Download reproduction in plants introduction

REPRODUCTION IN PLANTS
INTRODUCTION
1. The production of new individuals from the parents is known as reproduction.
2. Modes of reproduction: Plants reproduce by various methods. These methods can be
divided
into two types: (i) asexual reproduction, and (ii) sexual reproduction.
3. In asexual reproduction, the new individual is produced by a single parent. Seeds are
not
produced, and there is no union of gametes (sex cells). The new individual is identical
to the parent.
4. In sexual reproduction, fusion of two types of gametes takes place. The new individual
is not
identical to either of the parents.
5. Asexual reproduction: There are many methods of asexual reproduction in plants.
These
include budding, fragmentation, spore formation and vegetative propagation.
• Budding: Budding is commonly seen in yeast. A small bulb-like projection called the
bud is
formed in the body. The bud grows in size and finally detaches itself from the parent
body.
In this manner, a new individual is formed.
• Fragmentation: Fragmentation is a very common method of reproduction in filamentous
algae such as Spirogyra. Fragmentation means that an organism breaks up into two or
more pieces called fragments. These pieces or fragments grow into new individuals.
• Spore formation: Ferns, mosses and many fungi reproduce through spore formation.
Spores are very small (microscopic) bodies having thick protective walls. These spores
form new organisms when conditions are favorable.
• Vegetative propagation: When new plants can be obtained from roots, stems, leaves or
buds without the help of any reproductive organs, it is called vegetative propagation.
6. Sexual reproduction: Sexual reproduction is the most common method of reproduction
in
plants. In this process, two reproductive cells called gametes are produced from the
reproductive organs. The two gametes fuse to form a third cell called the zygote. The
zygote then undergoes cell division and growth, and forms the new individual.
7. Stamens are the male reproductive parts and pistil is the female reproductive part of a
flower.
8. The transfer of pollen grains to the stigma of a flower is called pollination. This
transfer
can take place with the help of wind, water or insects. These are called the agents of
pollination.
9. Types of pollination: Pollination is of two types:• Self-pollination: In self-pollination, pollen grains are transferred from an anther to the
stigma of the same flower or other flowers on the same plant.
• Cross-pollination: When the pollen grains are transferred from the anther to the stigma
of
a flower on another plant of the same kind (species), it is called cross-pollination.
10. Fertilization: The process of fusion of male and female gametes is called fertilization.
11. After fertilization, ovary develops into a fruit, whereas ovule develops into a seed.
Self pollination in flowers Cross pollination in flowers
ANSWER THE FOLLOWING QUESTIONS
Q1. Give differences between sexual and asexual reproduction.
Ans.
ASEXUAL REPRODUCTION SEXUAL REPRODUCTION
1. The process involves one cell or one parent.
2. The whole body of the parent may act as a
reproductive unit or it can be in a single cell or
a bud.
3. The offspring are similar to the parents.
4. Special sex organs are not formed.
5. It has no evolutionary significance.
The process involves two cells or gametes belonging to either the same or different
parents.
The reproductive unit is called gamete.
The offspring differ from the parents.
Special sex organs are formed.
It introduces variation, hence it is of
evolutionary significance.
Q.2. Describe the different methods of asexual reproduction, giving examples and
diagrams.
ANS. In asexual reproduction, the new individual is produced by a single parent. Seeds
are not
produced. New individual is identical to the parent. There are many methods of asexual
reproduction in plants example- budding, fragmentation, spore formation and vegetative
propagation.
1 BUDDING- It is commonly seen in yeast. A small bud is formed in the body. It grows
in
size and finally detaches itself from the parent body. In this manner, a new individual is
formed.
2 FRAGMENTATION- It means that an organism breaks up into two or more pieces or
fragments. These grow into new individuals, example- spirogyra.
3 SPORE FORMATION- Spores are microscopic bodies having thick protective walls.
These spores form new organisms when conditions are favorable. Example -ferns,
mosses and fungi(bread mould).
BUDDING IN YEAST
FRAGMENTATION IN SPIROGYRA
SPORE FORMATION IN BREAD MOULD
4 VEGETATIVE PROPAGATION-When new plants can be obtained from roots,
stems
,leaves or buds it is called vegetative propagation
a) Natural Methods
• Vegetative propagation in roots is common in plants like sweet potato, dahlia and
asparagus. Roots are swollen and store food. These roots give rise to new plants.
• Vegetative propagation by stems- takes place in many plants like potato, ginger,
turmeric,
sugarcane, onion, banana etc. Potato has scars called ‘eyes’ on its surface. These give rise
to new plants.
Ginger is also a modified swollen underground stem called
rhizome containing stored food material. In some plants, such as strawberry and grasses,
the main plant develops side shoots which have buds that grow into new plants.
• Vegetative propagation by leaves- In Bryophyllum, buds are present in the margins of
leaves. Plantlets develop from these buds. On being detached from the parent plant, the
plantlets grow into new plants.
b) Artificial Methods of Vegetative Propagation• Stem cutting is a short piece of a branch of a plant having a node. This cutting when
placed in the soil under suitable conditions develops roots and leaves .example-rose,
champa , sugarcane and bougainvillea.
• Layering-is a method in which roots develop on a shoot that is attached to the parent
plant. The stem is cut off only after it has rooted. Example -honey suckle, jasmine, rose,
forsythia.
• Grafting-New varieties can be developed from this method. Here the root portion is
taken
from one plant. This is called the stock. The stem portion with several buds is taken from
another plant called the scion. The ends of the stock and the scion are obliquely cut and
firmly tied together. In this manner a new plant variety is developed. Example-mango
and other fruits.
LAYERING IN PLANTS
Q3.What are the advantages of vegetative propagation
Ans. The following are the advantages of vegetative propagation• Plants produced by this method take less time to grow, and bear flowers and fruits
faster
than those produced from seeds.
• Seedless plants can be obtained.
• Plants produced are exact copies of the parent plant. No variations are present.
Q4.Draw and explain the reproductive parts of a flower.
Ans. Structure of stamen and pistil.
Stamen has a long stalk called the filament and the anther consists of very minute pollen
grains. Pollen grains are the male gametes. They have a tough protective coat and are
very light.
Pistil- It consists of ovary, style and stigma. Ovary is the basal swollen portion. It
continues into
a long style which ends in a knob like part called stigma. Ovary contains ovules and the
female
gamete (egg) is formed inside the ovule.
PARTS OF A FLOWER
Q5. Give the differences between self-pollination and cross-pollination.
Ans. Self-pollination-Type of pollination in which the pollen grains are transferred from
an
anther to the stigma of the same flower or other flowers on the same plant.
Cross pollination-Type of pollination in which the pollen grains are transferred from the
anther to the stigma of a flower of another plant of the same species.
Q6.What happens during fertilization in plants?
Ans. The process of fusion of male and female gametes is called fertilization.
During fertilization the following events occur• After landing on the stigma, the pollen grains germinate and produce their tubes. The
tubes are called pollen tubes. They carry the male gamete.
• Only one pollen tube reaches the ovule. Female gamete is present inside the ovule.
• Finally, the male gamete fuses with the female gamete ;thus fertilization occurs.
Q7. Describe the various ways by which seeds are dispersed.
Ans. Seeds and fruits may be carried away by wind, water and animals. Some seeds also
get
dispersed by special means.
Wind
• Winged seeds are found in maple and drumstick.
• Hairy seeds are seen in aak (madar) and fruits in dandelion.
• Very light seeds are found in grasses.
Water
Coconut fruit is a good example in which dispersal takes place by water. Water currents
carry
away the fruit from the parent plant.
Animals- Dispersal by animals in common in such fruits and seeds which have spiny
structures
with hooks. The hooks stick to the bodies of passing animals and are carried away several
kilometers before they are rubbed off and fall to the ground.Examples are gokhru and
Xanthium.
In balsom and castor seeds are dispersed when the fruits burst with sudden jerks.
Q8. Describe the functions of the following-stamens, ovary, stigma, pollen tube.
Ans. Stamens- They are the male reproductive parts which produce pollen grains. Pollen
grains
contain the male reproductive cells.
Ovary- It contains one or more ovules. The female gamete called egg is formed inside
the ovule.
Stigma-Pollen grains are transferred from stamens to the stigma of the flower for
pollination
Pollen tube-After pollination germinates and produces their tubes. The tubes are called
pollen
tubes.
Q9. Label the given diagram.
Ans. Diagram of fertilization in plants.
Answer the questions briefly.
Q1.Why is reproduction necessary for organisms?
Ans. In order to continue the species, each organism must make more individuals of its
own
kind. It ensures that organisms of the species continue to live even after the death of the
parents.
Q2. What is meant by sexual reproduction?
Ans. In this fusion of two types of gametes takes place. The new individual is not
identical to
either of the parents.
Q3.How are seeds formed?
Ans. The ovary increases in size and becomes the fruit. The ovules become the seeds.
• Once the zygote is formed, it divides rapidly to form an embryo.
• The embryo is enclosed within a protective seed coat.
• The embryo enclosed in the seed gives rise to a new plant.
Q4. Where does fertilization occur in plants?
Ans. It occurs within the ovule in the ovary.
WIND AND STORM
. Wind is the movement of air (usually horizontal) in the atmosphere.
.It is caused by a difference in temperature between different regions on the earth.
. The air above these surfaces absorbs different amounts of heat making it warm in some places and
cool in others.
. As warm air is light it rises and cold air being heavier sinks to fill the space it has left. This sets up a
current of air and is called wind.
. Moving air can provide lift.
WIND MOVING AIR CAUSED DUE TO
1. Uneven heating of land
2. Rotation of earth on its own axis
3. Uneven heating of land and water in winters and summer
a. In summer air with moisture moves from sea to land
b. In winter air moves from land to sea
CHARACTERISTICS OF WIND
. Wind is generally described by two characteristics- direction and speed. Direction is found out by an
instrument called the wind vane, while speed is measured ith the help of an anemometer.
. There are two types of anemometers- propeller and cup.
STORMS
. Storms are severe atmospheric disturbances accompanied by very strong, high -speed winds.
.Storms of great violence are given different names in different regions. They are called typhoons in
Eastern Asia, hurricanes in the Caribbean and North America, and cyclones in India.
.Large areas can be completely flattened by a strong cyclone.
.Proper safety measures should be taken during a storm to minimize loss of life and property.
THUNDERSTORM – Heavy rains with thunder and lightning
Tornado – A funnel shaped column from the cloud to the earth with wind moving at a speed of
500 km/h
Cyclone – Low pressure region at the centre with winds at a speed of 200 km/h around it.
LIGHT
Rectilinear propagation of light
.Light travels in straight lines.
. Shadows are formed as a result of rectilinear propagation of light.
Reflection of light
. All surfaces reflect light. That is why we are able to see them.
. We can see the reflected image of an object only if it is reflected by a highly polished surface.
Plane mirrors
. A highly polished reflecting surface that can return the rays of light into the same medium is called a
mirror.
. A flat mirror is called a plane mirror.
. The image formed by a plane mirror cannot be made to form on a screen. Such an image is called a
virtual image.
. A plane mirror forms a virtual, upright image. The image size remains the same as that of the object.
Convex and concave mirrors
. A curved mirror with a reflecting surface bulging outward at the middle is called a convex mirror.
. A curved mirror with a reflecting surface curving inward at the middle is called a concave mirror.
. A convex mirror can only form virtual images, whereas a concave mirror can form both virtual and real
images depending on the distance of the object from the mirror.
Lenses
. A lens is a curved and polished piece of glass or any other transparent material.
.Common lenses are of two types : convex and concave lenses.
. The type of lens that bulges out in the middle is called a convex lens.
. The lens that is thinner in the middle (as compared to the edges) is called a concave lens.
. A concave lens always forms a virtual image. A convex lens can form both real and virtual images
depending on the distance of the object from the lens.
Colours
. White light is composed of many colours. When these colours combine, they look white.
. Newton’s disc is a coloured disc which is painted with the colours of white light (i.e. VIBGYOR) in the
correct proportions so that when it is rotated very fast, the disc appears white.
SOIL
Soil is the uppermost layer of the earth’s crust and is usually composed of a thin layer of mineral
particles, and a layer of dead and decayed plant and animal remains called humus.
SOIL FORMATION
Soil formation is a slow, stepwise process and it takes thousands of years to form a layer of soil just a
few centimeters thick. I is a result of the continuous breaking down of rocks by a process called
weathering.
Weathering is the disintegration of rocks on the earth’s surface caused by exposure to natural forces
such as wind, water, frost, roots of plants, etc.
Factors Affecting Soil Formation
There are a number of factors which affect soil formation, namely
1. Climate
2. Characteristics of the parent rock
3. Slope of land
SOIL PROFILE
A vertical section that shows the distict layers of soil when we cut straight down into the soil is called a
soil profile.
There are four distinct layers of soil
1.
2.
3.
4.
A Horizon or Topsoil
B Horizon or Subsoil
C Horizon or weathered rock
D Horizon or bed rock
DIFFERENT CONSTITUENTS OF SOIL
1.
2.
3.
4.
5.
6.
Rock particles
Minerals
Humus
Moisture
Air
Soil organisms
Composition of soil
Particles
Diameter (in mm)
1.
2.
3.
4.
less than 0.002
0.002-0.05
0.05-2.00
2.00-5.00
Clay
Silt
Sand
Fine pebbles
Types of Soil
. Soils are of different types, depending on the colour and texture of the constituent particles.
. The three main types of soil are
1. Sandy soil
2. Clayey soil
3. Loamy soil
. Based on its place of formation and occurrence soil may be residual, transported, or mountainous.
Soils found in India are of six main types
.Alluvial soil
. Red soil
.Mountain soil
.Black soil
.Laterite soil
.Desert soil
SOIL EROSION
The removal of soil by running water and wind is known as soil erosion.
The major causes of soil erosion are
Deforestation
Floods and heavy rainfall
Overgrazing
Improper farming
Prevention of soil erosion
Reduction or prevention of soil erosion is called soil conservation.
1.
2.
3.
4.
5.
Afforestation
Flood control
Restricted animal grazing
Construction bunds
Terrace farming
Soil pollution
. The major causes of soil pollution include acid rain, improper dumping of sewage wastes, and excessive
use of pesticides and fertilizers.
. Soil pollution can be controlled by adopting proper measures for disposal of sewage, reduced use of
pesticides and fertilizers, and recycling of solid wastes.
WASTE WATER MANAGEMENT
• Waste is defined as material which has no immediate utility and is usually discarded.
• Waste can be solid, liquid, or gaseous.
Sources of wastewater
• Sources of wastewater are household, industry, mining and agriculture.
Where does the domestic wastewater or sewage go?
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Water containing faeces, paper, cloth, soap, detergent, oil grease, food scrap, etc. carried out of
our houses through sewers or drains is called sewage.
Wastewater from large cities is called municipal wastewater.
A channel system of pipelines, known as the sewerage system, carries sewage out of our homes
to treatment plants.
A manhole is a hole, usually with a cover, through which a person may enter a sewer or drain to
fix faulty pipes.
A wastewater treatment plant is a facility that treats wastewater from domestic as well as
industrial sources.
Inside the water treatment plant, wastewater is treated in three stages; primary, secondary, and
tertiary.
The primary treatment is a mechanical process. In this, sewage is passed through rotating
screens and huge sedimentary tanks. The solid waste, such as faeces, is allowed to settle down.
The light floatable waste such as soaps, oil, and grease rise.
Sludge refers to the solids accumulated in a wastewater treatment process.
Scum is the light waste that floats on top.
The secondary treatment is a biological process. Microorganisms such as bacteria act to break
down organic material and remove nutrients. The treatment at this stage can be speeded up, by
allowing water to flow to large, aerated tanks, where air is blown onto the sewage. The
wastewater then flows to settling tanks where the bacteria settle out.
The tertiary treatment is basically a chemical process. The methods involved vary with the
composition of the wastewater. Usually, chemicals are used to remove phosphorous and
nitrogen from the water, but may also include filter beds and other types of treatment.
Addition of chlorine and exposure to ultraviolet light kills the bacteria, and the water is
discharged.
What happens to the treated water
The treated water is released to water bodies such as streams and rivers. This water can be used
again for supplying drinking water, fertilizers for growing crops, and for aquaculture.
What happens to the sludge
Sludge consists of human faeces and other organic matter. It also has large amounts of water
and needs to be thickened so that it can be easily transported and used as compost in
farmlands.
There are three ways of treating sludge; namely incinerating, dewatering and composting.
Incinerating is a process in which the sludge is burnt into ashes. The ashes are used as soil
conditioner or in construction materials. Dewatering is a process in which the sludge can be
dewatered and then combined with other ingredients to create fertilizers and soil amendments.
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Composting is a process in which the sludge is composted or processed to produce gases that
can be used to supply heat.
What you should do to control sewage
Use flushes with low capacity.
Dispose off household products such as cleansers, beauty products, medicine, automobile oil
and paint properly. These contain chemical which the wastewater treatment plants may not be
able to remove.
Dispose off excess household grease, cooking oil, butter, meat fats, margarine and plastic in the
garbage can. These materials can clog pipes and could cause sewage to overflow in your home
or in public areas.
Fix leakages in your sewer pipes. Overflowing sewage can contaminate drinking water. It can
also be the breeding place of disease causing insects such as flies and mosquitoes.
Problems caused due to improper management of sewage
Water pollution can be caused as a result of the discharge of untreated or partly treated sewage
in water bodies, sometimes due to improper sewage handling processes of municipal bodies.
Leakages in several places in the main water supply line causes drinking water to get mixed with
sewerage water. The dirt often flows out into the open and enters the pipelines. Due to this, the
water supply gets contaminated.
People consuming contaminated water may suffer from diseases like gastroenteritis, dysentery
and typhoid.