter. It is a pear shaped
furnace having lining of fire bricks inside. Hot air
passes in the furnace. Bessemer converter can he
tilted or turned upside down. (fig 10.7)
A mixture of raw Iron and lime (CaO) is taken
in the converter and hot air is passed. The oxygen
present in the hot air oxidizes the various impurities
present in raw iron.
l
Carbon present as impurity in raw iron converts into carbon monoxide gas which oxidizes
at the surface of the converter to form CO2.
l
Sulphur, present as impurity reacts with oxygen of the air to form sulphur dioxide gas
which escapes out.
l
Manganese and silicon present as impurity get oxidize to form manganese oxide and
silicon oxide which react with each other to form mangnous silicate (Slag)
l
Phosphorous present as impurity in raw iron, reacts with oxygen to form Phosporous
pentaoxide (P2O5) which reacts with lime (CaO) to form calcium phosphate (slag)
Mangnous silicate and calcium phosphate being light, float on the surface of melted iron in
the converter and are separated. Thus only pure melted Iron remains in the converter. Necessary
amount of carbon is mixed in this pure melted Iron to get the desired steel.
Properties
Steel has intense strength, hardness and ductile capacity. The properties of steel depend
on the content of carbon present. Properties of steel can be modified by heat treatment.
Depending on the content of carbon, steel is mainly of two types1. Mild steel 2. Hard steel.
1. Mild steel - Iron containing 0.1 to 0.4% carbon is called mild steel. It is extremely strong,
durable, shock proof, ductile and elastic. It is used for making sheets, wires, chains, car’s body,
nuts, bolts, rail track, wheels, ships, bridge, cable, taps, guarder etc.
2. Hard steel- It contains more carbon than that present in mild steel. Iron containing 0.5 to
1.5% carbon is called hard steel. It is extremely hard and brittle. It is used for making cutting
instruments, knife etc.
SOME IMPORTANT CHEMICAL COMPOUNDS
141
Heat Treatment of Steel
The special properties of steel i.e. hardness and
elasticity can be obtained by suitable heat treatment. The
following are the types of heat treatment.
(i) Hardening or QuenchingWhen red hot iron (approximately having 8500C
temp.) is immediately plunged into cold water it becomes
extremely hard and brittle. The process of cooling red hot
Iron immediately is called Quenching or Hardening.
Important fact
The ordinary normal steel
may get rusted in the
presence of humid air but if
chromium and nickel
metals are mixed in it
stainless steel is obtained
which does not get rusted.
(ii) TemperingThe hardness of quenched steel can be increased or decreased. This process is called
tempering. When quenched steel is heated at 2000C-3500C and then cooled gradually, this
process is called tempering. Tempered steel is much less brittle. The steel of desired degree of
hardness can be obtained by adjusting the temperature of tempering. The brittleness of steel
can be reduced or destroyed by tempering.
(iii) AnnealingThe process in which red hot iron is cooled slowly is called annealing. The steel becomes
soft by this process. The annealing effect on steel is opposite to that of quenching.
Answer these questions.
1.
How is steel manufactured?
2.
What do you mean by Quenching and Annealing of steel?
Points to remember
l
The percentage of carbon in steel is mostly 0.1 to 1.5.
l
Steel is manufactured in Bessemer converter.
l
The percentage of carbon in hard and mild steel is different.
l
Stainless steel is an alloy having Nickel and Chromium.
l
The formula of washing soda is Na2CO3.10H2O.
l
Soda ash is an anhydrous sodium carbonate.
l
The number of fixed molecules of water in a unit formula/structure of the salt is
called crystalline water.
l
The Industrial preparation of sodium carbonate is done by Solvay Method.
l
On exposure to open air, washing soda loses its water of crystallization.
142
SCIENCE 10
l
The loss of water from a hydrated salt on exposure to open air is called
efflorescene.
l
Washing soda has detergent properties.
l
Sodium silicate is called water glass.
l
The chemical name of baking soda is sodium hydrogen carbonate (NaHCO3).
l
Baking powder is a mixture of baking soda and tartaric acid.
l
NaHCO3 is used in fire extinguishers and used an antacid to remove acidity
in stomach.
l
Calcium oxychloride (CaOCl2) is popularly known as bleaching powder.
although bleaching powder is a mixture.
l
Bleaching powder is used for bleaching and purifying water.
l
Hemi hydrate Calcium sulphate is called Paster of Paris. Its formula is CaSO4.1/
2H2O.
l
Gypsum is heated to form Plaster of Paris.
l
On mixing Plaster of Paris with water and keeping it for half an hour it sets into
a hard substance.
l
Calcium hydroxide (Ca(OH)2) is called slaked lime.
l
A clear solution of calcium hydroxide in water is called lime water.
l
Lime stone, clay and gypsum are used as raw materials in making cement.
l
Glass is an amorphous transparent or opaque substance which is a mixture
of sodium silicate, calcium silicate and silica.
l
Annealing is the process in which the prepared glass material are cooled slowly
and with a uniform speed.
EXERCISES
Very Short Answer Questions1.
What is Washing soda? Write its two important properties and uses.
2.
Which substances are used in making bleaching powder?
3.
Write two uses of Plaster of Paris?
4.
How is slaked lime obtained from quick lime?
5.
What is concrete and RCC?
6.
Why is gypsum mixed in cement?
7.
What do you mean by photochromatic glass?
SOME IMPORTANT CHEMICAL COMPOUNDS
143
Short Answer Questions 1.
What is hardening and quenching of steel? Explain.
2.
What is Gypsum? What happen when it is heated at 100°C?
3.
What is the chemical constitutions of glass?
4.
What do you mean by mild and hard steel? Write any one use of each of them.
Long Answer Questions1.
Describe the manufacturing of bleaching powder with the help of a neat and labelled diagram,
2.
Describe the manufacturing of cement with the help of a neat and labelled diagram.
3.
How is ordinary glass manufactured?
4.
Name the different types of glass? Write any one use of every type of glass?
5.
How is steel manufactured by Bessemer converter method? Explain.
6.
What is heat treatment of steel? Explain.
144
SCIENCE 10
Chapter - 11
METALS AND NON METALS
During the excavation carried out in valley of Sindhu river
and other parts pieces of ancient art and architecture and iron
lumps etc. obtained it means that metals like gold, silver, iron,
copper, lead and tin were known even at that time. In the vedic
and other literary books direct or indirect reference of metals
and non-metals are given.
We will study
At present, 118 elements natural and synthetic elements
are known. These elements are classified as metals, non-metals
and metalloids.* Out of these 22 are non-metals.
11.1 Metals and Non
Metals in daily life
Metals and non-metals are useful in almost every aspect
of life.
11.2 Metals; General
Introduction
11.1 Metals and Non-Metals in daily life
11.3 Ores and Minerals
Metallurgy,
Concentration of ore,
Extraction and
purification of metal
Extraction of metals,
Iron and Aluminium.
11.4 Metal activity series
We use Metals and Non-metals in our daily life. e.g. in
domestic and industrial apparatus, electric wires made of copper
and aluminium are used Tungsten wire is used in electric bulb,
Mercury in thermometer etc.
Metals are useful for our body e.g. Iron in haemoglobin,
Calcuim in bones, Potassium and Sodium in our blood etc. Nonmetals like carbon, oxygen, nitrogen phosphorous etc. are also
present is some or the other form.
11.5 Corrosion
11.2 Metals; General introduction
11.6 Alloys
Metals are those
elements which can easily
donate (lose) electrons to
form a positive ion. The
valency of the metal depends
on the number of electrons
donated (lost) by the atom of
that metal. Generally metals
are solid and have shining
surface. Most of the metals
are conductors of electricity
11.7 Non metals; General
Introduction
11.8 Hydrogen, Ammonia,
Sulphur dioxide,
Sulphuric acid
preparation,
properties and uses.
11.9 Difference between
Metals and Non
Metals and their
uses.
Anaemia
The body of a healthy person
consists of 4-5 litres of blood.
Anaemia means the decrease
in haemoglobin content (as per
the standard) of the blood.
Haemoglobin (Heam means
Iron) contain Iron as the main
element.
* metalloids show properties of both Metal and Non-Metal.
METALS AND NON METALS
145
due to the presence of free electron.
Answer these questions
1. Why are anaemic patients advised to eat spinach?
2. Name the metals available in your kitchen.
Properties of metals
1.
2.
3.
4.
5.
6.
7.
8.
Physical properties - The properties like state, colour conduction etc are known as
physical properties.
State - Metals are solid at ordinary temperature (exception mercury is in liquid state)
Malleability - Metals, when beaten or hammered can be changed into thin sheets this
property of the metals is called malleability. You might have seen silver foils on sweets.
Ductility - Metals can be drawn into thin wires, This property is known as ductility. The
ductility of different metals is different.
Conductivity - Metals generally are good conductors of heat and electricity. It is because
of the conductivity of heat, pressure cooker and saucepan are made with handles of non
conducting material like plastic or bakelite. Electric wires are made of copper, aluminium
etc because they are conductors of electricity. Silver is the best conductor of electricity of
all the metals, we know.
Metallic lustre - Most metals have a shining surface, this property of metals is called
metallic lustre. Metallic lustre decreases on exposure
to atmosphere. The oxygen, carbon dioxide and
moisture present in the atmosphere react with the
Let’s Know
metals and form a thin film of oxides, carbonates etc.
You might have seen the difference betwen a new Mercury is also known as Quick
antenna and an old one after using for a considerable Silver as it shines like silver.
time.
Hardness- Most metals are hard sodium and potassuim are soft metals, and can be cut
with a knife.
Melting and Boiling point- Generally metals have
high boiling and melting points.
Important Facts
Sonorous- When metals are beaten or when they
collide with other substances, a characteristic and a The conductivity of some metals
ringing sound is produced. This is called the sonorous highly increases on lowering the
property of metals. You might have experienced the temperature, this property is
characteristic sound produced when the Iron bell rings called super conductivity.
in your school.
Answer these questions.
1.
Why are handles of cooking vessels made up of non conducting material?
2.
Why are electric wires made up of metals?
3.
What is meant by the term sonorous?
146
SCIENCE 10
(b) Chemical properties- The characteristic properties of the elements due to the electronic
configuration are known as chemical properties. Metals are electro positive in nature.
1. Reaction with oxygen - Metals react with oxygen to form metallic oxides e.g.
→ 2Na2O (Sodium oxide)
2Mg + O2 → 2MgO (Magnesium oxide)
4Al + 3O2 → 2Al2O3 (Aluminium oxide)
4Na + O2
2. Reaction with water - Generally active metals react with water to form metallic hydroxide
and hydrogen gas,
2Na + 2H2O
→
2NaOH
+
Sodium hydroxide
H2 ↑
Caution : Sodium is a highly reactive metal. It instantly reacts with oxygen and carbon
dioxide present in the atmosphere and produce Na2O and Na2CO3. It reacts vigourously
with cold water and brisk evolution of hydrogen gas may cause fire. Hence it is kept
immersed in kerosene oil.
3. Reaction with dilute acids- Here formation of hydrogen gas takes place e.g.
2Na
+ 2HCl
Hydrochloric acid (dil)
→
2NaCl
+
H2 ↑
Sodium chloride
Hydrogen gas
4. Reaction with salt solutions : Highly reactive metal displaces less reactive metal
from its salt solutions. for example Zinc displaces Cu from CuSO4 solution.
Zn + CuSO4
→
ZnSO4 + Cu
Similarly iron displaces copper and copper displaces silver from its solution
Activity- 1
Take CuSO4 solution in a beaker. Place a zinc rod in it. After some time you may find that
the blue colour of copper sulphate solution slowly disappears and reddish brown coloured
copper gets deposited on the zinc rod.
CuSO4
+
Copper Sulphate
(Blue Solution)
Zn
Zinc metal
→
ZnSO4
Zinc sulphate
(colourless)
+
Cu(s)
Copper
(Brownish Red)
Conclusion - In the above reaction zinc metal displaces Cu metal from its salt solution.
Hence its clear that zinc metal is more reactive than copper.
METALS AND NON METALS
147
5.
Reaction with hydrogen- Active metals react with hydrogen to form metallic hydride.
2Na + H2 → 2NaH (Sodium hydride). In such hydrodos, hydrogen shows electronegative charactor.
Reaction with chlorine - Metals reacts with chlorine to form metallic chlorides
Ca + Cl2 → CaCl2 (Calcium chloride) Metallic chlorides are generally solid and electro
valent in nature. In molten state and aqueous solution they conducts electricity.
6.
Answer these questions.
1.
Which metal is more reactive copper or zinc? How will you prove it?
2.
Sodium metal should not be kept in water, why?
3.
What are the chemical nature of metals?
11.3 Minerals and Ores
Do you know?
The elements or compounds which occur in the
nature in the earths crust are known as minerals. Those All ores are minerals but all
minerals from which metals can be easily and profitably minerals are not ores.
extracted are called ores.
The earth’s crust is the major source of metals in nature. Most metals are found in a
combined state. Noble* metals like gold, silver, platinum etc. are found in free state. Some
important metals and their corresponding ores are given in the following table.
S.No. Name of
the metal
Symbol
Name of the Ore along with formulae
1.
Iron
Fe
Haematite (Fe 2O 3 ) Magnetite (Fe 3O 4 ), Limonite
(Fe2O3.3H2O), Siderite (FeCO3) Iron pyrite (FeS2)
2.
Aluminium
Al
Corundum (Al2O3) Bauxite (Al2O3.2H2O)
3.
Copper
Cu
Copper glance (Cu2S), Ruby Copper (Cu2O), Copper
Pyrite Cu2S. Fe2S3
4.
Magnesium
Mg
Carnallite KCl MgCl2. 6H2O Dolomite (MgCO3.CaCO3)
5.
Mercury
Hg
Cinnabar (HgS)
6.
Zinc
Zn
Zinc Blende (ZnS) Calamine (ZnCO3)
Metallurgy
The process of extracting the metals from their ores (in the refined form) is called metallurgy.
Obtaining pure metal from its ores involves various steps, they are 1. Concentration of the ore
2. Extraction of metal very less.
*Noble metals- Due to the very less activity, they are called Noble Metals.
148
SCIENCE 10
3. Refining of metals.
1. Concentration of the ore
Ores mined from earth contain some amount of impurities such as soil, sand etc called
gangue. The ore is concentrated by removing the gangue. Different methods are used for
concentration.
(I) Physical methods of concentration :
1.
Magnetic separation- This method is used to
separate ores with magnetic property. eg. Iron
ore.
2.
Gravity separation - In this method finely
powdered ore is washed in a stream of fast
running water. The lighter particles are washed
by running water while the heavier particles
remain at the bottom. Ores of tin and lead are
concentrated by this method. This method is also
known as hydraulic washing.
3.
Froth Floation Process - In this method finely
powdered ore is mixed with water and calculated
quantity of turpentine oil or pine oil taken in a
tank. A rapid stream of air is then passed through
the mixture. Ore particles get coated with oil,
adhere to air bubble in water (froth) and rise to
the surface. The froth is easily collected from the surface. Sulphides of copper, lead and
zinc are concentrated by this method.
(2 )
Chemical Method or Leaching- This method is employed on the basis of difference in
chemical properties of the ores and its components.
Bauxite ore contains impurities of ferric oxide and silica. The finely powdered ore is heated
with aqueous solution of Sodium hydroxide at 420-440 K. Soluble Sodium meta aluminate is
formed and the impurities remain unaltered.
∆
Al2O3 + 2NaOH → 2NaAlO2 + H2O
The solution is filtered and the filterate is treated with freshly precipitated aluminium
hydroxide. This aluminium is used to favouer precipitation of NaAlO2 as Al(OH)3. Precipitate of
Aluminium hydroxide is obtained. It is filtered and heated. In this way pure aluminium is obtained.
2NaAlO2 + 4H2O → 2Al(OH)3 ↓ + 2NaOH
∆
2Al (OH)3 → Al2O3 + 3H2O
Extraction of Metals
Extraction of metals from its concentrated ore depends on the nature of the ore and the
METALS AND NON METALS
149
impurities present in it. Extraction involves usually (takes place in) the following steps1. Conversion of the concentrated ore to its metallic oxides.
2. Reduction of metallic oxides to metals.
(1) Conversion of the concentrated ore to its metallic oxides
Extraction of metals from its concentrated ore is mainly done by reduction. It is easy to
obtain metals by reductions from their oxides than that of carbonates and sulphides. Therefore
metals are converted to their oxides before reduction. The concentrated ore is converted to its
metallic oxides by Calcination and Roasting.
(i) Calcination - The process in which the ore is heated strongly in the absence of air is
called calcination. This process removes moisture and volatile impurities from the ore. Calcinatiion
converts carbonate ores to its metallic oxides.
∆
ZnCO3
Zinc carbonate
→
ZnO +
CO2 ↑
Zinc oxide
Carbon dioxide
(ii) Roasting- The process in which the ore is heated strongly in the presence of excess
air at a temperature below its melting point is called roasting. This method converts sulphide ore
to its corresponding metallic oxides.
Roasting
2ZnS
+
Zinc sulphide
3O2
→
Oxygen
2ZnO
Zinc oxide
+
2SO2 ↑
Sulphur dioxide
(2) Reduction of metallic oxides to metals
The metallic oxides obtained by the above process is reduced to metals by the following
methods.
There are three methods for reduction of metallic oxides. They are as follows.
1.
Reduction by heat
2.
Chemical Reduction
(a) Reduction by carbon (b) Reduction by Aluminium
3.
Electrolytic Reduction
Refining of MetalsThe metals obtained from various reduction process contains certain impurities. The
process of obtaining pure metals by removing these impurities is called refining. The common
methods used for refining are :1.
Liquation method
2.
Distillation method
3.
Electrolytic refining
150
SCIENCE 10
Answer these questions.
1.
Write the various general steps involved in the metallurgy of a metal from its ores.
2.
Write down the name and formulae of two important ores of (a) Aluminium (b) Iron.
3.
“All minerals are not ores”- Explain this statement.
Extraction of some important metals
IRON
Iron is the second abundant metal found
in the earth’s crust. (after aluminium) Due to its
reactive nature it is not found in free state. In
combined form, iron is found as oxides,
carbonates and sulphides. The important ore of
Iron is haematite which contains sand (SiO2) as
the main impurity.
Extraction of iron from Haematite
The details of various steps involved in
extraction are as following.
1.
Concentration of the ore- The ore is
concentrated by hydraulic washing
(gravity separation) method.
2.
Calcination - The concentrated ore is
strongly heated in the absence of air,
thereby removing moisture and volatile
impurities like Sulphur, Arsenic etc. and the
ore becomes porous.
3.
Reduction - Calcinated ore is mixed with calculated quantity of coke and limestone. This
mixture is fed into the blast furnace through cup and cone arrangement. A blast of hot air
is blown at the bottom (Fig 11.3). The air provides oxygen for combustion. The following
reactions take place and thus metallic Iron is extracted.
I. Formation of Carbon monoxide
C+
O2
CO2 +
→
CO2 + heat
C
→ 2CO
(from coke)
II. Reduction of heamatite
400-6000C
Fe2O3
+
3CO
→
2Fe
Heamatite
Carbon monoxide (reducing agent) Iron
METALS AND NON METALS
+ 3CO2 ↑
Carbon dioxide
151
Role of Limestone in extraction of Iron : Iron ore used in the blast furnace contains
sand as impurity. It is necessary to remove this impurity other wise the blast furnace
gets blocked Hence Limestone is added as flux*.
∆
CaCO3 (s)
→
CaO + CO2 (g)
10000C
10000C-15000C
CaO (s) + SiO2 (s)
→
CaSiO3
↓ Calcium silicate (slag)
Flux is selected according to the nature of impurities present. Impurities combine with the
flux and form fusible material are called slag. Slag being lighter than the metal, floats on the
surface of the metal from where it can be easily removed.
Molten iron and slag are tapped off and collected separately through different outlets from
the bottom. The iron thus obtained is called pig iron. In India iron is found mostly in Bihar,
Chattisgarh, West Bengal and Karnataka. The main iron and steel plants for extraction of iron
are established at Bhilai, Durgapur Rourkela, Jamshedpur and Bhadravati etc.
Aluminium
It is a soft silvery metal. The earth’s crust consists about 7% of aluminium compounds.
The main source of aluminium is bauxite ore. Abundant deposits of bauxite occur in Mumbai,
Kolhapur, Jabalpur, Ranchi, Mirzapur (Sonebhadra) Balaghat and Amarkantak, Katni. The main
companies manufacturing Aluminium are National aluminium company (NALCO), Bharat
Aluminium company (BALCO) etc.
Extraction Aluminium is extracted from bauxite ore. The main impurities present in the ore are
oxides of iron and silica. The main steps involved in extraction of Aluminum are as follows.
(i)
Purification of Ore- When Iron oxide and silica are present as impurities, Bayer’s process
is employed to remove the impurities from the ore. The Bauxite ore gets converted to
Aluminium oxide by this process.
(ii)
Electrolysis of Aluminium oxide- Pure aluminium is obtained by electrolysis of alumina
by Hall’s method. Electrolysis is carried out in an Iron tank. Aluminum oxide is mixed with
cryolite **(Na3AlF6) and small quantity fluorsper. On passing electricity aluminium metal is
liberated at the cathode while O2 gas at the anode. As graphite electrodes are used as
anode, therefore these are likely to the attrached by oxygen and hence are replaced from
time to time,
* flux is a substance which is added in ore to remove non fusible impurities.
**Cryolite is added to decrease the melting point of aluminium oxide, (Alumina) and to increase electric conductivity.
152
SCIENCE 10
Reactions2Al+3 + 3O–2
Al2O3
Graphite [anode+]
At cathode
→
Al+3 + 3e–1
Al
At anode
O–2 – 2e–
O+O
→
→
O
Fig. 11.4 Extraction of Aluminium by Hall’s method.
O2 ↑
(iii) Refining of Aluminium- Aluminium metal obtained by electrolysis of molten aluminium
oxide is approximatly 99% pure. This metal is further purified by electrolysis method.
Answer these question.
1.
Explain the steps involved in extraction of Iron.
2.
What is the role of cryolite in extraction of aluminium.
3.
Describe briefly Halls process.
11.4 Activity series
All metals do not react in a similiar manner. Some metals are highly reactive as compared
to the other metals.
→
These metals are
more reactive
←
than hydrogen
→
These metals
are less reactive
than hydrogen
→
→
Potassium
K
Sodium
Na
Calcium
Ca
Magnesium
Mg
Aluminium
Al
Zinc
Zn
Iron
Fe
Tin
Sn
Lead
Pb
Hydrogen
H
Copper
Cu
Mercury
Hg
Silver
Ag
Gold
Au
METALS AND NON METALS
Most reactive
The activity
series is a list
of metals
arranged in
order of their
decreasing
reactivity
↓
Least reactive
153
Less reactive metals are generally found freely in nature
Answer these question
1.
What do you mean by activity series?
2.
Give name and symbol of metals which are more reactive than Hydrogen.
11.5 Corrosion of Metals
You might have observed that Iron and Iron articles when left for sometime gets coated
with reddish brown powder. Other metals like Silver, Aluminium, Copper etc. get tarnished the
same manner. Why does this happen? It is because metals react with atmospheric gases like
O2, CO2, H2S etc. in presence of moisture and form compounds which get deposited on the
surface of the metal and tarnish it. It is due to tramishing that to Iron oxide deposits (reddish
brown layer) on it Silver sulphide (black layer) on silver and basic Copper carbonate (green
layer) on Copper. The process by which metals react with moisture and atmospheric gases and
get slowly damaged is called corrosion of metal.
The Phenomenon by which new compound are formed on the surface of metal
when metal react with atmospheric gases and moisture and other reagents is called
corrosion.
Corrosion is an undesirable (unwanted) process. Corrosion of Iron is called rusting of
Iron.
Chemically, hydrated Iron (III) Oxide and it is exprimentally established that rusting is
fastered in presence of acidic oxides present on the atmosphere. (Fe2O3 × H2O) is rust. Rusting
of Iron takes place in presence of air and moisture.
Prevention of corrosion
(i)
Varnishing- It is the most widely used method.
(ii)
Application of Oil or Grease- Newly made cutting weapons like scissors and knife are
coated with grease to prevent rusting.
(iii)
Galvanisation- The coating of Zinc layer on Iron is called galvanisation. You might have
heared of G.I. sheets (galvanised iron)
(iv)
Electro plating- Metals like Tin, Chromium Titanium etc are corrosion resistant. Iron articles
are coated with a layer of these metals by electro plating whereby rusting of Iron is
prevented.
(v)
Making Alloys - Some alloys are corrosion resistant e.g. stainless steel.
Answer these Questions
1.
What is rusting? give chemical formula of rust.
2.
Explain two methods for prevention of corrosion.
* Iron shows variable valency, its valencies are +2 and +3.
154
SCIENCE 10
11.6 Alloys
The properties of a metal can be modified by combining it with other metals, thus alloys of
desirable properties are made. Alloy is a mixture of two or more then two metals. It can be
defined as.
“The homogeneous mixture of two or more metals in which the composition of the
components are in almost fixed proportion.”
We know that Iron is a widely used metal. Pure Iron is soft and expands on heating hence
it cannot be used in pure form. When small quantity of Carbon is added to Iron, steel is obtained.
Steel is camparatively hard and strong.
S.No.
Name of the
Alloy
Composition and
Its percentage (Appro.)
Uses
1.
Stainless Steel
Iron 82% Nickel and
Utensils, surgical
Chromium 18%
instrument, watches etc.
Copper 80% Zinc 20%
Utensils, pipes, radiator
2.
Brass
statues etc.
3.
Duralumin
Aluminium 95%
In making Aeroplane &
Copper 4% Manganese 0.5% Ship etc.
4.
5.
Magnalium
Bronze
Aluminium 95%
Manufacture of physical
Magnesium 5%
balance & light articles.
Copper 90% Tin 10%
Statues, coins, ornaments
utensils
6.
German silver
Copper 60% Zinc 20%
Electroplating and utensils
Nickel 20%
7.
Solder Metal
Lead 50%, Tin 50%
To join the elecric wires.
8.
Gun Metal
Copper 88%, Tin 10%
For making canons, guns,
Zinc 2%
matching parts
Alloys of GoldPurity of gold is expressed in carats. Pure gold is not used for making ornaments because
it is soft. Gold is made hard by combining it with Silver or copper. Generally 22 carat Gold is
used in making ornaments. It means 2 parts of Silver or Copper is added to 22 parts of pure
Gold as 24 carat gold is pure gold.
METALS AND NON METALS
155
Answer these Questions
1.
Define Alloys.
2.
What is Amalgum? Where is it used?
3.
Which alloy is used in manufacture of aeroplane?
11.7 Non metals
Those elements which accept electrons and form
negative ions are called non metals. The valency of the
non metals depends on the number of electrons accepted.
For example the formation of F–, O2– and N3– ions.
(a) Physical properties.
Important aspect
The alloy of mercury with
one or more metal is called
amalgum. It is used in filling
teeth and as Electrode.
Let’s know
Non-metal does not provide
electrons to convert hydrogen ion
to hydrogen gas. Hence H2 gas in
not produced during reaction of
non metal with dilute acids. This
property on the other hand is
usually showed by metals.
1.
State - At room temperature, non-metals exist in
solid, liquid and gaseous form. e.g. At ordinary
temperature Carbon, Sulphur, phosphorous etc are solid, Bromine is liquid while Hydrogen,
Oxygen and nitrogen etc are gases.
2.
Brittleness- Non metals, when hammered break into pieces. This property is called
brittleness. Solid non metals are brittle. e.g. Sulphur, Phosphorous, Iodine etc.
3.
Conductivity - Non-metals are bad conductor (insulators) of heat and electricity as there
are no free electrons. Graphite (Allotrop of Carbon) is an exception. It is a conductor of
electricity. as it assowated with for mobile electrons.
4.
Lusture - Non metals do not possess any metallic lusture (exception- Iodine is lustrous).
5.
Softness- Most non metals are soft. exception- diamond (allotrop of Carbon) is the hardest
substance. It is used for cutting glass.
6.
Tensile strength- The tensile strength of non metals is low, these break easily.
7.
Melting point and boiling point- Compared to metals, non metals have low M.P. and B.P.
8.
Density - Generally non metals are light in weight.
(b) Chemical properties
Non metals accept electron and form negative ion. For e.g. as stated earlier, oxygen accepts
two electrons and form oxide ion (O2–)
1. Reaction with oxygen- Non metals react with oxygen and produce acidic and neutral
oxides. Acidic oxides dissolve in water forming acids which turn blue litmus red.
2C + O2
C + O2
→
→
CO2 + H2O
156
2CO Carbon monoxide (neutral)
CO2 Carbon dioxide (acidic)
→
H2CO3 Carbonic acid.
SCIENCE 10
2. Displacement reaction - Highly reactive non metals displace less reactive non metals
from their salt solutions. e.g. on passing chlorine gas through a solution of sodium bromide,
Sodium chloride and bromine are formed.
2NaBr + Cl2
→
2NaCl + Br2
In the above reaction highly reactive non metal chlorine displaces less reactive non metal
Bromine from its salt solution (NaBr)
3. Reaction with chlorine- Non metals react with Chlorine to produce Non metallic
covalent chloride e.g. H2 + Cl2 → 2HCl and P4 + 10Cl2 → PCl5
4. Reaction with hydrogen - Non metals react with hydrogen and produce covalent
hydrides eg. H2 + S → H2S
and
3H2+N2 → 2NH3
11.8 Some important Non metals
1. Hydrogen- Hydrogen, the first element of the
periodic table is the lightest element. Being highly reactive it
does not exist in atomic form. hence two hydrogen atoms
combine to form a molecule of hydrogen gas. Therefore a
molecule of hydrogen has two atoms. A small quantity of
hydrogen is present around the Sun and stars in the outer
atmosphere. It is also found in gases evolved from volcanoes
l
Symbol = H
l Atomic No. = 1
l Electronic configuration= 1
l Valency = + 1
It is present in water, acids, bases and many other organic and inorganic compounds in
combined form. Hydrogen is the element, whose largest number of compounds are known to
us.
Laboratory Preparation
As shown in Fig. 11.5, take grannulated Zinc in a wolf’s bottle. Add dilute sulphuric acid
slowly with the help of a funnel. This reaction produces hydrogen gas which is collected in a gas
jar.
Zn + H2SO4
→ ZnSO4
+ H2 ↑
Physical Properties
1.
It is a colourless, odourless and tasteless gas.
2.
It is sparingly soluble in water
3.
It is Highly inflammable.
Chemial Properties
1.
Nature- It is a neutral gas
2.
Combustion- In presence of
oxygen it burns with a blue
flame and produce steam.
2H2(g) + O2 (g)
→ 2H2O
(g)
Fig. 11.5 Laboratory method for preparation of Hydrogen gas.
METALS AND NON METALS
157
3.
Reaction with metal oxides - Hydrogen is a good reducing agent. It reduces metal oxides
to corresponding metals.
∆
CuO + H2
→
Cu + H2O
Note- Hydrogen is capable of reducing oxides of those metal only, which are less reactive
than hydrogen, itself.
4.
Reaction with chlorine gas - In the absence of Sunlight hydrogen reacts with chlorine
and form as white fumes of hydrogen chloride.
H2(g) + Cl2 (g)
5.
→ 2HCl
(g) ↑
Reaction with Nitrogen - It is a reversible reaction. Ammonia is formed
[Fe]
N2 (g) + 3H2 (g)
→
2NH3 (g) ↑
Uses 1.
Being light in weight it is used in balloon and aerocraft. It is also used as a reducing agent
in laboratory and industry.
2.
Oxyhydrogen flame is used in cutting and welding metals.
3.
It is used in the preparation of vegetable oil and synthetic petrol.
4.
Liquid hydrogen is used as fuel in rocket.
Answer these Question
1.
How is Ammonia prepared from hydrogen gas?
2.
Write two industrial uses of hydrogen gas.
Ammonia
It is a gas with characteristic pungent smell. It is found in its combined state in Ammonium
chloride (NH4Cl) and Ammonium sulphate (NH4)2SO4 etc.
Laboratory Preparation - In the laboratory, ammonia is prepared by reaction of ammonium
chloride with slaked lime
Ca(OH)2 +
Slaked lime
2NH4Cl
Ammonium Chloride
→
CaCl2
Calcium chloride
+
2NH3 ↑ +
2H2O
Ammonia
Manufacture - Haber’s method
Ammonia is prepared by mixing nitrogen and hydrogen in the ratio 1 : 3.
N2 + 3H2
2NH3 + Heat
Nitrogen mixed with pure dry hydrogen and Compressed to 200-300 atmospheric pressure.
The compressed mixture is passed over (Iron and Molybidnum)* temperature maintained at
5000C to produce Ammonia.
*Molybidnum, acts a promoter of the catalyst.
158
SCIENCE 10
Physical Properties
1.
Colourless gas, lighter than air.
2.
It is extremely soluable in
water. A saturated solution of
Ammonia in water is called
Liquor ammonia or Ammonical
water (NH4OH).
3.
It liquifies when cooled under
pressure.
Caution- Ammonia is a
harmful gas, when inhaled
in large quantity it may
effects our respiration
system.
Fig. Manufacture of ammonia by Haber’s process
Chemical Properties
1.
Nature- it is basic in nature Aqueous solution of ammonia turns red litmus blue.
2.
Reaction with Hydrogen chloride gas
White fumes of Ammonium chloride are formed
NH3 + HCl
3.
NH4Cl ↑ White fumes
Combustion - Ammonia is neither combustable nor a supporter of combustion when
made to burn in an atmosphere of oxygen it burns with a yellow flame
4NH3 + 3O2
4.
→
→
2N2 + 6H2O
Oxidation - When a mixture of ammonia vapours and oxygen is passed over heated
Platinum calalyst, it is oxidised to Nitric oxide.
[Pt]
4NH3 + 5O2
→
4NO + 6H2O
1073K
2NO + O2
5.
→ 2NO2
Reaction with carbon dioxide - Formation of urea takes place
423-473K
2NH3 + CO2
→
150-200 A.P.
NH2-CO-NH2 + H2O
Urea
USES
1.
As a refrigerant.
2.
In the manufacture of Nitric acid, Sodium carbonate, Rayon and Fertilizers etc.
3.
As a laboratory reagent.
METALS AND NON METALS
159
Answer these questions.
1.
Describe Haber’s process for the manufacture of ammonia gas.
2.
Give chemical equation for preparation of ammonia gas in the laboratory.
3.
What is liquor ammonia?
Sulphur
In ancient time Sulphur was called Sulvari which
l Symbol - S
means ‘enemy of copper’. When copper is heated with
l Atomic number = 16
sulphur the properties of copper are destroyed. Perhaps,
l Electronic
the present name has been derived from ‘sulvari’. Chemist
configuration = 2, 8 ,6 Klm
Lavoisier studied the properties of sulphur and proved that
it is an element.
OccurrenceSulphur is obtained from volcanic sources at many places. It is present in edible items like
garlic, onion, mustard, radish, beetroot, egg etc. In minute quantity it is also present in wool and
hair. In combined state it occurs as Iron pyrites FeS2, Gypsum CaSO4. 2H2O and copper pyrites
Cu2S Fe2S3 etc.
Extraction of sulphur- Three methods are employed for extraction of sulphur1. Sicilian process (old method)
2. Frasch or Louisiana process.
3. From coal gas.
Frasch or Louisiana Process - At Louisiana in
America undergound deposits of sulphur as free element
is found deep below the surface of the earth. Chemist, H.
Frasch used a pump to extract sulphur convinently at
low cost.
In the Frasch process (Fig. 11.7) a hole is bored to
the Sulphur bed. Three concentric* pipes are pushed
through the boring. Super heated water (453K) is forced
down the outer pipe. This melts the sulphur in the bed. A
Jet of hot compressed air is forced through the inner most
pipe. The air forms froth with sulphur. This sulphur water emulsion is pushed into the middle pipe
which reaches the earth’s surface. It is collected in wooden tanks and cooled. Sulphur obtained
by this method is 99.5% pure approx..
Centre
Concentric
* Concentric having the same center
160
SCIENCE 10
Physical properties
1.
It is a light yellow, brittle, crystalline substance.
2.
Insoluble in water.
Allotropy - The existance of an element in two or more different form with different physical
properties but similiar chemical properties is called allotrpy. These different forms are called
allotropes.
Allotropes of sulphur- Sulphur exists in both crystalline and non crystalline allotrophic
forms.
(A)
Crystalline sulphur - There are two crystalline forms.
(1)
Rhombic sulphur - It is also known as α sulphur or octahedral sulphur. It is the most
stable form of sulphur at ordinary temperature.
(2)
Monoclinic sulphur- These
crystals exists in the form of a
needle. It is also known as
prismatic β sulphur
(B)
Non crystalline sulphur - These
are found in the following forms.
(1)
Plastic sulphur - When molten
sulphur is poured into cold water,
a soft rubber like mass is
obtained. This is called plastic
sulphur.
Allotropes of sulphur
(2)
Milk of sulphur - This is white in colour.
(3)
Colloidal sulphur - When H2S gas is passed into HNO3, colloidal sulphur is obtained.
Effect of heat on sulphur- When sulphur is slowly heated in a boiling test tube following
changes in its state take place At 1150C it melts and it changes into a light yellow coloured liquid.
↓
At about 1590 it becomes dense and the colour changes to brownish black.
↓
On further heating it again becomes dilute and at 200°C the colour also becomes fade.
↓
At 4440C it starts boiling and changes into yellowish brown vapours.
METALS AND NON METALS
161
The reason behind these changes is that Suphur molecules exist as a 8 membered atoms
arranged in a puckered ring.
Uses 1.
In treatment of skin diseases. In purification of blood.
2.
In manufacture of gunpowder, crackers etc.
3.
As a disinfectant.
4.
For vulcanising rubber.
5.
In in Dye Industry.
Answer these questions.
1.
Explain the effect of heat on Sulphur.
2.
Write three industrial uses of Sulphur.
3.
How is Sulphur extracted by Frash process?
Sulphur dioxide
Sulphur dioxide is a gas. Its molecular. formula is SO2. It pollutes the atmosphere. It is
responsible for acid rain.
Physical properties
1.
It is a colourless, pungent smelling gas.
2.
It is heavier than air.
3.
It is readily soluble in water.
4.
At high pressure it readily liquifies.
5.
Its a poisonous gas. It affects the respiratory system. Inhalation in excess
may lead to death.
Chemical Properties
1.
Nature- It is acidic in nature
SO2 + H2O
2.
H2SO3 Sulphurous acid
Reaction with base - Reacts with base to form sulphite salt.
2NaOH + SO2
Ca (OH)2+SO2
3.
→ Na2SO3 + H2O
→ CaSO2 +H2O
Sodium sulphite
Reaction with oxygen- It combines with oxygen at 4500C in presence of red hot
vanadium pentaoxide (V2O5) as catalyst to produce SO3. This reaction is exothermic
and reversible and is used from the manufacture of H2SO4.
[V2O5]
2SO2 + O2
2SO3 + Heat
Sulphur trioxide
162
SCIENCE 10
4.
As a reducing agent. In presence of moisture and an oxidising agent. SO2 acts as
a reducing agent. It decolourises, coloured acidic solution of Potassium permagnate
and converts Iodine in to hydrogen iodide.
2KMnO4 + 2H2O + 5SO2
moisture
5.
→
K2SO4 + 2MnSO4 + 2H2SO4
→ H2SO4 + 2HI
I2 + SO2 + 2H2O
Bleaching action- In presence of moisture it bleaches coloured substance to
colourless substance.
SO2 + 2H2O
→ H2SO4 + 2[H]
Coloured Substances + 2 [H] → Colourless.
Uses
1.
To decolourise sugar.
2.
In refrigeration.
3.
As a bleaching agent.
4.
As an insecticide.
5.
In the manufacture of Sulphuric acid.
5.
As preservative in squash, jams and dry fruits.
Answer these question.
1.
What happens when Sulphur dioxide is dissolved in water.
2.
Write down four important uses of Sulphur dioxide gas.
Sulphuric Acid
[Moleculer formula - H2SO4, Atomic Weight = 98]
It is used in almost every industry. It is known as the King of Chemicals
Manufacture : It is manufactured by contact process. The raw products used as are
Sulphur, Oxygen (air) and Water. V2O5 asbestos is used as catalyst. This is an exothermic
reaction. Sulphuric acid is manufactured in four steps.
→
1st Stage
S(s) + O2 (g)
2nd Stage
2SO2 (g) + O2 (g)
3rd Stage
H2SO4 (l) + SO3 (g)
4th Stage
H2S2O7 (l) + H2O (l)
SO2 (g)
→
2SO3 (g) + Heat
→ H2S2O7 (l) (Oleum)
→
2H2SO4 (l)
Sulphuric acid
Physical Properties
1.
It is a dense, colourless, odourless and oily liquid. It appears yellow due to the presence of
impurities.
METALS AND NON METALS
163
2.
It is a dehydrating agent.
Caution : Sulphuric acid is soluble in water.To dilute H2So4 it is added to water,
Never add water in conceotrated acid as it generates tremendous amount of heat. It
may break the glass container.
Chemical Properties
1.
Nature - It is acid an and hence turns blue litmus paper into red. It is a dibasic acid.
2.
Reaction with salts - Sulphuric acid reacts with salt.
NaCl + H2SO4
→ NaHSO4 + HCl
2NaBr + 3H2SO4
→ 2NaHSO4 + SO2 + 2H2O + Br2 ↑
NaI also reacts in this way to produce I2
3.
Reaction with base- It reacts with base forming salt and water.
2NaOH + H2SO4
4.
→
MgSO4 + H2↑
Reaction with non metals - Non metals get oxidised when reacted with sulphuric acid
e.g. carbon gets oxidised to carbon dioxide.
C + 2H2SO4
6.
Na2SO4 + 2H2O↑
Reaction with metals- It reacts with metals liberating H2 gas.
Mg + H2SO4
5.
→
→
2SO2 ↑ + CO2 ↑ + 2H2O
Effect of heat - Sulphuric acid gets decomposed to Sulphur trioxide and water on heating
H2SO4
→
H2O + SO3
On further heating SO2 and O2 are formed
2H2SO4
→
2H2O + 2SO2 + O2 (At higher temperature).
Uses of some Metals and Non Metals
(1)
Iron, Aluminium - In the manufacture of Vehicles, Weapons, Machines, Buildings, Electric
wires, Boiler etc.
(2)
Copper, Silver - In making Utensils, Ornaments, Coins, foils, mirror etc.
(3)
Mercury - In Thermometer.
(4)
Zinc and Carbon - In Dry cell.
(5)
Oxygen - Essential for respiration.
(6)
Salphars - In manufacture of Crackers, Match box industry etc.
(7)
Metals and non metals are also used for manufacture of fertilizers, insecticides etc.
164
SCIENCE 10
Difference between Metals and Non-metals
S.No.
Property
Metals
Non-Metals
1.
Conductivity
Good conductor
of electricity.
bad conductor
(exception-Graphite).
2.
Physical state
Generally solid (Mercury
is liquid)
Solid, liquid or gas.
3.
Lusture
Possess metallic lusture
Do not possess (exceptionIodine which is a shining
non metal)
4.
Maleability/ductility
Malleable and Ductile
Neither malleable nor ductile
5.
Nature
reducing agent
oxidising agents.
Points to remember
1.
At present 118 elements are known, 22 of them are non metals.
2.
Elements are classified into metals and non metals.
3.
All metals are solid at room temperature except Mercury.
4.
Bromine is a non metal which is liquid at room temperature.
5.
Metalloids show property of both metals and non metals.
6.
Metals donate (lose) electron to form positive ion (anion).
7.
Non-metals gain electrons and form cation (Negative ion)
8.
Metals are generally hard, malleable, ductile and good conductor of heat and
electricity.
9.
Non-Metals are generally brittle in nature.
10. The substances, which occur in the earth’s crust are known as minerals.
11. Metals are extracted from their ores.
12. Iron is extracted in the Blast furnace.
13. The homogeneous mixture of two or more metals is called an alloy.
14. Pure gold is of 24 carat. Silver or Copper is added to Gold while making ornaments.
15. Hydrogen is the lightest element.
16. The crystalline form of sulphur are Rhombic and monoclinic.
17. Sulphur dioxide is used as a bleaching agent.
18. Sulphuric acid is known as the “King of chemicals’’.
METALS AND NON METALS
165
EXERCISES
Very short answer type questions.
1.
What are amorphetic oxides?
2.
Define galvanisation.
Short answer type questions.
1.
Write the physical difference in between Metals & Non-Metals.
2.
What are alloys? give three examples.
3.
Define the terms (1) Mineral (2) Ore (3) Slag (4) Flux.
4.
Write only the chemical equations of reactions taking place in the blast furnace during
extraction of Iron from haematite ore.
5.
Write the different steps involved in the extraction of a metal from its ores.
Long answer type questions.
1.
What is the chemical formulae of bauxite? Which are the main impurities present in this
ore? How is the ore purified? Explain in brief.
2.
Give brief description of extraction of Sulphur by Frasch process.
3.
Give chemical equations of the reactions involved in manufacture of sulphuric acid by
contact process.
4.
Explain the Magnetic separation method.
Project Works1.
Prepare list of metals and non metals found arround school, House and other
public places.
2.
Minutely observe metals & non metals and also their various uses during your
educational tour. Prepare a table of them. If get chance, observe metal
extraction plant.
166
SCIENCE 10
Chapter - 12
ORGANIC COMPOUNDS
When we think of the articles of our daily use such as
clothes, food items, plastic etc., the question arises how they
originate and what is their structure? If these things were not
there, how the life would be? Normally we study about all these
natural and artificially prepared substances in the form of
Organic and Inorganic substances. In this chapter we will study
about Organic Compounds.
Carbon is the major constituent of majority of substances
found in nature. It is needless to say that carbon is the most
abundant element found in nature. It is the first member of group
14 in modern periodic table. It is found in both free and
compound states in the nature.
We will study
12.1 Organic
Compounds
12.2 Functional group
(containing
oxygen)
12.3 Alcohol
12.4 Formaldehyde
12.5 Acetone
12.6 Acetic acid
12.7 Some common
polymers
l
Soap
l
Detergent
ORGANIC COMPOUNDS
The major properties of Carbon are tabulized as followsSymbol Atomic Atomic
Electronic
n u m b e r weight
configu-
Valence Valency Boiling Melting
electrons
ration
C
6
12
2, 4
4
4
Atomic
point
Point
Radius
(K)
(K)
(A 0 )
5100
3800
0.77
12.1 Organic Compound
The compounds in which carbon is the essential
constituent and are derivates of hydrocarbons are called
Organic Compounds. At present, their number is very large.
For example protein, carbohydrate, vitamins, oils, fats etc.
The branch of chemistry which deals with the study of organic
compounds is called Organic Chemisty. It’s history is about
200 years old. According to Lavoisier, Organic compounds
were first originated from organic substance.
According to Berzeleius- “Organic Compounds can be
obtained only from living things, they cannot be prepared in
the laboratory.” This assumption of Berzelius was discarded
by F. Wohler in 1928, who prepared urea in laboratory with the
help of two Inorganic Compounds as follows :
NH3 + HCNO → NH4CNO
Ammonia Cynic acid
Ammonium Cynate
167
Rearrangement
→
NH4CNO
NH2 - CO - NH2
Urea
Many natural and artificial life substances are organic in nature. It is impossible to imagine
life without these organic compounds. The essence of plant kingdom is due to cellulose which
is a type of organic compound. The chlorophyll present in leaves and the haemoglobin present
in the blood of living organisms are also Organic Compound.
Types of substances containing Organic Compounds
↓
↓
Food items
↓
Clothes
↓
↓
↓
↓
Medicines
Fuel
Toiletry Items
Explosives
Other Items
Carbohydrate Cotton
Sulpha drugs
Wood
Soap
Dynamite
Paper
Oils and Fat
Linen
Penicillin
Coal
Detergent
T.N.T.
Plastic
Protein
Nylon
Aspirin
Petrol
Vaseline
Nitro-glycerine Rubber
Starch
Terylene
Quinine
Diesel
Lipstick
Dye
Vitamins
Decaron
Antiseptic medicines
LPG
Perfume
Sacchirine
Antipyratic medicines
Alcohol
Alkaloids
Kerosene oil
Vinegar.
Steroids
Organic compounds may also contain elements like nitrogen, oxygen, sulphur, halogen
and some other elements besides carbon and hydrogen. Organic Compounds are generally of
co-valent nature and exhabit the property of Isomerism*
Organic compounds are classified as Organic Compounds
Acyclic or open chain
Compounds (Aliphatic)
Cyclic or Closed chain
Compounds
Homocyclic
Alicyclic
Hydrocarbon
Heterocyclic
Aromatic
Hydrocarbon
derivative
* When two or more organic compounds having different structural formula, physical and chemical properties are
represented by one molecular formula, this property is called isomerism and the represented compounds are
called isomers. e.g. from the C2H6O atomic structure C2H5OH (Ethyl alcohol) and CH3-O-CH3 (Di methyl Ether) can
be displayed.
168
SCIENCE 10
12.1 Hydrocarbon
The organic compounds which are formed by Carbon and Hydrogen are called
hydrocarbon. e.g. Methane, Ethane, Propane, Ethene, Ethyne. (the initial study of these has
been done in previous class) benzene, cyclobutane etc.
H
|
H–C–H ,
|
H
Methane
H H
|
|
H–C–C–H ,
|
|
H H
H H
|
|
H–C=C–H
Ethene
Ethane
H
|
H–C≡C–H
Ethyne
Derivatives of hydrocarbon
H 2C
H–
–H
H–
–H
|
H
Benzyne
H 2C
CH2
 Butane

Cyclo
CH2
Derivative means compounds prepared from original compound. The organic compounds
which are prepared by replacing one or more hydrogen of the hydrocarbon by any other reactive
atom or group of atoms are called derivatives of hydrocarbon. e.g.
C2H5OH, CH3OCH3, CH3CONH2, CH3NH2 ,
CH3Br,
CH3COOH, CH3CHO,
CH3COCH3 etc.
When methane is reacted with chlorine in mild sunlight,
methyl chloride is formed.
Diffused
CH4 + Cl2
→ CH3Cl
+ HCl
Sunlight
Methyl Chloride
12.2 Functional group
When a derivative compound is made from hydrocarbon, then the hydrocarbon part (first
part) of the derivating compound is called alkyl* or aryl group and the remaining part is called
reactive or functional group. It can be an atom or a group of atoms. The properties of a compound
are to functional its group.
The atom or group of atoms which are specifically attached to an organic compound
and is/are responsible for the characteristic properties of that Organic compound, is
called functional group e.g. –CHO–OH, –COOH etc.
*Alkyl group is represented by ‘R’
ORGANIC COMPOUNDS
169
The double and triple bonds present in hydrocarbons are also categorized under functional
groups because the characteristic properties of these hydrocarbons are due to these bonds.
Ethylene (C2H4) and Acetylene (C2H2) are double and triple bond hydrocarbons
respectively. When these are reacted with bromine water, the red brown colour of
bromine water disappears. Alkanes do not give this reaction.
C=C
Double bond
–C≡C–
Triple bond
,
The following table gives information about some major functional groups.
Name of
Homologous
series
Alkane
Functional
group
structure
Name
of functional
group
IUPAC
name
Some member Compounds
and their IUPAC name
-
– ane
Methane (CH4), Ethane (C2H6)
–
Alkene
C=C
-
– ene
Ethene (CH2=CH2)
Alkyne
C≡C
-
–yne
Ethyne (CH≡CH)
Alcohol
–OH
Hydroxy
–ol
Ethanol (C2H5OH)
Methanol (CH3OH)
Aldehyde
–CHO
Carmyl
–al
Methanal (HCHO),
Ethanal (CH3CHO)
Ketone
C =0
Carbonyl
–one
Propanone (CH3COCH3)
Halide
–X
Halo
Halo Alkane
Bromo Ethane (C2H5Br)
F, Cl, Br, I
Carboxylic acid –COOH
Ester
–COOR
Fluoro, choloro
Carboxy group
–oic acid
Alkoxy–Carboxy
–oate
Ethanoic acid CH3COOH
Methyl Propanoate
CH3CH2COOCH3
Amide
–CONH2
Amide
Acid Amide
Ether
R–O–R
Alkoxy
Alkoxy Alkane
Acetamide CH3CONH2
Ethoxy Ethane
CH3CH2OCH2CH3
Answer these questions.
1.
What are organic compounds?
2.
What is the electronic configuration of carbon?
3.
What was the assumption of Berzelius?
4.
Name the first organic compound made the laboratory?
5.
Name any four hydrocarbon derivatives?
6.
What is a functional group?
170
SCIENCE 10
12.3 Alcohols
The hydroxy (–OH) derivatives of hydrocarbons are called alcohol. In these the –OH
functional group is attached to the carbon of the alkyl group. The common formula of alcohol
homologous series is CnH(2n+1)OH or CnH(2n+2)O.
Where n = number of carbon atoms
e.g. Methyl alcohol (CH3OH), Ethyl alcohol (C2H5OH) etc.
It is interesting that Phenol is also a hydroxy derivative of hydrocarbon, but in phenol the
–OH group, is linked to the carbon of aromatic ring.
Alkanols are is formed by replacing one Hydrogen atom of alkane by OH group. For
IUPAC nomenclature of alcohol, the –n of original alkane is replaced by such as –ol.
Name of hydrocarbon
IUPAC Name
Common Name
Alk-an-ol
R-OH
Alcohol
Methane
Meth-an-ol
CH3–OH
Methyl alcohol
Ethane
Eth-an-ol
Ethyl alcohol
Alkane (series)
–e
+ol
CH3-CH2-OH
Propane
Prop-an-ol
Propyl alcohol
CH3-CH 2-CH 2-OH
CH4
–H
CH 3OH
Methyl alcohol
CH 3CH 2OH
Ethyl alcohol
+OH
CH3–CH3
–H
+OH
In the common name, alcohol is written along with its alkyl group.
Ethyl Alcohol
Ethyl alcohol is an important compound of the alkanols
homologous series. It is commonly called Alcohol and it’s
molecular formula is C2H5OH or C2H6O
ORGANIC COMPOUNDS
Let’s Know
The full form of IUPAC is
International Union of Pure
and Applied Chemistry. Its
headquarter is in Geneva.
171
Manufacture of Alcohol by Fermentation
After separation of sugar crystals from sugarcane
juice a thick sticky liquid is obtained which is known as
molasses. Alcohol is prepared from molasses in
following stages1. Dilution - 8-10% dilute solution is prepared by
mixing water in molasses. Now Ammonium sulphate*
or Ammonium phosphate is added to this solution.
Important Facts
1.
Apar t from Molasses,
alcohol is also prepared
from some fruit Juices and
starch substances.
2.
Glucose and fructose are
isomers. Their molecular
formula is C 6 H 12 O 6 but
structural formula are
different.
2. Fermentation - Yeast is added to this mixture
and then it is kept for 2-3 days at 25-300C temperature.
After some time the following reactions take place-
(i) The sugar present in molasses is converted
into glucose and fructose by hydrolysis in the presence of invertase enzyme.
Invertase
C12H22O11+H2O
Sucrose (sugar)
Enzyme
C6H12O6 + C6H12O6
Fructose Glucose
(ii) Glucose and Fructose are reduced in the presence of Zymase enzyme to form ethyl
alcohol
Zymase
Enzyme (303 K)
C6H12O6
2C2H5OH + 2CO2↑
Glucose/Fructose
Ethyl alcohol
Modern Method of Alcohol Preparation
These day alcohol is prepared by hydration of ethylene in the presence of concentrated
Sulphuric acid.
CH2
||
CH2
+
Ethylene
H
|
OH
Conc. H2SO4
348 – 353K
CH3
|
CH2OH
Ethanol
This reactions is completed in following two stepsFirst Step CH2
=
Do you know?
The process in which
complex organic compounds
are reduced gradually, in the
presence of an enzyme, into
simple organic compounds is
called Fermentation.
348 - 353 K
→ CH3 CH2 HSO 4
CH2 + H2SO 4    
*Ammonium Sulphate or Ammunium Phosphate acts as food for Enzymes
172
SCIENCE 10
Second Step -
Let’s Know
CH3 CH2 HSO4 + H2O → CH3CH2OH + H2SO4
The H2SO4 obtained in the last step can be used
again but it becomes dilute gradually.
Other methods for preparation 1.
Hydrolysis of Alkyl halide.
2.
Reduction of Aldehyde and Ketone.
3.
From Grignard reagant
4.
From Starch.
Enzyme - Complex Organic
Compounds (containing
generally nitrogen) found in
some organisms which
have the capacity of
reducing complex organic
compounds into simple
organic compounds are
called Enzymes.
Yeast cell contains Invertase, Zymase and Maltase enzymes etc.
PropertiesA. Physical Properties 1.
It is a colourless, sweet smelling liquid of pungent taste.
2.
It’s boiling point is 780C (351K)
3.
Ethylalcohal is soluble in water in all proportions however solubility of alcohals in
water decreases with increase in molecular weight of alcohol.
4.
It is highly inflammable.
5.
It is neutral in nature.
B. Chemical Properties1.
Combustion- It combustion taken place easily in air with a blue flame to form carbon
dioxide and water
CH3 CH2 OH + 3O 2 → 2CO 2 + 3H 2O + heat
2.
Reaction with Sodium- It reacts with sodium rapidly to form sodium ethoxide and
hydrogen gas released out.
2CH3 CH2 OH
Ethyl Alcohl
3.
+
2Na
Sodium
→
2CH3CH2O Na
Sodium ethoxide
+
H2
↑
Hydrogen
Oxidation- Oxidation takes place as per the following conditions.
ORGANIC COMPOUNDS
173
(A) From Chromium trioxide (CrO3)- Acetaldehyde is formed in this condition. It is
called partial oxidation.
Ethyl alcohol
Acetaldehyde
Activity
Take 3 ml of ethyl alkhol in a test tube and add a solution of 5% chromium trioxide in
acetic acid slowly till the red colour of chromium trioxide disappears. Observe the
smell at the beginning and at the end of reaction. You will find a special type of smell
at the end of the reaction, which is of acetaldehye.
(B) From Alkaline Potassium Permagnanate solution (Bayer’s reagant) - Ethyl alcohol
is oxided by Bayar’s reagant to form acetic acid.
Alkaline KMnO4
CH3CH2 OH
Ethyl alcohol
Alkaline KMnO4
CH3 C=O
l
[O]
H
Acetylaldehyde
[O]
–H2O
H3C–C–O–H
ll
O
Acetic acid
4. Esterification - Ethyl alcohol reacts with acetic acid in the presence of concentrated
H2SO4 to form ester which has a sweet fruity smell.
C o n c. H S O 4
→C H 3 C O O C
C H 3 C O O H + H O C H 2 C H 3 2 
Acetic Acid
Ethyl alcohol
Ethyl acetate (Ester)
5. Reaction with chlorine - Chlorine acts both as an oxidant and for Chlorination
Acetaldehyde and Chloral are formed.
Cl 2
Cl 2
CH3 CH 2 OH   
→ CH3 CHO  
→ CCl 3 CHO
athyl alcohol
–HCl
Oxidation
Acetaldehyde
Chloral
Uses1.
As a solvent for paints, varnish, gums and dyes etc.
2.
In the manufacture of organic compounds such as chloroform, ether, chloral, iodoform
etc.
3.
In the form of power alcohol on a fuel.
174
SCIENCE 10
4.
As a germicide.
5.
Manufacture of artificial rubber.
6.
For making different types of alcohol.
Let’s Know
1.
Denatured Alcohol
The alcohol used in factories which contains some toxic substances such as
methyl alcohol, pyridine or copper sulphate and is not used for drinking purposes
is called Denatured Alcohol.
2.
Power Alcohol
The mixture of Ethanol, Gasoline and Benzene which is used as fuel is Power
Alcohol.
3.
Absolute Alcohol
Pure Alcohol containing no amount of water is called Absolute Alcohol.
Answer these questions.
1.
What is alcohol?
2.
Write the IUPAC name and structural formula of the first three member of
alcohol homologous series?
3.
What is fermentation?
4.
What is molasses?
5.
Write the names of any two enzymes.
6.
What is Esterification?
7.
Why is denatured alcohol not used for drinking?
8.
Which substance is obtained by oxidation of ethyl alcohol?
12.4 Aldehyde
O
||
group is present are included in the Aldehyde
–C –H
homologous series. The common/general formula of this series is CnH2nO where n is the number
of carbon atoms.
The organic compounds in which
For IUPAC nomenclature the suffix ‘e’ is substituted by relative alkane.
ORGANIC COMPOUNDS
175
Name of
Original
hydrocarbon
Formula
of
hydrocarbon
Common name
of Aldehyde
(Hydrocarbon
derivative)
IUPAC name
of aldehyde
Formula
of
aldehyde
Methane
Ethane
Propane
Butane
CH 4
CH 3CH 3
CH3CH 2CH 3
CH3CH 2CH2CH 3
Formaldehyde
Acetaldehyde
Propanaldehyde
Butanaldehyde
Methanal
Ethanal
Propanal
Butanal
HCHO
CH 3 CHO
CH 3CH 2CHO
CH 3CH 2CH 2CHO
Formaldehyde (Methanal)
It is the first member of the aldehyde homologous series. It’s molecular formula is CH2O
O
|| . It’s common name is formaldehyde and IUPAC name is
and structural formula is
H – C –H
Methanal.
Common Methods of Preparation1.
Catalytic dehydrogenation of methyl alcohol -
2.
When methyl alcohol vapours are passed through hot copper or silver catalyst,
formaldehyde is formed.
H
H
|
|
[C u / A g ]
H – C = O + H2 ↑
H – C– OH
57 3 K
|
H
Dry Calcium formate salt on heating gives formaldehyde.
O
||
H –C –O
2 50 - 30 0ºC
Ca
3.
∆
H
C = O + C aC O 3
H –C –O
H
||
O
Calcium formate
Formaldehyde
When ethylene is reacted with Ozone, Ethylene ozonide is formed which on
hydrolysis gives formaldehyde.
+ H2O2
Ethylene
176
Ethylene Ozonide
Formaldehyde
SCIENCE 10
Laboratory MethodThe laboratory preparation of formaldehyde involves the catalytic oxidation of methyl
alcohol.
2CH OH + O2
3
[Pt]

→ 2HCHO + 2H O
300-3500C
2
Method - Methyl alcohol is
taken in a round bottom
flask and two delivery tubes
are placed in it with the help
of a cork. (Fig. 12.1). One
tube is left open in the air
and the other tube is
connected to a tube
containing
platinized
asbestos at 300-350ºC
temperature. This tube is
connected with the help of
another tube to a conical
flask containing water. The conical flask has a suction pump. The round bottom flask
is heated on a water heater and air is absorbed with the help of suction pump so that
air comes in the round bottom flask and carries the vapours of methyl alcohol and
passes through the glass tube containing platinized asbestos. Thus methyl alcohol
on oxidation, converted into formaldehyde which is dissolved in water.
Physical Properties1.
It is a colourless, pungent smelling gas.
2.
It is highly soluble in water.
3.
It is neutral in nature.
Chemical Properties1.
Oxidation- It oxidizes easily to form
formic acid. Bayer’s reagant, Tollen’s
reagent, Fehling or Benedict reagant be
used are some of oxidising agent.
Bayer’s Reagant
HCOOH
HCHO + [O]
Formaldehyde
Formic acid
ORGANIC COMPOUNDS
Let’s know
40% aquous solution of methanal gas
(formaldehyde) is known as Formaline.
Formalin is used in laboratory, research
laboratories and in industries as a
preservative.
Bayer’s Reagant- Dilute solution of alkaline
Potassium Permanganate (KMnO4)
Tollen’s Reagant- Solution of Ammoniated
Silver nitrate.
Fehling solution- It is a mixture of following
two solutions (A) Alkaline solution of copper sulphate (B)
Solution of Sodium Potassium tartarate
(Roschell salt)
Benedict solution- Aquous Solution of
Copper sulphate in citric acid and sodium
carbonate.
177
Silver Mirror Test
Formeldehyde is easily oxidized and hence acts as a strong readucing agent. Formaldehyde
reduces Tollen’s reagant to Silver.
AgNO 3 + NH 4 OH — —— → AgOH + NH 4 NO 3
Ag2 O * ↓ + H2 O
2AgOH
M ild h e a t
→ H C O O H + 2 A g
H C H O + A g 2 O 
The silver released in this reaction deposits on the
inner wall of the test tube as a result of which the test tube
shines like a miror. Hence it is called silver mirror test.
Let’s make a mirror
Required Material - Glass piece of desired shape, soft or mulberry cloth, Tollen’s reagant,
Formaline, red colour varnish etc.
Principle - Silver Mirror test.
Method - Rub the glass with soft or mulberry cloth with clean hands so that no particle or
spot remains in it. Then keep this glass horizontally on the stand. Then put Tollen’s reagant
on the glass uniformly. After this mix almost equal quantity of Formalene in Tollen’s reagant.
After 2-3 hours tilt the glass carefully and remove the solution and dry the glass in the sun.
At the end apply red varnish on the surface (on which reaction has taken place) The
mirror is ready.
Precautions- (1) Keep the temperature of the laboratory (where experiment is carried
out) almost at 300C (2) Use the reagants carefully.
2. Reduction - Alcohol is formed on reduction of formaldehyde by hydrogen gas in the
presence of fine paladium powder.
Pd
→
HCHO + H2
Methanal
CH3OH
Methanol
Formaldehyde, reduces Fehling solution to Cu2O.
heat
HCHO
+
Formaldehyde
2Cu (OH)2 + NaOH
Copper
Sodium
hydroxide hydroxide
→
HCOONa + 3H2O + Cu2O ↓
Sodium
Cuprous oxide
formate
(Red precipitate)
Fehling solution.
*Brown precipitate of Ag2O is soluble is excess amount of NH4OH.
178
SCIENCE 10
3. Reaction with Sodium hydroxideReacts with concentrated Sodium hydroxide to form Methyl alcohol and Sodium farmate.
This reaction is called Cannizaro reaction2HCHO + NaOH
CH3OH
+
Methyl alcohol
HCOONa
Sodium formate
4. Reaction With AmmoniaReacts with ammonia to form Urotropin which is called
Hexamethylene Tetramine. It is used in treatment of urine
infections (fig 12.2)
6HCHO + 4NH3
N
CH2
CH2
CH2
N
(CH2)6N4 + 6H2O
Urotropine
N
CH2
CH2
N
Other aldehyde’s do not give this reaction.
CH2
Fig. 12.2 Urotropine
5. Reaction With PhenolReacts with phenol in the presence of alkali
to form Bakelite (Artificial Plastic)
NaOH
C6H5OH + HCHO → Bakelite Plastic
Phenol
Methanal
(Fig. 12.3)
OH
OH
CH2
CH2
OH
H – C –H
H – C –H
OH
Bakelite is a useful Polymer. It is used in
making many electrical appliances.
CH2
CH2
OH
OH
 
6. Polymerization -
Fig. 12.3  Bakelite
Methanal forms various polymers under different conditions. It’s aquous solution i.e.
Formalin is vaporized to form polymer.
Vaporization
n(HCHO)
(HCHO)n
Formaldehyde polymer
Uses1.
As a germicide.
2.
As a preservative.
3.
In making Urotropin.
4.
In making Pharmamint (which is a mixture of methanal and lactose).
ORGANIC COMPOUNDS
179
5.
In making Bakelite.
6.
In making medicines, dyes and mirrors.
Answer these questions.
1.
Write the IUPAC names of first three members of alkanal homologous series?
2.
How is ozonide formed?
3.
What is formaline?
4.
What is Silver mirror test?
5.
What is Cannizaro reaction?
6.
What is Bakelite? How is it prepered?
12.5 Ketones
The organic compounds in which
O
||
C
group is linked with an alkyl or an aryl group
are Ketone homologous series. The IUPAC name of ketone is alkanone. This group is called
O
carbonyl group. e.g.
( R – C|| – R ' )
Acetone where R and R’ may be same or different alkyl
groups.
According to IUPAC pattern, the naming of members of this category is done by replacing
the suffix ‘e’ of alkane by ‘one’ e.g.
General formula of
Alkanone compound
O
||
C H 3– C – C H 3
Common Name
Name of the related IUPAC Name of
hydrocarbon
Alkanone
Acetone
Propane
Propanone
Ethyl methyl ketone
Butane
Butanone
Diethyl Ketone
Pentane
3 - Pentanone.
O
CH3 CH2
CH3
O
||
CH3 CH2 – C– CH2 CH3
180
SCIENCE 10

O

||
Acetone 
 CH 3 – C – CH3




It is the first member of the alkanone homologous series. Its common name is acetone. It
is also found in blood and urine, minutely..
Common Methods of Preparation
1.
Oxidation of Isopropyl alcohol by acidic Potasium dichromate.
CH3
CH3
K Cr O
CHOH + [ O ] 2 2 7 →
CH3
H2SO 4
CH3
C = O + H2 O
Acetone
2.
Dehydrogenation of Isopropyl alcohol vapours by passing it through red hot Cu. or Ag.
CH3
CH3
CH3
Cu Ag
→
300º C
CH3
CHOH
C = O + H2
Laboratory Method - In Laboratory it is prepared by heating calcium acetate.
○
○
○
O
||
∆
CH3
CH3 – C – O
Ca →
CH3
CH3 – C – O
||
O
○
○
○
○
○
○
○
○
○
○
○
○
○
○
○
C = O + Ca CO 3
○
○
○
○
○
○
Calcium acetate
Acetone
Method
Dry calcium acetate is taken in a
retort and a small amount of Iron powder
is mixed in it (for increasing the rate of
reaction). The long neck of the retort is
connected to the recepter by attaching
it with Lebig condenser. Now the retort
is kept on a wire gauze and heated.
Acetone is formed as a result of the
reaction which is collected in the
Recepter
ORGANIC COMPOUNDS
181
4. ManufactureIndustrial preparation of acetone is done from an aromatic hydrocarbon, named Cumene
the reaction is as follows-
CH3
|
CH3 – CH +
|
C 6H 5
CH3
|
CH3 – C – COOH
|
HCl
C 6H 5
O2
Cumene
CH3
CH3
C
Acetone
Phenol
Phenol is obtained as a by product in this reaction.
5. Production in large scale - Acetone is manufactured in large scale as follows 1% HgSO4
CH3 – C ≡ CH+H2 O →
CH3COCH3
60°C
A. Physical Properties1.
It is a colourless, having a specific odour.
2.
It’s boiling point is 56ºC.
3.
It is highly inflammable.
4.
It is soluble in water in all proportions.
5.
It is a good solvent.
B. Chemical Properties1.
Oxidation- It does not oxidize easily- In the presence of strong oxidants like acidic
Potassium dichromate, it is converted into acetic acid.
K Cr O 7
→ CH3 COOH + H 2 O + C
CH3 – CO – CH3 + 4(O) 2 2
H2SO4
Acetone
2.
Acetic acid
Reduction (i) It is reduced by hydrogen in the presence of palladium powder to form Isopropyl alcohol.
CH3
CH3
*
C = O + H2
[P d ]
CH3
CH3
CHOH
Isopropyl alcohol (2 - Propanol)
*Catalyst is always written in brackets [ ] For e.g. [Pd] where Palladium acts as catalyst.
182
SCIENCE 10
(ii) It is reduced in the presence of Zinc amalgum and HCl to form Propane.
CH3
CH3
C = O + 4 [H ]
CH3
Zn - Hg / HCl
CH3
C H 2 + H 2O
This reaction is called Clemenson’s Reduction.
(3) Iodoform ReactionAcetone is heated with iodine solution in the presence of alkali to form bright yellow
precipitate of Iodoform. This reaction is completed in two steps-
First StepAcetone Iodine
Tri iodo Propanone
Second Step
Sodium Acetate Iodoform (Yellow precipitate).
4. Addition Reactions - Additional Compounds are formed by reaction of Sodium bisulphite,
hydrogen cynide Grignard reagent, Ammonia and Ammonia derivatives e.g. Cynohydrin is formed
by reaction with Hydrogen cynide.
Acetone Cynohydrin
(ii) Additional compound named Acetone Sodium bisulphite is formed by reaction with
Sodium bisulphite.
CN
O
|
||
CH3 – C – CH3
H 3C – C – C H 3 + H C N
|
OH
(Acetone cynohydrin)
(V) Condensation ReactionsOn heating with Barium hydroxide a condensation product named Diacetone alcohol is
obtained.
Di acetone alcohol
Diacetone alcohol has both Carbonyl
ORGANIC COMPOUNDS
and Alcohol (–OH) functional groups.
183
Uses1.
As a solvent in cellulose, varnish, resin, plastic etc.
2.
As a laboratory reagent.
3.
In the manufacture of artificial leather, plastic etc.
4.
For removing nail polish.
5.
In making medicines etc.
Stain to stainless
Required Material - Acetone, cotton, cloth having paint or polish stain in it.
Principle - Acetone is a solvent.
Method - Take the cloth or article having stain/spot of food items, oil, polish, paint
etc. Rub acetone on the spot with the help of a cotton, gradually. Continue this process
till the stain disappears. The stain on nails or body can also removed similarly.
Answer these questions.
1.
Write the IUPAC name and structural formula of acetone?
2.
How is acetone prepared in the laboratory?
3.
What is Cumene?
4.
Write iodo form doform reaction?
5.
What is Aldol condensation?
Do you know?
The nail polish
remover available
in the markets for
removing polish
from nails contains
acetone.
Organic Acids
12.6 Carboxylic AcidsThe organic compounds in which carboxy
carboxylic acid. The
functional group is present are called
group is formed from two groups, first is the
carbonyl and
the other is the (–OH) hydroxyl.
In IUPAC system the ‘e’ suffix of alkane is replaced by-oic acid.
Molecular Formula
Common Name
Name of
Hydrocarbon
IUPAC
Name
HCOOH
CH 3COOH
CH3CH2 COOH
Formic acid
Acetic acid
Propionic acid
Methane
Ethane
Propane
Meth-an-oic acid
Eth-an-oic acid
Pro-an-oic acid
184
SCIENCE 10
Acetic Acid (CH3COOH)
It is the second member of the carboxylic acid homologous series. It’s IUPAC name is
Ethanoic acid. Its major source is Vinegar (Latin name acetum), on the basis of acetum it is
named Acetic acid.
1. Rapid Vinegar* Method- Fermentation of dilute solution of Ethyl alcohol (CH3CH2OH)
in the presence of air is done by bacteria named Microderma Acetee.
Micoderma acete bacteria
CH3CH2OH+O2
CH3COOH + H2O
Ethyl alcohol
Acetic acid
Process - A bucket shaped container having pores on the lower end and filled with wood
cuttings dipped in old vinegar solution. A 10%
ethyl alcohol (containing some amount of
ammonium sulphate) is dropped down
gradually. Vinegar is obtained on the lower
surface (fig. 12.5).
2. From Pyrolignius acid - Pyrolignius
acid obtained by fractional distillation of wood,
contains 8-10% acetic acid. The pyrolignius
acid is heated and it’s vapours are passed
through milky lime to form Calcium acetate
which on reaction with concentrated Sulphuric
acid gives Acetic acid.
3. Modern Method
Methyl alcohol is reacted with Carbon monoxide in the presence of Iodine-Rhodium catalyst
[I2-Rh] to form acetic acid.
* 4-8% solution of acetic acid is called vinegar.
ORGANIC COMPOUNDS
185
[I2–Rh]
CH3OH
+
CO
→
Methyl alcohol Carbon Monoxide
CH3COOH
Acetic acid
Properties
A. Physical Properties1.
It is sour in taste and colourless liquid with special vinegar
odour.
2.
It’s melting point is 1660C and boiling point is 1180C
3.
It is soluble in water in all proportions.
Do you know?
Pure acetic acid on
cooling to about 288K
becomes hard like ice
and shines like a glacial so
it is also known as Glacial
acetic acid.
B. Chemical Properties1.
Acidic nature- (i) Converts blue litmus red. (ii) Reacts with Sodium to form hydrogen gas
2CH3COOH + 2 Na
2.
2CH3COONa + H2 ↑
Hydrogen.
Reaction with Sodium bicarbonate- Carbon dioxide gas comes out with a bubbling
sound on the reaction with Sodium bicarbonate.
CH3COOH + NaHCO3
CH3COONa + CO2 ↑ + H2O
(Note : The above reaction is generally used for the testing of carboxylic group).
3.
Reaction with Phosphorous penta chloride - Acetyl chloride is formed when acetic
acid reacts with PCl5
Acetyl Chloride
4.
Reaction with Phosphorous Pentaoxide (P4O10) - It is just like dehydration* reaction,
Acetic anhydride is formed.
P 4O 10
5.
Acetic acid (2 mole)
Acetic anhydride.
Halogenation - When Acetic acid is heated with chlorine in the presence of red
phosphorous, chloro acetic acid is formed.
CH3COOH + Cl2
ClCH2COOH + HCl
Chloro Acetic acid.
* Removal/Elimination of water molecule is called dehydration.
186
SCIENCE 10
UsesDo you know?
1.
As a preservative.
Dilute solution of Acetic acid
2.
As a laboratory reagent.
is used for the preservation
3.
In the synthesis of many organic compounds.
of pickles, sausage etc.
4.
In making medicines.
5.
In making perfume, colour, plastic etc.
6.
In the manufacture of polyvinyl acetate, cellulose acetate and artificial silk etc.
Answer these questions.
1.
What is carboxylic acid?
2.
Write the name and structural formula of first two members of carboxylic acid
homologous series.
3.
What is vinegar?
4.
How is pyrolignius acid obtained?
5.
What is glacial acetic acid?
6.
How is carboxylic group tested?
12.7 Some other organic compoundsSome other organic compounds like rubber, plastic, nylon etc. used in our daily life are
described briefly as follows PolymerPolymers are large molecules, consisting of a large number of small units called monomers
e.g. when Ethylene is heated at high temperature and high pressure, its molecules unite together
to form a high molecular weight compound called Polythene. This process is called
Polymerisation.
Polymerisation
n (CH2 = CH2)
High temperature
and high pressure
(–CH2–CH2–)n
Polythene
Where n is the number of molecules.
In the same way Poly Vinyl Chloride (P.V.C), Teflon, Neoprin etc are also polymers.
Some important polymers, their method of preparation, properties and uses 1. Polythene (Poly + Ethene = Polythene) - It is a synthetic polymer of the additional
series. It’s monomer unit is ethylene.
ORGANIC COMPOUNDS
187
1000-200A.P.*
n (CH2 = CH2)
200-4000C
(–CH2–CH2–)n
temp.
Polythene
Property - It is a transparent, elastic, strong and solid plastic.
Use- It is used in making raincoats, toys, pipes, bags etc.
2. Poly Vinyl Chloride (P.V.C.)
It is also a synthetic polymer of additional series. It’s monomer unit is Vinyl chloride.
Poly Vinyl Chloride
Properties- It is a hard polymer.
Uses - It is used in making floor tiles, pipes, toys etc.
3. Teflon - It is a synthetic polymer of additional series. It’s monomer unit is Tetra Fluro
Ethene.
n (CF2 = CF2)
(–CF2 – CF2–)n
Tetra** Fluro Ethene
Teflon.
Properties - It is a hard and heat resistant substance.
Uses - It is used in making non stick utensils.
Soap These are Sodium or Potassium salts of carboxylic acids (fatty acids). Their general formula
is R-COONa or R-COOK where R = C17H35 or other higher alkyl group.
Soaps are mainly made from animal fat or vegetable oils. It is prepared by alkaline hydrolysis
of fats or oils (Esters of higher fatty acids). Glycerol is obtained as bye product.
NaCl
Important Fact
Soap is a mixture of
salts of saturated and
unsaturated long chain
carboxylic acids.
The process of making soap by hydrolysis of fats or oils by alkalis is known as
Saponification.
* A.P. means Atmospheric pressure
** Tetra means four as Tri means 3, Di means 2 & Mono means 1
188
SCIENCE 10
For preparing soap in the laboratory or home, castor oil, cotton seed oil or soyabeen oil is
taken in a beaker and the same volume of concentrated NaOH solution added to it. This mixture
is stirred and the solution is heated till the paste of soap is not obtained.
The soap obtained is separated and some amount of sodium chloride is added to the
remaining solution so that the complete soap gets precipitated.
How does soap work?
The molecule of soap is made of two parts- One long hydrocarbon part (R) and the other
small ionic part (-COONa). It can be represented as Let’s Know
Long hydrocarbon
Part
(water repellent)
Small Ionic
Part
(water attractive)
How does soap clean the clothes?
Soap can be hard, soft or transparent. Soft
soap is used for bathing. Sodium salt of
higher acetic acid is used in soft soap
whereas potassium salt of higher acetic
acid is used in hard soap. In making
transparent soap the normal/ordinary soap
is dissolved in alcohol, filtered and the
solution is vaporized. Alcohol is vapourized
where as the transparent soap is left behind.
The oily particles present in the sweat
coming out of the human body stick to the
clothes. The dust particles stick to these oily
particles and make the clothes dirty. When dirty
clothes are mixed with water and soap, the ionic part of the soap being water attractive, dissolves
in water whereas the hydrocarbon part of the soap being water repellent unites with the oil or
greese part. When dirty clothes are rinsed with water, the dirt particles attached with the soap
molecules, dissolve in water and come out. In this way, clothes become clean.
Activity
Let’s Prepare Soap
Required Material - Mahua Oil (Higher Fatty acid), silicates or Besen, indigo, water,
Sodium hydroxide, stirrer etc.
Principle- Soap is the Sodium or Potassium derivative of higher fatty acids.
Method- Take higher fatty acid like Mahua Oil in a container. Add some amount of
water, indigo and silicate and mix thoroughly this mixture with stirrer. Add concentrated
solution of Sodium hydroxide gradually and stir continuously. Keep this mixture
overnight. The soap used for washing clothes is ready.
Quantity of material/Proportion
If 1 Kg. of Mahua Oil is used, then 4 litre water, 1 kilogram silicate or 250 gm. besen,
300 gram sodium hydroxide should be taken.
ORGANIC COMPOUNDS
189
Salient Features of the method 1.
The quality of soap may affect if besen is used in place of silicate
2.
This is a cold method. For making more amount of better quality soap, hot
method is used.
3.
Bathing soap may also be made by this method.
Precautions - Sodium hydroxide (caustic soda) is of corrossive nature. Itching
occurs if it drops on body or clothes. Hence it should be handled carefully.
Limitations of SoapSoap is not able to clean clothes properly in hard water. It is because of following reasonsl
The salts present in hard water, react with soap to form insoluble precipitate called
scum.
l
The scum sticks to clothes and decreases it’s washing.
DetergentsDetergents are Sodium salts of long chain Alkyl or Aryl sulphonic acid. Their working
capacity is more than that of soaps.
For example- Sodium alkyl sulphate- CH3(CH2)10 CH2SO4– Na+
Sodium alkyl sulphonates - CH3(CH2)11 C6H4 – SO3 Na+
Structure of detergents- It is similar to soap. It has also two parts- (1) long hydrocarbon
chain. 2. Ionic part.
Long hydrocarbon chain
(Water Repellent end)
Detergents can produce foams in soft
as well as in hard water because they do
not form insoluble substances with the Ca
and Mg Salts present in hard water. Thus
detergents are considered better than soap.
Detergents can be prepared with the help
of the these substances 1. Long chain hydrocarbon.
190
Ionic part
(Water attractive end)
Do you know?
Synthetic detergents are commonly
known as Syndates. They are alternative
of soap. They are of two types- (1)
Sodium alkyl sulphate. (2) Sodium Alkyl
benzene sulphonates. They are much
better than soap, for washing purposes.
SCIENCE 10
2. Sulphuric acid.
3. Sodium hydroxide, etc.
Action of Detergents- When detergent
is dissolved in water if forms a colloidal
solution. The detergent molecules of this
solution unite together in the form of bunches
to form micelle. In the micelle, the detergents
molecules are arranged in such a manner that
the hydrocarbon end is towards the centre and
the ionic part is outside. The grease or oily
particles of dirty clothes get attached to the
hydrocarbon end of the detergents. Thus the
dirt particles get stuck. On rinsing with water,
these particles come outside and the cloth
becomes clean.
Action of detergent
Answer these questions.
1.
What are polymers?
2.
How is polythene made?
3.
What is the full form of PVC?
4.
What is the use of Teflon?
5.
What is soap?
6.
What are detergents?
7.
What are Syndates?
8.
How cloth is cleaned with the help of detergents?
9.
Soap does not give foam in hard water. Why?
Points to remember
l Chemical compounds are mainly of two types - Inorganic and Organic.
l Compounds in which carbon is the major constituent are called organic
compounds.
l
Organic compounds are not only originated from living substances, but majority
of them are made in the laboratory.
l
Urea was made in laboratory firstly from two inorganic compounds.
l
Organic compounds also contain other elements like oxygen, nitrogen, sulphur,
halogen etc. besides carbon and hydrogen.
ORGANIC COMPOUNDS
191
l
Organic compounds are of covalent nature. They show isomerism.
l
Organic compounds are studied mainly in two forms- Aliphatic and Aromatic.
l
Compounds containing Carbon and Hydrogen are called Hydrocarbons.
l
The reactivity of hydrocarbons is due to the presence of functional group.
l
The functional group is responsible for the chemical properties of an organic
compound.
l
The modern system of nomenclature is IUPAC.
l
Fermentation takes place in the presence of Enzyme.
l
Enzymes are nitrogenous compounds.
l
Ethyl alcohol is also used as power alcohol.
l
Consumption of denatured alcohol leads to probability of death.
l
Both Aldehydes and Ketone contain Carbonyl group. That is why aldehydes and
ketones have some similar properties.
l
Fehling solution is the mixture of alkaline solutions of Copper sulphate and Sodium
Potassium tartarate.
l
Bakelite is a useful thermosetting plastic.
l
The aquous solution of formaldehyde is called formalin.
l
Dilute solution of acetic acid is called Vinegar.
l
Polythene, Nylon, Bakelite, PVC etc. are examples of Polymers.
l
PVC is a polymer of Vinyl chloride.
l
Sodium and Potassium salts of higher fatty acids are called Soap.
l
The process of making soap is called Saponification.
l
Synthetic detergents are called Syndates.
l
Detergents can wash clothes in hard as well as in soft water.
EXERCISES
Very short answer questions1.
What was the assumption of Lavoisier about organic compounds?
2.
Which compound did Wohler make in the laboratory first and how?
3.
What are hydrocarbons?
4.
Explain any two hydrocarbon derivatives?
5.
Explain esterification?
6.
What is fermentation?
7.
What is denatured alcohol?
192
SCIENCE 10
8.
Write the IUPAC name and structural formula of first three members of Alkanol series?
9.
What is the use of Formaline solution?
10.
What does methyl alcohol give on condensation with phenol in the presence of an acid?
11.
What is polymerization?
12.
Explain Haloform reaction ?
13.
Specify the types of carboxylic acids?
14.
How is carboxylic acid tested?
15.
What are syndates?
16.
Write the uses of Teflon?
17.
What is absolute alcohol?
18.
Define saponification?
Short answer type questions.
1.
Write the full name of PVC?
2.
What is Fehling solution A and Fehling solution B ?
3.
Write the names of two enzymes used in alcohol preparation from molasses?
4.
Why are detergents better than that of soap?
5.
How are organic compounds classified?
6.
What is a functional group? Explain with the help of examples.
7.
What is alcohol? Write the names and structural formula of the first four members of this
series?
8.
Write the main uses of alcohol.
9.
What are the similarities in between aldehyde and Ketone?
10.
Write a short note on silver mirror.
11.
Write the general formula of Alkanone. Describe diagramatically the laboratory preparation
of propanone?
12.
Explain reduction in acetone.
13.
What is carboxylic acid? Write the formula of vinegar.
14.
What is pyrolignius acid? How is acetic acid prepared from this?
15.
What is glacial acetic acid and why it is called so?
16.
What are polymers. Explain with examples.
17.
What is soap? How many types of soap are there?
18.
What is the difference between soap and detergent? How are clothes cleaned with a
detergent?
ORGANIC COMPOUNDS
193
19.
Write the main uses of acetone?
Long answer type question.
1.
What is meant by an organic compound? Explain functional group by describing some
special properties of carbon?
2.
How is Ethanol manufactured?
3.
What are aldehydes and ketone? Write the methods of preparation, properties and uses
of methanal.
4.
What are carboxylic acids? How many types of carboxylic acids are there? Write the
methods of preparation, properties and uses of acetic acid.
5.
Write short notes on following(A) Soap (b) Polymers (c) Detergents
6.
Explain quick vineger method?
7.
Write notes on(A) Denatured Alcohol (B) Aldol Condensation (C) Polythene.
Project
1.
Write down the name of Organic compounds used in your daily life. Classify
and tabulise them.
2.
Observe and note down different type of Organic compound, their properties,
uses etc, while you are having an educational tour.
194
SCIENCE 10
Chapter - 13
NUTRITION
Energy is necessary for growth, maintenance and to
perform various activities going on within the body of a living
organism. Energy is required for all living organisms to carry
out various functions of life. This energy is obtained from food
that the organism take. In food, main components like
carbohydrates, fats, proteins, minerals, vitamins and water are
present. [Food synthesis is done by autotrophic plants.
Autotrophic plants can utilize the energy of sunlight, directly or
Indirectly for food synthesis.]
We will Study :
13.1 Nutrition
and
types of Nutrition
13.2 Nutrition in plant
13.3 Photosynthesis
13.4 Factors affecting
photosynthesis
13.5 Nutrition In
animals
13.6 Nutrition in
different animals.
13.7 Digestive
system in
humans
13.1 NutritionAll those processes in which food is taken from
external environment and these food materials release
energy which is used for growth are called nutrition.
Nutrition in organism besides producing energy is also
used in formation of organic matter, growth of organism and
also for metabolic processes.
Types of NutritionThere are basically two types of nutritionl Autotrophic Nutrition, l Heterotrophic Nutrition
13.2 Nutrition In Plants- Autotrophic Nutrition takens place in
green plants. For this process plants need carbondioxide (CO2),
water (H2O), chlorophyll and sunlight to react and form a
substance carbohydrate. This process is called photo-synthesis.
In this way, carbohydrate, forms complex organic matter Like
Autotrophic
Plant
Parasites
Saprophytes
Hetero
trophic
Symbionts
Insectivorus
protein fats by chemical synthesis. There are two types of
plants.
NUTRITION
195
Chlorophyll pigments are present in the plant leaves. Due to its presence plant makes
food. Carbohydrates are formed in plants by the process called photosynthesis. In ecosystem
autotrophic plant is called producer.
Autotrophic Plant-Those plants which prepare their own food, are called “Autotrophic
plants”.
Hetrotrophic Plant- Those plants which depend on any other living or dead organic
materials for their growth and get their food directly or partially are from them called “hetrotrophic
plants.” They are of four typesParasitic Plant- In this type of plants nutrition of one
Stipe
organism depends upon an other organism for getting food
and is known as parasite and the organism on which it
depends is known as host. Special types of root are present
in the parasitic plants which are called parasitic roots. These
parasitic roots enter the body of the host to suck the food.
There are two types of parasitic plants.
Rhzomorph
1. Holo Parasitic- Those which are completely
Fig.
13.1
Fungi
Agaricus
dependent on host plants. ex: Orobanki- This is found on
the roots of patato, tomato and brinjal plants.
2. Partial Parasitic- Some plants partially depend on
others, and are called partially parasite Ex. Sandal wood
plant.
Saprophytic- In this mode of nutrition, when plants
depend for food on dead and decaying material, they are
called saprophtic plants. These plants secrete some
enzymes and decompose the surrounding dead or decaying
organic matter into a soluble substance and then it absorbs
the nutrient. Ex. : Fungi, bacteria, Agaricus (Mushroom).
Lichen
Symbiotic - When two plants live together and spend
life with each other. they are called symbionts. Ex. : lichens.
Fig. 13.2 Symbioticplant : on
In lichens, Algae and fungi live together. Lichens are found
the branch of lichen
in branches of trees, whereas algae make food by
photosynthesis and fungi absorb the water and minerals.
Other example is Rhizobium bacteria which can be
seen in root nodules of legume plant. The bacteria fixes the
atmospheric nitrogen for plant and the plant gives food for
bacteria.
Insectivorus- Some plants depend upon insects for
Tendrillar
their food. These plants are found on the land where
petiole
percentage of Nitrogen is less. This is known as Insectivorus
Plant because it feeds on insects and fulfills the need of
nitrogen. Ex. : Drosera, Utricularia, Sundew etc.
Method of capturing the insects in Nepenthese- In
Nepenthes, leaves are modified into a pitcher like structure.
196
Fig. 13.3 Pitcher Plant
SCIENCE 10
The lamina of actual leaf is modified into pitcher and the upper part of petiole is modified into the
cap of the pitcher. This is beautifully coloured. Whenever any insect enters and falls down into
pitcher the cap is closed. Pitcher contains water and digestive juice. The digestive juice digests
the insect and obtains nitrogenous substance from it. After digesting the insect, the cap of
thepitcher opens again.
13.3 PhotosynthesisAll green plants, manufacture their own food in presence of sunlight, carbondioxide +
water. This manufacturing process of food is called photosynthesis.
“Photosynthesis is a metabolic process. In this process carbondioxide and water
combine in the presence of sunlight and chlorophyll to form carbohydrates and oxygen
released as by product.”
In Photosynthesis processSun-light
Chlorophyll
6CO 2 + 12H2O   → C 6H12O 6 + 6O 2 + 6H2O + 673 kg. Cal. energy
Important FactsPhotosynthesis is a :l
Biochemical process.
l
Photolysis of water.
l
Reduction of carbondioxide.
Scientists had given
an
information on the history of
photosynthesisAristotle- Plants absorb all their
food from roots.
13.4 Factors Affecting PhotosynthesisThe factors influencing
photosynthesis are given below 1.
the
rate
of
Carbondioxide - Despite of its low
concentration (0.03%) in atmosphere it is
sufficient for photosynthesis. At optimum
temperature and light intesity, if the CO2 is
increased the rate of photosynthesis increases
markedly but after some time the rate is
decreased.
2.
Light - With the increase in the light intensity
the rate of photosynthesis increases.
3.
Temperature - Between 10OC-30OC rate of
photosynthesis increases with the rise in
temperature. Temperature above 30 0C and
below 10 0 C, show adverse effect on
Stephenhales- Leaves take air and
make their food with the help of light.
Joseph Priestley- Green plants
purify the foul air and convert into
pure air.
Jean Senebier- Plants absorb CO2
and release O2.
Robert Mayer- Green Plants convert
solar energy into chemical energy.
Black mann - Photosynthesis is a
bio-chemical process.
photosynthesis process.
4.
Water - Rate of Photosynthesis decreases with the decreasing quantity of water.
NUTRITION
197
Experiment : Demonstration of starch formation during photosynthesis.
Blue
Green
Colourless
Non green
Leaf Before the Starch Test
Leaf After the Starch Test
l
Take a potted plant with variegated leaf e.g. Money plant or crotans.
l
Keep the plant in a dark room for 3-4 days so the starch present in the leaf is used up.
l
Now keep the plant in sunlight for 6 hours. Pluck a leaf from the plant and mark the
green areas of the leaf on a sheet of paper.
l
Dip the leaf in boiling water for a few minutes.
l
After this, immerse it in a beaker cantaining alcohol.
l
Place the above beaker in a water bath and heat till the alcohol begins to boil.
l
We will see that the leaf becames colourled and the alcohol turns green.
l
Now dip the leaf in dilute solution of iodine for a few minutes.
l
we will observe that the portion of the leaf, which was green turns to blue colour,
showing the presence of starch.
Answer these questions.
Q. 1 Why is nutrilion required?
Q. 2 Why is crow called omnivorus?
Q. 3 How does carbondioxide affect the photosynthesis/ what is the effect of carbondioxide
on photosynthesis?
Q. 4 What is the meaning of symbiotic plant?
13.5 Nutrition in Animals- Animals are heterotrophic. Animals require food and energy
for their growth, multiplication and other biological activities. They obtain energy from food
components like carbohydrates, fats, protein, minerals. These are complex molecules and
insoluble in water. It is necessary for absorption that these molecules are converted into
simple ones for absorption. These simple molecules reach to the different parts of body
through blood circulation after the digestion of food. Thus we can say- “The process in which
large insduble, complex molecules of food materials get converted in to simple and soluble
198
SCIENCE 10
molecules is called Digestion.”
Why is it required
l
For energy l For formation of protoplasm
l
For metabolic reactions l For growth Three types of nutrition occur in animal.
Holozoic
Saprozoic
Parasitic
Holozoic - When solid food is ingested by mouth and digestion of food, absorption and
assimilation process is completed, it is called Holozoic nutrition. This type of nutrition is found in
following main groups of animals.
(a) Herbivorus - They feed exclusively on plants e.g. sheep, goat.
(b) Carnivorus - They feed upon other living animals. They feed on the flesh of other
animals. e.g. hyena, lion, tiger.
(c) Omnivorus - They feed on both plants and animals. e.g. dog, human beings, cockroach.
Saprozoic - When organisms get food from dead or decaying organic material, they are
called saprozoic. ex. : Insects.
Parasitic - When organisms depend upon other organisms for their food. These are two of
types(a) Ectoparasites - Parasites obtain predigested organic food from the out side of the
host. Ex - bed bug, head house, mosquitoes etc.
(b) Endoparasites - Parasites obtain predigested organic food from the inside of the
host. e.g. tapeworm.
13.6 Nutrition In different Animals Amoebae - Amoeba is a unicellular organism which
has no digestive system. In this type of nutrition ,food are
ingested through phagocytosis. Amoeba engulf the food
with the digestive tube, the food material reaches the food
vacuoles. Then it is digested by the enzyme inside the
cell. Enzyme or digestive juice come out from the cell
and here the process of digestion takes place.
Nutrition In grass hopper- In grass-hoppers
Holozoic type of nutrition occurs. For the digestion
process, alimentary canal is divided into there parts 1. Foregut (Stomodaeum), 2.
(Mesenteron), 3. Hindgut (Proctodaeum)
NUTRITION
Midgut
Fig. 13.5 Phagocytosis
in Amoeba
199
Stomodaeum (foregut) - Salivary gland occurs in buccal-cavity.
The buccal carity continue with pharynx oesophagus and crop. Inner
wall of crop contains horizontal folds. This crop opens in a portion known
as gizzards. The Inner wall of gizzards is made by cutaneous solid
material, which contains finger like folds.
Mesenteron (Midgut) - it is long tube structure which
contains various malpigian tubes.
Proctodaeum (HInd gut) - It is a small tube for absorption of food.
Food is stored in crop where the partial digestion of food begins.
From crop food reaches the gizzard. Here food is ground and mixed
with digestive juice. In midgut the digestion of food is completed. After
digestion, food reaches in the Hindgut. Here absorption of food takes
place.
Pharynx
Salivary duct
Salivary gland
Foregut
Crope
Hepatic
Midgut
Maglpigioun
tubules
Hindgut
Urinary
blodder
Anus
Fig. 13.6
13.7 Digestive System in Man
Salivary glands
Nutrition in Man
Mouth
Digestive Organ
Digestion Process
Alimentary Canal
Pharynx
Buccal
cavity
Oesophagus
Liver
Stomach
Digestive Gland
Ingestion
Buccal cavity
Salivary glands
Digestion
Oesophagus
Liver
Absorption
Stomach
Pancreas
Intestine
Gastric Glands
Assimilation
Egestion
Gall bladder
Poncreas
Small intestine
Large intestine
(1) Buccal Cavity - It is bound by two jaws Tongue,
teeth and salivary glands are present in it.
Urinary bladder
Anus
Fig. 13.7 Digestive system
Tongue- This is a muscular structure.
A large number of taste buds are located on the tongue. Different taste buds meant for sweet
sour, salty and bitter taste are present. It helps in chewing and swallowing of food. Tongue
mixes-saliva with food and makes food soft and slippery for chewing.
Teeth - Mammalian teeth are heterodont (i.e. of different kinds and of various shape and
size and structures) There are four kinds of teeth in mammals : (a) Incisors (b) Canines (c)
Premolars (d) Molars.
Oesophagus - The posterior extremity of the buccal cavity narrows into a short pharynx.
The muscular long tube leading directly to the stomach is called Oesophagus. Food passes
200
SCIENCE 10
down the oesophagus into the stomach. No digestion takes place in oesophagus as there are
no digestive glsands.
Stomach - Stomach is a large elongated sac lying just under the diaphragm. Its contains
digestive glands known as gastric glands.
Intestine - Intestine of man is divided into two parts- (1) Small Intestine (2) Large Intestine.
Digeative GlandsSalivary Gland - Three pairs of salivary
glands are present in the buccal cavity, which
secret saliva. Saliva contains salivary amylase
or ptyalin enzyme and mucus
Parotid
gland
Duct of
parotic gland
Ptyalin- converts starch into sugar.
As food is chewed, it becomes
sweetend because food mixes with ptyalin
and converts into sugar.
Sublingual
gland
Duct of
sublingual
gland
Duct of
submaxillary
gland
Liver Liver is the largest gland situated in the
upper part of the abdominal cavity. It consists of
two lobes. Gall-bladder present underneath the
liver stores bile juice.
Fig. 13.8 Salivary glands in man
Functions of liver1.
Secretion of bile juice. It is alkaline and decreases acidic effect of food.
2.
Excess quantity of glucose in blood in converted into glycogen and stored in the liver.
3.
Lipase breaks down fats in to fatty acids.
4.
Liver converts ammonia into urea.
5.
Liver cells deactivate toxic materials and protect our body.
6.
Storage of vitamins. Particularly vitamins A .
7.
Synthesis of RBC .
NUTRITION
201
Pancreas - It is an irregular, light yellow
gland. It secretes pancreatic juice and insulin.
Horomone Insulin controls the amount of
glucose in the body.
Hepatic duct
Cystic
duct
Gall
sladder
common hepatic duct
Common bile duct
Pancreas
Digestion ProcessDigestion in Buccal Cavity- In the
buccal cavity, food is chewed and ground by
teeth. With the help of tongue it gets mixed with
the saliva secreted by salivary glands. By
chewing food is converted into a paste and
salivary amylase or ptyalin enzyme converts
starch into sugar.
Duodenum
Pancreatic duct
Fig. 13.9 Pancreas
Digestion in Stomach : Gastric juice secreted by the gastric gland mixes with food.
Gastric juice contains dilute Hydrochloric acid (HCl), mucous, inorganic salt and enzyme Mucous
protects the wall of stomach from acid. Dilute HCl destroys the bacteria in the food and also
converts inactive pepsinogen into active from called pepsin.
Following enzymes are present in the gastric juice :Pepsin- In the presence of gastric juice it decomposes protein molecules into the pepton.
Rennin - In the presence of Ca++ ions, soluble proteins of milk are converted into insoluble
casein.
Gastric lipase - It Partially decomposes fats into fatty acid and glycerol.
Gastric Mucin - It decreases acidic nature of gastric juice and it emulsifies the food.
The wall of stomach undergoes periodic muscular contraction producing churing movement.
After chemical digestion food mixs with the gastric juice. Most of the part of digestion process
takes place in stomach.
Digestion in Intestine- There is no digestive juice secreted by the Intestine but bile juice
from gall bladder and gastric juice from pancreas come out and mix with each other.
Function of Bile juice l
Due to the alkaline nature it helps in neutralizing the acidic effect.
l
Bile juice destroys the harmful bacteria present in chyme.
l
It helps in Emulsification of fat.
Nature and action of pancreatic enzymes are given below:l
Trypsin - Acts upon all proteins and converts them into peptones.
Lypase - Lypase acts on emulsified fats and converts them into fatty acid and glycerol.
Absorption - Most of the digested food is absorbed by the villi found in the small intestine.
The outer layer of villi is covered with a thin layer of epithilial cells. Absorption of different
food material by villi is given below:202
SCIENCE 10
Absorption of Carbohydrates - In the form of glucose passes through villi and enters
the blood capillaries.
Absorption of protein - In the form of Aminoacid, directly reaches the blood.
Absorption of fat - In the form of fatty acid and glycerol, It reaches different parts of body
through blood transportation.
Absorption of salt- By cell and intestine. It reaches the whole body with the blood
transportation.
Absorption of water - Mostly absorption of water occurs in the large intestine.
Assimilation :
After absorption, food in the form of liquid
food material reaches the cells. On reaching
the cell, the absorbed material is mixed with
protoplasm which is diffused by the blood cells.
This process is called assimilation.
Egestion - The removal of faeces through
the anus.
Importance of Nutrition
Biological
Process
Importance
of nutrient
Answer these questions.
Q. 1 What is Holozoic Nutrition?
Q. 2 Which type of nutrition occurs in
Tapeworm, Mosquito, Cock-roach and
Human being?
Q. 3 Where does the grinding of food occur
in grasshopper?
Formation
of
protoplasm
Production
of energy
Metabolic
Activities
Growth
Genetics
Growth of
body and
repairing
Creative and
distructive
process
Synthesis
of DNA
and RNA
Points to rememberl
The total form of substance which organisms take and release energy from food
material for their growth is called nutrition.
l
Nutrition is of two types- Autotrophic and Hetrotrophic.
l
Autotrophic nutrition is found in green plants which produce food from photosynthesis.
l
Heterotrophic organisms are of three type e.g. Herbivorus, Carnivorus and Omnivorus.
l
Those organism which depend upon other animals are called parasites.
NUTRITION
203
l
Organisms which obtain food from
dead or decaying material are called
Saprophytes.
Digestion Process
Digestion process are successfully
complete in five steps-
l
Organisms which spend life with each
other and benefit mutually and depend
on each other for their food are called
symbiotic.
1. Ingestion
l
Organisms which feed upon insects
in the form of their food are called
insectivorus.
l
In the presence of sunlight and
chlorophyll plant take carbonidioxide
and water and produce organic
compound. Such process is known
as photosynthesis.
l
In the form of chemical equation,
photo-synthesis process is given
below-
6CO2 + 12H2O
l
From
mouth
Food accept from mouth
2. Digestion
Conver ts complex organic
material into the simple molecules
From
Carbohydrates - Glucose
Buccal
Protein
- Amino Acid
cavity to
Fats
- Fatty acid
stomach
3. Absorption
Digested food absorbed by
the different organs. This
work is possess in the small
intestine.
In Small
Intestine
sunlight
C6H12O6 + 6O2
Chlorophyll
+ 6H2O
Ingestion of solid food is known as
4. Assimilation
Using absorbing food by
different cells of the body.
By
Cells.
Holozoic nutrition.
l
In amoeba, Phagocytosis method is
5. Egestion
used for the injestion of food.
Removal of faecs matter by
Anus.
from
Anus
l
Cellular matter of Amoeba secretes
digestive juice for the digestion of food.
l
Digestive system in humans include alimentary canal and digestive glands.
l
A process in which different food materials like carbohydrates, protein and fats etc.
are converted into simple or small molecule capable for absorption is called digestion.
l
Main digestive glands are- Salivary glands, Gastric glands and Pancreas.
l
Digestion process is completed in five stepsIngestion, Digestion, Absorption, Assimiliation, Egestion.
204
SCIENCE 10
EXERCISES
Very short answer type questions1.
What is nutrition?
2.
What are the different types of nutrition.
3.
What do you understand by Heterotrophic Nutrition?
4.
Give example of a saprophytic plant.
5.
Name the type of nutrition found in sandalwood tree?
6.
Mention two factors affecting the process of photosynthesis?
7.
Name the method of ingestion of food in Amoeba?
8.
Names the various parts in the alimentry canal of grass hopper.
9.
Names the different parts of the alimentary canal of human beings.
Short answer type questions1.
Explain different types of Hetrotrophic organism.
2.
What do you understand by Autotrophic plant?
3.
Explain the method of ingestion of food in Nepenthes (Pitcher plant).
4.
Explain the process of photosynthesis.
5.
Explain the necessity of nutrients in animals.
6.
Write the names of digestive glands and their juice.
7.
Write the names of enzymes found in gastric juice.
8.
What do you understand by Assimilation?
Essay answer type questions1.
What do you understand by Nutrition? Explain with the help of example different types of
nutrition in plants.
2.
What do you understand by plant photo-synthesis? Write the factors that affect
photosynthesis.
3.
Explain the process of Nutrition in a Grass hopper.
4.
Explain the process of digestion in human beings.
5.
Explain the various digestive glands in human beings.
NUTRITION
205
Chapter - 14
RESPIRATION
All living organisms need energy to perform vital activities
and to maintain life. Animal cells produce chemical energy from
degradation of organic compounds and plants decompose the
food synthesised from photosynthesis process and energy is
produced.
Thus respiration is an important biochemical reaction
We will Study :
process of oxidation by which food material is oxidized to
Respiration
produce carbondioxide, water and energy. Here, we will try to
14.1
Respiration in
plants
14.2
Respiration
process in plants
14.3
Respiration in
Animals
14.4
Breathing
14.5
Respiration in
animals through
different organs.
14.6
14.7
working and
structure
of organs involved
in the process of
respiration of
human beings
Respiration
process in human
beings.
understand the process of respiration and the respiratory
ograns in plants and animals.
Respiration in plants :
Definition : Respiration is an oxidation process in which
complex organic compound decompose into carbondioxide and
water with the release of energy.
“Respiration is exhibited by living organism which
involve production of energy for doing their work with
stepwise degradation of organic substances.”
During respiration, plants take in oxygen from environment
and release CO2 in the atmosphere. Respiration is a continuous
process of plant cell, although at the noon, in the presence of
sunlight, the process of photosynthesis also takes palce.
CO2 released during Respiration is used in the process
of photosynthesis and the resultant carbondioxide and oxygen
are balanced in atmosphere.
The Process of Respiration is shown by following equationC6H12O6 + 6O2 → 6CO2 + 6H2O + 38 ATP.
Types of Respiration :
(i) Aerobic Respiration (ii) Anaerobic Respiration
206
SCIENCE 10
(i) Aerobic Respiration - When respiration
occurs in the presence of free oxygen, it is
called Aerobic respiration. Plants sustain
this process and are called Aerobes. Food
material is completely oxidized in this
process into CO 2 and water and large
amount of energy in released.
C6H12O6 → 6CO2 + 6H2O + 673 kg. cal or
38 ATP.
(ii) Anaerobic Respiration - When
respiration takes place in the absence of
oxygen then it is known as Anaerobic
Respiration. In this process incomplete
oxidation of food material takes place and
produce CO2 and ethyl alcohol. Besides
this, other organic matter like citric acid,
malic acid, oxalic acid, butyric acid or
lactic acid are also produced. This process
is also known as Intramolecular
Respiration. Very low amount of energy
Knowing facts
Anobligate Aerobic Organisms- Some
plants produce energy from aerobic
respiration in the presence of O2 and
cannot survive in the absence of O2.
Such plant are called Anobligate Aerobic.
Obligate Aerobic Organisms- Some
plants which produce energy from
aerobic respiration in general but can live
in the absence of O 2 and produce
energy, are called obligate Aerobic
Organisms.
Ex. - Butyric Acid bacteria, Lactic Acid
bacteria.
Anobligate Anaerobic OrganismsSome plants live in the absence of
oxygen by aerobic respiration and cannot
survive in the presence of oxygen. They
are called Anobligate Anaerobic
organism. Ex. ; Clostridium bacteria.
is released in this process.
This process is shown by this equation :C6H12O6 → 2C2H5OH + 2CO2 + 21 K. Cal. or 2 ATP
Difference between Aerobic Respiration And Anaerobic Respiration
Aerobic Respiration
Anaerobic Respiration
1.
It takes place only in the presence of O2
1. It does not require O2.
2.
Food materials are completely oxidized.
2. Food materials are incompletely oxidized.
3.
End product are CO2 and H2O.
3. End products are C2H5OH and CO2.
4.
High amount of energy
4. Low amount of
is produced (38 ATP).
5.
Enzymes responsible for this process
are found in mitochondria.
RESPIRATION
energy is produced (2 ATP).
5. Enzymes responsible for this process
are found in cytoplasm.
207
Aerobic Respiration
6.
Anaerobic Respiration
This process takes place in most
organisms.
6. This process takes place in
comparatively less organisms.
7.
8.
It is shown by the following equation-
7. It shown by the following equation-
C6H12O6 + 6O2 → 6CO2 +
C6H12O6 + 6O2 → 2C2H5OH +
6H2O + 673 K. cal.
2CO2 + 21 K. cal.
38 ATP are produced
8. 2 ATP are produced.
14.2 Mechanism of respiration In plants :
Respiration process is a complicated process which is controlled and regulated by
enzymes. Enzymes are obtained from cellular matter and mitochondria. Energy is released in
the form of chemical bond by this process.
Respiration Process are performed in three steps1.
Glycolysis or EMP pathway
2.
Kreb’s Cycle
3.
Electron transport chain or Cytochrome System.
(1) Glycolysis It is a stepwise series of various interactions, which results in breakdown of one molecule
of glucose, to 2 molecules of Pyruvic acid.
C6H12O6 + 2NAD → 2CH3CO.COOH + 2NADH2
Glucose Hydrogen acceptor
Pyruvic Acid
Reducing Hydrogen Acceptor
Main steps of Glycolysis(i)
This process takes place in the absence of oxygen and does not remove CO2.
(ii)
From one molecule of glucose, 2 molecules of Pyruvic acid are formed.
(iii)
Glycolysis is an oxidation process which involves oxidation of each glucose molecule,
and 2ATP molecule are formed.
(iv)
Chemical energy are stored in the molecules of ATP and NADH2.
(v)
Stepwise reaction of respiration is performed in the cellular matter. It does not requires O2
208
SCIENCE 10
(2) Kreb’s Cycle or Tri carboxilic acid CycleThis reaction takes place in matrix of mitochondria. The whole reaction process of Kreb’s
cycle is in the form of a closed chain. This reaction was described by British Scientist Kerb
(1937) and thus the name of this cycle of reactions was known as Kreb’s Cycle.
This process produces organic acid which involves citric acid and other acids with 3
carboxylic radical (COOH).
Some features related to the formation of pyruvic acid to Kreb’s cycle are given below:
1.
This reaction take place in Mitochondria.
2.
This process takes place in the presence of oxygen.
3.
One molecule of pyruvic acid releases one molecule of H2 and CO2 in the begining of krab
cycle.
4.
In Kreb’s Cycle, five molecules of hydrogen are released from one molecule of pyruvic
acid and 2 Molecules of CO2 are formed. Hence in this process total of 12 molecules of
Hydrogen and 6 molecules of CO2 are released. How? What happens in this process?
(3) Electron transport SystemIn this process all free enzymes are found in the Mitochondria. The whole process is
known as Electron Transport System.
Answer these questions.
1.
What is the name of the organism which performs aerobic respiration?
2.
How many stages are required for the process of respiration?
3.
Write the main steps of Glycolysis.
14.3 Respiration in animalsRespiration process in animals are of three types1. External Respiration - In this process, animals take in oxygen and release
carbondioxide. In higher animals it is known as breathing. This has mainly two phases(A) Inspiration : It is the process by means of which oxygen is taken to the lungs.
(B) Expiration : During expiration carbondioxide is expelled out from the respiratory organs
into the environment.
2. Gaseous exchange through blood- During this process, oxygen mixes with blood
and reaches different parts of body and CO2 reaches in respiratory organs or lungs whereas it
is thrown-out from the body.
3. Internal or Cellular Respiration - It refers to those processes which produce
RESPIRATION
209
carbondioxide and water. This reaction takes-place in the presence of enzymes.
14.4 Breathing-
Trachea
Breathing is a mechanical process,
which involves taking in O2 into the lungs and giving
out CO2. This process also known as pulmonary
respiration.
Diaphragm
Pulled
down
Rib
Breathing is accomplished in two phases(i)
(ii)
Inspiration or Inhalation- Taking atmospheric
air into the lungs. This process is called
inhalation. Coming out air depends on the
pressure of air present inside the lungs. When
atmospheric air pressure is more than that of
the lungs, then air enters the lungs.
Expiration or exhalation - The process which
involves discharging the air from lungs is called
exhalation. When air pressure in lungs is more
than the atmospheric pressure then air comes
out of lungs into the environment.
Contracted
muscle of
diaphragm
Inhaling
Spinal
coloumn
Fig. 14.1 Exhaling
The combined steps of inspiration and expiration is called breathing.
14.5 Respiration in Animals through Different organs.
(1) Cutaneous Respiration - (In earth worm) No specific respiratory organs are present
in the earth worm, nereis, leaches and other annelids.
The skin of earth worm is very thin and moist. Many blood vessels are spread on its skin.
Oxygen from the environment first gets dissolved in the mucus and then diffused into the blood
through skin. In blood, oxygen and haemoglobin combine with each other and reach in the
tissue
cells. Here this oxidizes with nutrient
elements to produce energy and CO2.
Gillrakers
Carbondioxide is returned back to blood and
released from body with diffusion through
skin.
Gill-orch
Mouth
(2) Respiration through GillsIn fishes specially bony fishes have
internal gills. In this type of fish, gills are
protected by external bony plate called
operculum. Under the operculum chambers
210
Water
Gill filament
Fig. 14.2
SCIENCE 10
are present which is called gill pouch. This
maintains the flow of water in the gill pouch
and thus the gills remain in contact with
water. Gills are arranged in row a comb like
structure called gill- filaments. Gill filamants
are raised into numerous horizontal flat folds
called gill lamellae which are richly supplied
with blood capillaries. Here exchange of
CO 2 and O 2 take place by diffusion
Gaseous exhange takes place through
blood.
l
Formation of thoracic cavity by back
bone, sternem and diaphragm.
l
Lungs have five lobes.
l
There is swelling in parietal pleura. Both
the membrane are stiff, which shows
problem in breathing. This disease is
known as plurisy.
l
Lungs do not have muscles so there is
exchange of air with the decreasing or
increasing of thoracic cavity.
(3) Tracheal Respiraton -
l
All four car tilages, at the time of
respiration protect from rubing larynx
cells from friction. These cartilages
belong to the vocal producing organ
which produce sound by the vibration.
In a Grasshopper, transportation of
gas or gaseous exchange takes place by
a special type of fine tube called trachaea.
After entering the body, the trachea forms
a network of tracheoles which are fine
branches of the trachea. The structure of
network, looks like a ladder. Each tube
opens in the peripheral part of the body.
(4) Respiraton by lungs-
Nose
Mouth
In all higher living organisms the main respiratory
organ is lungs and gaseous exchange or air exchange
take place from the lungs. In human beings also the
respiratory organ is the lungs.
Lungs
14.6 Structure of respiratory organs in human
Diaphragm
beingsThe respiratory system in human beings is
divided into two parts(1)
Main organ - Lungs
(2)
Associate organs-
Fig. 14.3 Passage of air in
human beings
Trachea
Lung
Bronehus
(i) Nostril and Nasal passages
(ii) Throat or Pharynx (iii) Larynx (iv) Bronchi
1. Main Organ
1. Lungs- In human beings, a pair of lungs are
situated in thoracic cavity. They are soft, spongy and
Fig. 14.4 Human Lungs
RESPIRATION
211
light pinkish in colour. It is connected with pharynx by tracheoles surrounded by a double walled
membrane called pleural membrane. Lungs and membranes are separated by a small space
called pleural cavity, which contains pleural fluid that allows membranes to move easily on one
another while breathing It keeps them always moist and help them in breathing process.
2.
Pharynx - Posterior part of the nasal passage, is called pharynx which is connected to
mouth. Pharynx has two openings. First opening allows air to pass through glottis to
reach lungs for breathing and other way allows passage of food for digestion by alimentary
canal. The opening of eustachean tube of ear is linked to the pharynx.
3.
Larynx - Larynx is a sound producing
organ which is the enlarged upper end of
the trachea. It has four types of cartilages-
4.
5.
(i)
One thyroid cartilage (ii) One
cricoid corti lage
(iii)
Paired arytenoid cartilages, which
has one pair of vocal cords is a
sound producing organ.
Bronchi - At the level of thoracic
ver tebrae, trachea divides into two
branches. These branches are called
bronchi, these enter the lung of their own
side and immediately divide into different
branches. These branches are called
branchioles.
The thoracic Cavity and diaphragmThoracic cavity is a hollow cavity divided
into two pleural cavities each on closing a
lung. Floor of the thoracic cavity is
completely closed by a thin muscular
membrane called diaphragm.
14.7 Respiration Process In Humanbeings-
Tongue
Glottis
Epiglattis
Cartlalage
Laryngopharyndx
Oesophagus
Fig. 14.5 Larynx
Bronchiole
Alveoli
Fig. 14.6 Bronchi
Ribs
Vertebrae
Like other animals, respiration in human
beings also completes in the following steps(1) Breathing (2) Gaseous Exchange
(3) Cellular Respiration.
(1) Process of BreathingBreathing is a process which involves
taking atmospheric air into the lung, where
exchange of gases takes place and CO2 mixed
Sternum
Diaphragm
Thoracic
cavity
Fig. 14.7 Diaphragm and Thoracic cavity
212
SCIENCE 10
air is expelled out from the lungs. Lungs do not
For gaseous Exchange In Animals,
have muscles in humans, therefore breathing
Following accomodation should
occurs due to the increase and decrease of
becomes arevolume of thoracic cavity. When expansion of
1.
Respiratory membrance or surface
cavity occurs in the human beings and other
should become permeable.
animals the air pressure in thoracic cavity is
2.
Respiration surface should be thin
reduced which results in inhalation of the air, but
because the distance of capicity of
diffusion is still only 1 milimeter.
by the contraction of intercostal muscles, volume
3.
Respiration surface should be moist
of the thoracic cavity is decreased which results
for dissolving oxygen and
in exhalation of the air. The contraction and
carbondioxide.
expansion of the lungs depends upon the
4.
Respiration surface should always
contraction and expension of diaphragms and
being contact with oxygen.
other inter costal muscles. Inter costal muscles
5.
The surface area of respiration
are of two types:should be more, so that gaseous
(i)
External Inter-costal muscles
exchange these can be more.
(ii) Internal Inter-costal muscles.
(i)
External Inter-costal muscles - These
muscles arise from upper end of each rib
Expiration
Inspiration
and extend to joint with lower end of
posterior rib.
(ii) Internal Inter-costal msucles - These muscles
arise from the lower end of each rib and extend to
join the upper end of anterior rib.
Breathing process or exhalation or inhalation takes
place in two ways(A) Inspiration (B) Expiration
(A) Inspiration - It is a process by which atmospheric
air is taken into the lungs and is called inspiration.
This process is accomplished by stimulating effect
Diaphragm
coming from the respiratory centre of brain which
effects external inter costal muscles to contract, Fig. 14.8 Inspiration and Expiration
causing the ribs to move forward and outward, and
sternum move downward. At the same time, during
inspiration the muscles of diaphragm contract, due to which the dome shape of the
diaphragm disappears. It move downwards and becomes flattened. Due to this the volume
of pleural cavity increases, resulting in increase of the lungs, due to which the atmospheric
air enters the lungs. The gaseous exchange takes place in the alveoli of the lungs.
(B)
Expiration : Expiration is a process by which CO2 mixed air is expelled out from the
lungs. Due to the effect of the respiratory centre of brain, the contraction of internal inter
costal muscles, the internal organ of thoracic cavity and diaphragm is pushed forward
due to which the volume of thoraic cavity puts pressure on the lungs which is more than
RESPIRATION
213
atmosphric pressure and causing contraction of lungs due to which the air is expelled out.
2. Gaseous Exhange Gaseous exchange in lungs- The cells of the lungs and pulmonary alveoli is more
permeable to oxygen and carbondioxide gas. There is a difference between concentration of O2
and CO2. Due to this the diffusion of O2, gas will occur in blood capillaries, and carbondioxide
from blood capillaries into the alveoli and accomplished by completing gaseous exhange in
lungs.
1.
Pulmonary flowing Volume - 500 mm, 4500 mm. in Male
2.
Pulmonary Bio Volume - 3000 mm. in Female.
3.
Pulmonary Expiration Reserve Volume - 1000 mm.
4.
Pulmonary Inspiration Reserve Volume - 2000 mm. - 3500 mm.
5.
Pulmonary Remaining Volume - 1500 mm.
Difference between Respiration and Breathing
Respiration
Breathing
1.
It is a biochemical process
1. It is a Mechanical process.
2.
Oxidation of food material takes
place in this process.
2. CO 2 gas is expelled out and
O2 gas taken into the body in this process.
3.
This process produces energy in the
form of ATP.
3. This process does not produce energy.
Points to Remember
l
Respiration is a biochemical reaction which involves oxidation of food materials.
l
Breathing is completed in two steps - inhalation or exhalation.
l
Gaseous exchange is accomplished by blood.
l
Cellular respiration take place in three steps- Glycolysis, oxidation of pyruvic acid
and electron transport system.
l
The air that we breath is contains 78% N2, 21% O2 and 0.03% CO2 gases.
l
Breathing process in Human beings is being 16-20 times in one minute.
l
Tracheoles have rings (like. “C” shape), due to which it prevent shrinking.
214
SCIENCE 10
l
Respiration should not be done by mouth
because it is not safe.
l
Inspired inhaled air contains 20.96% O2,
0.03% CO2, 79% N2 and 0.25% water
vapour.
l
In exhaled air contain 16.3% O2, 4.0%
CO2, 78.7% N2 and 6.2% water vapour.
l
Aerobic oxidation involve more energy
then Anaerabic respiration.
l
Respiration by skin takes place in the
earth-worm.
l
Respiration by gills takes place in the
fishes.
l
Respiration by trachea takes place in the
Important Notesl At resting time, A healthy human
does completed breathing process,
16-20 time approximately in one
minute.
l Cellualr respiration in animals also
like plant, which are completed in
following steps1. Glycolysis
2. Kreb’s cycle
3. Electron Transport system.
l A human taking six liter air in the form
of breath in one minute.
l Controlling of respiration in human is
accomplished by a pairing center of
the respiration which is situated is the
medulla oblengata of the brain.
grass-hopper.
l
The energy 673 K. cal. is obtained from oxidation of one molecule of glucose.
l
Due to photosynthesis, gaseous exchange in plant takes place with the help of
stomata.
l
Plants does not have respiration process (breathing), except lower animals, all
remaining animals have respiration process.
l
Rate of breathing process increases at higher altitudes.
l
Transportation of oxygen is accomplished by haemoglobin.
EXERCISES
Very short answer type questions1.
What is the name of respiratory organ in fish and insect?
2.
Which steps are required for breathing process in human beings?
3.
Give details of aerobic respiration with example.
4.
Where does photosynthesis process occur?
RESPIRATION
215
5.
Trachea does not shrink even after losing air why?
6.
Which material is formed in the end of anaerobic respiration?
Short answer type questions 1.
Explain aerobic respiration.
2.
Write the difference between respiration and breathing.
3.
How does respiration take place by gills? Explain.
4.
How many steps are required for respiration process in human beings.
5.
Explain Inhalation or expiration or exhalation.
6.
Explain Anaerobic respiration.
Essay answer type questions 1.
Write the difference between Aerobic and Anaerobic Respiration.
2.
Describe the lungs in detail with the help of a diagram.
3.
Write the difference between Respiration and Breathing.
4.
Explain the respiration process in Grasshopper by tracheal respiration.
5.
Explain cutaneous respiration in the earth-worm.
6.
Explain the process of respiration in plants.
Project WorkPrepare a report based on collection of pictures of respiration in different organism.
216
SCIENCE 10
Chapter-15
CIRCULATION
Study of circulation and its associated parts is not the
out come of the recent times, but its knowledge has been
given in ancient books. Jaundice and diseases related to
heart and their treatment by sun therapy has been mentioned
in “Yajurveda Sanhita”, 19-81-93.
The mechanism of digestion of food, sleep, and dreams
along with the description of vessels of the heart has been
given in “Chandogya Upnishada”. Beside this, explaination
of heart and its associated vessels, the description of
organs of human being and comparison between man and
plants is given in “Brahamdarnaya Gopnishada”.
15.1 Circulation in higher organisms :
We will study :
15.1 Circulation in Higher
organisms.
15.2 Translocation
15.3 Translocation in
Plants.
(Water, salt and
nutrients)
15.4 Circulation in animals
15.5 Circulatory system in
Man.
Presence of the extracellular fluid in the body, transport
of nutrients, oxygen and water to each cell of the body and
the removal of the waste products from the body, is called
ciruclation.
Circulation, distribution and exchange of the useful and
waste products in the body of the animals is carried out by
special organs. All these organs together form the circulatory
system.
15.2 Translocation :
The mechanism of circulation; distribution of water and
soluble food material from one part to another part in plants
is called as Translocation. The mechanism of translocation
in plants takes place from downward to upward (from root
to leaves) and from upward to downward (from leaves to
roots).
15.3 Translocation in plants (Water, Salts and nutrients):
15.6 Blood Vessels
15.7 Structure and
functions of Blood
The translocation of water, salt and nutrients in plants
takes place on the basis of the following points.
1.
Direction of Translocation : The translocation of
nutrients and organic solutes takes place in the plants
in all direction.
(i)
Upward direction : The upward movement from roots
to different parts of the stem and into the leaves.
15.8 Blood clotting
15.9 Blood Groups
15.10 Blood Transfusion.
CIRCULATION
217
Example : during the germination of seeds, from the
leaves to the developing buds, flowers and fruits.
(ii)
(iii)
In radial direction : The food materials are
translocated radially from the cells of pith to cortex
and epidermis.
Downwardly : The food material synthesized in the
leaves are translocated downwardly to the stem and
to the root.
The translocation of food material in plants takes place
continuously from more concentrated organs to low
concentrated organs.
2.
Sugar
Leaf
Phloem
Stem
Xylem
Path of translocation : The xylem and phloem are
the main channels of the translocation.
The translocation of organic solutes in plants through
phloem, can be proved by the following experiments :
Phloem
Root
Use of food
Stuff in growth
Respiration
and in
photosynthesis
(i)
Girdling experiments : In this experiment the
Translocation Medanism
continuity of vascular tissues disturbed by their
removal, is called as the girdling experiment. In this
leaf
experiment girdling is employed for the removal of all
the tissues outer to vascular cambium- bark cortex
from the woody stem. In this condition the upper part
swollen tossne
of the plant is attached to the lower part by the pith
roots
and the central xylem cylinder. After some time it
Bask
results in the accumulation of food material from above
removed pait
the ring, which is evident by the swelling of the bark,
Stem
because the food material can not move down wardly
and as the food material can not be supplied to all the
parts below the girdle, the growth of the plant stops
and the new part can not develop at the removed part,
gradually the roots die. This is clear from the
Girdling Experiment
experiment, that it cuts the supply of organic
substances to the roots. The roots cannot synthesize
their own food material, therefore the roots die. As the roots die, the upper part of the
plants gradually dies. The upper part of the plants is dependent on roots for water and
mineral salts supply.
(ii)
The translocation of food materials upwardly :
The translocation of food material in the plants to upward direction takes place through
xylem. According to some scientists the translocation of food takes place through phloem.
(iii)
Translocation in radial direction :
Some of the mineral salts are transferred radially from xylem to the phloem through
parenchymatous cells. In plants the mineral salts are translocated by the phloem cells.
218
SCIENCE 10
The movement of ions in the phloem occurs both in upward and downward and radially
direction. By this process the mineral salts reach to the younger leaves and to the apical
regions of stem and root.
15.4 Circulation in Animals :
In higher grade of animals there is a distinct transport system for the circulation of food
material, which is of two types :
(i)
Open circulatory System : In this type of circulation the blood does not remain confined
to the blood vessels but flows freely in the open spaces of the body cavity and lacunae
sinuses and remains in direct contact with organs. The body cavity filled with blood is
called as the Haemocoel. Example : Leech, Prawn, Coackroach and other insects.
(ii)
Closed circulatory system : In such type of
circulation, the blood never comes in direct contact
with organs; while the blood flows in closed arteries
and veins. Example : fish, frog, lizards, snakes,
pigeon and man etc. Closed type of circulatory
system is found in all the vertebrate animals and some
developed inver tebrate animals. Example :
earthworms, closed circulatory system comprises
heart, blood vessels and blood. Single Circuit
Circulation is found in fishes, while double circuit
circulation is found in birds and mammals.
Advantages of closed
circulation
1. This type of circulation is
pigmented, so that transprt
of oxygen takes place
effectively.
2. Removes the excretory
products from the body
much rapidly.
15.5 Circulatory system in Man :
Two types of circulatory systems are present in man. 1. Blood vascular system, 2. Lymph
circulatory system.
1. Blood vascular system : Blood vascular system in man, like other animals comprises
heart, blood vessels and blood.
(a) Heart : (External structure ) : Heart
of man is muscular, conical and hollow. Heart in
man is situated in between the two lungs inside
the pericardial cavity in thoraic region. Around
this pericardial cavity a double walled pericardial
membrane is present. In between these two
membranes a fluid called pericardial fluid is
present. Heart is made of a red coloured
muscular wall. The muscular wall of the heart is
made of three layers- (i) outer layer Epicardium,
(ii) Middle layer Mesocardium and (iii) internal
layer Endocardium. Size of the heart is length
12.0 cm, width 9.0 cm and 6.0 cm thick and the
weight is 300 gm.
Internal structure : The human heart is
CIRCULATION
Precaval
vein
Aorta
Left Auricle
Right
auricle
Pulmonary
artery
Left
coronary
vein
Right
coronary
artery
Left
ventricle
Right
ventricle
Structructure of Heart
219
four chambered. Heart is divided into Right and Left
sides. The two halves are entirely separated by a
septum upper chambers of right sides called as right
auricle and the lower chamber is known as right
ventricle. Similarly the upper chamber of the left side is
the left auricle and the lower chamber is called as the
left ventricle. Right and left auricles are separated from
left ventricle by a muscular septum, called as the interauricular septum. Similarly right ventricle is separated
from left ventricles by a muscular septum called as
inter ventricular septum. Both the auricles of the
heart open into both the ventricles by an aperture of its
own side, these apertures are called as the left and
right auriculo- ventricular aperture. The left auricle
and ventricle are separated by a pair of flaps and right
auricle and ventricle are separated by three flaped
valves. These valves are called as Bicuspid and
Tricuspid valves respectively. These valves allow the
blood to flow from auricles into ventricles, but never
allow the blood to go back from ventricle into auricles.
These valves are held rigidly by cords the chordae
tendinae to the inner muscular walls of the ventricles.
Important points
1.
William Harvey (1628) was the
first who described the functions
of heart and blood circulation.
2.
Heart works like a pump.
3.
The capillaries were first
discovered by malpighii (1661).
4.
Maximum number of chambers
are found in cockroach heart.
Functions of pericardial cavity
fluid
1.
Keeps the heart moist.
2.
Protect the heart from friction.
3.
Protect the heart from external
shock.
4.
Does not inhibit the heart
beating.
Carotico - Systemic arch arises from the left ventricle, and after coming out from the
heart, it is divided into carotid and systemic artery; which supplies the blood to head and various
parts of trunk. Pulmonary artery arises from the right ventricle and immediately it divides into
two branches- Right and left pulmonary artries and supplies the blood to right and left lungs
respectively.
Anterior and Posterior Vena - Cava
opens into right auricle by separate
apertures and brings the impure blood from
various parts of the body. A membranous
valve- the eustachian valve is present from
posterior caval vein aperture upto the intra
auricular septum. Thabesian valve is present
on the aperture of anterior vena cava.
Precaval
vein
right
Left
pulmonary
vein
Pulmonary
semilunar
value
Left
pulmonary
vein
auricle
Pulmonary veins open by an aperture
Left auricle
in left auricle, no valve is present on this right
auriculo
aperture. This vein supplies the pure blood ventricular
valve
from lungs into left auricle. right and left posterior
Left auriculo
ventriculo valve
auricle supplies its blood into right and left vena
cava
Right
Left
ventricles respectively.
ventricle
ventricle
Fig. Mechanism of blood how in heart
SCIENCE 10
220
Working of Heart :
Working of heart depends on the contraction of its
muscular walls. The rhythmic contraction and relaxation of
the auricles and ventricles takes place continuously in the
heart. The action of contraction and relaxation is initiated
from the sinu-auriculr node, situated in the internal wall of
the right auricle. Firstly the action of contraction of heart
starts from the auricle. When both the auricles contract
simultaneously, their blood enters into right and left ventricles
through the respective auriculo-ventricular apertures. As
soon as the the auricles are filled by the blood, the wave of
contraction starts from the sinu-auricular node, and this
wave of contraction spreads in the entire auricles, hence
both the auricles contract together. After the completion of
auricular contraction, both the auricles come to their own
relaxed condition; as soon as the contraction is more, the
blood immediately enters into the veins.
important Points :
l Rhythmic contraction and
relaxation takes place in the
muscles of the heart.
l The heart of a man at rest
beats about 72 times per
minute. Beating rate in rats is
175 times per minute and an
Elephant 75 times per
minute.
l Contraction phase is called
as systole, and relaxation
phase as diastole.
l During 50 years period the
heart by beating 2 billion
times pumps one million 30
thousand ton blood.
As soon as the ventricles are filled with blood the ventricles contract much more rapidly
than auricles. Due to this contraction the pressure increases on the blood. Contraction of ventricle
starts by its contraction centre- auriculo-ventricular node, and the wave of contraction spreads
in the ventricular walls, both the ventricles contracts simultaneously. Due to contraction the
apertures between the auricle-ventricle closes. The deoxygenated blood from right ventricles
enters into the lungs by pulmonary artery. The oxygenated blood of the left ventricle is distributed
to whole of the body parts by caroffico-systemic artery. From all parts of the body the blood
comes back by the veins. After the completion of ventricular contraction, the contraction again
starts in the auricles. Blood from auricles passes into the ventricle. This cycle continues regularly.
15.6 Blood Vessels :
The blood vessels are the systems of channels in the body, through which the blood
flows. The blood vessels are of the following types :
(i)
Arteries : Those blood vessels which carry oxygenated blood away from the heart to
different parts of the body are known as arteries. These vessels are deeply seated in the
body. They have thick and highly elastic walls.
(ii)
Veins : Those blood vessels which return the deoxygenated blood to the heart from various
parts of the body. The veins are seated near the superficial layer of the body. The walls
are thin and collapsible.
CIRCULATION
221
(iii)
Capillaries : The arteries and veins after entering into different organs in the body, are
divided into fine branches. These thin fine branches are called as capillaries. The fair
branches of arteries are called as arterioles. The various capillaries formed from arterioles,
afterwards join together to form venules, venules joins to forms the veins.
Structure of Blood Vessels :
Three layers are present in the walls of the blood vessels.
(i)
Tunica externa/Adventia : it is the outermost layer. Cells are loosely arranged and elastic.
Collagen and elastic fibres are present in it.
(ii)
Tunica media : This
layer is made of
circular, unstriated or
smooth muscles fibres
and elastic connective
fibres.
(iii)
Tunica Externa
Tunica Media
Endo Phelium
Inter elastic
membrane
Tunica interna : It is
the innermost layer. It is
made up of flat endothelial cells. This is lined by elastic membrane.
Difference between arteries and veins
Artery
1. The walls of arteries are elastic
and thick
2. Lumen of the artery is narrow.
3. Carries of oxygenated blood
to the whole body.
4. Valves are absent in arteries.
5. No change in the volume of the artery.
6. The blood flows intermittently in arteries
with much pressure.
Vein
1.
The wall of the vein is thin and elastic
2.
3.
Lumen of the vein is wide.
Returns deoxygenated blood from all
the body parls to heart.
Valves are present in the veins.
Change in the volume of the veins.
The blood flows slowly, continuously
with less pressure.
4.
5.
6.
Functions : The blood is circulated by the blood vessels. Oxygenated blood is circulated
by the arteries, except the pulmonary artery which supplies deoxygenated blood. Deoxygenated
blood is transported by the veins, only pulmonary vein transport the oxygenated blood. The
nutrients oxygen, water and salts, CO2 are transported with the help of blood vessels.
15.7 Structure and functions of Blood :
Blood is the main circulating medium in the body of man. Blood is soft, fluid, connective
tissue. Blood is red, salty in taste and specific gravity is 1.05 to 1.06, and pH range from 7.3-7.5.
Blood has two main components.
(a) Blood plasma : it is 55% of the total volume of the blood. Its colour is light yellow and
slightly alkaline in nature. Plasma is composed of 91-92% water, 7% Proteins, 0.9% inorganic
222
SCIENCE 10
components, 0.1% glucose etc.
(b) Blood corpuscles : Their volume is
45% of the total blood volume. Blood corpuscles
are of the following types :
(i) Erythrocytes or red blood corpuscles
(RBC) : if contains heamoglobin pigment, due to
which the colour of the blood becomes red. It
transports oxygen and corbon-di-oxide. Nucleus
is absent in the human RBC.
(ii) Leucocytes or white blood
corpuscles : They are colourless, because
pigment is not present in them. Their life span is
of 12-13 days. Nucleus is found in the
corpuscles. These corpuscles are of two types :
Erythrocytes
of frog
Erythrocytes
of Man
Cosinophils
Neutrophils
Large
Lymphocyte
Monocylte
Basophils
Small
Lymphocytes
Platellete
Spindle cells
A. Granulocytes : Several granules are present in its cytoplasm. These are of three
types :
1. Neutrophils : These corpuscles destroy the micro-organisms. They are about 12µ-15µ
in size. Nucleus is divided into 2-6 lobes.
2. Basophils : Size is of 10µ-15µ. They protect from infection.
3. Eosinophils : Size is of 10µ-15µ. Lifespan is of 14 hours. They play a role in allergy
and immunity.
B. Agranulocytes : In the cytoplasm of these corpuscles granules are not present. These
are of two types :
1. Monocytes : Size is of 12µ-20µ diameter. Protects from the bacteria.
2. Lymphocytes : Nucleus is large and spherical; they produces antibodies.
(iii) Thrombocytes : their number ranges from 2-5 millions per cubic millimeter. Nucleus
absent. Diameter is 2 m-4m. They help in the clotting of blood .
Main functions of Blood :
l
Transport of food.
l Transport of oxygen and carbon-di-oxide.
l
Transport of waste products.
l Maintain the equillibrium or balance ot water.
l
Transport of heat.
l Maintain the body.
l
Regulation of Temperature.
l Control the blood loss by clotting
l
Maintains the chemical coordination.
l Healing of the wounds and destroyed tissues.
15.8 Clotting of Blood :
On account of any reason, when a man is injured, then the blood vessels and capillaries
of that place get ruptured, blood flows out from them, but after some time at the injured point the
CIRCULATION
223
blood changes into a jelly-like substance. Plasma is
separated, jelly like structure is known as clot and the
mechanism is called as the coagulation. This process
prevents the blood flow and protects the man.
At the injured place/point where blood flows, a
protein-named Lipoprotein or thromboplastein comes out
and liberates injured or ruptured thrombocyte phospholipids
which combines with Ca++ and plasma forms an enzyme
prothrombinase. Prothrombinase in the pressence of Ca++
ions changes the inactive prothrombin into active thrombin.
Thrombin changes or converts the soluble fibrinogen into
insoluble fibrin. As soon as the fibrin comes in contact
with external environment, its converts into thread like
network. In this fibrin network the corpuscles entangle and
blood flow stops and the blood at that place clot, it is called
as the blood clot.
Knowable Points :
l At the place of blood clot a
yellow coloured substance is
present which is called as
serum.
l Heparin substance is present
in the blood of blood vessels,
which keeps the blood in
soluble stage.
l At the injured place the blood
clots with in 2-5 minutes.
l The time of blood flow from
wound is of 1-3 minutes.
l The site of injury is 1-3
minutes.
15.9 Blood Groups :
On account of any reason, when there is a deficiency of blood in the body of man, then
man requires blood from outside. Sometime to remove the deficiency of blood, the blood of
another person is transfused, even then the man dies. In this respect Karl Landsteiner in 1900
made the discovery. it was known from the discovery of this scientist that two types of proteins
are present in the blood, due to which clumping of blood occur. On the outer membrane of red
blood corpuscles a protein named antigen is present. Another protein- antibody is present in the
blood plasma. On the membrane of red blood corpuscles in man two types of antigen- antigen
“A” and antigen “B” are present. To oppose this in the
blood plasma of man two types of antibodies- antibody
Knowable Points
“a” and antibody “b” are present.
l Do you know that the blood in the
Clumping of blood occurs when antigen “A” and
blood bank kept inside a bottle
antibody ‘a’ or antigen “B” and antibody ‘b’ are present
never clots?
together in red blood corpuscles. At the time of
l Why? the reason for it is a
agglutination the antigen A or B becomes sticky, and
chemical substance.
all the red blood corpuscles stick together and forms
a clump. This is due to the reaction of antigen and l Sodium and potassuim salts, and
oxalate or citrate is mixed into the
antibody. On the contrary when antigen “A” and
blood. This react with the calcium
antibody ‘b’ or antigen ‘B’ and antibody ‘a’ are present
of the blood and forms an insoluble
in the blood of any person, than no agglutination of
compound, inactivate the calcium
blood occur. On the basis of this Karl Landstemier
and never allows the blood to clot.
have shown four blood groups. The antigen and
By this process the blood is kept
antibodies found in different blood groups is shown in
in blood bank for blood transfusion.
the following tables.
224
SCIENCE 10
Blood
Groups
Antigen present
in Red Blood
Antibody present
in Plasma
% Percentage in
Indian man
corpuscles
A
A antigen
antibody b
23.5%
B
B antigen
antibody a
34.5%
AB
AB antigen
No antibody
7.5%
O
No antigen present
Presence of both
34.5%
antibodies a and b
l
Blood of group ‘A’ can be given to those persons, having blood of group ‘A’ and ‘AB’
l
Blood of group ‘B’ can be given to those persons, having blood of group B, AB.
l
Blood of group AB can be given to only persons having blood groups ‘AB’ only. The blood
serum/plasma of the person of blood group AB, does not show clumping with the corpuscles
of other blood groups, that is why the persons of this blood groups are called as universal
recipient.
l
Blood of Blood group O can be given to any other type of blood group of a person. So, a
person with blood group O is called as universal donor.
Possibility of Blood Transfusion of different blood groups.
Blood
Groups
O
A
B
AB
To which group
the blood can
be transfused
From which group
the blood can
be received
Remark
O
-
-
-
-
O, A, B, AB
only O
Donor
A
+
-
+
-
A, AB
O and A
-
B
+
+
-
-
B, AB
O and B
-
AB
+
+
+
-
AB
O, A, B, AB
Recipient
In 1948 two scientists Landsteiner and Weiner discovered the presence of an antigen in
american monkey- Macacus rhesus. If is called as antigen ‘D’. If is also called as Rh factor.
Such antigen if present in the blood of those persons, they are called as Rh-positive and those
person in the blood of whom this antigen ‘D’ is not present, they are called as Rh-negative.
Answer these questions.
1.
What harm occurs in human beings due to deficiency of thrombocytes.
2.
Which disease is found in human beings due to the deficiency of blood?
3.
What is the name of the disease which is caused when no clotting of blood takes
place at the place of injury?
4.
How many chambers are present in the heart of a frog?
CIRCULATION
225
15.10 Blood Transfusion :
Whenever there is a deficiency of blood in the body, blood is given to compensate it. This
process is called as blood transfusion. Blood is given to any person after comparing the blood.
Blood banks are present in hospitals too.
Points to remember :
l
Red blood corpuscles of man are the smallest in size.
l
The size of these corpuscles in man is 0.7µ-1.0µ in diameter and 1-2µ thick.
l
Red blood corpuscles are maximum in number.
l
The size of the red blood corpuscles in musk deer are smallest.
l
The life span of red blood corpuscles in man is of 90-120 days. In frog the life span
of these corpuscles is of 100 days.
l
The average number of red blood corpuscles in man is 5.4 to 5.5 million per cubic
millimeter and in females their number is 5 million per cubic millimeter.
l
In frogs, the red blood corpuscles are four lacs per cubic millimetre of blood.
l
Red blood corpuscles in all the mammals are non nucleated except the members of
the family of Llamas and camels. At the time of formation of red blood corpuscles.
nucleus is present, but as soon as the adult stage is attained the nucleus along with
cell organelles are lost.
l
The number of white blood corpuscles in man is 7,000 to 10,000 per cubicmilliliter of
blood. At the time of infection their number increases.
Blood Lymph :
Lymph is a colourless fluid. Red blood corpuscles are totally absent in this fluid, but the
number of white blood corpuscles is much more. In this fluid much quantity of soluble protein is
present. Oxygen and nutrients are present in less number.
Flow of Lymph :
In man the flow of lymph is only in one direction from organs towards heart. Valves are
found in the lymph vessels to prevent the backward flow, but to maintain the lymph flow towards
heart pressure is required. Lymph pressure- due to the wave movement produced by the
unstriped muscles found in the walls of lymph vessels, respiration process occur in the direction
of diaphragm and mu scles, and in the lymph vessels flow from nearest parts to distant parts
occur due to increase in pressure continuously.
Functions of Lymph :
1. If is helpful in the healing of wounds. 2. Lymph vessels helps in transportation of fats. 3.
Lymph corpuscles repair the tissues and destroy the bacteria. 4. Plasma protein comes to
blood through lymph. 5. Formation of Lymphocytes. 6. Engulfing the bacteria and protects the
body.
226
SCIENCE 10
Points to remember :
l
The transfer of nutrient solution in plants from one organ to another is called the
translocation.
l
In plants the translocation of nutrients and solutes takes place in three directiondownwardly, radially and upwardly.
l
For the translocation of nutrients and solutes munch hyprothesis is mostly accepted.
l
The translocation of organic substances in plants takes place through phloem. This
can be proved by girdling experiment.
l
The more concentrated part of the plant is the initiation end, and less concentrated
part is called as the consumption end.
l
Transport of various substances in the body is called circulation.
l
Circulatory system is of two types- (i) Open circulatory system, (ii) Closed circulatory
system.
l
Closed circulatory system was first discovered by scientist William Harvey.
l
Closed circulatory system is that system in which blood always flows in closed
vessels.
l
In mammals and man heart is divided into four chambers, in which two auricles and
two ventricles are present.
l
In man the double blood circulation is present- (i) Systemic circulation and (ii)
Pulmonary circulation.
l
Oxygenated blood is known as pure while the deoxygenated blood is known as
impure.
l
In mammals the red blood corpuscles are non-nucleated, and their life span is of
120 days.
l
The wall of artery is thick and valves are absent in them. Arteries circulate the blood
from heart to various parts of the body.
l
The wall of the vein is thin and valves are present in them. The veins circulate the
blood from various parts of the body towards the heart.
l
Auricle is that chamber of the heart, in which blood enters.
l
The wave of contraction of heart beat is iniated from sinu-auricular node situated in
the wall of right auricle.
l
Due to contraction of heart the pressure exerts on the walls of arteries is called as
the blood pressure.
l
Blood is red, alkaline, opaque fluid connective tissue.
l
If the blood clot is not formed at the point of injury, the disease is called as the
haemophilia.
l
Heart beat per minute in larger animals is less and it is much more in small sized
animals. Elephant heart beats 25 times one minute. In a healthy person the heart
beats 72 times per minute.
l
Lymph is a clear fluid, which flows in lymph vessels.
CIRCULATION
227
EXERCISES
Very short answer type questions.
1.
How are the nutrient in solvent state translocated?
2.
Give the importance of phloem in the translocation of food material.
3.
Which hypothesis is universally accepted for the translocation of food substances and
solutes?
4.
How many chambers are found in the heart of man?
5.
Where is the bicuspid valve found?
Short answer type questions.
1.
What do you mean by the translocation of food substances in plants?
2.
By which tissue the translocation of food material and solutes takes place in plant? Explain
your answer with the help of an experiment.
3.
Describe the method of blood transfusion in man.
4.
Describe the functions of blood.
5.
What do you mean by closed circulatory system?
6.
Describe the functions of pericardial cavity fluid.
7.
Describe the functions of lymph.
8.
Explain the difference between arteries and veins.
9.
How does circulation take place in unicellular organisms?
Essay answer Type questions.
1.
Describe the Munch hypothesis for the translocations of food material and solutes.
2.
Describe in how many directions the translocation of food material takes place in plants.
3.
Explain the translocation of organic solutes by girdling experiment.
4.
Describe with diagram the process of translocation in plants.
5.
Describe the structure of human heart.
6.
Describe the working of human heart.
7.
Describe the structure and functions of blood.
8.
Describe the blood groups.
9.
Describe the mechanism of blood clotting.
10.
Describe the blood transfusion.
228
SCIENCE 10
Chapter - 16
EXCRETION AND OSMOREGULATION
16.1 Excretion -
We learn 16.1 Excretion
16.2 Excretion in
Animals
l Amoeba
l Earth-worm
16.3 Excretion in human
16.4 Osmoregulation
In every living organism there are some constant
metabolic activities which take place due to which energy and
other products are formed. These are called metabolites. Out
of these, some useful and required material are absorbed by
the tissues or cell of body while remaining material are waste
for body. If these waste products are stored for a long time in a
body then they convert into toxic material, which may cause
death. These harmful or waste products must be eliminated
out of the body. The process of removal of metabolic waste is
called as excretion.
The organs by which metabolic waste products or
excretory products are eliminated out of the body are called
excretory organ.
Excretory productsFollowing excretory products are found in the different
animals(A) Digestive waste Products- Excess quantity of undigested
food is harmful for the body which is excreted in the form
of faeces.
(B) Respiratory
waste
products- By respiration
process, Foul CO 2 is
eliminated directly into the
environment through the
general body surface but in
higher animals it is eliminated
through the lungs.
(C) Nitrogenous
waste
products- Nitrogenous
waste products are formed
in the different animals by
different process which are
given below-
EXCRETION AND OSMOREGULATION
Significance of Excretion
l Removal of excretory
substances formed from
metabolic activities,
outside the body.
l Maintenance of the
concentraion
of
excretory substances in
the body.
l To
maintain
the
structure, pH and
osmotic pressure of the
body fluids.
l To
maintain
homeostasis.
the
229
Table : 1 Nitrogenous Waste Products
Products
Property
Example
Category of
organism
1. Ammonia Colourless, easily soluble
Protozoan, Spongy
in water, toxic for animals.
Hydra, Taenia, solium
It is present in very less
Polyinsects, Annelides,
quantity in blood.
Prawn, Pila, Octopus,
Ammonotelic
Boney fishes, Frog.
2. Urea
Colourless, Insoluble- in
Ascaris, Earth-worm,
water, less toxic comparatively
Unio, Elasmo brankal
Ureotelic
to ammonia. Urea is excreted in fishes, Frog, Alligators,
the form of urine. It requires less Turtles, Mammals
amount of water for excretion.
Urea is formed in the liver.
Ammonia mix with CO2 and
synthesise the Urea.
3. Uric Acid Colourless, Insoluble in water,
1. Cock-roach,
so that, less quantity of water
mostly Insects.
is required for excretion, It is
2. Lizard, Reptiles,
secreted in solid form or
Pigeon, Duck, Hen,
paste form.
and all Aves.
Uricotelic
Besides above Nitrogenous substance, other nitrogenous waste products are
as follows (i)
Amino Acid : Soluble in water, less toxic, it is excreted by Pila and Unio.
(ii)
Guanine : This nitrogenous waste product is excreted by Spider and Earth-worm.
(iii)
Pyrimidine : Insect, Birds, Fishes, Amphibians, Mammals.
(iv)
Cretine and Creatinine : This is excreted from body with nitrogenous waste products.
16.2 Excretion in Animals :
Excretion process is different in different animals, In the same way excretory organs are
also different in different animals.
230
SCIENCE 10
(i)
(ii)
Amoeba : Amoeba is a unicellular organism, found in
surface of pure aqueous medium near by dead or
decaying material. Generally amoeba does not have
excretion process. They mostly eliminate nitrogenous
waste product like ammonia and carbondioxide is
excreted by diffusion method. According to few
scientists, some excretion work is done by contractile
vacuoles. Due to this reason work of excretion is done
by general body surface in Amoeba.
Fig. 16.1
Earth worm - In earth-worms, ammonia and urea is excreted from body in the form of
excretory product. Nephridia are the main excretory organs in earth-worm. Nephridia are
delicate small, coiled ectodermal structure which are found in all body parts (except only
anterior first four and posterior last ten segment of body).
According to the structure and their work, three types of Nephridia are found (i) Septal Nephridia
(ii) Integumentary nephridia (iii) Pharyngeal nephridia.
Structure of NephridiaA typical septal nephridium of earthworm consists of three main parts:(A)
Nephrostome- It is funnel like
ciliated structure. which opens into
the coelomic cavity. Nephrostome is
provided with a mouth with an upper
and lower lip on the respective sides.
(B)
Neck - It is the main congested
Upper lip
Twisted
lobe
Distal limb
Proximal limb
Lower lip
Central canal
Straight
lobe
tubular part of nephridia which
consists of coelomic cavity.
(C)
Body of the nephridium- It does
Nephrostome
Neck
not contain cilia. It opens to the
exterior by Nephridiophore.
Fig. 16.2 Structure of Nephridia of Earth worm
Outer surface of Nephridia has a network of blood capillaries. Excreted material is collected
by ciliated wall as glandular cell. These material is discharged by the Nephridiophore.
16.3 Excretion in humanProcess of excretion is done by a special organ called “kidney” in human. In man, two
kidneys, two ureters, one urinary bladder and one urethra are found.
1. Kidney- Kidney is bean shaped,
EXCRETION AND OSMOREGULATION
231
reddish-brown in colour which are located in the
abdominal cavity on either side of the vertebral
colums just beneath the diaphragm. Each kidney
is surrounded by peritoneum membrane. Kidney
is attached to the dorsal abdominal wall by
peritoneum membrane.
Adrenal gland
Kidney
Cortex
Medulla
Pelvis
Kidney is about 10 cm long, 5 cm. wide
and 3 cm. thick in man. In an adult the,
approximate weight of a kidney is about 120170 gm. Both the kidney are not situated in the
same position. In human beings the right kidney
is situated a little below the left kidney. There is
difference of 0.4 inch in both the kidneys. The
outer margin of kidney is convex and the inner
is concave. Concave margin possesses a notch
called Hilum.
Posterior venacava
Ureter
Urinary bladder
Fig. 16.3 Exeretory system of human
Ureter and renal veins come out of kidney and the renal artery enters through Hilum.
Internal part of the kidney is divided into two parts :- Outer part is called cortex and other
internal part is Medulla. The expanded opening of the ureter is formed by a pressed funnel like
cavity. Which is protuded towards the hileum, It is known as Renal Pelvis. Medulla contain
conical pyramids which contain the collecting and discharging tubules of nephron. Nephron is
the structural and functional unit of kidney. Half portion of nephron is situated in the cortex and
other half is in the medulla.
Afferent
arteriole
Structure of Nephron-
Efferent
arteiole
Glomerulus
Bowman capsule
Nephron consists of two parts(A)
end of the nephron comprises a cup-
Malpighian
Tubule
Distal
convoluted
tubule
Proximal
convolated
tubules
Bowman’s Capsule - The closed
}
shaped structure called Bowman’s
capsule, which contains a bunch of
Collecting duct
glomerulus. It is situated in the
cortex region of kidney.
(B)
Secretory tubular part - It is the
coiled posterior part of bowmans
capsule. It has three parts -
Loop of Henle
blood capillaries, are known as
Descending limb
}
Ascending limb
Vasa recta
Fig. 16.4 One Nephron
232
SCIENCE 10
1.
Proximal convoluted tubule.
2.
“U” shape of Henle’s loop situated in the medulla.
3.
Distal convoluted tubule opens in a collecting tubule of kidney.
Ureter : From each kidney arises a thin, muscular tube called ureter. It is about 25 to 30
cm. in length. They are running backward along with the wall of abdominal cavity to open into the
urinary bladder.
Urinary bladder :- In each human being thre is a small single sac like structure which is
situated in a posterior part of abdominal cavity. According to the quantity of urine, it changes it’s
shape and position. Its wall is made of non linear muscles. Ureter carries urine or other excretory
products from the kidney to the urinary bladder.
Answer these questions1.
Write the names of the excretory organs of human body other than the kidney.
2.
Write the names of excretory organs of the earthworm?
3.
In which organ of a frog does the process of osmosis take place?
Process of Urine formationThe formation of urea takes place in the liver of human beings and from the blood it enters
the efferent artery which forms a network of arterial capillaries over.the uriniferous tubules or
nephron. Urine formation is a complicated process, which take place in three steps:1.
Ultrafiltration.
2.
Reabsorption
3.
Secretion
1.
Knowing facts
l In mostly human, Henle loops of
nephron in kidney contain small
Ultrafiltration :- This process takes place in
“U” or “V” shape like structure.
Bowman’s capsule of kidney. Filtration is the first l In human beings living in
step of urine formation in which urine is filtered by
deserts, length of Henle loop is
the semipermeable walls of glomerulus and
more, which extends to the
Bowman’s capsule. The blood flows very fast from
pelvis.
afferent arteioles into glomerulus. Therefore the l Some blood capillaries of the
blood pressure of blood capillaries of glomerulus
kidneys come with the Henle
increases, this pressure is about 70 mm Hg. In
loops to the pelvis cavity
glomerulus the hydrostatic pressure of blood is 70
become “U” shaped. These
blood capillaries are called
mm Hg, opposite pressure is 50 mm Hg. Therefore
“Vasa recta”.
effective filtration pressure of glomerulus is 70-50
= 20 mm Hg. Due to this, blood containing urea, l Blood contains some materials
uric acid, glucose, salt and other materials are
like urea, sugar and menitol etc.
which increase the amount of
filtered and come into the Bowman’s capsule. Rate
urine. These are known as
of filtration in a normal adult is about 125 ml per
Diuretic material.
minute. About 1.5 litres of urine is passed out daily.
EXCRETION AND OSMOREGULATION
233
2.
Reabsorption : Blood contains many useful items like glucose, water, salt etc. come
along with the other excretory products which are filtered by glomerulus into the Bowman’s
capsule. If these useful materials, which are eliminated out from the body in the form of
urine then dehydration will occur and may cause death. So these useful materials are
surrounded by the blood capillaries. These useful materials are reabsorbed by the epithilial
cells of nephron and thrown into the blood cells. In addition absorption of water also takes
place. With this the remaining fluid in the nephron becomes thick or dense which is called
urine. This urine comes from collecting tubes to the pelvis and again come out from the
urinary bladder through the urethra. According to the necessity, urine discharges from the
body through urinary bladder.
Some Important Notes
l
Expelling of faeces is not strictly considered excretion as it is not a metabolic waste.
l
In excretion process, uric acid is thrown out from the body in human.
l
Frogs discharge water, equal to the weight of their body in 24 hours.
l
The pale colour of urine is due to the presence of a pigment “Urochrome” formed
from dead R.B.Cs in liver cells.
l
If the amount of O2 is less in human beings then in this condition kidneys play an
important role in the formation of R.B.Cs.
l
Earthworm is a ammonotelic animal but due to the deficiency of water, it become
uriotelic.
l
In the urine of human beings, concentration of urea may be more than 100 time to the
blood concentration.
Functions of kidney1.
It excretes harmful and other toxic substance from the body.
2.
It controls blood pressure.
3.
It maintains the amount of minerals salts in the blood.
4.
It maintains the amount of water in the body.
5.
It controls the hydrogen ion concentration (pH) of the body.
16.4 Osmoregulation Osmoregulation word was first discovered by the scientist “Hober”. The process by which
living organism maintain a particular condition for making the transportation and concentration
of water in internal environment called osmoregulation. Or osmoregulation is that process by
which living organisms regulate the amount of water in their proto-plasm and also maintain
optimum osmotic pressure and salt concentration in their body fluid.
234
SCIENCE 10
In a human body working of
osmoregulation is done by kidney. All higher
category vertebrate or invertebrate animals, the
osmotic pressure is also regulated by excretory
organ present in their body. Amount of water may
be lower or higher in the body, both conditions
are harmful for the organism, due to this, kidney
or other organs maintain the amount of water. In
human body, water transportation is in the form
of blood transportation, water in blood comes
from the absorption of food. Regulation of amount
of water, present in the blood, is maintain by the
nephrons present in kidney.
When higher amount of water is present
in the human or other animals, then this high
amount of water from blood is excreted through
the nephron. In this condition urine become
hypotonic. When opposite, excessive loss of
water from the human body or other animals
takes place. In this condition, urine becomes
hypertonic, which helps in maintaining the
osmotic concentration of blood.
Knowing Facts
l Plasma membrane is a semipermeable
membrane.
l Both side of plasma membrane, the
transportation is of the solvent molecule
being only, due to this reason it is called
selective permeable membrane.
l Two solutions, which differ in
concentration are separated by
semipermeable membrane then
transportation of solvent molecule is
carried from lower concentration to the
higher concentration. This method is
known as osmosis.
l A pressure may be involved in a osmatic
process is called osmotic pressure.
l Due to the osmotic pressure, amount of
water is balanced in the protoplasm of
living body.
Concentration of urea depend upon the length of Henle loop. When Henle loop become
long, then hypertonic urine must be excreted by animals or living things.
Osmoregulation of quantity of Urine through kidneyIt is maintain by the Henle loop, present in the kidney.
Answer these questions1.
Which adaptation occur in fresh water fishes for osmoregulation?
2.
Write the name of part, which collects the water in camels.
3.
What is the work of contractile vacuoles in Amoeba?
Points to Rememberl
Nitrogenous waste product is excreted in the excretion process.
l
Formation of urea takes place in the liver and formation of urine takes place in the
kidney.
l
Removal of faecal matter is not associated with excretion.
EXCRETION AND OSMOREGULATION
235
l
On the basis of nitrogenous product, animals have been classfied into three
categories- Ammanotelic (Ammonia), Ureotelic (Urea), Uricotelic (Uric acid).
l
Animals having less amount of water excrete uric acid.
l
Excretion of ammonia is generally found in the aquatic animals.
l
A healthy man contains water- approximately 95%, Urea-2%, salt-2%, Uric acid0.4% and other also present in 0.4% like inorganic matter and ammonia in normal
condition.
l
Urine formation take place in three steps they are- Ultrafiltration, Reabsorption and
secretion.
l
A healthy human excretes 1 to 1.8 litres urine in a day in normal condition.
l
A healthy person produces 180 litres or 45 gallans of glomerular filtrate in normal
condition.
l
The pale colour of urine depends upon the quantity of Urochrome.
l
Formation of excess urine and its discharging is called Diuresis.
l
Osmoregulation is maintained by the kidney.
l
Two fluids flow with each other in opposite direction in different tubules into the counter
current system.
l
Excretion of hypotonic urine from the kidney is due to the excessiveness of water in
body.
l
Excretion of hypertonic urine is due to the deficiency of water in body and absorption
of water.
l
The process by which organism maintain the transportation or regulation of water
with a particular condition in internal environment is called osmoregulation.
EXERCISES
Very short answer type questions1.
What is the process of excretion of waste products from body called?
2.
Which scientist had discovered the water balance?
3.
What is the weight of the kidney in a normal person?
4.
What is the difference between excretion an egestion?
236
SCIENCE 10
5.
Where does ultrafiltration process take place?
6.
Which steps are required for completing urine formation?
7.
Where does urea formation take place in the body?
Short answer type questions1.
Write any four functions of kidneys.
2.
Give the amount of substances present in normal urine.
3.
Why is the colour of urine yellow?
4.
What are the reasons of Haemodialysis?
5.
Describe Utrafiltration process.
6.
Describe the structure of nephron.
7.
Draw a labelled diagram of excretory system.
Eassy answer type questions1.
What is excretion? Explain the excretion process in human beings.
2.
Describe the structure and function of kidney in human beings.
3.
Explain the role of kidney in excretion process.
4.
Where does urine formation take place? Explain the process of ultrafiltration and
reabsorption in nephron.
5.
Explain uriotelic, uricottelic and ammonotelic animals with example.
6.
What is the Osmoregulation? Explain Osmoregulation process by kidney.
7.
Describe the process of Haemodialysis.
EXCRETION AND OSMOREGULATION
237
Chapter -17
CONTROL AND COORDINATION
17.1 Control and Coordination :
Behaviour of the living beings depends on all the
biological activities of the body. The organisation of body of
multicellular organisms is much more complicated. In the
body of living beings, the development of tissues, organs,
organs systems, the metabolic activities of the body have
increased much. Nervous system and Hormonal Systems
are present to maintain the integrity of the body of
multicellular organisms. These two systems maintain the
coordination between external and internal environments.
Nervous system is found only in animals, hormonal
or endoecrine system is found both in animals and plants
and these systems control and coordinate, slow moving long
lasting biological activities. While in animals the nervous
system controls and coordinate the biological activities with
high speed.
17.2 Coordination in Plants and Animals :
(a) Nervous control and coordination in animals :
We will study :
17.1 Control and
coordination.
17.2 Coordination in plants
and animals.
17.3 Nervous System in
man.
17.4 Reflex action.
17.5 Hormonal
Coordination and
Control.
In the multicellular organisms the various activities of
the body are controlled and regulated by a specific system,
called as Nervous system. In nervous system the signals
are generated in the form of nerve impulses, which are
associated with the fast responses to environmental stimuli.
The impulses received from external environment, stimulate
the neuron to maintain the coordination and regulation in
various parts of the body. In internal environment neurons
maintain the coordination in various organs of the body of
living beings. In this way the coordination and regulation is
maintained in the extermal environment, internal
environment, equillibrium and sense organs of the body of
man and other animals.
Nervous System :
“In animals, along with understanding, thinking and
remembering any substance, a system maintaining the
coordination and regulation in the functioning of various
organs is present–The Nervous system.”
238
SCIENCE 10
In man and animals, the nervous system is
formed by specific types of cells, these cells are called
as neurons. Each neuron cell consists of nerve cells
and nerve fibres. Nerve fibres are of two types– Axon
and Dendrons. Axon is single, long and it is a process
of similar thickness. Axon carries the information from
cyton to other neurons, muscles and glands.
Dendrite : They come out from cyton in large
numbers. Their basal parts are thick and gradually
becomes fine and thin. Dendrites carry information
from sensory parts or other neuron cells to nerve cells.
The cytoplasm of the cyton is granular. A large
nucleuas, large number of mitochondria and Nissles
granules are present in the cyton.
Functions of Nervous System :
l
l
l
l
l
Regulate and control all the
activities of the body.
The sensory organs of this
system receives all the activities
occuring in the external
environment.
Protect the body by reflex
action.
Maintain coordination in all the
tissues and organs of the body.
Controls
the
intemal
environment.
17.3 Nervous system of Man :
Nervous system of man and other vertebrate
animals is divided into three parts. (i) Central Nevous
System, (ii) Peripheral Nervous System, (iii)
Autonomic Nervous system.
(i) Central Nervous System : That main part of
the nervous system which controls the whole bodyorgans, systems and autonomic nervous system. This
includes two parts- Brain and spinal cord.
15.4 (A) Brain :
Brain of man remain well protected in skull. The
total weight of human brain is 1400 gram or 3-pounds.
It is the main central point of nervous system, by which
various biological activities of the human body are
controlled. The three membranes made of connective
tissues are present around brain, and they are called
as meninges. A fluid is present in a space in between
these membranes, it is called as cerebro – spinal fluid.
Structure of Brain :
For the convenience of study brain is divided into three parts :(i) Fore Brain (ii) Mid Brain (iii) Hind Brain.
(i) Fore Brain : It is the front or anterior part of the brain, it consists of cerebrum and
Hypothalamus.
(a) Cerebrum : This part of the brain of man is highly developed. It is 2/3 part of the entire
brain. On the outer surface of cerebrum folds and furrows of gyri and sulei are present. Both the
CONTROL AND COORDINATION
239
hemispheres are joined together by a transverse
band called as corpus callosum. Cerebrum is
divided into four lobes. The outer layers of the
cerebral lobes is called as cortex. If is made of the
grey matter. Its internal surface is made up of white
matter. Those animals and man in which the
cerebrum is large and as much as the gyri and sulci
are present, he is considered to be more intelligent.
At the anterior end of cerebral lobes, two lobesthe offactory lobes are present.
(b) Hypothalamus : It is the ventral and
lateral part of cerebral hemisphere called as
Hypothalamus, and it is the organisational centre
of the nervous system : Below the cerebral
hemisphere a small part diancephalon is situated
which is covered by a funnel shaped structure, to
which an endocrine gland- the pituitary gland remain
attached.
(ii) Mid Brain : This part connects the fore
brain with the hind brain. It is made up of two parts
corpora quadrigemina and cerebral fibres. Corpora
quadrigemina is in the form of two pairs of round,
solid structures. Both these round part act as centre
for auditory and visual reflexes.
Functions of cerebro-spinal
fluid
l If protects the brain from
mechanical shocks.
l If maintains the pressure in
nerv vessels.
l If exchange the excretory
products and nutrients.
Hemisphere
Cerebrum
(iii) Hind Brain : It consists of cerebellum,
pons verolli and Medulla oblongata.
(a) Cerebellum : It is the solid and hinder
part of the brain. This maintain the body balance
and organ. It is divided into three lobes, its middle
part is called as vermix and on each side of it two
lateral lobes are present. Pons is situated infront of
the cerebellum and it connects cerebellum and
medulla oblongata.
Cerebellum
(b) Medulla oblongata : It is the
posterior most part of the brain, and
extends posteriorly making spinal cord.
cavities are present in it.
(c) Pons verolli : It is a band like
structure made of nerve fibres; which
carries the impulses from one part to
another part of the cerebellum.
240
SCIENCE 10
Mid brain, diancephalon, Pons Verolli and medulla oblongata forms an axial part, called as
the Brain stem.
Cavities of Brain : The Brain of human being is a hollow structure, a cavity is present in
it. Two cavities are present in cerebral hemisphere, which are called as first or second cavities
or lateral ventricles. The cavity of diancephalon is called as the third ventricle, and the cavity of
the medulla oblongata is called as fourth cavity/ventricle. A cerebro spinal fluid is filled in these
cavities.
Functions of Brain :
1.
Olfactory lobes act as organ of smell.
2.
cerebrum is the centre of feelings, emotions, intelligence, memory, reasons and will.
3.
It is the seat of consciousness and control weeping and laughing in man.
4.
It is the centre of various sensations- visual and auditory.
5.
It stimulate the behaviour for cold, heat, touch and light etc.
6.
Cerebrum directly or indirectly controls all the activities of the body.
7.
It controls the involuntary action of nervous system and also hunger, thirst, heat sleep,
faligue, hatred, sexual activities.
8.
Mid brain- this part controls the vision, hearing and reflex activities.
9.
Controls voluntary movements.
10.
Regulation of swallowing, vomiting etc. activities.
11.
Control the heart beating, respiratory rate and peristaltic movements of the Alementary
canal.
B. Spinal Cord :
it is situated inside the neural canal of the vertebral column extending from the first
vertebrae to the sixth lumber vertebrae. Similar to brain it is also surrounded by three layers of
connective tissue. In spinal cord the white matter is present out wardly and grey matter inwardly.
In between these three layers cerebro spinal fluid is present. This protects the spinal cord from
external shocks.
Internal structure of spinal cord :
In the centre of the spinal cord central canal
is present, surrounded by a central core of grey
matter. In cross section of the spinal cord, grey
matter resemble the letter ‘H’ on the dorsal side
the grey matter forms dorsal horn, similarly the grey
matter in thorasic and lumber region forms the
lateral horns. Around the grey matter, white matter
is present. On the dorsal side of the spinal cord is
CONTROL AND COORDINATION
Dorsal
241
dorsal fissure and on the ventral side ventral fissure is present. Similar to ventricles of brain in
the central canal of the spinal cord cerebro-spinal fluid is present. From the dorsal horn of spinal
cord arises fine sensory fibres, and from ventral horn arises finest motor fibres; the swelling of
these fibres at the point of origin is called as dorsal and ventral roots.
31 pairs of spinal nerves arise from the spinal cord. Each spinal nerve is attached to the
spinal cord by two roots. The sensory fibres enter the spinal cord by way of dorsal root, while
motor fibre emerge out from ventral root.
Functions of spinal cord
1.
It transmits the impulses or stimulli coming from the brain.
2.
Coordinate and regulate the reflex action.
17.4 Reflex action :
In the body of the animals or human beings,
those involuntary actions, which occur due to any
impulse or stimulus or due to any reaction is called
as the reflex action. In the beginning the reflex action
is the function done by the nervous system. It is
important for protective behaviour : such as- Blinking
of eyes in the presence of sharp light, removal of hand
or legs due to pricking of sharp pointed objected.
Mechanism of Reflex action :
Importance of Relfex action
l
On account of reflex action the
body of the animals is
protected.
l
It is controlled by spinal cord, it
takes less time and there is
safety from any accident.
l
Protects from external shocks
and accidents.
Reflex action is conducted by the spinal cord.
Nervous elements which conducts the reflex action,
forms the arc, which is known as the reflex arc.
In a reflex action any sensation, or impulse, or environmental effect reaches the spinal
cord through sensory nerves. This sensation or impulse enters into spinal cord through dorsal
root by the sensory fibres. Axon
of the cyton carries the impulse or
sensation to grey matter of spinal
cord. Impulse or sensation from the
grey matter reaches the motor
nerve. Motor nerve after emerging
from the ventral root of the spinal
cord reaches the muscles and
divide there. Muscles function
according to impulse or stimulus.
Reflex arc constitute the functional
unit of the central nervous system.
Reflex Action Mechanism
242
SCIENCE 10
Answer these questions.
1.
Which system protects the body and regulates the functions of all the organs.
2.
Give the functions of cerebro spinal fluid.
3.
How many pairs of nerves emerge from spinal cord.
4.
Explain the reflex action with the help of diagram.
Knowable important points :
l
On the outer surface of brain and spinal cord, a three layered covering is
present. It is called as Menings.
l
The total weight of brain in a human being is 1400 gram.
l
The cerebral hemispheres of man are highly developed. Controlling centre for
heat, cold, brain, touch, pressure, vision, taste, and smell, speech action are
present on cerebral hemisphere.
l
In human being 12 pairs of cranial nerves and 31 pairs of spinal nerves are
present.
l
Heart beating is controlled by medulla oblongata.
l
In man and woman the weight of brain is 50 & 45 ounce.
l
Nervous system is absent in plants.
17.5 Hormonal Coordination and control :
Hormones are such specific chemical substances which are secreted by specific parts
or cells after secreting into blood influence the activity of the various organs of the body, and
control and coordinate the various activities of the body.
Hormones are found in both plants and animals.
(I) Hormonal control and coordination in plants :
In plants specific types of chemical substances are found which controls or regulate the
growth and differentiations in plants.
(i)
Gibberllins : This hormone is found in all types of plants. This hormone is secreted from
germinating embryos and apical parts of stem.
Functions : By the use of this hormone in plant following functions are performed by it.
(a) Seeds initiate germination immediately (b) growth and elongation of dwarf plants. (c)
Use of this in some plants, leaf/leaves become broad. Pea, bean, tomato etc.
(ii)
Auxin : This hormone is commonly found in plants. This hormone is secreted from apical
buds, stem apex and embryo of the seed.
CONTROL AND COORDINATION
243
Function :
1.
If is important for cell division and cell elongation.
2.
By the use of this roots in plant cutting develops speedily.
3.
Some auxins inhibit the plant growth.
4.
Elongation of dormancy period.
(iii) Cytokinin : This hormone along with auxin regulates and control the cell division and cell
differentiation. This hormone is secreted from the actively dividing tissues of the plants.
Functions :
1.
If along with auxin induces the cell division in plants.
2.
This hormone breaks the dormancy of many seeds and also promote their germination.
3.
This hormone helps in the development of some parts of the plants and cell differentiation
in plants.
(iv) Absissic Acid : It is growth inhibiting hormone and inhibits the growth of plants.
Functions :
1.
This inhibits the growth of buds and germination of seeds in plants.
2.
It causes closure of stomatal openings of leaves and inhibit the transpiration.
3.
This hormone helps in the dormancy
and germination of seeds.
(II)
Hormonal Coordination and control
in Animals :
Hormones in animals are secreted by
the special glands found in the body.
These secrete various types of
(chemical substances) hormones, by
which they control the various
activities of the body. Generally after
being secreted from glands hormones
mix in the blood.
Properties of hormones :
1.
Hormone is soluble in water and blood.
2.
Hormones are active and act in very less concentration.
3.
They function similar to organic catalysts.
4.
They are not specific to any species or animal.
5.
They effect or influence the activity of organs of the body.
244
SCIENCE 10
6.
They remain stored in the body. They are secreted regularly and continuously. They are
disintegrated after the completion of the function and are eliminated out from the body.
7.
The activity of hormones remains continuous in the farget cells.
Hormones secreted from various glands and their effects :
1.
Pituitary gland : It is also called as master gland, many hormones are secreted from it.
Main hormones are as follows :-
(i) Growth hormone : It controls the growth of the somatic cells. It also influences the
protein, carbohydrate and fat metabolism.
(ii) Thyriod stimulating hormone : 1. Control the growth of Thyroid gland. 2. Regulate
the production of thyroxin hormone.
(iii) Vasopressin or antidiuretic hormone : It regulate the reabsorption of water from
uriniferous tubales of kidney. It increases the blood pressure.
(2) Thyroid gland :
(i) Thyroxine : 1. It controls or regulates the metabolic rate of protein, carbohydrate and
fats in the body.
2. Regulate the heat production. 3. It effects the metamorphosis in the larva of frog.
(ii) Thyrocalcitomin : It regulates the quantity of calcium in the blood.
(3) Parathyroid gland : Paratharmone :
1. Mainly parathormone regulates the quantity of calcium in the blood.
2. Regulates the phosphate metabohsim.
3. It increases the calcium level in the plasma & reduces the phosphorus level.
(4) Thymus gland :
(i) Thymosin : It controls the immune system of the body.
(5) Penial gland :
Melatonin : It controls the sexual maturity.
(6) Pancreas : (Islets of Langerhans)
(i) Insulin
1. It converts glucose into glycogen in blood. Regulates the quantity of sugar in blood.
2. It reduces protein metabolic activity in the body.
(ii) Glucagon : It converting the blood sugar level (glycogen) into glucose and regulate it.
(7) Adrenal :
(a) Cortex : (i) Aldosterone :
1. Control sodium (Na++), Potassium (K+) and water balance or equillibrium.
CONTROL AND COORDINATION
245
(ii) Glucocorticoids :
1. It maintains the glucose level in the blood.
2. It controls the carbohydrate, fat and protein metabolism.
3. Controls the sexual behaviour.
(b) Medulla : (i) Adrenalin :
1. Controls heart beating rate and blood pressure.
2. Controls the carbohydrate metabolism.
3. Produces relaxation in skeletal muscles and contraction in skin and abdominal internal
organs.
(ii) Nor-adrenalin :
1. Controls the common blood circulation.
2. Reduces the heart beating rate.
(8) Gonads :
(i) Androgen hormone
1. It controls the sprematogenesis process in the testls.
2. Controls the secondary sexual characters in male/man.
(ii) Progesterone and Estrogen :
Both these hormones are formed in ovary and control the reproduction ability, menstruaation
cycle and secondary sexual characters in girls.
Answer theses questions.
1.
What is the name of the master gland? Why it is called as mastergland?
2.
Name that hormone, which is responsible for water reabsorption in uriniferous
tubule/nephron?
3.
Write two properties of hormones.
4.
Name the hormone which affects the size and number of red blood corpuscles
and from which organ it is secreted.
5.
Name the hormone secreted from the adrenal gland.
6.
The study of endocrine glands and hormone is called as endocrinology.
Effects of hormones on the body cells
Cells affected by hormones are called as Target cells. Hormones reaches the various
parts of the body through blood, and after reaching the target organs controls and coordinate
the activities of the cells, growth, reproduction, Blood pressure, balance the quantity of various
246
SCIENCE 10
substances in blood. Generally the hormones are secreted in minute quantity, but on account of
any reason if they are secreted in less or more quantity (Hypo-or-Hyper), then they will be
harmful to body.
Points to remember :
l
Liver is the largest gland in the body of man. It never functions as an endocrine
gland.
l
Thyroxine hormone is a useful hormone for the metamorphosis in the tadpole larva
of frog.
l
The hormane for controlling the sugar/glucose level in the blood of man is insulin.
l
At the time of hunger, thirst and fear the adrenalin hormone is secreted. This hormone
is called as emergency hormone.
l
Science for the study of hormones is called as endocrinology.
l
Hormones attracting the insects are called as pheromones. These are secreted by
the exocrine glands.
l
Diabetes is a type of disease in which much quantity of sugar is present in the urine
of the patient.
l
Hormones are of two types : (i) Proteins and peptides, (ii) steroids.
EXERCISES
Very short answer type questions:
1.
In how many parts is the brain divided?
2.
How many cranial nerves are found in man?
3.
Where is the cerebro-spinal fluid present?
4.
What is the weight of brain in men and women?
5.
What do you mean by nervous system?
6.
What is reflex action?
7.
Name the hormone controlling the sugar level in blood.
8.
By which cells the insulin hormone is secreted?
9.
What controls the quantity of water in urine?
10.
By which gland the growth hormone is secreted?
11.
What is the function of pheromone.
CONTROL AND COORDINATION
247
Short answer type questions:
1.
Write the functions of cerebrum in man.
2.
Explain the reflex action.
3.
Describe the structure and function of spinal cord.
4.
What do you mean by nervous system? In how many parts is the nervous system divided?
5.
By which gland is the insulin hormone secreted? Describe its functions.
6.
Describe the function and effects of gonadial hormones.
7.
Describe the functions of hormones secreted by adrenal gland.
8.
Describe the functions of hormones secreted by the pituitary gland.
Essay type questions
1.
Describe the Nervous coordination and control.
2.
Describe the structure and functions of brain.
3.
What is reflex action?
4.
Describe the cranial nerves.
5.
Describe the function of brain.
6.
Write an article on nervous and hormonal coordination and control.
7.
Describe the function and effects of hormones of pituitary glands.
8.
What is reflex action? How many types of reflex actions are there? Explain it with example.
248
SCIENCE 10
Chapter - 18
REPRODUCTION AND GROWTH
We will study18.1
Reproduction
18.2
Type of
Reproduction
18.3
18.4
18.5
Vegetative
Reproduction in
plants
Aexual
Reproduction.
Sexual
Reproduction
18.6
Reproductive
organs of plants.
18.7
Pollination.
18.8
Human
Reproduction
System
18.9
Physical and
mental changes
during the evolution
of man.
18.10 Growth.
REPRODUCTION AND GROWTH
18.1 Reproduction :
The ability of an organism to produce
morphologically and anatomically similar young ones is
called reproduction.
18.2 Types of reproduction :
In order to maintain the continuity of the species all
living beings reproduce by any of the following methods1. Vegetative Reproduction.
2. Asexual Reproduction.
3. Sexual Reproduction.
18.3 Vegetative ReproductionIn this type of reproduction some part of the plant
gets separated from the main plant and independently
gives rise to a new plant. For this purpose plants possess
some specific organs as bulbs, corm, stolans, leaves,
branches etc. These parts detach from the main plant
and produce new plants. For personal profit man has
developed many new techniques of vegetative
reproduction.
Different artificial methods of vegetative
reproduction are as follows1. Cutting- In this process stem cuttings are taken
from the mother plant and allowed to grow in soil medium.
After some time the cutting develops into a new plant
similar to parent plant as the root arises from the lower
part of the stem
cutting and bulbs
and leaves from
the upper part of
the stem for
example - rose,
grapes, sugarcane tec.
249
2. Grafting- In this method two parts of different plants
are joined together in such a way that they will unite and
grow as one plant. The joint is covered with the mixture of
soil and dung, and it is tied up with a piece of cloth. By this
method various types of a fruits or flowers can be produced
simultaneously on the same plant. For example- rose, citrus,
orange
3. Layering- This process is used for those plants in
which roots are not developed easily. In layering a part of
the stem of the plant is pulled out and bark is separated the
portion is burried in soil while it is attached and supported
by the parent plant. Soon the layered part strikes out root.
Now the rooted part is separated from the mother plant as a
new one. For example- chameli, apple, pear etc.
18.4 Asexual ReproductionThis type of reproduction is found only in lower
organisms. Lower organisms produce same young ones by
this method. Gametes are not produced in this method. All the organisms produced by this
method are exactly similar to parents.
Living heings reproduce asexually by following methods1. Budding- In this type of reproduction
bulging appears on the body of the adults.
After some time they develop bud like out
growth, with the time these out growths
detached itself from the parent plant and grows
to an adult one. For example- hydra, yeast,
bryophyllum etc.
Yeast- In yeast cells a number of such
out growth are observed, giving rise to a chain
of buds and with the time these buds detach
from each other and then give rise to a new
individuals.
Bryophyllum- In case of bryophyllum
budding is observed by the development of out growth on the leaf margin which develops and
get detached from the old leaf and grow separately.
2. Fission- This type of asexual reproduction is found in lower organisms like members of
protozoa, in plants like algae fungi and bacteria. Here two young ones are produced by single
250
SCIENCE 10
fission. Usually this process occurs in favourable conditions. Some time it can also occur in
unfavourable conditions. Cells divide mitotically in this type of reproductions. Some time spore
formation also takes place by several divisions. For example- amoeba, plasmodium,
paramoecium, algae & fungi.
Amoeba- In amoeba, nucleus in the cell elongates and divide into two parts from the
centre. After nuclear
division
the
cell
membrane divides into
two parts by constriction
and along with this the
cytoplasm also divides
due to which two young
one are produced from the parent amoeba which develops individually and spend their life.
4. Regeneration - It is the ability of an organism to reproduce its lost part of the body or
regeneration is a complicated process in which damaged or broken pieces regenerate.
l
Organisms like hydra, planaria and
fins of fish have the capability of
regeneration.
l
In amphibians like frogs and toads,
limbs, tail and jaws have the ability to
regenerate.
l
In lizards only tail regenerates where
as in birds beaks can regenerate.
l
In human beings and all other
mammals muscles, tissues, tendons,
liver, cells, digestive glands and blood
corpuscles can regenerate.
Parthenogenesis- It is a process in which young ones are developed from female gamete
or egg cell without the process of fertilzation. For eg.- honey bee & rotifer etc.
18.5 Sexual ReproductionIn this type of reproduction special type of reproductive cells are developed in organisms.
These cells are called gametes. Two types of gametes. male gamete and female gamete are
found. By the Fusion of these two gametes zygote is formed zygote produces offsprings. Sexual
reproduction is the only process of reproduction in most of the higher plants animals and human
beings.
REPRODUCTION AND GROWTH
251
Importance 1. In sexual reproduction there are chances of variation among the same species.
2. As the gametes come from two different parents (male and female) there are more
chances of variation which help in evolution and adaptation.
18.6 Reproductive organs of plantsIn plants gametes are formed in special type of organs. called flower. A flower has four
important whorls called 1. Calyx 2. Corolla 3. Androecium 4. Gynoecium. Androecium and
Gynoecium are male and female reproductive organs
respectively.
1. Androecium- This is the third whorl of the flower
which perform the function of male reproductive organs.
Its single unit is called stamen. A stamen possess a long
and thin filament with an anther lobe at the apex. Pollen
grains are formed inside the anther lobe. Anther lobes are
remain connects to the filament with the help of a tissue
called connective.
2. Gynoecium- This is the inner most whorl of the
flower and perform the function of female reproductive
organs. It consists of a pistil or carpel basal part of the
carpel is called ovary. Ovules remain attached with the
ovary wall by the tissue called placenta a bulging structure.
Ovary has long tube like structure called style which end
in a structure called stigma. Stigma may be long knob like
or pointed. Its structure may be rough, hairy or sticky.
Pollen grains reach the stigma at the time of pollination
and stick there.
L.S. of Carpel structure
Ovule- Female gamete is present inside is called
ovules. It remains attached with a filament like sturcture
called funicle. The main part of the ovule is called nucellus.
Ovule may be covered by single or bilayered membrane.
In these layers there is pore through which pollen grains
enter the egg surounded by embryosac.
18.7 PollinationIt is a process in which pollengrain comes out from
the anther lobes of the stamen and reach to the stigma of
another flower.
252
SCIENCE 10
There are two types of pollination in plants
(a) Self pollination- The transfer of pollengrains from the flower to the stigma of the same
flower or any other flower of the same plant is called self pollination, for this process it is necessary
that either the flower should is bisexual or the plant should be bisexual.
Advantage1. It is an easy process as well as common process.
2. Pollen grains are not required in abundence.
Disadvantage1. Plants produced by self pollination may be weak and unhealthy.
2. Only few seeds can be produced by self pollination which may be weak and light weight.
(b) Cross Pollination- The transfer of pollengrains from one
flower to stigma of the another flower of different plant of the same
species is called cross pollination. In this process pollengrains
required a medium for their transfer. On the basis of these medium
pollination is of following types.
1. Wind pollination- when pollen grain are transferred by
air is called wind pollination e.g. wheat, maize and rice.
2. Water pollination- when pollen grains are transferred by
water is called water pollination for e.g.- hydrilla & vallisnaria.
3. Insect pollination- When pollengrains are transferred by insects are called insect
pollination for e.g- chameli & ratrani etc.
4. Animal pollination- When pollen grains are transferred by animals is called animal
pollination for e.g. gulmohar.
Difference between self & cross pollination.
Self Pollination
Cross Pollination
1.
The process occurs only in bisexual
flowers.
2.
The pollen grains of the flower reach
to the stigma of the same flower.
No medium is required for the
transfer of pollen grains.
The process may occur in both unisexual
and bisexual flower or plants. Flowers have
colours and fragrance.
The pollen grains fall on the stigma of the
other flower but of the same species.
Any medium like air water insect or animal
is required for the transfer of pollen grains.
3.
18.8 Human reproductive system.
Human beings are the most evolved organisms of the class-Mammals. Human beings are
a unisexual organism. Both type of reproductive cells are formed in different bodies. The human
REPRODUCTION AND GROWTH
253
body which produces male gametes called sperms is classified as male where as the body
which produces female gametes called ovum is classified as female.
(A) Male Reproductive Organs
1. Testis and Scrotal Sac- These are most
important male reproductive organs. Testis are two
oval shaped structure. The testis lies in a small
sac like structure called scrotum outside the
abdominal cavity. The function of testis is to
produce sperms.
There are two structures attached to the
testis called vasa efferentia and Epididymis.
I. Vasa efferntia- Each testis is divided into
many chamber like structure. Each chamber
possesses two to three coiled tubes called vasa
efferntia sperms are produced by these tube these
tubules may be four hundred to six hundred in
numbers. These tubules fuse to form 15-20 big
tubes known as Epididymis.
II Epididymis- These are 5 to 6 metres or
22 feet long coiled tubules. Their narrow end is
called vas deferens. Sperms mature inside the
tubules, A viscous liquid called semen is formed
inside the testis.
2. Vas Deferens- This is a pair of 30 cm.
long narrow membranous tube coming out through
the inguinal canal and open in the semina vesicles
of their side. Thus the semen reaches to the
seminal vesicles.
3. Seminal-vesicles- This is a pair of 4 cm.
long membranous bag like structure. A common
duct called ejaculatory duct emerges out from
seminal vesicle of both the sides open into urethra.
4. Urethra- This is a muscular tube which
helps to excrete out urine and semen it opens at
the apex of the penis.
l
l
l
l
l
l
l
l
l
Do you know?
Single organism can reproduce
asexually.
Cell divide mitotically.
Number of new organisms increase
Frequently.
A single organism can produce
many young ones.
Asexual reproduction helps in
spreading organisms at distant
place.
Possibility of evolution is lesser in
this type of reproduction.
As there is no fusion of gametes in
this type of reproduction so there
is no chance of variation and
mutation in young one.
Plant reproduction is a process by
which plants can maintain their
continuity and the species remains
constant.
In plants asexual reproduction is
performed by spores.
Prostrate
Epididymis
5. Penis- It is an external mating organ of
human being. Under normal condition it is about 9
254
SCIENCE 10
cm long and at the time of copulation it elongates upto 14 cm. Its apical part is bulbous and
smooth called glans penis the skin cover which covers it is called perpuce.
6. Acessory Glands- Prostate and coupers glands are found near the opening of urethra.
The prostate gland secretes a thin liquid which causes smell in semen. Under the prostate
gland there is a pair of pea sized another glands called cowpers gland which secretes an alkaline
liquid.
(B) Female Reproductive Organs
1. Ovary- A pair of ovaries present on both sides
of the vertebral column behind the kidney. Each ovary
is 4 cm in length and 2.5 cm. in breadth. Ovaries
remain hanged with the help of peritonium membrane
in the abdominal cavity.
Fallopian tube
ovary
Function- The main function of ovary is to
produce ovum and to secrete Esterogen and
progestrone Harmones.
2. Fallopian tubes- These are 2 in number.
These tubes remain situated on both sides above
the uterus.
3. Uterus- It is a muscular structure. Its upper
part is bigger in size where as lower part is a narrow
structure which converts into vulva. The anterior end
of uterus opens in it.
Do you know?
l
Fertilization process held
twice in Angiosperms firstly
through eggcell and
secondly
through
secondary cell.
l
In flowers calyx, corolla
and stamen shed down
after fertilization.
18.9 Physical and mental changes in human
beings-
l
Seeds are formed by
ovules.
In human beings following changes occur from
childhood to an adult-
l
Fruits are formed by ovary.
l
Two types of reproduction
are found in orgamismssexual and asexual.
l
Sperms have three partshead body & tail.
l
Females attains puberty at
the age of 12 to 16 years.
4. Vulva- It is a tubular structure. There is a
clitories near the outer part of the vulva.
5. Clitoris- A fleshy structure is formed above
the urinogenilal tract called clitoris. It is equivalent to
penis in male.
1.
In human beings other body organs grow at a
faster rate as compared to that of the head.
2.
A child’s head is comparitively bigger than his
feet.
REPRODUCTION AND GROWTH
255
3.
Till adulthood growth of head is less than that of the feet.
4.
Secretion of digestive juices decreases with increase in age thus affecting the digestive
system
5.
With the increase in age, cells of the body lose their capacity to hold water- causing loose
skin wrinkles.
6.
With age, the capacity of lungs to hold oxygen decreases therefore adult and old people
face difficulty in breathing.
7.
With the development human kidney becomes weak and number of nephrons decreases
leading to low urine formation. This causes bodyaches.
8.
With the increase in age the capacity of human heart to pump blood decreases therefore
only 80% and 42% blood reaches the brain and kidney respectively.
9.
With the increase in age ability of numeroas sensations also decrease.
10.
Upto the age of 50 to 55 the ability of bone marrow to produce RBC’S decreases due to
which volume of blood decreases in body.
11.
With the increase in age human weight decreases about 12%.
12.
Holding ability of hands decreases about 40 to 45%.
13.
Ability of taste buds of tongue also decreases with age.
14.
The abiity to reproduce completely disappears by the age of 45 to 55 years.
15.
Bones become weak.
16. The number of active cells of brain decrease.
Answer the following questions.
1.
When does adoloscence start in human male and female?
2.
How does pollination occur in plants bearing flowers that never opens.
3.
Where does fertilization take place in humans?
18.10 GrowthGrowth is a regular process in all living beings. Growth causes increase in shape volume,
weight and cellular substances like cytoplasm synthesis etc. Due to the different physiological
process every living being grow in shape and weight. That is called growth.
In other words with the change in shape and volume there is an increase in dry weight of
all living beings is known as growth. The growth is limited in all animals. It is stopped after a
certain time. The internal growth also occurs in living beings.
Zygote is formed after sexual reproduction. Multicellular structure is formed by the
continuous division of cells in zygote. These cells differentiate and form tissues. The tissues
256
SCIENCE 10
form organs. This type of growth is called development. Growth is a quantitative word where as
development is a qualitative word. Growth and development are correlated.
Phases of Growth- Following phases are found in living beings.
(a) Long Phase- During this phase growth takes place very slowly in all living beings.
(b) Elongation Phase- Growth occurs very fast in this phase.
(c) Short Phase- In this phase growth again occurs slowly.
(d) Fixed Phase- The growth is fully stopped at this stage.
Growth in Animal Body- Following type of physical growth is found in an animal body.
1. Accessory Growth- Here the size of the cell increases, there by increasing the volume
of the organism but the number of cells do not change for example- Nematodes.
2. Duplication growth- There is no change in the shape of the cells only number of cells
increase with the result of cell division. For example animal embryo.
3. Essential growth- This type of growth occurs in the mitotic division of specific cells to
form other specific cells during the post embryonic growth. These cells perform special type of
function in body for example formation of red blood corpuscles from bone marrow.
Growth of human body part- Rate of different body parts like head, neck, chest, arms,
skeleton and internal organs varies in a human body. Different organs have different growth
rate. We can study the growth rate by studying the different phase of growth of a person since
birth to adult stage. We can observe out change in structure, shape and volume etc.
For example
1.
Head of human embryo
is bigger during the
primary stage of
development
as
compare to an adult.
2.
Arms and hands
become proportionate
just after the birth but
feet takes time about
10 years to come in
proportion.
3.
In girls reproductive organs get maturity at the age of 12 where as boys obtain sexual
maturity at the age of 14.
4.
Brain and spinal cord- In childhood brain develop faster and obtain the full size at the age
of 9 years.
REPRODUCTION AND GROWTH
257
5.
The whole body grows along with the skeletal growth.
The growth rate reaches its highest point by the age of 14 to 18 years in human being.
After 18 years the physiological growth gradually starts decreasing.
Growth in plantsPlants grow through out the life. In plants new parts grow continuously for example seed
is the smallest unit of a plant, the seed germinates and gives rise to a sapling which grows its
different parts and gradually gives rise to a new tree.
Conditions necessary for growthFollowing factors are necessory for the normal growth of plantsNutritive substances like water, oxygen, optimum temperature, light and minerals should
be supplied in required amount to the growing parts of the plant. It can be easily observed by an
experiment. Those plants which do not get sufficient amount of sunlight mineral, water remain
ill-developed, where as plants which receive sufficient amount of all the above mentioned things
grow property. In plants growth is mainly observed in root and shoot apex. Here the cells of
meristmatic tissue divide rapidly resulting in growth.
Points to remember
l
Various types of plants reproduce by different methods.
l
Flower bearing plants mostly reproduce sexually.
l
Male gametes fuse with female gametes inside the embryosac.
l
Two male gemetes are formed in side the pollen tube from the reproductive cell.
l
Pollen tube enter in embryosac through micropyle.
l
A ‘2X’ zygote is formed by the fusion of male and female gametes.
l
Double fertilization and triple fusion occur in plants bearing flowers.
l
In unisexual organism male and female reproductive organs are found in
separate bodies. For example man, monkey and dog etc.
l
Bisexual organisms have male and female reproductive organs in a single body
for eg- leech and earthworm.
l
Number of young ones remain lesser in number in sexual reproduction.
l
Temperature of testis always remains less 2 to 3ºC than that of the body.
l
Formation of ovum and sperm is a continuous process. Production of sperm
occur in testis whereas production of ovum occur in ovary simultaneously
only.
l
An elephant’s testis is found inside the abdominal cavity.
l
Growth occurs only in a particular period, at the specific rate and in a definite
sequence.
258
SCIENCE 10
l
Growth is permanent development of shape and volume.
l
Growth is a result of proper and successful metabolism.
l
Along with auxinr, cytokinin hormone promote cell division.
l
The growth during embryonic development is called embryonic growth.
l
The growth occuring after the birth is called post embryonic growth.
l
In some organism growth rate is slow, yet continuous.
l
Reptiles and fishes grow for many years.
l
The working ability of different body parts decreases along with increase in age
after adoloscence stage.
l
In multicallular organisms the individual growth depends upon the activities of
cell.
l
Length wise growth of the plant can be measured by Auxanometer.
EXERCISES
Very short answer type questions1.
Where does spermatogenesis take place in humans?
2.
Which type of reproduction is found in bryophyllum?
3.
Give two examples of asexual reproduction?
4.
Where is testis found in human beings?
5.
How many ovaries are present in human beings?
6.
Name the process of fusion of sperms and ovum.
Short answer type questions1.
Describe grafting with example.
2.
Describe layering with example.
3.
Describe budding with example.
4.
Describe the process of fission in amoeba.
5.
What is- pollination? How many types of pollination occur in plants.
6.
Describe testis.
7.
Describe ovary.
Essay type questions1.
Describe male reproductive system of humans.
2.
Write an essay on pollination.
3.
Differentiate between self pollination and cross pollination.
4.
Describe the structure of a flower.
5.
Describe the female reproductive organs of human.
6.
Write an essay on growth rate.
7.
Describe physical changes occuring during the development of man.
REPRODUCTION AND GROWTH
259
Chapter - 19
GENETICS
Do You know?
l
Theory of heredity and generation conceptwere known by ancient Indians.
l
Charak and Subhoot explaind that the embryo
devloping in the flower containg all the organs
in small form.
l
As it grows all the characters comes out one
by one.
19.1 Genetics and variation
In living beings the young ones produced by
reproduction have characters similar to their parents.
These characters have been transferred from parents to
offsprings.
We will study
19.1 Heredity and variation.
19.2 Basic concept of
Heredity
In sexual reproduction during the fusion of gametes
these characters get transferred from one generation to
another generatoins. This transfer of characters maintains
the continuity between the parents and offspring and this
further continues from generation to generation.
“This transfer of characters in living being from
one generation to another generation is called
heredity” and its study is called Genetics.
19.3 Chromosome DNA
(Preliminary know
ledge)
In this chapter we will study about different
processes which are responsible for variation and
heredity. Study of long term effects of variation and heredity
are interesting. These are studied under development.
19.4 Gene
l
Transfer of different characters from one generation
to next generation in living being is called Heredity.
19.5 Sex- Determination in
Man.
l
The characters which are transferred from one
generation to next generation are called hereditary
characters.
l
Study of Hereditary characters, their transfer
processes and causes is called Genetics.
260
SCIENCE 10
Variation- Similarities are maintained by parent with the offspring from generation to
generation still we know that none of the two organisms are similar. Even different offspring of
the same parent differ from each other. This is known as variation, because of this variation
each organism is different from the other organism in shape, behaviour, colour etc.
For the conveniance of studies, variation is divided in to two parts.
1. Hereditary Variation : The variations which get transferred from one generation to
next generation are called hereditary variation.
2. Environmental Variation - The variations which are caused due to the effect of
environment and which are not transferred from one generation to next are called environmental
variation.
Temperature, humidity, food habits etc are the causes of environmental variation and are
originated during the individual development of the organisms. So these characters are called
acquired characters. Heriditary variation and control of characters, transfer from one generation
to next generation is performed by genetic materials, which are found on the chromonemeta of
chromosome in the nucleus in the form of gene. Genes are made up of D.N.A. (chemical
molecule). Changes in their number, arrangement and structure cause hereditary variation.
Colour of eyes, hair and skin and blood group etc are example of hereditary variation.
Reasons of hereditary variations are as follows1.
Change in number of chromosome- Changes in chromosome’s number causes change
in hereditary material due to which variation occur in offsprings.
2.
Gene Mutation- Any change in gene structure causes variation.
3.
Change in structure of chromosome- If there is any change in structure of chromosome or
number of gene variation is caused among the organisms of the same species.
4.
Sexual reproduction- During sexual reproduction variations are caused at the time of
gene regulation.
19.2 Basic concept of heredityIn living beings, though the basic characteristics of offsprings are same but still they differ
form their parents. They show certain variations. The rules of inheritance of characters depend
upon this fact. There are two possibilites for each character to appear in offspring. In 1865
Mendel described all these possibilities of appearance of characters in next generation in the
form of laws. These are called law of heredity.
Through his various experiments Mendal studied seven different hereditary characters in
pea plant but he selected single character for his experiment at one time.
Mendel selected pea plant for his experiments becuase of the following reasons:1.
Pea plant is an annual plant and with a short life cycle.
2.
Its flowers are bisexual that is male and female reproductive organs are found in same
flower. Self pollination occur in the plant.
GENETICS
261
3.
4.
The plants can be grown easily.
Because of self pollination plants are homozygous. So that they show pure characters in
each generation.
5.
Artificially cross pollination can be done easily in pea plants.
6.
Many contrast characters are observed in pea plants.
Technical Terminology of Heredity1.
Allele or Allelomorph- Factors which control contrasting expression of a character are
said to be alleles or allelomorph.
2.
Genotype- Genetic character which is present in the individual but not visible from out
side it called Genotype.
3.
Homozygous- An individual whose genotype contains two identical alleles of a gene is
called homozygous.
4.
Heterozygous- An individual whose gehotype contains two different alleles of a gene is
called heterozygous.
5.
Dominant and recessive- When two pure breeding variety are crossed the parental
character that expresses itself unchanged in the first generation is called dominant and
the one which does not appear in first generation but appears in second generation is
called recessive.
6.
Hybrid- Two genetically different organisms are crossed and they produce the new
organism. This new organism is called hybrid.
7.
F1 Generation- The generation which is produced by parental generation is called F1
Generation.
8.
Incomplete Dominance- When the dominent characters are not expressed completely it
is called incomplete dominance.
9.
Factor- The character which transfers the hereditary characters from one generation to
another generation is called factor. Presently it is known as gene.
10. Monohybrid and Dihybrid cross- A cross which involves only one character from each
parent is called monohybrid cross, whereas a cross in which two characters are involved
is called dihyobrid cross.
Genetics Study of heredity has been an interesting subject since ancient times. Aristotle and
pythagorus etc and many philosphers presented their views on it but they could not get success
German Scientist Kosper Fredrick started Heredity science as post reproductive concept. But
Greger John Mendel achieved great success in this field.
Mendels law of Inheritance
1. Mendel’s Law of dominance- According to this when a pair having different alleles is
crossed only dominant characters will appear in first generation.
e.g.- Mendel crossed pure tall plants (TT’) with dwarf plant (tt). He found all the plants tall
in first generation.
262
SCIENCE 10
2. Mendel’s Law of Segregation or
law of purity of gametes- When a pair of
contrasting characters is taken in parent
generation, both the characters remain
present in F1 Generation but get segregated
in F2 generation as pure without
containminating one another. This is also
known as Law of purity of gametes.
For example in monohybrid cross experiment of Mendel in F1 Generation long and dwarf
characters of plants remained together but they did not affect each other and the gametes
produced were of two types. That is half were of (T) gene where as other half are of (t) gene.
That is why mendel postulated that gametes always remain pure.
3. Law of Independent Assortment- According to this law Mendal crossed a pair having
two contrasting characters by dihybrid cross and observed character of one gamete transmitted
to next generation without affecting the character of other gamete. The characters assorted
independently. That is why it is called Law of independent assortment.
19.3 ChromosomeIn all eukaryotic cell nucleus contains along thin thread like structures whose hereditary
material remains in some specific structure is called chromosome.
Definition of Chromosome- The chromosomes are filamentous linkage structure carrying
linear sequence of genes visible in the nucleus during the cell division and multiplied by frequent
cell divisions and maintain their morphologial structure and functions.
GENETICS
263
General Structure of Chromosome- Chromosomes of all the organisms are almost same.
Generally a chromosome has the following structural components.
1. Pellicle 2. Matrix 3. Chromatid 4. Chromomere 5. Centromere 6. Sattelite.
1. Pellicle- It is outer most thin layer of chromosome. It is a membranous structure. It
encloses the matrix of the chromosome.
2. Matrix- It is found in side the pellicle and chromonemeta remain embedded in it.
3. Chromatid- Chromatid or chromonema is
found in each chromosome and each chromatid
contains long coiled filaments. These filaments are
known as chromonemata.
4. Chromomere- Chromomere are the knot like
structures present on the chromonemata at equal
distance. Genes are located in chromomere.
5. Centromere- The place from where the
chromosome is constricted is called centromere or
primary constriction. In some chromosomes more
than one constriction is found, these constrtrictions
are called secondary constriction.
6. Sattelite- Anterior part of the secondary
constriction is called satellite.
Function and Importance of chromosomes.
1.
Play important role in heredity. They are also responsible for protein synthesis.
2.
New cells are produced by the replication of chromosomes.
19.4 GeneGene is a unit of heredity. A segment of DNA which contain a genetic character is called
gene. Gene has a great capability of replication. Gene controls the various processes that
occur in living beings. According to Mendel, genes are called allele. Concept of gene first of all
was given by Sutton. Later on Morgan, Muller, Watson and Krick also explained the gene.
Salient fertures of gene concept1.
Genes are located on chromosomes.
2.
Genes control the physical and physiologial processes of an organism.
3.
Gene is a physical unit which is transmitted from parent generation to offsprings.
4.
Genes are arranged as a garland of beads on chromosome.
5.
Each gene is located at a specific place on a specific chromosome.
264
SCIENCE 10
6.
Genes show reoccurrance.
7.
Each gene is responsible for the synthesise of special type of protein.
Modern concept of geneAccording to the concepts presented by Watson and Krick in (1953) and Witkinson
in (1962), gene is considered as a macromolecule without which any structural change
transfers from one cell to another and from one generation to the next generation.
Thus gene is a complex compound of carbon, hydrogen, oxygen, nitrogen and phosphorus
including carbohydrates and nuclic acids. So gene is a physical unit.
De oxy-ribonucteic Acid (DNA) Genetic Material
Structure of Nucleic Acid- In all living being cells have two types of nuclic-acid that is DNA
and RNA found in nucleus RNA is mainly present in cytoplasm. Small amount of DNA is found
in mitochondria and chloroplast. In each cell DNA is found in condensed form in nucleus and
synthesize chromatin network (Chromosome) with the help of protein, Watson & Crick in 1953
explained the molecular structure of DNA for which they received noble prize jointly. According
to them DNA is a complex structure made up of 2 chains of polynucleotides, whose atomic
weight is several lac.
Chemical constitution of DNA
It is as follows1.
Pentose Sugar- It is deoxyribose sugar.
2.
Phosphoric Acid-
3.
Nitrogenous bases- These are of two type.
(a) Purine (b) Pyrimidine.
(a) Purine - It is a double ring nitrogenous organic alkaline compound. These are of two
types. Adenine & Guanine denoted by ‘A’ & ‘G’
(b) Pyrimidine- It is single ring nitrogenous organic alkaline compound. These are of two
type called cytosin and thymine dehoted by C & T.
Characters of Helical structure of DNA
1.
DNA molecule is made up of two helix which remain coiled on the axis in sprial
manner.
2.
Both the chains coiled in opposite direction.
3.
Each helix contains long chains of nucleotides.
4.
Each nucleotide contains nitrogenous base, deoxyribose pentose sugar and
phosphoric acid (one molecule of each). Molecule of nitrogenous base is remains
GENETICS
265
attached with deoxyribose from the inner side. Whereas on outer side it remains
attached with phosphate molecule.
5.
All the molecules of nucleotides of a chain remain attached with phosphate molecules.
6.
Nucleotides of both the helix remain attached to each other. Nitrogenous bases
remain attached with weak hydrogen bonds.
7.
Both the chains of DNA contain equal amount of purine and pyrimidine. Purine of
one helix remain attached with pyrimidine of
another helix.
8.
Adenine & Thymine are attached with double
hydrogen bond where as cytosine and guanine
are attached with tripple hydrogen bond.
19.5 Sex Determination In Man
As you know after meiosis the gametes formed have
half the number of chromosome, than in mother cell. In higher
organisms male and female reproductive organs are well
developed. Male and female gametes are developed by
spermatogenesis and oogenesis in reproductive organ.
In each human cell 46 or 23 pairs of chromosomes are
found. Out of these 22 pairs of chromosomes are same in
male & female. These are called autosomes. The 23rd pair of
266
SCIENCE 10
chromosome of female is also same but in male 23rd pair of chromosome differs from the other
pairs of chromosomes. It has a long ‘X’ and a small ‘Y’ chromosome so 23rd pair of chromosome
of female is expressed as ‘XX’ where as of male is expressed as ‘XY’. This pair of chromosome
is called sex chromosome and this pair only determinates the sex of the young one.
During the process of spermetogenesis in males two types of chromosomes are produced
half contain ‘X’ chromosome where as another half ‘Y’ chromosomes, while in female ovum all
the chromosomes are of same type.
During the process of fertilization if sperm containing ‘X’ chromosome gets fertilized with
ovum containg X chromosome produce female child (xx). If the sperm containing ‘Y’ chromosome
get fertilized with ovum having X chromosome will produce a male child. It prooves that ‘Y’
chromosome of man is responsible for the sex determination.
Answer these questions.
1. How is it known which character is dominant or recessive by mendel’s
experiment?
2. Explain the different ratios of hereditary characters on the basis of mendel’s
experiment?
3. How is the sex determined in a human child, explain?
4. With the help of diagrams describe the different ratio of the young ones in next
generaton?
Points to remember
l
Indian Philosphers like Charak and Sushrut initiated to contribute in concept of
heredity.
l
Pythagorus and Aristotle have given their lines about heredity. Greger John Mendel
reached to the important decision with the help of his experiment.
l
Transfer of characters from parents to young ones is called heredity.
l
Greger John Mendel explained dominant and recessive characters with the help
of the experiments performed on 34 varieties of pea observing seven character.
l
Mendel named the carrier of hereditary character as allele.
l
Chromosomes present in the nucleus of he cell carries hereditary characters
from one generation to the next generation.
l
According to the Mendel each character is due to the specific allele. Modern
research shows the carrier present on the chromosome is called gane.
Chromosomes are always found in pairs.
l
The characters which are transferred from one generation to the next are called
hereditary characters.
l
Carriers showing different contrast characters of the same is called allele.
GENETICS
267
l
DNA is a heriditary substance. It is a coiled structure having the property of
replication.
l
In human beings 46 or 23 pairs of chromosomes are found. 22 pairs of
chromosomes are called Autosome, where as the 23rd pair of chromosome is
called heterosome or sex chromosomes. Female have ‘XX’ and males have ‘XY’
chromosomes. ‘Y’ of male is responsible for the sex determination in human beings..
EXERCISE
Very short answer type questions.
1.
What is heredity?
2.
Who is the father of heredity?
3.
Explain Mendel’s Law of independent assortment.
4.
Explain Mendel’s Law of dominance.
5.
Explain Mendel’s Law of segregation.
6.
Define and explain gene.
7.
Which pair of chromosomes is responsible for sex determination in man.
8.
Explain the role of chromosomes in sex determination.
9.
Which is the most suitable concept to describe origin of life.
Short answer type questions1.
What do you understand by heredity.
2.
Explain the importance of Mendel’s laws.
3.
What is dihybrid cross. Explain it with suitable example.
4.
Explain the reasons responsible for variation.
5.
Explain the functions of chromosomes.
6.
Which pair of chromosome is responsible for sex determination?
7.
Explain the sex determination process in man by line diagram.
Essay type questions
1.
Explain Mendel’s law of independent assortment in brief Draw a line diagram of dihybrid
cross in support of your answer.
2.
Verify the ratio 9:3:3:1 by Chekers Board Method.
3.
Explain the causes of variations.
4.
Explain the structure of DNA with diagrams.
5.
Explain the process of sex determination in man.
268
SCIENCE 10
Chapter - 20
ORGANIC EVOLUTION
20.1 Organic Evolution
In nature we observe various types of organisms, If
we observe them closely, then we will get several
similiarities in their body organisation, structure etc.
l
Non-living or living beings are made of atoms and
molecules.
l
Living substances are formed from protoplasm,
which is found in the cell.
l
All the living beings have their own species, Hence:
We will study
20.1 Organic Evolution
20.2 Evidences of organic
Evolution
20.3 Theories of organic
evolution
l
Lamarck theory
l
Darwin theory
l
Modern theory of
organic evolution.
ORGANIC EVOLUTION
From ancient time or immemorable time that
process of slow and gradual sequence of changes
from primitive, simple organism to modern time
developed, more complex organisms, is called as the
organic Evolution.
Thus it is now clear that development of each modern
living species has taken place in due course of time in
changed environmental conditions through gradual
sequence of changes from minute, simple, primitive low
grades of living species.
Modern scientists agrees that theories of organic
evolution are proper, correct, It has occured, it is occuring
and will continue to occur, because by the study of this,
much information regarding the important facts about
nature has been received. Hypothesis of organic evolution
is based on the following facts :
l
The nature’s environment and their condition are
never stable or permanant, in them continuous
changes occur.
l
In the recent times, several living species are found
on the earth, such numbers will not be present in the
ancient period, because on account of evolution from
single living species, several living species have
originated and evolved.
l
Structure of the living species found in the ancient
time must have been simple from that of the living
269
species found now a days.
l
Descendants of the living species are similar.
20.2 Evidences of organic evolution
Various biologists have proved the
mechanism of organic evolution with the help
of several important evidences. Evidences in
support of the hypothesis of organic evolution
are as follows:
1. Evidences from Taxonomy :
Evidence of organic evolution is deduced from
taxonomy. On the basis of similar structure and
size, firstly the organisms have been divided
into two kingdoms. Evidence from taxonomy
indicates that the similar organisms (size,
origin, function) have been placed in the same
class and dissimilar were kept in another class.
Higher classes of animals have evolved from
gradual evolution of lower class.
Humenrus
Radio-ulna
Carpals
Metacarpals
Phalanges
Seal
Bird
Bat
Horse
Man
2. Evidence from comparative
anatomy : It is clear from the study of structure
of animals and plants that much variations
exists in both types of organisms, but there is
a similiarity in certain characters of them. The
body of all the living beings is made of cells,
protoplasm is found in these cells. The study
of structure and morphology of living beings
shows similiarity. The study of anatomy of
various animals proves the organic evolution.
Three main evidences of this are observed :
(a) Homologous organs : Such organs
in the body of animals, which have the common
origin and structure and different in their
functions are called as homologous organs.
Example : A human hand, wings of bat
and birds, fore limbs of crocodiles and lizards
etc. are similar in origin and structure. Fore
limbs in man are used for grasping, in bats
and birds for flying and for crawling in
crocodiles and lizards, and in horse the fore limbs are used for running.
(b) Analogous organs : Such organs in the body of animals, which are quite different in
origin and structures but similar in function.
270
SCIENCE 10
Example : The wing of a bat, bird and in sects
are similar in function, wings of insects are not bony,
but they are bony in bat and bird.
(c) Vestigeal organs : In the body of the animals
such organs are present which are generally nonfunctional parts or organs and are incompletely
developed, but they are found developed in some other
related animals. Such organs are called as vestigeal.
Example : Man also prossess some vestigeal organs
in their body, which have no function. The vestigeal
organs of man are shown in Fig. 4 : Scientists have
postulated a hypothesis that once these organs were
functional in their ancestors, but during the course of
evolution their utility was over and they becomes
degenerated.
3. Evidence from Embrylogy : Embryology
produces strong evidences in favour of organic
evolution. Different animals are related to each other
and they have evolved from the same ancestor (old
ancestors). In all their stages of animals, they are so
similar to each other, that is very difficult to differentiate
between them. (Fig. 5). In the embryonic development
of animals such condition arose, that in the shape of
different animals much similarties have been observed.
The tadpole larva of frog is similar to fish, this proves
that all the vertebrate animals have evolved from fish
like ancestors.
Fig. 4 Vestigeal organs in man
4. Evidence from connecting link : In animal
groups such animals are found in which along with
undeveloped characters, some developed characters
are also present. Such animals forms/functions like a
link or bridge in between the old ancestors and
developed animal classes. These animals are known
as the connecting link.
Example : Archaeopteryx, Echidna.
5. Evidence from fossils : Dead remains of
various types of plants and animals of ancient times
(past records) are found preserved in rocks, they are
called as fossils. The study of Dianosaurs and
Archaeopteryx fossils shows this that complex
organisms have evolved from simplest organisms.
ORGANIC EVOLUTION
271
6. Evidence from Geographical distribution : The distribution of plants and animals on
the earth gives evidences of organic evolution. The distribution of plants and animals depends
on weather and climate. It is observed that specific types of plants and animals are found in
specific places. Example : Kangaroo in Australia and Lion and Elephants in India.
Answer these questions
1.
What are the reptilian characters of archaeopteryx?
2.
What do you mean by fossils?
203. Theories of organic Evolution :
It has been proved that new species have evolved through the organic evolution and
further or in future the species will continue to be evolved. How organic evolution has occured?
To explain the organic evolution various scientists have postulated their own theories. The
description of main theories is given in this chapter.
Lamarck’s Theory : Jean
Baptiste de Lamarck, a French
scientists in 1809 for the first time has
given the theory of organic evolution
in his book philosphic Zoologique.
According to Lamarck theory the
development of all the living organisms
is effected by the environment.
Lamarck theory is based on the
following points.
1.
Direct effect of environment.
2.
Use and disuse.
3.
Inheritance
characters.
of
l
l
l
acquired
Lamarck’s theor y can be
postulated by the following four
hypothesis.
(a) In all types of organisms the
organs found in their body, they
themselves have the tendency to
increase in their size.
(b) Organs
develop
as
a
consequence of want or need.
272
l
l
l
l
l
Do you know?
Palaeontology was established by Cuvier in
1800.
Study of fossils is called as palaeontology.
Primary living organisms were of simple
structure from which complex organisms have
evolved.
Von Baer (1828) is regarded as father of
embryology. Von Baer states that organisms
during its embryonic development tends to
repeats the embryonic stages of their
ancestors.
By seeing the dissimiliarities of animals A.R.
wallace had divided the earth surface into 06
region.
Vestigeal organs were well developed in our
ancestors but as there was no necessity of
them they were degenerated during organic
evolution. These organs are still found in the
body of animals as vestigeal organs.
Andreas Wegner in 1861 studied the fossil of
Archaeopteryx.
The determination of the age of fossils and
rocks is done with the help of radio Isotopes.
SCIENCE 10
(c) The organs which are continuously and excessively
used by the organisms, these organs develops much
and those organs which are not used regularly remained
undeveloped.
(d) In the whole of the life span of the organisms the
acquired characters are inherited in the coming
generation of that organisms, this results in the origin of
new species.
Example : Giraffe animal is found in Africa. Giraffe was
animal similar to deer and remained alive by eating small
plants, on account of increasing effect of desert environment
vegetation gradually becomes scarce, and large trees were
found in much more numbers. On account of increasing height
of the trees, stretch in the neck and fore limbs of giraffe have
started, increasing from one generation to another. On
account of which the height and the length of the neck in
giraffe have increased much.
Darwin’s theory :
7 : Development of Neck
and fore legsin giraffe.
According to Darwin animals used to survive by
adjusting or making themselves according to their own environment. On the contrary of it those
who could not adapt themselves will die after sometime. Selection by nature goes on continuously.
Darwin has called this theory as “theory of natural selection” which is based on the following
facts :
(i) Enormous power of fertility in animals : All types of animals and plants has got a
power to reproduce enormously to maintain their own species stable.
Example : A female ascaris lays more than 2.5 crores of eggs. More than 02 thousands of
spores are formed in the capsule of moss plant. If all the tiny species develops completely than
they tend to increase in geometrical ratio and cover or occupy the entire earth, and there will be
no room left out to stand on the earth.
(ii) Struggle for existance : To maintain the natural balance, and there starts a great
competiton for getting food, water, light and well protected place to live.
(iii) Survival of fittest : Such organisms could survive which shows such variations
which are proved to be more beneficial and those organisms which develop harmful variations,
than such organisms will die in the struggle for existance. Fittest members reproduces healthy
offsprings, which are beneficial to the growth of species and race.
In nature, natural selection goes on continuously and the inheritance of beneficial important
variation goes on continuously thus resulting in the origin of complex species.
ORGANIC EVOLUTION
273
Modern Theory of Organic Evolution :
The theories given by Lamarck and Darwin have some demerits, after removing these
demerits the modern concept of organic evolution was postulated. This theory is known as NeoDarwinism. This recent theory is based on the following facts :
1.
Enormous power of reproduction is found in all organisms, therefore in struggle for existance
some organism remain alive.
2.
There is a definite places of living/habitats and the quantity of food on the earth.
3.
Mostly in every living species death rate is more.
4.
On account of gene-recombination, gene-mutation, and polyploidy in the structure and
physiology of organism much variations are observed.
5.
Isolation of natural population is due to small units, by which sub-species are originated.
6.
In this theory both mutation and isolation are essential for organic evolution.
Answer these question
1.
Which theory was postulated by Darwin to explain the inheritance of
variation?
2.
Write two evidences of organic evolution.
3.
Describe some examples of natural selection?
4.
What do you mean by connecting link?
Points to remember
l
The various species of recent plants and animals have evolved from the species
present in the ancient times by the process of slow, gradual sequence of
changes, it is called as organic evolution.
l
We proved the process of organic evolution by several important evidences
obtained from the biological regions and sources.
l
Evidence of homologous and analogous organs gives the evidences in favour
of organic evolution.
l
Structure of vestigeal organs proves that organisms have evolved from those
ancient ancestors in which these organs were functional.
l
Every organism during its development (life history) tends to repeat the
evolutionary history of its ancestors.
l
Ancestors of ancient times functions as a connecting link between the modern
developed classes of organisms.
l
Now a days by the study of radioactive elements we can estimates the fossils
and their age and prove this that the continuity of the life is maintained from the
time of origin till the present time.
274
SCIENCE 10
l
Lamarck has given the theory of inheritance of acquired characters and Darwin
has given the theory of natural selection.
l
Darwin was the originator of survival of the fittest.
l
Zoological name of man is Homo sapiens.
EXERSISE
Very short answer type questions :
1.
In which year the Darwinism was published in a book.
2.
Give the example of homologous organs.
3.
Give the example of analogous organs.
4.
Give two names of vestigeal organs.
Short answer type questions :
1.
What are vestigeal organs? Write four names of vestigeal organ found in man.
2.
Describe in brief : Homologous organs, Analogous organs.
3.
Give difference between homologous and analogous organs.
4.
What is the importance of fossils in organic evolution.
5.
What is evolution?
6.
How does natural selection take place according to Darwin?
7.
What do you mean by survival of the fittest?
8.
Give important characters of Lamarckism.
Essay answer type questions :
1.
What is evolution Explain the organic evolution by the study of comparative morphology.
2.
What are vestigeal organs? How they explain the organic evolution.
3.
Explain the organic evolution on the basis of evidences.
4.
What do you mean by evolution? Describe in brief the Darwinism.
5.
Explaning the important characters of Lamarckism give the merits and demerits of
Lamarckism.
6.
What are the important characters of evolution on which the Darwin theory is based,
describe?
ORGANIC EVOLUTION
275
Chapter - 21
ENVIRONMENT AND ENVIRONMENTAL PROBLEMS
We shall learn:
21.1 Environmental
problems
21.2 Pollution:
21.3 Forest conservation
21.4 Waste material
21.5 Eco- system
21.6 Environmental
conservation.
21.7 Mass awareness for
environmental
preservation
21.8 Greenhouse effect
and global warming
21.9 Depletion of the
ozone layer
21.10 Acid rain
The concept of Indian culture and human society is
based on the principle of environmental preservation. Right
from the day civilization came into being, to love nature
and the living being has been a common characteristic of
human society. Our beautiful life is a precious gift of nature.
Human beings consider themselves fit to have total control
over the valuable treasure that nature has given to them.
But it is the duty of human beings to refrain from reckless
exploitation of natural resources. They should try to protect
and preserve them so that life could be pleasant and these
resources could be saved for the future generation.
Industrialization, urbanization, technologicalisation and the
market based economic system have increased the
exploitation of natural resources resulting in an
environmental crisis confronting humanity as a challenge.
These days there are many environment related problems
which attract the attention of all. What are the problems?
What are their causes? How could they be avoided to
preserve the environment? Let us try to learn about all
these things in this chapter.
Every living being has his/her/its environment. It
can be of a plant or living organism. Environment means
all those biotic or abiotic components that are found around
living things which have a mutual effect on that biotic or
abiotic component. All those components which have an
effect on our life together make the environment i.e. the
temperature, air, water,
trees, plants, animals, birds,
Mahatma Gandhi Said:
insects
and
micro
organisms. All these have l Nature has everything to
give to man. But nature
effect on us. Hence all these
gives nothing to give to
are the components of our
a greedy man
environment.
Some Main Definitions:
Environment is not the
name of any single
276
l
It is high time that
pollution free and
environment friendly
techniques are adopted
for development.
SCIENCE 10
De
p
of letio
oz
n
lay one
er
ENVIRONMENT AND ENVIRONMENTAL PROBLEMS
n
tio
ica ation
tef
es ific of
for ert ion
De to d tinct lant
p
e
du d ex l & s
an nima eeie
a sp
component; it is the sum total of all those conditions which directly or indirectly have a mutual
effect on the life and development of all living beings.
Environment is an external power which affects us.
Environment is the sum total of external conditions prevailing all around in which a
living being or a community lives.
Environment is the foundation of life. Without it life on earth cannot be imagined. Its pollution
has given birth to numerous environmental problems.
21.1 Environmental Problems:
Man has to depend on natural resources for all his needs like food, clothing, shelter and
technological
and
industrial
development. The increasing
De
population and the ever increasing
sli sert
f
o
d
on
Ch ing , lan
demand of things for physical
uti ater,
a
l
l
rou ng Floo d
Po r, W &
in d,
te
amenities have resulted in the fast
i
l
S
A oi d
oil of r the
S un
ero ive
exploitation of natural resources.
sio r,
So
n
Tampering with natural resources has
resulted in many environmental
1 2
problems.
8
3
21.2 Pollution:
Problem
E
n
Mixing of harmful substances
4
7
io
w G ffec
at
ar lo t
c
g
i o
with soil, air and water is pollution.
6 5
re m ba of
tif t
en ing l
er dye lts
D
Unwanted change in the physical,
ef h a
sa
fe ou nd
ct s
R
chemical
and
biological
ed
. e
of ucem
Collection
characteristics of air, water and soil
Re Natu ent of garbage
so ral
is pollution.
rce
s
For example mixing of filth and
gases like carbon dioxide in the
drinking water makes the water
polluted
Pollution:
The substances that pollute air, water or soil are called pollutants. In other words pollutants
are those substances which cause pollution e.g. dust particles in the air, carbon dioxide, sulphur
dioxide.
1. Biodegradable Pollutants : Biodegradable substances are those which are easily
decomposed by micro organisms. The substances made by decomposition do not hurt the
nature e.g. domestic waste, human and animal refuse, waste material obtained from agricultural
processes, animal dung, paper, animals bones, leather etc. All these pollutants get decomposed
in a natural way.
2. Non biodegradable pollutants: These pollutants cannot be decomposed by micro
organisms. D.D.T., plastic, bags of polythene, germicides, pesticides, aluminium ware, mercury,
arsenic, synthetic fibre, glass ware, iron nails, silver foil, radio active substances are the examples
of non-biodegradable pollutants.
277
Find out the answers to these questions yourself:
Main Air Pollutants:
1.
Name two environmental problems related to air
pollution.
l
Carbondioxide
2.
What do you know about pollution?
l
Carbon monoxide
3.
Which are more harmful among the biodegradable
and non-biodegradable pollutants?
Types of pollution:
l Sulphur dioxide
l
Hydrogen sulphide
l Carbon sulphide
Main pollution
l Florine compound
l Air Pollution
l
l Water Pollution
l Ammonium sulphide
l Soil Pollution
l Sound Pollution
Nitrogen oxide
l Cancer producing substances,
radio active substances
Air Pollution: Air is formed by nitrogen, oxygen and carbondioxide in a certain fixed
proportion. If this proportion increases or decreases it causes air pollution.
Unwanted change in the physical, chemical or biological
characteristics of air is called air pollution.
The substances that pollute the air are called air pollutants.
1.
Natural Sources:
l
Dusty winds cause dust particles to mix into the air thereby polluting it.
l
Eruption of a volcano brings out smoke which contains ash and hot gases. These pollute
the air.
l
Micro organisms decompose the bodies of dead plants and animals. In this process
ammonia gas is discharged which causes air pollution.
l
Pollen grains let out by plants fly in the air and cause air pollution.
The pollution caused by natural pollutants is far less in quantity than the one caused by
man made substances.
2.
Man made sources:
Houses, factories and mills, automobiles, industries, nuclear plants, use of chloro-flouro
carbon in mining, smoking, deforestation are the major agents to cause damages are created
by man. All these contribute to air pollution. Hence they are called man made sources. Man
made main sources are created because of the following : combustion, motor vehicles, industries,
thermal power plants, chemical fertilizers, pesticides, deforestation, use of CEC while mining.
All these man made sources pollute the air.
278
SCIENCE 10
Effects of Air Pollution:
Air pollution causes the following effects on human beings, vegetation and substances:
l
Effects of nitrogen oxide: Inflammation of the tissues of lungs, causing lung cancer and
pneumonia, diminishing the capability of carrying oxygen to different parts of the body.
Concentrated nitrogen oxide causes burning sensation in the eyes. It also weakens the
immunity system.
l
Effects of Sulphur dioxide : Burning in eyes, phlegm and cough, headache and diseases
like asthma.
l
Effects of carbon mono oxide : Head-ache, vomiting, dozing, difficulty in breathing,
muscular weakness and diminishing of the ability of carrying oxygen to the cells of lungs.
l
Effect of agricultural activities: Skin allergy because of pollen grains, diarrhoea, headache, difficultly in breathing and muscular lethargy.
l
Effects on Seasons: Different polluting substances affect the formation of clouds and the
temperature. The excretion from industrial factories also affects the formation of clouds.
Controlling Air Pollution:
l
Avoiding the use of cheap fuel.
l
Factories and industrial units should be built far from residential areas. Air pollution can be
minimized by raising the height of the chimneys of factories.
l
Persons assigned to use chemical/synthetic paints and sprays should wear masks.
l
Avoiding smoking.
l
Fixing of filter/after burner on gas releasing pipes of vehicles.
21.2.2 Water Pollution:
Indian culture considers water as life. It is believed that it
is a holy gift from nature which should always be saved from
pollutions and filth. These days the fast growing population
industrial development urbanization and the changes in the
standard of living are causing water pollution.
Change in the physical, chemical and biological
characteristics of water which adversely affect human and other
living beings is called water pollution.
The holy Vedas warn man
ceeHees DeewºeefOeefnbmeeri.e. Don’t kill
water and medicines. It
means that one should not
pollute water because
there is nectar and healing
capability in pure water
Reasons of water pollution and water preservation:
1.
Running Refuse and Domestic Running Refuse : It includes soap, detergents, metals,
standing water, floating mud in pits and trenches, human excreted wastes. They all pollute
the underground water resources. Efforts should be made to prevent them from mixing
into the sources of water.
2.
Industrial effluents : The watery residuals coming out of industrial units are poisonous.
These chemical substances are: cyanide, plastic, rayon and edible oil. They should be
ENVIRONMENT AND ENVIRONMENTAL PROBLEMS
279
prevented from mixing with the sources of water.
3.
Detergents : Soap and detergent industries cause water pollution.
4.
Weed eradicating chemicals and germicides/pesticides: Chemicals like Pandrin and
Melathian which are used to protect crops from weed and pests also cause water pollutions.
5.
Chemical fertilizers : Chemical fertilizers are used to increase the yield of crops. These
chemicals get mixed with irrigational and rain water and flow into rivers, ponds and lakes
and result in water pollution.
6.
Radio active Substances: Nuclear energy is released at the time of nuclear explosion.
Nuclear substances pollute water by getting mixed into water currents.
Protection of surface water : The water found at a depth of about two feet underground
is called surface water. The following steps may be taken to protect the surface water from
pollution:
l
By stopping deforestation and planting new trees as vegetation completes the water cycle
l
If there are different kinds of grass on the ground the surface water remains at desired
level.
l
By adopting flood management techniques to use the additional flood water.
l
By preventing wastage and mis-use of water in daily life the surface water can be saved.
l
By protecting the surface water from different types of pollution.
l
By treating the contaminated water which flows out of industrial units or domestic use
before it mixes with the surface water.
l
Absorption of water into the source of surface water can be facilitated by planting trees
near and around the sources of surface water.
l
Making all types of water pollution free.
l
By making pucca irrigational channels in agricultural farms water can be conserved.
l
By building pucca water reservoirs.
l
By digging wells on both the banks of rivers and connecting them with the river through
pucca channels. It can save us from the fury of floods also.
Effects of water pollution:
The following are the effects of water pollution:
1-
On animals: Eggs of animals at the stage of larva are destroyed by the polluted water and
the life of animals is endangered. Polluted water is deficient in oxygen which may result in
the death of animals.
2-
On vegetation: Polluted water decreases the rate of the process of photosynthesis. The
use of germicides and pesticides increases blue green algae which reduces oxygen in
water. Decomposition of algae increases the speed of erosion and decaying.
280
SCIENCE 10
3-
On human beings: Polluted water causes many diseases in human beings. Some of
these diseases are: typhoid, diarrhoea, cholera, dysentery, jaundice, hepatitis. Polluted
water affects human kidneys, liver, lungs, brain etc.
In the holy Vedas we find some tips about the ways to prevent water from being
polluted and to purify polluted water. The main method of purifying water is
through mantras or by entering solar heat into the water through a natural process.
Kusha is a particular type of grass which acts as a water purifier.
Control
Following are the methods of controlling water pollution:
Do you know?
1-
Treating the flowing refuse before letting it flow into
the sources of water
l
2-
The harmful substances found in industrial waste
should be chemically neutralized before they get
merged into sources of water.
3-
Waste materials like paper, plastic, rotten fruit,
vegetables and food should not be thrown away
in the open.
4-
Solid wastes that contain biotic substances should
not be thrown into water reservoirs.
l
5-
If oil happens to pollute water sources, the oilish
layer should be removed
l
6-
People should strictly be made to adhere to the
regulations and laws made by the government for
the purpose of controlling water pollution.
l
l
Water pollution can also be
controlled with the help of water
hyacianth or pistia.
Sometime ago pistia was
considered to be a water
pollutant. But now its special
characteristics are considered
to be beneficial for human
beings.
Pistia or water hyacinth
Absorbs the water pollutants.
The long roots of pistia or water
hydranth puck up cadmium and
pewter in 24 hours.
It can soak the phenolicl
substances found in industrial
and domestic wastes.
RAIN WATER HARVESTING
Underground water table has been
continuously going down. Hence the challenge
to preserve water has come before us. That is
why rain water harvesting has come to be
considered as an important remedy. Let us,
therefore, try to understand the reasons behind
the going down of the underground water table.
l
Over exploitation of underground water by
means of hand pumps, borewell, etc.
l
Lack of availability of alternative sources
of water at the local level.
l
Rain water Harvesting
Heavy pressure on underground water development due to the misuse of ancient water
preservation tools like village ponds and bawaries (wells having steps).
ENVIRONMENT AND ENVIRONMENTAL PROBLEMS
281
l
Underground preservation of rain water
is called rain water harvesting.
l
Following is the method of rain water
harvesting at our homes:-
l
The roof of the house should be so
constructed that water should flow only
in one direction. With the help of a pipe
this water be brought into the ground and
Roof water harvesting
from there should flow to the well or the
hand pump. This rain water runs from
the roof into the ground and can enable us to draw more water from the well or hand pump.
Both the banks of such rivers which generally get flooded, wells should be dug and the
extra water of the rivers be diverted to these wells. In Tamil Nadu this method is called
Tappakulam.
Main aims of rain water harvesting:
l
Preservation of water for the coming years.
l
Improve the quality of the characteristics of underground water.
l
Prevent soil erosion and too much flow of water.
l
Recycling of industrial and urban waste.
l
Recharging of underground sources of water which are getting depleted due to over
exploitation.
In India the technique of the management of the sources of water is quite ancient. We find
description of the ways of water storage and water preservation in the holy Vedas and other
religious books. People had the knowledge of building the barrages in 300 B.C. Raja Bhoj had
constructed a huge lake near Bhopal in the year 1100 AD. From a technical point of view this
lake is a matchless marvel. At present this lake is performing the three fold functions of storing,
preserving and supplying water to the people of Bhopal.
In Jhabua district of M.P. there are 1000check dams, 1050 lakes/ ponds and 1100
community lift irrigation facilities.
In Dewas district of M.P. the administration has made it compulsory for every home having
a hand pump to install a rain water harvesting system. Similar rules are being enforced in the
whole of M.P.
The M.P. Govt. has started the Jal Abhishek programme with a view to emphasize the
need of water preservation and roof water harvesting so that the problem of scarcity of water
could be over come.
Underground Water (Recharging of ground water)
Collecting water under the ground by using the techniques of water conservation and rain
water harvesting and reusing it and then repeating the same techniques for again collecting
water under the ground is called water recharging.
282
SCIENCE 10
Answer these questions
1-
Between 5-0 to 7-0 P.M. air in the city is more polluted. Find out the reasons for it.
2-
Between the natural sources of pollution and the man made ones, which are more
harmful and why?
3-
Make a list of such religious sites and rituals which are the cause of water pollution.
21.2.3 Soil Pollution:
Increasing population has affected natural
resources. Residential houses, buildings for industrial
use are being built on a large scale. Chemical fertilizers
and pesticides are being sprayed on agricultural farms Reasons
for obtaining minerals and mining activities are going on of Soil
at a rapid pace. Our earth is being made unclean by Pollution
littering chemical and all kinds of other waste materials.
All these poisonous substances get added in the soil
and then pollute water. The use of pesticides
bactericides, germicides and chemical fertilizer in farming
activity results in soil pollution.
Industrial Activities
Urban
Radio Activity
Agriculture
Process
Chemical Metallic
pollution
Mining
Soil Erosion
Soil is polluted when undesirable substances (pesticides, bactericides, germicides,
chemical fertilizers etc.) get dissolved in it. This is called soil pollution.
Industrial Activity:
Industrial wastes are either mixed with the soil or are thrown into rivers. These wastes act
as pollutants and change the biological and chemical character of soil.
Urban Wastes :
Useless waste substances, both domestic and industrial come out of urban areas. These
include: l dried up slime of floating excreta. l litter l useless substances l plastic l metallic
objects l residues of fuel l useless aero planes and motor cars, trucks etc. l useless utensils
etc. Of these, sheets of plastic and polythene do not biodegrade and are the main reason of soil
pollution.
Agriculture Process : Soil is being polluted because of the use of pesticides, germicides
and chemical fertilizers. Because of these fertility of soil gets diminished too.
Mining: Because of mining the vegetation on the upper surface of earth has been getting
less and less and grazing land and fertile farm land is becoming scarce. Carbon dioxide increases
because of mining activities and gives birth to green-house effect acidic rain, global warming
which cause climatic changes.
Soil Sedimentation: Windy storms, high velocity winds and flood water transport soil
and mineral salts away from agricultural and grazi ng land. This transportation of soil and mineral
salts is called sedimentation. After the floods, dirty water is filled in pits and ponds. It results in
widespread dirt and filth which reduces the water storage capacity of the flooded place.
ENVIRONMENT AND ENVIRONMENTAL PROBLEMS
283
Harmful effects of Soil Pollution:
l
Solid waste and litter are the breeding agents for flies and mosquitoes which are the
reasons for diseases.
l
Industrial waste adversely affects the fertility of land by disturbing the balance of acidity
and basicity.
l
Acid rain decreases the fertility of soil which adversely affects the yield of crops.
l
Spray of germicides causes the germicides to penetrate into the food chain and harm our
health.
l
Floating excreta make the environment stinking and cause diseases.
l
Nutritional ingredients of soil get depleted by soil erosion.
Land Management and Preservation:
Preventing geological depletion, erosion and
land slides is called land management.
People’s cooperation in forest
preservation:
Let us now try to know as to how depletion and
erosion of land and land slides harm the land.
Some national efforts have been
able to create awareness in the
people about the need and
importance of preserving forests.
The credit for this awareness goes
to the government and social
service organizations. The chipko
compaign of U.P. the Mitti Bachao
campaign of Hoshangabad in M.P.
and the pledge of the women of
Rishikesh and Dehradoon not to cut
wood are some examples of
awareness of the importance of
forests and environment. These
effor ts have enhanced social
contribution for the preservation of
Land slides : When mountaineous rocks crack
due to some natural or man made reasons and due to
gravitational force fall on to the ground, it is called a
land slide.
Earthquake: The shaking, trembling and
shivering of a part of land or earth is known as an
earthquake. An earthquake is a terrible natural disaster
which causes immense loss to life and property.
Earthquake Management: An earthquake is a
natural disaster. It is not possible for man to prevent it.
But its consequences can be minimized by human
efforts. For this protective measures can be taken for
example:
l
With the help of earthquake measuring system,
fore casting an impending earthquake and thus
preventing the loss of life and property.
l
Construction of earthquake resistant buildings by using light and simple building material.
Land Erosion:
l
The sun, wind and water remove the upper layer of earth crust. This process is called
land erosion.
l
Main causes of land erosion:
l
The soil of the upper layer of earth’s crust is transported off by the rain water to rivers and
seas.
284
SCIENCE 10
l
Tornadoes and wind storms also transport the soil from one place to another.
l
Places having scarce vegetation and grass experience more land erosion.
l
Grazing by animals and removal of vegetation cause land erosion.
l
Putting forests to fire.
l
There is more land erosion on slopes.
Management:
l
By plantation l
l
By using organic manure l
By using crop cycle
By making steps like structures on slopes
Land Preservation/Protection
Maintaining the area and fertility of cultivable land is called land preservation. The following
steps can be taken for land preservation:1-
Harmful substances of industries cause land erosion. It is therefore necessary that
industrialization is done on appropriate places.
2-
Canals built for irrigational purposes help in preventing soil erosion.
3-
The help of cyclic alternate farming or cycling of crops must be taken to preserve the
basic structure of land.
4-
Rocks should not be destroyed in mountainous and slopy area.
5-
Plants should be grown on the bundings of farm land.
6-
In the hilly areas land should be ploughed in the opposite direction of the slope and trees
should be planted.
7-
The least possible use of pesticides and weedicides should be done.
8-
Dependence on natural manure should be
increased.
9-
Urbanization of cultivable land should be
prevented.
10-
Uncontrolled grazing by animals in the grazing land
should be prevented.
11-
Prevention of the loss of soil due to the flow of
water by building dikes and barrages.
12-
Controlled use of germicides and weedicides.
13-
Urban waste litter, floating excreta etc. should be
first chemically treated and then used. Stagnation
of water be prevented.
14-
More and more trees should be planted to prevent
soil erosion
15-
Recycling of obstinate soil pollutants like plastic
and petroleum by-products should be done.
ENVIRONMENT AND ENVIRONMENTAL PROBLEMS
Do yon know?
l
Pesticides/germicides should
be used very carefully and in a
balanced manner because they
kill not only harmful germs and
pests but eliminate the
beneficial ones too.
l
Many producers spray
germicides on vegetables with
a view to give them a look of
freshness. It is a condemnable
act as it affects our healthy
body. It is therefore necessary
to wash the vegetables before
using them.
285
21.2.4 Sound Pollution:
Important Facts:
The modern way of living has given birth to a
new pollution. It called the sound pollution or noise
pollution. In the crowded cities the noise of motor
vehicles and industrial units and the noise created by
loudspeakers for propaganda and advertisement is on
the increase. This noise disturbes the peace of our
life. The ear friendly melodious music of the past has
now turned into noise.
l
The sound measuring unit is
decibel which is denoted as db
l
Sound higher than 60 db causes
sound pollution
l
Normal conversation - 30-60 db
l
Tick Tick of the clock - 30 db
l
Telephone bell - 70 db
The disturbance of noise created in the
environment through different undesireable
means is sound pollution.
l
Whistle of train - 110 db
l
Lighting - 120 db
l
Crackers - 120 db
Effects of sound Pollution:
l
Aero planes - 120 db
l It impairs hearing ability. One may go deaf.
l Creates headache and irritation.
l
Adversely affects the unborn child.
Control:- The noise can be controlled in three ways
By controlling the
sources of sounds
By erecting barrier in
the course of sound
By protecting the
senses properly
1. Playing the loud speaker,
radio, television, stereo etc.
in a low volume.
1. Planting trees on the
sides of roads so that
sound be blocked.
2. Establishing industries far
from the city.
2. Using sound absorbing 2. By putting cotton inside
substances in the
the ears.
course of sound.
3. By moving away from the
place of loud sound.
3. Proper maintenance of
industrial machines.
1. To avoid loud sound, ears
should be blocked
by inserting fingers.
4. Using high quality fuel
in vehicles.
5. Using silencers.
21.3 Conservation of Forests:
Forest conservation means the use of forests and its produce and resources in such a
way that we may fulfill our needs without harming them and that they are left in such a state that
future generations may benefit from them for the longest possible time.
First of all let us know the main reasons responsible for the depletion and destruction of
forests:
286
SCIENCE 10
1. Expansion of agricultural land, 2.Eating up of vegetation by the animals as fodder,
3.Construction of dams, 4. Setting forests to fire, 5. Cutting trees for fire wood, 6.Felling trees for
industrial purposes, 7. Natural disasters.
These are some of the reasons which are depleting our forests which is giving birth to
many serious problems.
Hazards of deforestation:
1.
Scarcity of rain
2.
Changes in climate
3.
Expansion of deserts
4.
Diminishing grazing land
5.
Decreasing of underground water level
6.
Diminishing of forest resources.
Efforts are being made at national and international levels for the preservation of forests.
Some steps that could be taken to preserve and protect forest are:
1.
Afforestation by planting new plants.
2.
Raising trees on the basis of genetic technology.
3.
Raising disease immune and insect immune trees.
4.
Giving preservation of forest and forest animals in the form of a mass campaign.
5.
Encouraging social forestry.
6.
The M.P.Government has established a special cell under the Chief Conservator of
Forests in 1987. This cell looks after the activities of the conservation of forests and
the developments related to it.
21.4 Waste Material:
The material abandoned after using it, whether it comes out of homes or factories or
agriculture and which pollutes the surrounding environment is called the waste material. It is
found in three forms:
1- Solid Waste 2- Gastric Waste 3. Liquid Waste
1- Solid waste : The unwanted wastes which are solid and are thrown away by man from
homes, schools, shops, factories, hospitals etc. are called solid wastes, e.g. the wrapper of the
tooth paste, polythene bags, litter etc.
Solid wastes are of five kinds: (1) Industrial waste (2) Domestic or Municipal waste (3)
Waste created by agriculture (4) Mining waste (5) Other waste.
Industrial waste: It includes: copper, aluminum, hazardous materials coming out of melting
plants, poisonous material produced by plastic making.
Domestic waste : It consists of domestic litter, plastic bags, shells, of fruit and vegetables,
corks of bottles, the waste coming out of slaughter houses etc.
ENVIRONMENT AND ENVIRONMENTAL PROBLEMS
287
Waste created by agriculture: It includes:The chaff obtained after harvesting of crops, leaves, grass etc.
Mining waste : The waste material littered around mines.
Other waste : The waste material coming out of hospitals, poultry farms etc.
Management of solid waste: Solid waste is of two kinds : biodegradable and that
which can be recycled. Biodegradable waste can easily be eliminated while the other wastes
are difficult to dispose of
Technique of Management: Biodegradable, combustible and non-combustible wastes
should be categorized separately. Containers for dumping litter and waste should be placed at
all places. Proper arrangement should be made to transport waste to the dumping place. Solid
waste should be converted into manure by using the technique of vermi composting.
Answers these questions.
1.
How do insecticides cause soil pollution?
2.
What is decibel?
3.
Describe the way of controlling the pollution of sound?
21.5 Ecosystem:
The living organism found in the environment interact with the atmosphere around them
for example living organisms have to depend upon both the living and the non-living for their
needs of habitation and food. So there is a mutual inter relationship between the living and nonliving. This inter relationship creates a system which is called the ecosystem. The branch of
science under which the ecosystem is studied is called Ecology.
Main components of the Ecosystem:
Biotic Components: They consist of all living beings such as trees and plants, human
beings, animals, micro organisms etc. Living being have been put in three categories according
to their work:(A)
Producers : These are green plants that synthesise/prepare their food through
photosynthesis.
(B)
Consumers: Those who depend on others for food are the consumers. Consumers
are of the following kinds: Primary consumers, Secondary consumers, Tertiary
consumers.
Primary consumers : They are herbivores. They consume plants and plant products.
Hare, deer, insects and elephants are good examples of primary consumers.
Secondary consumers: They are also called primary carnivores. They eat up herbivores
animals. Their examples are cat, fox, dog, wolf etc.
Tertiary consumers: They are also called secondary carnivores. They consume both
the herbivores and carnivores animals. They are also called the top consumers and the last
consumers. Examples: Lion, kite etc.
288
SCIENCE 10
(C) Decomposers: They are micro organisms. They obtain their food from orgnic
compounds available in dead bodies. They are also called micro consumers. examples: Bacteria,
fungus.
Abiotic components: Abiotic components include
l
Carbonic and acarbonic matter, l
physical environment.
Acarbonic matter includes : carbon, hydrogen, oxygen, nitrogen, phosphate
Carbonic matter include : protein, carbohydrate, fat.
Physical environment includes : light, temperature, humidity, soil
Interdependence of abiotic and biotic components:- The producer of biotic components
(i.e. green plants) produce their own food. They are autotrophs. consumers depend on them for
their food. Producers produce food in the presence of abiotic components. It means that the
producers need carbonic components and physical environment. Similarly consumers too depend
on abiotic components. So we can say that the first interaction of biotic takes place with
environmental components and the second interaction happen between biotics themselves.
After the death of biotic components decomposers them and the basic matter found in them like
minerals and salt is assimilated by them into a biotic environment. In this process of decom
posing microorganisms use some carbonic matter for their own nutrition. Therefore they are
called micro consumers.
Food chain: Plants can produce their own food other living beings who are herbivores
get food from them. Carnivores obtain their food from herbivores. In this way the food advance
forward as a link of a chain. This cycle goes on
Important Fact: Nutritional levels : There
uninterrupted. It is called the food chain.
are various levels in the food chain. Their
The transfer of energy in the form of food
number is not more than 5-6. These levels
from plants and vegetation to herbivores and from
of the food chain are called nutritional
herbivores to carnivores and its consumption by
levels.
them continues without interruption and is called
the food chain.
Terrestrial
Floating Algae
↓
Grass
↓
Zooplanktons
↓
Deer, Cow, Goat
↓
Small Fish
↓
Man, Lion, Tiger
↓
Big fish
↓
Crocodile, Alligators
ENVIRONMENT AND ENVIRONMENTAL PROBLEMS
289
If we look at the terrestrial food chain we will find that in it the producers are the green
plants whose products are consumed by deer, cow, goat etc. as their food. These herbivores
are eaten up by carnivores like man, lion, tiger etc. In this way different ecosystems have
different food chains.
Food web: Generally food chains are simple and small. Because there occur a loss of
energy in the process of energy transfer from one to the other level. Therefore food chains are
those by which energy is transferred from one to the other living organism. When numerous
food chains by joining together form a complex course a web of all the chains is formed. This
web of the food chains is called the food web.
21.6 Environmental conservationWays and efforts for conservation means protection. Therefore environmental conservation
means that the environment is kept healthy and congenial in spite of developmental activities by
preventing over exploitation of natural resources
Objectives of Environmental Preservation:
l
Preserving natural resources continuously and for all times to come. Trying to increase
them and using them properly.
l
Using renewable and non renewable natural resources discreetly.
l
Maintaining a proper balance between living and non living beings. Environmental
preservation means the preservation of the natural resources which are the following.
1. Water, 2. Soil, 3. Forests, 4. Energy, 5. Minerals.
Conservation of water : It is a renewable resource. It can be preserved by proper
drainage and proper storage systems.
Soil Conservation : It is also a renewable resource. Blocking the current of water, terrace
farming, bunding the farm lands and forestation are some of the means by which the soil can be
conserved.
Conservation of forests: Forests too are a renewable natural resource. Their preservation
can be assured by proper maintenance, afforestation, establishment of more and more national
parks, social forestry, encouraging agro, forestry, stabling germplasm and genebanks, using
biotechnology and tissue culture etc.
Energy conservation : It is a non- renewable resource. For its conservation alternative
sources of energy like solar energy and nuclear energy should be used. Use of fossil fuel
should be minimised as far as possible.
Mineral conservation : This too is a non-renewable resource. Limited and controlled use
of minerals, discovering alternatives and recycling of minerals are some of the ways by which
this natural resource can be conserved.
21.7 Mass Awareness for Environment:
In view of the ever increasing environmental imbalance the need and importance of its
conservation is more compelling. For environmental imbalance different people at different levels
290
SCIENCE 10
are accused. But we should know that there are different reasons for environmental imbalance.
Now let us identity those areas about which a general awareness may be created. These
areas are:
1. Population Growth: The ever growing population has disturbed the balance of demand
and supply. In the developing countries the growing population is the main reason of environmental
imbalance. The steps taken by the government to check population growth cannot succeed
unless the people themselves are aware of the hazards of population growth. It is therefore,
necessary to create mass awareness to prevent population growth.
2. Proper use of resources: Discreet and proper use of natural resources is essential to
maintain environmental balance. In this way water, forests, minerals, soil etc. can be conserved
for a long time to come. The resources which cannot be renewed should be managed properly.
3. Awareness to remain alert against pollution: It is necessary to make people aware
of pollutants and of the activities which spread pollution and of the ways and means by which it
can be prevented. People should be properly sensitized in respect of the following:
l
Deforestation.
l
Soil pollution due to germicides etc.
l
Excessive use of sound amplifying equipment.
l
Use of a common vehicle to save energy.
4. Awareness for conservation: How can energy, water, soil, forests and wild life be
conserved? Why is their conservation necessary? When people will know the answers to these
questions their knowledge will greatly help the conservation efforts.
5. Reforming the habits (Discreet spending):- Man’s attitude towards the expending of
electricity, water, wood etc. is rather of carelessness. Man can change his habits and can save
the precious natural resources by minimizing their use.
By creating awareness in respect of all the above mentioned areas much can be achieved
for environmental preservation.
Environmental education plays an important role in creating environmental awareness. It
can also help the students to become democratic citizens. Through it they come to know about
their rights and duties towards the general masses and towards nature.
l
For creating environmental awareness seminars, workshops, exhibitions, rallies,
competitions etc. play an important role.
l
Along with the government voluntary organizations too work for environmental conservation.
21.8 Green House Effect:
Carbon dioxide, methene, nitrogen oxide, chlorofloro carbons are known as green house
gases. These gases mix into the atmosphere because of excessive consumption of coal and
petroleum products, deforestation, melting of snow etc. These green house gases make a shield
like layer between the atmosphere and the earth. This layer works like a woollen blanket. It
ENVIRONMENT AND ENVIRONMENTAL PROBLEMS
291
absorbs the heat of the sun. This layer is transparent, so the rays of the sun pass through it and
reach the earth. When the short wave length rays of the come after radiation, enter the
greenhouse, there they turn into long wave length rays. But the green house gases stop these
rays and do not let them go into the atmosphere. Due to these rays the temperature inside the
green house shoots up. This temperature is higher than the out side temperature. This is called
the Green House Effect.
To exhibit the green house effect a house of glass/fiber is built on the earth. Plants are
kept in this glass house. The sun’s rays (short wave length rays) enter it. From there they reflect
and are absorbed by the glass walls. Due to this the temperature inside the glass house gets
higher than the out side temperature. This is called the green house effect.
Global warming:
Gases are produced because of a number of human activities and also by some natural
activities. Among them there are green house gases too. All these gases accumulate in the
atmosphere and form a huge layer which does not let the heat of the earth enter the atmosphere.
The human activities which make the temperature higher than normal are: breathing by living
beings, swimming, walking etc.
Main Reasons of Global Warming: Deforestation :
l
The continuous felling of trees results in increased quantity of carbon dioxide. As this
carbon dioxide will be ued in photosynthesis, planting more and more trees becomes
necessary.
l
Impossibility of complete and total combustion of fossil fuel like coal, petroleum, diesel etc.
This also increases the quantity of carbon dioxide, carbon mono oxide etc. in the
atmosphere. So efforts must be made for the total combustion of fossil fuel.
l
Global warming takes place due to the use of refrigerators, fire extinguishing equipments,
aerosols, foam etc. because they contain chloroflorocarbons which gets released from
then and deposits in the atmosphere.
l
Global warming is caused by many biotic activities like melting of snow, decaying of
vegetables and dead bodies. The biotic activities happening in agricultural farms, the
chemical actions/reactions taking place in the dumps of litter and waste materials etc.
l
Nitrogen oxide gas is formed by chemical fertilizers used in agricultural farms and by the
vehicles run by petrol or diesel.
Destructive effects of global warming:
1.
Continuously rising temperature of the earth results in increased vaporization which leads
to the scarcity of water.
2.
Rising temperature will result in the melting of polar snow. The melting of snow of the
poles will raise the water level of oceans which will endanger the coastal cities and their
population. The quantity of salt will increase in the water and will lead to the scarcity of
drinking water.
3.
It may cause untimely death of trees, plants and animals which may cause erratic and
untimely rain fall or drought.
SCIENCE 10
292
4.
It will hasten the speed of water and air pollution
Protection from global warming:
1.
Complete and full combustion of fossil fuels.
2.
Total ban on the use of chloro -floro carbon.
3.
Stopping the use of chemical fertilizers by increasing the use of biological manures.
4.
Use of solar energy and bio-gas instead of conventional energy.
21.9 Depletion of Ozone Layer:
Ozone layer is found at a height of 32 to 80 kilometers from sea level. It contains ozone
gas (o3) This layer acts as filter for earth. This layer does not let the ultra violet rays of the sun
reach the surface of the earth. In this way it acts as a protective shield for the earth. If these ultra
violet rays could reach the surface of the earth germination of seeds will stop and many more
problems will be there. Some chemicals have been harming this layer. The ozone layer is getting
thinner and thinner and now it has got a hole and the ultra violet rays, reaching the surface of the
earth, have been harming life on earth. The chemical that is harming the ozone layer is chloro
floro carbon. It is composed of chloroform and carbon which is used in refrigerator and air
conditioners. The chloro floro carbon (CFC) is disinte-grated by ultra violet rays and the chlorine
emitting out of it depletes the ozone layer. Following are the reasons for the depletion of the
ozone layer:1.
Chloro floro carbon destroys thousands of molecules of the ozone layer and harms it.
2.
On the ozone level there are numerous gases like Hallone 1301, chloroform, carbon
tetrachloride, methene, aerosol, foam etc. which are depleting it.
3.
The ozone level gets adversely affected when a volcano erupts and the quantity of sulpher
dioxide increases in the atmosphere.
4.
The emission of smoke from motor vehicles, two wheelers, industrial units, power
generating units contains sulphur dioxide, hydrocarbon, lead, carbon mono oxide etc.
These gases deplete the ozone level.
5.
Space ships get Jet planes etc. emit nitrogen oxide. It also harms the ozone level.
Polar regions are the most affected by the depletion of the ozone layer. On the Arctic the
ozone level has thinned so such that the surface of ozone layer has got holes in it.
Effects of the depletion of ozone layers.
These are the effect of the depletion of ozone layer:1.
The cells of the upper surface of human skin are damaged. Damaged cells let a chemical
substance called histamine which destroys into the immune system of our body resulting
in diseases like pneumonia, bronchitis, ulcers etc.
2.
Skin cancer may occur as an effect of ultra violet rays that come from the sun due to the
ENVIRONMENT AND ENVIRONMENTAL PROBLEMS
293
depletion of the ozone layer.
3.
Some genetic disorders and long duration diseases may occur.
4.
Very serious eye diseases like inflammation and cataract wounds may inflict us.
5.
Temperature shoots up.
6.
Micro organisms and vegetations are being adversely affected. Deficiency of proteins,
defective photosynthesis process and metabolic activities are some of the adverse effects
that are harming plants and vegetation.
7.
The food chain is also badly affected. Producer algae is destroyed. With the destruction of
algae water animal, like fish, aquatic birds, sea mammals (aqua life) whales, seals etc. as
well as human beings are adversely affected.
21.10 Acid Rain:
Acid rain is the distructive effect of air pollution. Canbondioxide, nitric oxide and sulphur
dioxide emitting out of industries, factories, vehicles and oil refineries dissolve in the air.
The heat of the sun rays activate the process of vaporization on the surfaces of the seas,
lakes and rivers. This vaporized water goes up into the atmosphere. There it is condensed in the
form of humidity. If it is meets congenial conditions, this vaporized water falls on to the earth as
rain but when this vaporized water is condensed and reacts to sulphur dioxide nitric oxide and
gases which are already there in the atmosphere, this reaction creates sulphuric acid, nitric
acid and carbonic acid. When they fall on to the earth like rain, it is called Acid Rain.
The effects of acid rain on the environment are the following:
The lush green cover look of the earth is destroyed; leaves begin to fall down the trees.
Roots of plants shrink. The disease resistance power of the plants begin to decrease. All biotic
activities are retarded.
l The fertility of soil diminishes. Standing crops are destroyed.
l Potable water gets poisonous.
l
Human eyes and skin develop irrilation Diseases of lungs become common.
l
Buildings of historic importance are discolored by the drops of acids.
Points to remember
l
Environment is the sum total of all those external conditions in which a living
being or a community lives
l
Main environmental problems: Pollution (air, water, soil, sound) depletion of ozone
layer, global warming, acid rain, waste management.
l
The substances that pollute air, water and soil are called pollutants.
l
Pollutants are of two types i.e. biodegradable and non-biodegradable.
294
SCIENCE 10
l
The sources of air pollution are of two types i.e. natural sources and man made
sources. Man made sources are more hazardous than the natural sources.
l
The physical, chemical and biological changes in the characteristics of water
which adversely affect human and other life is called water pollution.
l
When undesirable substances dissolve into soil, it is polluted. This is called soil
pollution.
l
The disturbance created by different unwanted loud sounds is sound pollution.
l
Sound pollution adversely affect hearing ability as also the physical and mental
abilities.
l
There is mutual interrelationship between the living and non-living. This
interrelationship creates a system which is called the ecosystem. The branch of
science which studies the ecosystem, is known as ecology.
l
The main components of eco system are biotic and abiotic.
l
In any ecosystem the biotic components (living) interact with the abiotic (non
living) components found around them and are interdependent on one another.
l
The main natural resources are air, water, soil, forests and energy.
l
70% of earth’s area contains water.
l
About 55% to 65% population of the world has been facing some kind of water
problem.
l
Natural balance is being disturbed by the uncontrolled exploitation of forest
resources.
l
We get raw material, timber, firewood, gum, sealing wax etc. from forests.
l
Awareness should be increased for the conservation of environment.
l
CO2, CH4 nitrogen oxide and chlorofloro carbon are called the green house gases.
l
Due to global warming the temperature of the world has been going up.
l
At a height of about 80 km. in the atmosphere the layer of ozone gas is found. The
ultra violet rays that emanate from sunlight and tend to enter the earth are
prevented from doing so by the ozone layer.
l
Chloro floro carbon (CCl2 f2) deplete the ozone layer.
l
Acid rain ruins the green and fresh look of the earth.
EXERCISE
Very short answer type questions :
1.
Which system is used to collect rain water?
2.
Which are the green house gases? Name them.
3.
Mention the formula of chloro floro carbon.
4.
Write the full name of C.F.C. gas
ENVIRONMENT AND ENVIRONMENTAL PROBLEMS
295
Short answer type questions:
1.
How is acid rain caused?
2.
Why is awareness necessary for the conservation of environment?
3.
What has been happening due to uncontrolled exploitation of forest resources?
4.
What is global warming? Explain.
Long answer type questions:
1.
Describe the techniques of water management and water conservation.
2.
Explain the techniques of forest management and forest conservation.
3.
Explain the all effects of the depletion of ozone layer.
4.
Explain the green house effect.
Project:
What are the reasons of soil pollution in your area? What will be your role in preventing
soil erosion in your area?
296
SCIENCE 10
Chapter - 22
MEDICINAL PLANTS
22.1 History of medicinal
plants.
Besides food Man
gets aromatic oil, wood and
medicines form plants. With
the
advancement
of
civilization, man in the
present time, with the help of
plants and their products
has contributed a lot to
economical and social
development of Nation.
We will study
22.1 History of medicinal
plants.
22.2 Classification of
medicinal plant
22.3 Description of
medicinal plants
22.4 Trees and perennial
plants
Do you know?
l The branch which deals
with the study of plants
known as Botany.
l Theophrastus is the
father of Botany.
l In economic Botany we
study the importance of
all the plants and its
par ts as well as its
medicinal value.
is
Medicinal properties of l Dhanvantri
worshiped as god of
plants and their nature has
medicinal science.
been described in ‘Rigaveda’
for the first time in ancient l Medicinal plants are
time. Peepal, mango and
cultivated.
palash etc. have been
described in various lines of
the rigveda. Now a days more than 2000 medicines are in
use. Most of them are obtained from plants. Plants are used
in various systems of treatment like Ayurvedic, Unani,
Homeopathy, Allopathy and Aromapathy etc.
22.2 Classification of medicinal plants :
Different scientists have classified medicinal plants
in various ways. In this chapter medicinal plants are
classfied on the basis of Morplology, age and their
importance.
(a) On the basis of the size of the plant- On the basis of
the size of plants medicinal plants are divided in three groups.
1. Trees 2. Shrubs 3. Herbs.
1. Trees- are well developed plants. Their height may
vary from 1 metre to several metres. The trees have all the
297
MEDICINAL PLANTS
297
organs like roots, stems,
branches, leaves flowers and
fruits, for example mango
peepal & neem etc.
2. Shrubs- These
plants are smaller than trees
for eg. -Mehndi.
3. Herbs- These are
smaller than shrubs for
example spinach & gram.
(b) On the basis of age- On
the basis of the life period of
plants they are divided in
three groups.
1. Annual or seasonal
2. Binneal 3. Perinial
1. Annual or
SeasonalAnnual plants are those plants which complete their life cycle in one year. for eg.- wheat,
maize, rice and tobacco. etc.
2. BinnealBinneal plants are those plants which complete their life cycle in two years for example
carrot & cabbage. They develop in first season and reproduce in the next season.
3. PerennialPerinneal plants are those plants which complete their life cycle in many years. They have
vegetative growth for many years and reproduce every year in a fix season. eg.- mango and
guava etc.
(c) On the basis of the Importance- Medicines are obtained from different parts of the plant as
root, stems, barks, leaves, flower, fruits and seeds etc.
22.3 Seasonal plantsThere are many plants which are shown in various seasons, having great importance in
medical science for eg.1.
Tulsi/BasilIt is a harbaceous perennial plant. The plants may he shruby too. Some times it is found in
India & Africa. In India the Hindus worship the plant. Leaves of the plants are used in
stomach disorder and cough & cold. It is an aromatic plant. It is used in joint pain and
298
SCIENCE 10
paralysis treatment. It is also used for the treatment of skin diseases.
2.
Ginger- It is an underground stem known as Rhizome. It is a stimulant and flavouring
agent. It is used in vomiting sensation . It helps in digestion. It is used for the treatment of
headache and dropsy.
3.
Haldi- It is an underground stem called rhizome having great medicine value. It is aromatic
stimulant antiseptic in nature. So it is used for the treatment of various diseases.
4.
Mustard and Sarson- Oil is extracted from the seeds. It is used as stimulant, antipyretic,
hepatic and diuretic. The oil is used for massaging the body. The Plant is used as insecticide.
It is also used for the treatment of earpain. The parts of the plant are also used for urinary
disorder.
5.
Garlic- It is obtained from its underground part called bulb. It has great medicinal value. It
is used for heart diseases, whooping cough, bronchitis. It has diuretic properties. It is also
used to reduce fat from the body.
6.
Ajwain- It is used as stimulant, and for the treatment of stomach disorder. It is also used
for the treatment of vomiting etc. Respiratory diseases are also cured by this. It is an
insecticide.
7.
Saunf- It is used or carminative and stimulant. Boiled water of saunf is used for the treatment
of stomach diseases, and seasonal cough and cold.
8.
Jeera- Fruits of this plant are used for lactating mother. It is also used for digestion and for
the treatment of diarrhoea.
9.
Methi- Seeds and fruits are used as medicines. It is used to reduce fat from the body. It
also controls diabetes. It is also used for the treatment of seasonal cold & constipation. It
is used to cure nervous disorders.
10.
Ashwagandha- Roots of this plants are used for whooping cough. It is also used to cure
diseases related to females. It is used to reduce puscells. It helps in curing ulcer and
arthirities.
11.
Sarpgandha- Medicines are obtained from the roots of the plants and used to control
blood pressure and excitment. It is used as a sedative to reduce tension. It is also used for
curing fever and dysentry.
12.
Lajvanti- Leaves of this plants are used for the treatment of piles and fistule. Leaves and
roots are also used to control diabetes.
13.
Adusa or Vasak- Medicine is obtained from the leaves of the plant and is used for the
treatment of asthma, cough, cold and joint pain. Plants are used as insecticides.
14.
Arandi (Castor) - Seeds are used as purgative. Oil is used for massage of the body.
15.
Amla- Raw fruits are used to cover the deficiency of vitamin-C. It is used for the treatment
of stomach disorder, dysentry, diarrhoea and liver diseases. It is also used to cure jaundice.
16.
Buch- Expectorent is made from the Rhizome. It reduces the body fat. It is also used to
cure asthma and diarrhoea.
299
MEDICINAL PLANTS
299
17.
Giloe- Roots of this plants are used for the remedy of intestinal disorder. Paste made
from the seeds is used to reduce inflamatory action of hands and legs.
18.
Soya- The plant is used to treat cough, ashtma, constipation and indigestion. It also covers
the defficiency of vitamins.
19.
Patharchatta- The plant is used to cure piles and fistula. Fleshy part of the leaf is tied on
the body part to reduce body pain. It also controls the menstrual cycle of female.
20.
Mahua- Leaves, seeds and fruits of the plants are used for the treatment of skin diseases.
It is also used to cure seasonal cold & cough.
21.
Satavar-Smoke of the root is used to control fever.
22.
Harjor- The paste of the plant is used to rejoin the broken bones. Its paste along with milk
is drunk to rejoin bones.
22.4 Trees and perennial plants
1.
Neem - All the parts of this tree have medicinal value. Oil extracted from seeds is used for
curing skin diseases and arthiritis. etc. Bark is used to treat Malaria fever. Leaves are
used as insecticides Flowers are used as tonic in stomache. Branches are used to treat
pyarria disease of teeth.
2.
Harrah- It is used for stomachache and used as tonic
blusters of buccal cavity can be treated by its gargles.
Fruit powder is used for the treatment of Asthama. Bark
is used for urinary disorder treatment.
Do you know that fruits of
Harrah, Bahera and Amala
are mixed togather to form a
Ayurvedic Medicine “Triphala”
3.
Bahera- Dry fruits of this plants are used for the
treatment of stomach diseases. Fruits are used as
antibacterial. Substance oil is used for the treatment of Asthama.
4.
Arjuna- Bark, leaves and fruit contain medicinal qualities. It is used to control berry-berry
disease and to rejoin broken bones. It is also used as remedy for gynecological diseases.
Leaf extract is used to get relief from earpain.
5.
Amaltas- Leaf extract is used to cure dermal diseases. Bark, root, leaves and fruits are
used as medicines for the treatment of different diseases.
6.
Bel- Fruit juice is used as medicine. Boiled, baked or half ripe fruits are used for controlling
dysentry and diarrohea.
7.
Chandan- The oil extracted from the wood is used to treat dermal diseases.
8.
Amla- Raw fruits are used to recover the defficiency of vitamin C. It is used for stomach
disease like dysentry diarrohea and liver diseases etc. It is also used to cure jaundice.
9.
Karang- Oil extracted from the seeds is used for the treatment of arthritis cold and skin
diseases.
10.
Kuchla- The medicine named Nux-vomica is obtained from the plant. It is a stimulant and
used in treatment of nervous disorders. It is also used for remedy in paralysis.
300
SCIENCE 10
11.
Kaner- Different parts of the plants are used as medicines.
12.
Neelgiri- Oil is extracted from the leaves and used for the treatment of nose and throat
infection. It is also used for malaria and Asthama diseases.
13.
Katha- Medicine is obtained from the bark and is used for the treatment of stomach.
14.
Kachnar- Different parts of the plants are used purgative. Bark extract is used for the
treatment of Jaundice. Dry buds are used to control dysentry and piles.
15.
Aak - Flowers of the plants are used in the treatment of seasonal cold. Roots, leaves,
stem & bark are used to cure elephantitis.
16.
Harsingar- It is treated as a religious plant and its different-parts have medicinal value.
Burnt powder of the bark is used as an insecticide. Leaves are used to cure seasonal
cold and muscular pain.
17.
Bhrangraj- Leaves and stem are used to cure dermal diseases and healthy growth of
hairs. Extract is used for the treatment of diseases related to abdominal cavity.
18.
Bhui-Amla- All parts of the plant and ripe and uniripe fruits are used for the treatment of
jaundice, hepitities, leprosy, the fruit helps in digestion and is used as supplement of vitamin
C.
19.
Pipal- Bark is used in itching sensation and treatment of wounds. Its fruits are used with
milk to remove impotancy.
20.
Meethi Neem- All parts of this plants are used as medicine. Leaves are used for the
treatment of stomach diseases. It is a blood purifier. It is also used as insecticide. it is also
use to protect-teeth from pyarria.
21.
Babul- Gum is extracted from the plant which is used to control diarrohea, dysentry,
cholera, diabetes etc. Tender branches of the plant are used to clean teeth.
22.
Maulshri- Fruits and roots of the plant are used for the treatment of sexual weakness and
urinary disorder. It is also used to get strength.
23.
Sheesham- Mostly the plant is used for furniture and printing paper. Seeds and leaves are
used for getting relief from dermal diseases and arthiritis.
24.
Annar- Fruits grains are digestive and used for curing stomachache. The juice helps to
remove the difficiency of iron in blood. Its leaves are used as insecticide.
Answer these questions
1.
From which plant do we get Opium? Which diseases are cured with it?
2.
From which plant do we get cocain? Name the part from which it is obtained.
3.
From which plant do we get gossypium? Name the part from which it is obtained.
4.
From which plant do we get Arnika medicine?
5.
Fruit of which plant is used for the treatment of scurvey disease?
6.
The wood of which plant is used for making railway sleepers/
301
MEDICINAL PLANTS
301
Points to remember
l
Quinine the medicine for the treatment of malaria is obtained from the plant known
as cinchona.
l
With the help of plant indicator we can know the deepness of the water table of
any place.
l
Different parts of aromatic plants are used as spices.
l
Besides medicine, plants produce fuel and fodder in nature.
l
Aromatic oil is obtained from the plants and is used for cleanliness, beauty and as
insecticide.
l
Antibiotics are obtained from lower plants like fungi and bacteria and used for the
treatment of gonorrhoea, syphilis, rickettes and it makes the body disease
resistant.
l
Van Mahotsava is celebrated to protect environment and to grow more plants.
EXERCISE
Very short answer type questions.
1.
Which vitamin is found in abundance in Amla?
2.
Which medicine is obtained from Adusa?
3.
Which book first described the medicinal properties of plants in India?
4.
From which part of the plant ginger is obtained?
5.
Which medicine is obtained from Amaltas?
Short answer type questions.
1.
Which plants are used for the preparation of Triphla?
2.
Which diseases are cured with Tulsi?
3.
Write in brief about :
(a) Arandi, (b) Haldi (c) Harah, (d) Babool, (e) Kaner.
Long answer type questions.
1.
Explain in detail the importance of Medicinal Plants.
2.
Describe following medicinal plants :(a) Katha , (b) Bahera, (c) Aswagandha, (d) Saunf, (e) Adusa.
3.
Describe the classification of plants on the basis of their importance.
4.
What do you mean by seasonal plants? Descibe some important seasonal medicinal
plants.
302
SCIENCE 10