Download cbse class – x science solutions

CBSE CLASS – X
SCIENCE SOLUTIONS
(31/1, 2, 3)
Series LRH
(ALL INDIA)
19.
19.
20.
20.
21.
21.
22.
22.
23.
23.
24.
24.
SET 1
SECTION – B
State any one difference between autotrophic and heterotrophic modes of nutrition.
Autotrophic nutrition
Heterotrophic nutrition
Organisms which adopt autotrophic mode of
nutrition depend upon inorganic raw
materials like CO2, H2O and sunlight for
their nutritional requirement.
Organisms which adopt heterotrophic
nutrition depend upon autotrophs for their
nutritional requirements.
Give one reason why multicellular organisms require special organs for exchanges of gases between
their body and their environment.
In multicellular organisms, all the cells are not in direct contact with the environment so direct exchange
of gases can not take place and thus they require special organs for exchange of gases.
Mention one example of chemotropism.
Growth of pollen tube towards the ovule
Name the two main organs of our central nervous system. Which one of them plays a major role in
sending command to muscles to act without involving thinking process? Name the phenomenon
involved.
Two main organs of our central nervous system are: Brain and spinal cord. Spinal cord sends the
command to muscles to act without involving thinking process. This phenomenon is known as reflex
action.
With the help of an example show that ‘reuse’ strategy is better than ‘recycling’.
Reuse strategy is better than recycling. For example, if plastics are sent for recycling, then they would
be subjected to melting; causing additional cost of machinery and an unnecessary strain on the
energy sources. Also it will lead to environmental pollution. These all factors are ignored during reuse
e.g. using the plastic bottles again for drinking water will save the energy.
Construct an aquatic food chain showing four trophic levels.
Trophic levels
25.
25.
Hydrilla ⎯⎯→ Scorpio ⎯⎯→ Fish ⎯⎯→ Crane
1
2
3
4
Explain the process of breakdown of glucose in a cell (i) in the presence of oxygen, (ii) in the absence
of oxygen.
Presence of O2
CO2 + H2O + energy
(in mitochondria)
Glucose
In cytoplasm
(6-carbon molecule)
Pyruvate
(3-carbon
molecule +
energy)
Absence of O2
Ethanol + CO2 + energy
(In yeast)
www.steps.TCYonline.com
Page : 1
26.
26.
27.
The first step is the break – down of glucose, a six-carbon molecule, into a three-carbon molecule
called pyruvate. This process takes place in the cytoplasm. Further, the pyruvate may be converted into
ethanol and carbon dioxide. This process take place in yeast during fermentation. Since this process
takes place in the absence in air (oxygen), it is called anaerobic respiration. Break-down of pyruvate
using oxygen takes place in the mitochondria. This process breaks up the three-carbon pyruvate
molecule to give three molecules of carbon dioxide. The other product is water. Since this process
takes place in the presence of air (oxygen), it is called aerobic respiration. The release of energy in this
aerobic process is a lot greater than in the anaerobic process.
Explain the mechanism of sex determination in humans.
All human chromosomes are not paired. Most human chromosomes have a maternal and a paternal
copy, and we have 22 such pairs. But one pair, called the sex chromosomes, is odd and not always
being a perfect pair. Women have a perfect pair of sex chromosomes, both called X. But men have a
mismatched pair in which one is a normal-sized X while the other is a short one called Y. So women are
XX, while men are XY.
As figure shows, half the children will be boys and half will be girls. All children will inherit an X
chromosome from their mother regardless of whether they are boys or girls. Thus, the sex of the
children will be determined by what they inherit form their father. A child who inherits an X
chromosomes from her father will be a girl, and one who inherits a Y chromosome from him will be a
boy.
(a)
(b)
(a)
(b)
Draw a longitudinal section of a flower and label the following parts:
(i)
Part that produces pollen grain
(ii)
Part that transfers male gametes to the female gametes
(iii)
Part that is sticky to trap the pollen grain
(iv) Part the develops into a fruit
Differentiate between pollination and fertilization.
OR
Explain the role of placenta in the development of human embryo.
Give example of two bacterial and two viral sexually transmitted diseases. Name the most
effective contraceptive which prevents spread of such disease.
www.steps.TCYonline.com
Page : 2
27.
(a)
(i)
(ii)
(iii)
(iv)
Part that produces pollen grain: anther
Part that transfers male gamete to the female gamete: style
sticky part to trap pollen grain: stigma
Part that develops into fruit: Ovary
(b)
Pollination
Fertilization
1.
1.
Fertilization is the process of fusion of
male gamete with the female gamete.
2.
It takes place by the growth of pollen
tube towards the ovary.
2.
Pollination is the process of transfer
of pollen grains from anther to the
stigma of the same or different flower.
It takes place with the help of
pollinations like wind, water insects
etc.
OR
(a)
(b)
Placenta is a temporary organ which is formed from the tissues derived from the foetus and the
mother. The placenta contains villi on the embryo’s side of tissue and blood spaces on the
mother side of tissue. The blood space surrounds the villi. The villi provides a large surface area
for glucose and oxygen to pass from the mother to the embryo.
Thus, through placenta, the maternal blood passes food (glucose, amino acids, lipids and
proteins), oxygen, hormones, water, antibodies to the foetal blood and the foetal metabolic
wastes (carbon dioxide, urea) pass into the maternal blood.
BACTERIAL INFECTION – which includes gonorrhoea (inflammation of mucus membrane of
urinogenital tract) and syphilis (lesions in the mucus membrane of urinogential tract).
VIRAL INFECTION – which includes warts, HIV-AIDS, Hepatitis-B.
Use of condoms can prevent the spread of these diseases to a great extent
19.
SET – 2
SECTION – B
Name the process in plants where water is lost as water vapour.
19.
The loss of water in the form of water vapour takes place through stomata in the plants and the process
is known as transpiration.
20.
Mention the function of the hind brain in humans.
20.
Main function of hind brain in humans is to maintain the posture and balance of the body. It is
responsible for the precision of voluntary actions like walking in straight line, riding a bicycle.
22.
Name the hormone secreted by human testes. State its functions.
22.
Hormone secreted by human testes. Testosterone function of testosterone is the development of
secondary sexual characters in males like growth of hair, hoarse voice, moustaches etc.
www.steps.TCYonline.com
Page : 3
23.
List any four changes you would like to incorporate in your lifestyle in a move towards a sustainable use
of available resources in our country.
23.
25.
(i)
Use of bicycle instead of scooter to go to school.
(ii)
Switching off the lights, fans etc, when not in use
(iii)
Pool in the car instead of using individually
(iv)
Minimizing use of plastics
Name the organism Mendel used for his experiments. Explain about F1 and F2 progeny obtained by
Mendel when he bred the tall and the short varieties of the organism he experimented with.
25.
Mendel used garden pea for his experiments.
Parents
TT
tt
Tall
short
T
t
Gametes
F1 Generation
Tt
Tall
F2 Generation
T
t
T
TT
Tt
t
Tt
tt
TT
1
Tall
3
:
:
Tt
2
:
:
:
:
tt
1
Short
1
All the plants in the F1 progeny came out to be hybrid tall when Mendel bred tall and short varieties of
the organisms.
In the F2 generation there were 25% per plant as pure tall, 50% the hybrid tall and 25% as the short
pea plants.
19.
SET – 3
SECTION – B
Name the plant hormone that retards growth of the plant.
19.
20.
Abscieic acid is the plant hormone which retards plant growth.
What is ‘translocation’ in plants?
20.
Translocation in plants is the process of movement of the dissolved food to all the parts of the plant
through phloem.
Name and explain the function of the hormone secreted by the pituitary gland in humans.
22.
22.
23.
23.
Growth hormone is secreted by the pituitary gland. This hormone regulates growth and development of
the body. If there is a deficiency of this hormone in childhood, it leads to dwarfism and excess of this
hormone leads to giant body size.
Explain ‘biological magnification’ with the help of an example.
We use several pesticides and other chemicals to protect our crops from diseases and pests. These
chemicals are either washed down into the soil or into the water bodies. From the soil, these are
absorbed by the plants along with water and minerals, and from the water bodies these are taken up by
aquatic plants and animals. This is one of the ways in which they enter the food chain. As these
chemicals are not degradable, these get accumulated progressively at each trophic level. As human
beings occupy the top level in any food chain, the maximum concentration of these chemicals get
accumulated in our bodies. This phenomenon is known as biological magnification.
www.steps.TCYonline.com
Page : 4
25.
Name the two homologous structures in vertebrates. Why are they so called? How do such organs help
in understanding an evolutionary relationship?
25.
Limbs of birds, reptiles and humans are all the examples of homologous structures in the vertebrates.
They are called so as the basic structure of the limbs is similar. Though it has been modified to perform
different functions in various vertebrates.
These are organs which are inherited from a common ancestor. Such a homologous characteristic
helps to identify an evolutionary relationship between apparently different species.
www.steps.TCYonline.com
Page : 5