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14
Multiplication in Plants
KNOW THESE PoINTS BEFORE YoU START
Learning Objectives
Formation of new organisms from the parents is called reproduction. The students will be able to
+understand the meaning
of reproduction.
Asexual reproduction involves only one parentand but no reproductive organs. It
may occur by budding, fission, fragmentation and spore formation.
Vegetative propagation is also found in flowering plants and occurs by modified
vegetative parts like roots, stems and leaves.
learn different modes of
reproduction in plants.
study various means of
The male gametes in plants are pollens and female gametes are ovules.
Transfer of pollen grains from a male flower to the stigma of a female flower is
called pollination.
vegetative reproduction.
understand sexual
reproduction in flowering
plants.
Fusion of male gamete with female gamete is called fertilisation. study fruit formation and
germination of seeds.
Fertilised ovum develops into embryo and ovule with embryo forms the seed.
Now, study the chapter in detail.
WHAT IS MULTIPLICATION OR REPRODUCTION
To produce their own kind is a characteristic of all living organisms.
Thus, the production of new individuals from their parents is known
as reproduction or multiplication. Now, we can say that:
Reproduction is the most important characteristic of living
organisms.
It is the basic life process that helps maintain the continuityofrace.
Modes of reproduction Budding
Plants exhibit two types of reproduction, Microscopic organisms,
budding.
such as
In
ye
yeast
thi
namely asexual and sexual. In addition, reproduce asexually by budding. In
some
plants multiply by vegetative process, a small bulb-like
projectionco
out from the parent cell. It is called bud
come
reproduction.
Asexual reproduction: It involves simple bud gradually grows and gets separatedf.
the parent cell and forms a new
yeastcellT
The
division of the plant body into two or
more
plants or the formation of spores under
unfavourable conditions.
new yeast cell grows, matures and
produ
andprodu
Vegetative reproduction: It is also a type
of asexual reproduction in which a cell,
tissue or a part of plant body develops into
a new organism. It is also called vegetative
propagation.
Sexual reproduction: It takes place by
the formation of gametes. In this case, two
parents are needed to give rise to a new
individual.
Bud
New cells
Parent
Fig. 14.1 Budding in yeast
Activity
To observe budding in yeast
Take some yeast powder from a bakery or chemist
shop. Place a pinch of yeast powder in a 100 mL
beaker having some luke warm water. Add a
spoonful
of sugar and shake it well to dissolve sugar.
After an hour or so, put a drop of this liquid on a
glass slide and observe it under a microscope. You
will see the formation of new yeast cells. Draw a
simple line diagram of what you see on the slide.
Does your diagram match with figure?
Now, let us study these processes in detail.
ASEXUAL REPRODUCTION
In asexual reproduction, a
single organism i
able to
reproduce on its own. Common forms
of asexual reproduction are
budding, fission,
fragmentation and spore formation.
MODES OFREPRODUCTIONIN PLANTS
Asexual Reproduction
Vegetative Propagation Sexual Reproduction
1. Fission
2. Fragmentation
3. Budding
4. Sporulation
Methods of natural
Methods of artificial
vegetative propagation vegetative propagation
1. by root
2. by underground stem
3. by aerial stem
4. by adventitious buds on leaves
1. by cutting
2. by layering
3. by grafting
4. by tissue culture
moreyeast cells. If this process continues for Spore formation
come
ore
time, a large number of yeast cells are
This is the most common method of asexual
produced in a short time.
reproduction in most of the fungi and
bacteria. The spores develop in a structure
Fission
Fission is a process of asexual reproduction called sporangium. When the spores are
in which an individual divides into two released, they keep floating in the air. Since
(binary fission) or more (multiple fission) new they are tiny and very light, they can cover
individuals. It is seen in bacteria. long distances and remain in the air for a
long time.
The spores are asexual reproductive bodies.
Each spore is surrounded by a hard protective
coat and can withstand unfavourable
conditions, such as high temperature and
drought. Under favourable conditions, it
germinates and develops into a new individual.
Activity
To study spores of Rhizopus under a microscope
Collect a slice of bread having bread mould
(Rhizopus). Take a clean slide and with a forceps
put some blackish threads on it. Observe under
the microscope. Black-coloured spores are seen in
sporangium borne on a sporangiophore.
Fig. 14.2 Reproduction in bacteria by
binary fission
Fragmentation
Fragmentation is another form of asexual
reproduction. It is commonly found in algae.
In algae, the adult organisms just break
into two or more fragments. Each of these
fragments grows up to form a new organism
filament). This process is seen in spirogyra
pond scum).
Sporangium
Spores
Sporangiophore
(Erect hypha)
Fragmentation is also seen in liverworts and
Stolon
mosses.
Have you ever seen slimy green
patches in a pond or a lake? Rhizoids
Yes, these patches are of algae. When
water and nutrients are available
in
plenty, algae grow and multiply
rapidly by fragmentation. This process
continues and the algae cover a large
area in a short period of time. This
process is called eutrophication
Fig. 14.3 Spores in sporangium of Rhizopus
Bread mould (Rhizopus) reproduces asexually
by spore formation. Plants like mosses and
ferns also reproduce by means of spores.
ored
Asparagus become swollen due to foodsto.
in them. In the next season, new
plants a
VEGETATIVE REPRODuCTION
Vegetative reproduction is a type of asexual
reproduction in which new plants are produced produced from these roots.
from roots, stems, leaves and buds. These are
vegetative parts of a plant. Therefore, this
type of reproduction is called vegetative
propagation. All the plants produced by
vegetative propagation from one plant are
exact copies (clones) of the parent plant.
I have never seen the seeds of
potatoes, sugarcane, rose and
Bougainvillea. How do these plants
reproduce?
Sweet potato Dahlia
ahlia
Fig. 14.4 Tuberous roots of sweet potato and Dahlia
By stems
The underground and subaerial stems are
especially modified for vegetative propagation,
These plants reproduce vegetatively
through their stems. OO
Banana, garlic, mint, grapes, roses and Underground stems:These are offollowing
many other plants are grown by vegetative
propagation. There are a number of natural
as well as artificial methods by which plants
reproduce vegetatively.
types.
Tuber: Potato is an undergroundstem
tuber that is swollen due to food stored in
it. It has buds in the depressionscalledthe
eyes. These buds give rise to new plants.
The stored food is used up by the new
plants to grow.
Rhizome: It is an undergroundstem that
bears buds. These buds grow to give rise
to
newplants.Rhizome is found in ginger
Why are potato, ginger, sweet potato,
o,0 etc. swollen?
These plant parts store food in the
form of carbohydrates. So they
become swollen. This stored food is
used by the plants when theymultiply
by vegetative propagation. and turmeric.
Bulb: It is a very short underground
stem surrounded by fleshy scale leaves.
The scale leaves store food. It is found
Methods of natural vegetative propagation
By roots
Tuberous roots of Dahlia, sweet potato and
Germinating Nodes Fleshy scale
bud leaves
Scales Bulb
Eye Apex
Bud
Disc
Root
(b) Rhizomes of ginger
Fig. 14.5 Underground stems showing vegetative propagation
(a) Tuber of potato C) BUID or onion
142
in onion. In the spring, the stem shoots adventitious buds in the notches present
1D from the centre of the scale leaves to along their
margin. When such a leaf falls on
form a new plant.
Subaerial stems: In grasses, mint, Oxalis, plant.
Chrysanthemum and strawberry, vegetative Plants with fleshy stems, such as
cacti,
the soil, each bud grows into an
independent
hem, roots and aerial branches arise from detached from the main plant body. Each
nodes forming the new plants.
propagation occurs by subaerial stem. In
produce new
plants when their parts get
detached part can grow into a new
plant.
Activity
To observe vegetative reproduction in potato
Take a potato and locate depressions (eyes) on its
surface. Each eye has a bud which can grow into a
Fleshy
leaf
new plant.
Cut a few pieces of the potato, each with an eye.
Bury them in moist soil. Keep the soil moist by
adding water regularly. After a few days, each bud
grows into a new plant. Likewise, you can also grow
A notch
bearing an-
adventitious
bud
New plants
arising from
notches
ginger or turmeric.
Roots
SomethingMore
Fig. 14.7 Adventitious buds on the
leaf of Bryophyllum
Methods of artificial vegetative
propagation
Vegetative propagation is a simple, fast and
less expensive method of plant propagation.
It is, therefore, commonly used in horticulture
and agriculture. The techniques used are stem
The eyes in potato are nodes and buds in the
eyes are axillary buds. These buds develop into
new plants. Anode is a part of stem at which a leaf
arises.
By adventitious buds on leaves
The fleshy leaves of Bryophyllum bear
cutting, layering, grafting and tissue culture.
New plant
Subaerial
Subaerial stem
stem
Node
Node
Roots
Roots
(a) Oxalis (b) Strawberry
Fig. 14.6 Vegetative propagation in Oxalis and strawberry by subaerial stems
the stock
In this method, cutting of a healthy young one plant, called the scion, isken
In this method, a
bud or
cutting with bud
bude
pt over the
Stem cutting
branch of a plant having leaf buds is planted cut stem of another plant, called the th
The scion and the stock are then firmi
mly
grows into a new plant. This method is to together. I he care is to be taken
that
tieg
After some time, the tissues of the st
and scion join together to form one
plant
tied
in the moist soil. Cutting develops roots and Ihe
Sc1Onand the stock are then
stock
root system under the
propagate plants like chameli, Bougainvillea, has an extensive root system under
rose and sugarcane.
s to
The stock supplies the essential nutrient
Stem cutting
the scion.
This is a common method to develop new
varieties of rose, guava, mango, lemon and
orange.
Scion
Adventitious root formation
Fig. 14.8Vegetative propagation
in rose by stem cutting
Scion and
stock fixed
Layering together
In this process, a young branch is bent
towards the ground and covered with moist
soil forming a layer. After some time, roots
develop from the covered part. The branch is
then cut offfrom the parent plant and allowed
to grow into a new plant. This method is
commonly used by gardeners to develop
plants like jasmine, vines and Bougainvillea.
Stock
Fig. 14.10 Vegetative propagation through
grafting in plants
Something More
Grafting is the technique of combining thefeatures
of two plants. For example, a high yielding varity
may be grafted to a disease-resistant variety to have
characteristics of both the plants. Many new vaieties
of mangoes available in the market are developed
by this method.
Roots arising
Tissue culture (Micropropagation)
In tissue culture method, a small pieceo
tissue (called explant) is cut off from t*
growing tip of the plant. The cells ofthe
tissue are separated and kept in a nutrie
from covered
part
Fig. 14.9 Layering in jasmine
Grafting
to develop new varieties ofornamental plants
medium. The cells ofthe tissue dividerap
and form an organised cell masscalledcal
This is a common method used in horticulture
and fruit trees.
144
Thecallus istransferred into another nutrient Check PINT 1.
containing plant hormones. The 1. Fill in the blanks.
m e d i u m
(a) There are
primarily two modes of
reproduction:
cells of callus in his nutrient medium
asexual and.
(b) The process of.
ensures continuity of life.
(c) Yeast multiplies by
divide
and difterentiate into roots and shoot
and form a new plantlet. The plantlets so
formed can now be grown in pots filled with
in living organisms
soil. Asparagus, Chrysanthemum, orchids and 2. Identify the method of artificial propagation in
the following.
(a) Twig of one plant tied to the cut stem of
another.
(b) Young branch put into moist soil.
(c) Tissue from growing tip is grown under
controlled conditions in the laboratory.
many
other plants are now grown by this
method.
Advantages ofvegetative propagation
Vegetative propagation is a more rapid,
easier and cheaper method of plant
propagation as compared to seeds. Such
plants take less time to grow and bear
fowers and fruits early.
The new plants are exact
copies of the fusion of male and female gametes. The
parent plant as they are produced from a gametes are produced in separate male and
single plant.
9EXUAL REPRODUCTION
Sexual reproduction occurs as a result of
female reproductive organs which may be
It produces a large number of plants in a and
present
female
in the
plants.
same plant or in separate male
short time. and female plants.
Plants grown vegetatively usually need less Flower The reproductive part
attention in the early stages than the plants of a plant
grown from seeds.
Plants like banana, seedless grapes, the reproductive parts of a
plant. The stamens
roses, pineapples and dahlias which do are the male reproductive parts and the pistil
not produce seeds can
only be grown is the female reproductive part ofa flower.
vegetatively.
You have learnt in Class VI that flowers are
Usually, a flower contains both male and
Plantlets
Callus
Culture Culture medium
medium containing plant
hormones
Fig. 14.11 Tissue culture in plant cell
45
female parts. Such flowers are called bisexual Pollination
flowers. The lowers which contain either The transfer of pollen grains (containin,
stamens or
pistil are called unisexual flowers. male gametes) from the anthers to ,the
Both male and female unisexual flowers may stigma of pistil is known as
pollination
be
present in the same plant or in different This is the first step in the process of see
the
plants. Mustard, rose and Petunia have formation.
bisexual flowers. Maize, papaya and cucumber
Types of pollination
produce unisexual flowers as they contain
Pollination is of two types: self-pollination
either male or female parts in them, but not
both.
Types ofpollination
Pollination is oftwo types: self-pollination
and cross-pollination.
Self-pollination: In this process, polen
lands on the stigma of the same Hower or
of a different fHower of the same
plant.
Cross-pollination: In this case, pollen
lands on the stigma of a fiower borne on a
different plant of the same kind.
Stamens-The male reproductive parts
of a flower
Each stamen is formed of a swollen apical
part, the anther and a long slender stalk
called the filament. Pollen grains are formed
inside the anther. Pollen grains produce male
gametes.
Pistil-The female reproductive part of
a flower
Pistil is the female reproductive part of a
flower. It consists of stigma, style and ovary.
The ovary contains one or more ovules.
The female gamete or the egg is formed in
the ovule. The ovules develop into seeds after
fertilisation. In sexual reproduction, a male
and a female gamete fuse to form a
zygote. Fig. 14.12 Types of pollination
Self-pollination (A and B), Cross-pollination (C)
Mechanism of sexual reproduction Agents ofpollination
Sexual reproduction in
plants involves the
Pollination takes place with the helpofsome
Pollination takes place with the help of some
following steps.
external agents such as wind, water, insects,
Pollination: Transfer of pollen grains from birds or mammals. These external agents are
birds or mammals. These external agents are
anthers to the stigma. called agents of
pollination.
Fertilisation: Union ofmale gamete with
Pollination by insects: Insects like honey
bees, wasps, moths and butterflies visit
Formation of seed: Development of zygote flowers for nectar. While collecting nectar
some
pollen grains stick to the body of these
Formation offruit: Maturation of ovary insects. When these insects visit another
flower, the pollen grains are brushed oft, som
the female gamete to form zygote.
into seed.
into fruit.
Germination of seed: Formation of young of which fall on the stigma.
plant from the seed.
i46
Insect-pollinated flowers have following Bird-pollinated flowers are much more
common than mammal-pollinated flowers.
characteristics:
Sun birds and hummingbirds are two
large
Anthers are large and loosely attached.
Stigma hang out
ofthe flowers to trap the groups of birds which pollinate flowers.
pollen grains.
They usually have nectaries that produce
Hummingbirds hover in front of flowers
while sipping the nectar. Sun birds sit on the
flower stalks to collect the nectar.
nectar.
Bird-pollinated flowers have the following
They have sweet smell and bright colours.
They have sticky stigma and sticky pollen characteristics:
grains. They are not scented because birds do not
have a well-developed sense of smell.
They are ofbrightred, yellow or orange in
colour to attract the birds.
Bird of paradise, Salvia and Bignonia are
some bird-pollinated flowers.
Fig. 14.13 Insect pollination in Salvia flower
Examples of insect-pollinated flowers are
Salvia, orchids, buttercup, sunfower, etc.
Whyare flowers generally so colourful
and fragrant?
Flowers are colourful and fragrant to
attract insects for pollination.
Fig. 14.14 Hummingbird sipping
nectar of a flower
Pollination by mammals and birds: Even
some birds and small mammals like bats and
Something More
rodents also pollinate flowers.
Mammal-pollinated flowers have the
tollowing characteristics:
Flowers are quitesturdy in order to bear the
vigorous activity of small mammals, while
Teeding on the nectar of these flowers.
The structure of a flower determines whether it is
self-pollinated or
cross-pollinated. A self-pollinated
flower has its anthers located higher than the stigma
hile a
cross-pollinated flower hasa long pistil that
extends beyond the stamens.
They are usuallybrown or white in colour.
They often have a strong scent.
Pollination by wind: Flowers of wheat, rice,
maize and rye grass are
pollinated by wind.
Wind-pollinated flowers have the following
Sausage tree, kadamba and Agave are characteristics:
pollinated by bat.
4
A germinating
pollen grain
They are not brightly coloured and are
usually white.
They do not produce nectar.
Stigma
Pollen tube
Style
They produce small and light pollen
grains in large number to be carried away
by wind.
Ovary wall
Integument
Antipodal.
cells (Future seed coat
Pollination by water: Pollination in aquatic
plants is usually carried out by water. The
examples of water-pollinated plants are
Sea
grass, Hydrilla and Vallisneria. Water-
pollinated flowers release their pollen grains
into the water. These pollen grains are
passively carried to other flowers by water
Currents for pollination.
Polar nuclei
Ovary
Eggcell
Synergid
2 male-
gametes Micropyle
Fig. 14.16 Germination of pollen grains on
stigma and one of them reaches to
ovule to carry out fertilisation
Fruit and seed formation
Floating pollen grains
After fertilisation, following changes ocur
in the flower:
Female-
The fertilised egg, now
calledzygote,grows
into the embryo.
It has two parts. The shoot-formingpart
called plumule and
root-torming part
called radicle.
flower
Female
flower
The ovary grows into a fruit and otherparts
of the flower fall off.
coils
after
Male
flower
receiving
The ovules develop into seeds.
The seed contains an
embryo enclosedin
a
protective seed coat.
pollen
grain
Fig. 14.15 Pollination by water in Vallisneria A seed is a mature ovule that contains the
embryo and the stored food. It isenclosed by
a seed coat formed of two
coverings.
Fertilisation
On reaching the stigma, pollen grain grows A fruit is the seed-bearing structure of a
out into a thin pollen tube. It extendsiowering plant. Actually, it is the ripene
through the style, reaches the ovary and ovary of the plant and seeds are the matured
enters the ovule. The pollen tube contains two ovules of the fruit.
male gametes, one of
which fuses with the Fruits may be fleshy and juicy or dry an
female gamete or egg and forms a
zygote.
The process of fusion of a male and a female
juicy fruits whereas almonds and walnutsar
hard. Mango, apple and orange are
fiesny
gamete is called fertilisation.
dry and hard fruits.
4
severe
competition for space, sunlight, water
and minerals. Therefore, dispersal of seeds is
beneficial to
plants as:
It ensures that the plants are
dispersed over
wide areas.
It avoids overcrowding and competition
among the plants for space, sunlight, water
and minerals.
(b) Mango
(a) Apple
Fig. 14.17 Fleshy and juicy fruits
Seeds and fruits are
dispersed by wind, water,
animals and
explosive mechanism.
ARTIFICIAL POLLINATION
The improvement of quality of seeds and Di
increase in the production of grains, cereals,
fruits and vegetables has become essential to
Fruits and seeds scattered by wind are
Dispersal by wind
usually small and light. Seeds of maple and
drumsticks have wings attached to them,
provide food for rapidly increasing population.
drumsticks have wings attached to them,
pollination."This is
also called hybridisation.
which
Light
help
seeds
them
of grasses
float in
or
air
hairy
for long
seeds
distances.
of oak
This is made possible by controlled artificial
Light seeds of grasses or
hairy seeds of oak
and cotton, and hairy fruits of sunflower
In hybridisation, plants with desired
characteristics are selected. The pollen from
get blown to far away places by wind. Fruits
one such plant is transterred to the stigma of poppy are
very small and get scattered by
ofother selected plants.The pollinated pistils wind.
of these flowers are covered with polythene
bags to avoid polination from uncontrolled
SOurce.
The seeds so obtained are called hybrid
seeds. They are stored to be sown in the next
season. The plants obtained from these seeds
are hybrid plants.
The aim of obtaining hybrid seeds is to have:
high-yielding variety of plants.
disease-resistant plants. Fig. 14.18 Maple seed with a wing
plants that can grow and mature in short
duration. Dispersal by water
The fruits and seeds of aquatic plants like
those of water lily, lotus and coconut float on
The main function of the fruit is to help water surface and are carried to far off places
the seeds to disperse to different places to by water current. Coconut has a fibrous coat
increase their chances of survival. In case with hard covering which is carried away to
SEED DISPERSAL
Seeds fall at the same place, there would be long distances by water currents.
149
Fig. 14.19 Coconut fruit floating on water Fig. 14.21 Explosive mechanism in Geranium
Dispersal by animals Germination of seed
Some seeds have spines or hooks which On reaching the moist soil, the seed swels
cling to the bodies of animals and are up by imbibing water. The embryo starts
carried to long distances as in Xanthium and growing. Its radicle grows down into the
soil and forms the root. The plumule grows
upward in the air, develops leaves and forms
Urena.
the shoot of the young plant.
Fig. 14.20 Xanthium seeds with hooks
Man, animals and birds eat the pulp or the
edible part of fleshy fruits and throw their
seeds. This helps in their dispersal. The small Check PeINT 2
Fig. 14.22 Germination of seed
and undigested seeds come out oftheir body. 1. Name the male and female reproductive parts of
The seeds of guava and berries are dispersed a flower.
this way. 2. What are unisexual plants?
3. Define the term pollination.
4. Name the means of pollination.
5. What is the difference between self and cross
Explosive mechanism
Fruits and seeds of balsam, pea, Geran1um
and castor burst with sudden jerks and get
scattered away from the parent plant.
pollination?
6. Give a structural modification found in insect
pollinated flowers.
50

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Plants Reproduce Through Various Modes

  • 1. 14 Multiplication in Plants KNOW THESE PoINTS BEFORE YoU START Learning Objectives Formation of new organisms from the parents is called reproduction. The students will be able to +understand the meaning of reproduction. Asexual reproduction involves only one parentand but no reproductive organs. It may occur by budding, fission, fragmentation and spore formation. Vegetative propagation is also found in flowering plants and occurs by modified vegetative parts like roots, stems and leaves. learn different modes of reproduction in plants. study various means of The male gametes in plants are pollens and female gametes are ovules. Transfer of pollen grains from a male flower to the stigma of a female flower is called pollination. vegetative reproduction. understand sexual reproduction in flowering plants. Fusion of male gamete with female gamete is called fertilisation. study fruit formation and germination of seeds. Fertilised ovum develops into embryo and ovule with embryo forms the seed. Now, study the chapter in detail. WHAT IS MULTIPLICATION OR REPRODUCTION To produce their own kind is a characteristic of all living organisms. Thus, the production of new individuals from their parents is known as reproduction or multiplication. Now, we can say that: Reproduction is the most important characteristic of living organisms. It is the basic life process that helps maintain the continuityofrace.
  • 2. Modes of reproduction Budding Plants exhibit two types of reproduction, Microscopic organisms, budding. such as In ye yeast thi namely asexual and sexual. In addition, reproduce asexually by budding. In some plants multiply by vegetative process, a small bulb-like projectionco out from the parent cell. It is called bud come reproduction. Asexual reproduction: It involves simple bud gradually grows and gets separatedf. the parent cell and forms a new yeastcellT The division of the plant body into two or more plants or the formation of spores under unfavourable conditions. new yeast cell grows, matures and produ andprodu Vegetative reproduction: It is also a type of asexual reproduction in which a cell, tissue or a part of plant body develops into a new organism. It is also called vegetative propagation. Sexual reproduction: It takes place by the formation of gametes. In this case, two parents are needed to give rise to a new individual. Bud New cells Parent Fig. 14.1 Budding in yeast Activity To observe budding in yeast Take some yeast powder from a bakery or chemist shop. Place a pinch of yeast powder in a 100 mL beaker having some luke warm water. Add a spoonful of sugar and shake it well to dissolve sugar. After an hour or so, put a drop of this liquid on a glass slide and observe it under a microscope. You will see the formation of new yeast cells. Draw a simple line diagram of what you see on the slide. Does your diagram match with figure? Now, let us study these processes in detail. ASEXUAL REPRODUCTION In asexual reproduction, a single organism i able to reproduce on its own. Common forms of asexual reproduction are budding, fission, fragmentation and spore formation. MODES OFREPRODUCTIONIN PLANTS Asexual Reproduction Vegetative Propagation Sexual Reproduction 1. Fission 2. Fragmentation 3. Budding 4. Sporulation Methods of natural Methods of artificial vegetative propagation vegetative propagation 1. by root 2. by underground stem 3. by aerial stem 4. by adventitious buds on leaves 1. by cutting 2. by layering 3. by grafting 4. by tissue culture
  • 3. moreyeast cells. If this process continues for Spore formation come ore time, a large number of yeast cells are This is the most common method of asexual produced in a short time. reproduction in most of the fungi and bacteria. The spores develop in a structure Fission Fission is a process of asexual reproduction called sporangium. When the spores are in which an individual divides into two released, they keep floating in the air. Since (binary fission) or more (multiple fission) new they are tiny and very light, they can cover individuals. It is seen in bacteria. long distances and remain in the air for a long time. The spores are asexual reproductive bodies. Each spore is surrounded by a hard protective coat and can withstand unfavourable conditions, such as high temperature and drought. Under favourable conditions, it germinates and develops into a new individual. Activity To study spores of Rhizopus under a microscope Collect a slice of bread having bread mould (Rhizopus). Take a clean slide and with a forceps put some blackish threads on it. Observe under the microscope. Black-coloured spores are seen in sporangium borne on a sporangiophore. Fig. 14.2 Reproduction in bacteria by binary fission Fragmentation Fragmentation is another form of asexual reproduction. It is commonly found in algae. In algae, the adult organisms just break into two or more fragments. Each of these fragments grows up to form a new organism filament). This process is seen in spirogyra pond scum). Sporangium Spores Sporangiophore (Erect hypha) Fragmentation is also seen in liverworts and Stolon mosses. Have you ever seen slimy green patches in a pond or a lake? Rhizoids Yes, these patches are of algae. When water and nutrients are available in plenty, algae grow and multiply rapidly by fragmentation. This process continues and the algae cover a large area in a short period of time. This process is called eutrophication Fig. 14.3 Spores in sporangium of Rhizopus Bread mould (Rhizopus) reproduces asexually by spore formation. Plants like mosses and ferns also reproduce by means of spores.
  • 4. ored Asparagus become swollen due to foodsto. in them. In the next season, new plants a VEGETATIVE REPRODuCTION Vegetative reproduction is a type of asexual reproduction in which new plants are produced produced from these roots. from roots, stems, leaves and buds. These are vegetative parts of a plant. Therefore, this type of reproduction is called vegetative propagation. All the plants produced by vegetative propagation from one plant are exact copies (clones) of the parent plant. I have never seen the seeds of potatoes, sugarcane, rose and Bougainvillea. How do these plants reproduce? Sweet potato Dahlia ahlia Fig. 14.4 Tuberous roots of sweet potato and Dahlia By stems The underground and subaerial stems are especially modified for vegetative propagation, These plants reproduce vegetatively through their stems. OO Banana, garlic, mint, grapes, roses and Underground stems:These are offollowing many other plants are grown by vegetative propagation. There are a number of natural as well as artificial methods by which plants reproduce vegetatively. types. Tuber: Potato is an undergroundstem tuber that is swollen due to food stored in it. It has buds in the depressionscalledthe eyes. These buds give rise to new plants. The stored food is used up by the new plants to grow. Rhizome: It is an undergroundstem that bears buds. These buds grow to give rise to newplants.Rhizome is found in ginger Why are potato, ginger, sweet potato, o,0 etc. swollen? These plant parts store food in the form of carbohydrates. So they become swollen. This stored food is used by the plants when theymultiply by vegetative propagation. and turmeric. Bulb: It is a very short underground stem surrounded by fleshy scale leaves. The scale leaves store food. It is found Methods of natural vegetative propagation By roots Tuberous roots of Dahlia, sweet potato and Germinating Nodes Fleshy scale bud leaves Scales Bulb Eye Apex Bud Disc Root (b) Rhizomes of ginger Fig. 14.5 Underground stems showing vegetative propagation (a) Tuber of potato C) BUID or onion 142
  • 5. in onion. In the spring, the stem shoots adventitious buds in the notches present 1D from the centre of the scale leaves to along their margin. When such a leaf falls on form a new plant. Subaerial stems: In grasses, mint, Oxalis, plant. Chrysanthemum and strawberry, vegetative Plants with fleshy stems, such as cacti, the soil, each bud grows into an independent hem, roots and aerial branches arise from detached from the main plant body. Each nodes forming the new plants. propagation occurs by subaerial stem. In produce new plants when their parts get detached part can grow into a new plant. Activity To observe vegetative reproduction in potato Take a potato and locate depressions (eyes) on its surface. Each eye has a bud which can grow into a Fleshy leaf new plant. Cut a few pieces of the potato, each with an eye. Bury them in moist soil. Keep the soil moist by adding water regularly. After a few days, each bud grows into a new plant. Likewise, you can also grow A notch bearing an- adventitious bud New plants arising from notches ginger or turmeric. Roots SomethingMore Fig. 14.7 Adventitious buds on the leaf of Bryophyllum Methods of artificial vegetative propagation Vegetative propagation is a simple, fast and less expensive method of plant propagation. It is, therefore, commonly used in horticulture and agriculture. The techniques used are stem The eyes in potato are nodes and buds in the eyes are axillary buds. These buds develop into new plants. Anode is a part of stem at which a leaf arises. By adventitious buds on leaves The fleshy leaves of Bryophyllum bear cutting, layering, grafting and tissue culture. New plant Subaerial Subaerial stem stem Node Node Roots Roots (a) Oxalis (b) Strawberry Fig. 14.6 Vegetative propagation in Oxalis and strawberry by subaerial stems
  • 6. the stock In this method, cutting of a healthy young one plant, called the scion, isken In this method, a bud or cutting with bud bude pt over the Stem cutting branch of a plant having leaf buds is planted cut stem of another plant, called the th The scion and the stock are then firmi mly grows into a new plant. This method is to together. I he care is to be taken that tieg After some time, the tissues of the st and scion join together to form one plant tied in the moist soil. Cutting develops roots and Ihe Sc1Onand the stock are then stock root system under the propagate plants like chameli, Bougainvillea, has an extensive root system under rose and sugarcane. s to The stock supplies the essential nutrient Stem cutting the scion. This is a common method to develop new varieties of rose, guava, mango, lemon and orange. Scion Adventitious root formation Fig. 14.8Vegetative propagation in rose by stem cutting Scion and stock fixed Layering together In this process, a young branch is bent towards the ground and covered with moist soil forming a layer. After some time, roots develop from the covered part. The branch is then cut offfrom the parent plant and allowed to grow into a new plant. This method is commonly used by gardeners to develop plants like jasmine, vines and Bougainvillea. Stock Fig. 14.10 Vegetative propagation through grafting in plants Something More Grafting is the technique of combining thefeatures of two plants. For example, a high yielding varity may be grafted to a disease-resistant variety to have characteristics of both the plants. Many new vaieties of mangoes available in the market are developed by this method. Roots arising Tissue culture (Micropropagation) In tissue culture method, a small pieceo tissue (called explant) is cut off from t* growing tip of the plant. The cells ofthe tissue are separated and kept in a nutrie from covered part Fig. 14.9 Layering in jasmine Grafting to develop new varieties ofornamental plants medium. The cells ofthe tissue dividerap and form an organised cell masscalledcal This is a common method used in horticulture and fruit trees. 144
  • 7. Thecallus istransferred into another nutrient Check PINT 1. containing plant hormones. The 1. Fill in the blanks. m e d i u m (a) There are primarily two modes of reproduction: cells of callus in his nutrient medium asexual and. (b) The process of. ensures continuity of life. (c) Yeast multiplies by divide and difterentiate into roots and shoot and form a new plantlet. The plantlets so formed can now be grown in pots filled with in living organisms soil. Asparagus, Chrysanthemum, orchids and 2. Identify the method of artificial propagation in the following. (a) Twig of one plant tied to the cut stem of another. (b) Young branch put into moist soil. (c) Tissue from growing tip is grown under controlled conditions in the laboratory. many other plants are now grown by this method. Advantages ofvegetative propagation Vegetative propagation is a more rapid, easier and cheaper method of plant propagation as compared to seeds. Such plants take less time to grow and bear fowers and fruits early. The new plants are exact copies of the fusion of male and female gametes. The parent plant as they are produced from a gametes are produced in separate male and single plant. 9EXUAL REPRODUCTION Sexual reproduction occurs as a result of female reproductive organs which may be It produces a large number of plants in a and present female in the plants. same plant or in separate male short time. and female plants. Plants grown vegetatively usually need less Flower The reproductive part attention in the early stages than the plants of a plant grown from seeds. Plants like banana, seedless grapes, the reproductive parts of a plant. The stamens roses, pineapples and dahlias which do are the male reproductive parts and the pistil not produce seeds can only be grown is the female reproductive part ofa flower. vegetatively. You have learnt in Class VI that flowers are Usually, a flower contains both male and Plantlets Callus Culture Culture medium medium containing plant hormones Fig. 14.11 Tissue culture in plant cell 45
  • 8. female parts. Such flowers are called bisexual Pollination flowers. The lowers which contain either The transfer of pollen grains (containin, stamens or pistil are called unisexual flowers. male gametes) from the anthers to ,the Both male and female unisexual flowers may stigma of pistil is known as pollination be present in the same plant or in different This is the first step in the process of see the plants. Mustard, rose and Petunia have formation. bisexual flowers. Maize, papaya and cucumber Types of pollination produce unisexual flowers as they contain Pollination is of two types: self-pollination either male or female parts in them, but not both. Types ofpollination Pollination is oftwo types: self-pollination and cross-pollination. Self-pollination: In this process, polen lands on the stigma of the same Hower or of a different fHower of the same plant. Cross-pollination: In this case, pollen lands on the stigma of a fiower borne on a different plant of the same kind. Stamens-The male reproductive parts of a flower Each stamen is formed of a swollen apical part, the anther and a long slender stalk called the filament. Pollen grains are formed inside the anther. Pollen grains produce male gametes. Pistil-The female reproductive part of a flower Pistil is the female reproductive part of a flower. It consists of stigma, style and ovary. The ovary contains one or more ovules. The female gamete or the egg is formed in the ovule. The ovules develop into seeds after fertilisation. In sexual reproduction, a male and a female gamete fuse to form a zygote. Fig. 14.12 Types of pollination Self-pollination (A and B), Cross-pollination (C) Mechanism of sexual reproduction Agents ofpollination Sexual reproduction in plants involves the Pollination takes place with the helpofsome Pollination takes place with the help of some following steps. external agents such as wind, water, insects, Pollination: Transfer of pollen grains from birds or mammals. These external agents are birds or mammals. These external agents are anthers to the stigma. called agents of pollination. Fertilisation: Union ofmale gamete with Pollination by insects: Insects like honey bees, wasps, moths and butterflies visit Formation of seed: Development of zygote flowers for nectar. While collecting nectar some pollen grains stick to the body of these Formation offruit: Maturation of ovary insects. When these insects visit another flower, the pollen grains are brushed oft, som the female gamete to form zygote. into seed. into fruit. Germination of seed: Formation of young of which fall on the stigma. plant from the seed. i46
  • 9. Insect-pollinated flowers have following Bird-pollinated flowers are much more common than mammal-pollinated flowers. characteristics: Sun birds and hummingbirds are two large Anthers are large and loosely attached. Stigma hang out ofthe flowers to trap the groups of birds which pollinate flowers. pollen grains. They usually have nectaries that produce Hummingbirds hover in front of flowers while sipping the nectar. Sun birds sit on the flower stalks to collect the nectar. nectar. Bird-pollinated flowers have the following They have sweet smell and bright colours. They have sticky stigma and sticky pollen characteristics: grains. They are not scented because birds do not have a well-developed sense of smell. They are ofbrightred, yellow or orange in colour to attract the birds. Bird of paradise, Salvia and Bignonia are some bird-pollinated flowers. Fig. 14.13 Insect pollination in Salvia flower Examples of insect-pollinated flowers are Salvia, orchids, buttercup, sunfower, etc. Whyare flowers generally so colourful and fragrant? Flowers are colourful and fragrant to attract insects for pollination. Fig. 14.14 Hummingbird sipping nectar of a flower Pollination by mammals and birds: Even some birds and small mammals like bats and Something More rodents also pollinate flowers. Mammal-pollinated flowers have the tollowing characteristics: Flowers are quitesturdy in order to bear the vigorous activity of small mammals, while Teeding on the nectar of these flowers. The structure of a flower determines whether it is self-pollinated or cross-pollinated. A self-pollinated flower has its anthers located higher than the stigma hile a cross-pollinated flower hasa long pistil that extends beyond the stamens. They are usuallybrown or white in colour. They often have a strong scent. Pollination by wind: Flowers of wheat, rice, maize and rye grass are pollinated by wind. Wind-pollinated flowers have the following Sausage tree, kadamba and Agave are characteristics: pollinated by bat. 4
  • 10. A germinating pollen grain They are not brightly coloured and are usually white. They do not produce nectar. Stigma Pollen tube Style They produce small and light pollen grains in large number to be carried away by wind. Ovary wall Integument Antipodal. cells (Future seed coat Pollination by water: Pollination in aquatic plants is usually carried out by water. The examples of water-pollinated plants are Sea grass, Hydrilla and Vallisneria. Water- pollinated flowers release their pollen grains into the water. These pollen grains are passively carried to other flowers by water Currents for pollination. Polar nuclei Ovary Eggcell Synergid 2 male- gametes Micropyle Fig. 14.16 Germination of pollen grains on stigma and one of them reaches to ovule to carry out fertilisation Fruit and seed formation Floating pollen grains After fertilisation, following changes ocur in the flower: Female- The fertilised egg, now calledzygote,grows into the embryo. It has two parts. The shoot-formingpart called plumule and root-torming part called radicle. flower Female flower The ovary grows into a fruit and otherparts of the flower fall off. coils after Male flower receiving The ovules develop into seeds. The seed contains an embryo enclosedin a protective seed coat. pollen grain Fig. 14.15 Pollination by water in Vallisneria A seed is a mature ovule that contains the embryo and the stored food. It isenclosed by a seed coat formed of two coverings. Fertilisation On reaching the stigma, pollen grain grows A fruit is the seed-bearing structure of a out into a thin pollen tube. It extendsiowering plant. Actually, it is the ripene through the style, reaches the ovary and ovary of the plant and seeds are the matured enters the ovule. The pollen tube contains two ovules of the fruit. male gametes, one of which fuses with the Fruits may be fleshy and juicy or dry an female gamete or egg and forms a zygote. The process of fusion of a male and a female juicy fruits whereas almonds and walnutsar hard. Mango, apple and orange are fiesny gamete is called fertilisation. dry and hard fruits. 4
  • 11. severe competition for space, sunlight, water and minerals. Therefore, dispersal of seeds is beneficial to plants as: It ensures that the plants are dispersed over wide areas. It avoids overcrowding and competition among the plants for space, sunlight, water and minerals. (b) Mango (a) Apple Fig. 14.17 Fleshy and juicy fruits Seeds and fruits are dispersed by wind, water, animals and explosive mechanism. ARTIFICIAL POLLINATION The improvement of quality of seeds and Di increase in the production of grains, cereals, fruits and vegetables has become essential to Fruits and seeds scattered by wind are Dispersal by wind usually small and light. Seeds of maple and drumsticks have wings attached to them, provide food for rapidly increasing population. drumsticks have wings attached to them, pollination."This is also called hybridisation. which Light help seeds them of grasses float in or air hairy for long seeds distances. of oak This is made possible by controlled artificial Light seeds of grasses or hairy seeds of oak and cotton, and hairy fruits of sunflower In hybridisation, plants with desired characteristics are selected. The pollen from get blown to far away places by wind. Fruits one such plant is transterred to the stigma of poppy are very small and get scattered by ofother selected plants.The pollinated pistils wind. of these flowers are covered with polythene bags to avoid polination from uncontrolled SOurce. The seeds so obtained are called hybrid seeds. They are stored to be sown in the next season. The plants obtained from these seeds are hybrid plants. The aim of obtaining hybrid seeds is to have: high-yielding variety of plants. disease-resistant plants. Fig. 14.18 Maple seed with a wing plants that can grow and mature in short duration. Dispersal by water The fruits and seeds of aquatic plants like those of water lily, lotus and coconut float on The main function of the fruit is to help water surface and are carried to far off places the seeds to disperse to different places to by water current. Coconut has a fibrous coat increase their chances of survival. In case with hard covering which is carried away to SEED DISPERSAL Seeds fall at the same place, there would be long distances by water currents. 149
  • 12. Fig. 14.19 Coconut fruit floating on water Fig. 14.21 Explosive mechanism in Geranium Dispersal by animals Germination of seed Some seeds have spines or hooks which On reaching the moist soil, the seed swels cling to the bodies of animals and are up by imbibing water. The embryo starts carried to long distances as in Xanthium and growing. Its radicle grows down into the soil and forms the root. The plumule grows upward in the air, develops leaves and forms Urena. the shoot of the young plant. Fig. 14.20 Xanthium seeds with hooks Man, animals and birds eat the pulp or the edible part of fleshy fruits and throw their seeds. This helps in their dispersal. The small Check PeINT 2 Fig. 14.22 Germination of seed and undigested seeds come out oftheir body. 1. Name the male and female reproductive parts of The seeds of guava and berries are dispersed a flower. this way. 2. What are unisexual plants? 3. Define the term pollination. 4. Name the means of pollination. 5. What is the difference between self and cross Explosive mechanism Fruits and seeds of balsam, pea, Geran1um and castor burst with sudden jerks and get scattered away from the parent plant. pollination? 6. Give a structural modification found in insect pollinated flowers. 50