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12                   Reproduction in Plants

T
        o produce its kind is a               and (ii) sexual reproduction. In asexual
        characteristic of all living          reproduction plants can give rise to new
        organisms. You have already           plants without seeds, whereas in sexual
learnt this in Class VI. The production       reproduction new plants are obtained
                                              reproduction,
of new individuals from their parents is      from seeds.
known as reproduction But, how do
            reproduction.
plants reproduce? There are different
modes of reproduction in plants which                  Paheli thought that new
we shall learn in this chapter.                     plants always grow from seeds.
12.1 MODES     OF   REPRODUCTION                But, she has never seen the seeds
                                                of sugarcane, potato and rose. She
In Class VI you learnt about different
                                                 wants to know how these plants
parts of a flowering plant. Try to list the
                                                            reproduce.
various parts of a plant and write the
functions of each. Most plants have
roots, stems and leaves. These are called
the vegetative parts of a plant. After a      Asexual reproduction
certain period of growth, most plants         In asexual reproduction new plants are
bear flowers. You may have seen the           obtained without production of seeds or
mango trees flowering in spring. It is        spores.
these flowers that give rise to juicy
                                              Vegetative propagation
mango fruit we enjoy in summer. We eat
the fruits and usually discard the seeds.     It is a type of asexual reproduction in
Seeds germinate and form new plants.          which new plants are produced from
So, what is the function of flowers in        roots, stems, leaves and buds. Since
plants? The flowers perform the function      reproduction is through the vegetative
of reproduction in plants. Flowers are        parts of the plant, it is known as
the reproductive parts of a plant. A          vegetative propagation.
flower may have either the male part or
                                              Activity 12.1
the female part or both male and female
parts.                                        Cut a branch of rose or champa with a
   There are several ways by which            node. This piece of branch is termed a
plants produce their offspring. These are     cutting Bury the cutting in the soil. A
                                              cutting.
categorised into two types: (i) asexual,      node is a part of the stem/branch at
which a leaf arises (Fig. 12.1). Water the                                       Eyes
cutting every day and observe its
growth. Observe and record the number
of days taken for roots to come out and
new leaves to arise. Try the same activity
by growing money plant in a jar of water
and record your observations.




                                             Fig. 12.2 Potato plant sprouting from an ‘eye’

                                             of a potato, each with an eye and bury
                                             them in the soil. Water the pieces
      Node
                                             regularly for a few days and observe
                                             their progress. What do you find?


                     Bud in
                     the axil


         Fig. 12.1 Stem-cutting of rose

   You must have seen flower buds
developing into flowers. Apart from
flower buds, there are buds in the axil
(point of attachment of the leaf at the
node) of leaves which develop into
shoots. These buds are called vegetative
buds (Fig. 12.2). A bud consists of a
short stem around which immature
                                              Fig. 12.3 Ginger with new plants sprouting
overlapping leaves are folded. The                              from it
vegetative buds can also give rise to new
plants.                                          Likewise you can also grow ginger or
                                             turmeric (Fig. 12.3).
Activity 12.2
                                                 Bryophyllum (sprout leaf plant) has
Take a fresh potato. Observe the scars       buds in the margins of leaves (Fig. 12.4).
on it with the help of a magnifying glass.   If a leaf of this plant falls on a moist
You may find bud(s) in them. These scars     soil, each bud can give rise to a new
are also called “eyes” Cut a few pieces
                 “eyes”.                     plant.

134                                                                                 SCIENCE
multiply every few hours if sufficient
                                                 nutrients are made available to them.
                                                 Remember that yeast is a single-celled
                                                 organism. Let us see how they
                                                 reproduce?
                                    New plant
Fig. 12.4 Leaf of bryophyllum with buds in the   Activity 12.3
                     margin
                                                 (To be demonstrated by the teacher)
   The roots of some plants can also             Take a piece of yeast cake or yeast
give rise to new plants. Sweet potato and        powder from a bakery or a chemist shop.
dahlia are examples.                             Take a pinch of yeast and place it in a
   Plants such as cacti produce new              container with some water. Add a
plants when their parts get detached             spoonful of sugar and shake to dissolve
from the main plant body. Each                   it. Keep it in the warm part of a room.
detached part can grow into a new                After an hour, put a drop of this liquid
plant.                                           on a glass slide and observe under a
                                                 microscope. What do you observe? You
                                                 may see the formation of new yeast cells
        Boojho wants to know if                  (Fig. 12.5).
       there is any advantage of
                                                                                 Chain of buds
        vegetative propagation.                               Developing bud
                                                                               New bud
                                                 Yeast cell


    Plants produced by vegetative
propagation take less time to grow and
bear flowers and fruits earlier than those
produced from seeds. The new plants
are exact copies of the parent plant, as
                                                   Fig. 12.5 Reproduction in yeast by budding
they are produced from a single parent.
    Later in this chapter you will learn
that plants produced by sexual                       The small bulb-like projection
reproduction have characters of both the         coming out from the yeast cell is called
parents. Plants produce seeds as a result        a bud The bud gradually grows and
                                                   bud.
of sexual reproduction.                          gets detached from the parent cell and
                                                 forms a new yeast cell. The new yeast
Budding                                          cell grows, matures and produces more
You have already learnt about the tiny           yeast cells. If this process continues, a
organisms like yeast can be seen only            large number of yeast cells are produced
under a microscope. These grow and               in a short time.

REPRODUCTION IN PLANTS                                                                    135
Fragmentation
You might have seen slimy green
patches in ponds, or in other stagnant
water bodies. These are the algae. When
water and nutrients are available algae
grow and multiply rapidly by
fragmentation. An alga breaks up into
two or more fragments. These fragments
or pieces grow into new individuals
(Fig. 12.6). This process continues and
                                                 Sori
they cover a large area in a short period
of time.

                                                 Fig. 12.8 Reproduction through spore formation
                                                                     in fern

                                                 like mesh on the bread. When spores
                                                 are released they keep floating in the
                                                 air. As they are very light they can cover
Fig. 12.6 Fragmentation in spirogyra (an alga)   long distances.
                                                     The spores are asexual reproductive
Spore formation
                                                 bodies. Each spore is covered by a
In Chapter 1 you learnt that the fungi
                                                 hard protective coat to withstand
on a bread piece grow from spores which
                                                 unfavourable conditions such as high
are present in the air. Repeat Activity
                                                 temperature and low humidity. So
1.2. Observe the spores in the cotton-
                                                 they can survive for a long time. Under
                      Sporangium                 favourable conditions, a spore
                                                 germinates and develops into a new
                                   Spores
                                                 individual. Plants such as moss and
                                                 ferns (Fig. 12.8) also reproduce by
Hypha                                            means of spores.
                                                 12.2 SEXUAL REPRODUCTION
                                                 You have learnt earlier the structure of
                                                 a flower. You know that the flowers are
                                                 the reproductive parts of a plant. The
                                                 stamens are the male reproductive part
Fig. 12.7 Reproduction through spore formation   and the pistil is the female reproductive
                  in fungus                      part (Fig. 12.9).

136                                                                                     SCIENCE
Activity 12.4                                        Both the male and the female unisexual
                                                     flowers may be present in the same plant
Take a mustard/china rose/petunia
                                                     or in different plants.
flower and separate its reproductive
                                                         Could you identify the anther and
parts. Study the various parts of a
                                                     the filament of a stamen? [Fig. 12.9 (a)].
stamen and pistil.
                                                     Anther contains pollen grains which
   The flowers which contain either
                                                     produce male gametes A pistil consists
                                                                    gametes.
only the pistil or only the stamens are
                                                     of stigma, style and ovary. The ovary
called unisexual flowers The flowers
                   flowers.
                                                     contains one or more ovules. The
which contain both stamens and pistil
                                                     female gamete or the egg is formed in
are called bisexual flowers Corn,
                        flowers.
                                                     an ovule [Fig. 12.9 (b)]. In sexual
papaya and cucumber produce
                                                     reproduction a male and a female
unisexual flowers, whereas mustard,
                                                     gamete fuse to form a zygote
                                                                             zygote.
rose and petunia have bisexual flowers.




                                                           Boojho wants to know how the
                              Anther                      male gamete in the pollen grain
                                                         reaches the female gamete present
                                                                   in the ovule.

                              Filament
                                                     Pollination
                                                     Generally pollen grains have a tough
                                                     protective coat which prevents them
               (a) Stamen                            from drying up. Since pollen grains are
                                                     light, they can be carried by wind or
Stigma
                                          Stigma
   Style                                                    Pollens
                                                                                              Stigma
                      Ovule                                           Anther


                     Ovary




                     (b) Pistil
                                            (a) Self-pollination               (b) Cross-pollination
           Fig. 12.9 Reproductive parts                    Fig. 12.10 Pollination in flower

REPRODUCTION IN PLANTS                                                                            137
Boojho wants to know why
      flowers are generally so colourful
         and fragrant. Is it to attract
                   insects?


water. Insects visit flowers and carry
away pollen on their bodies. Some of
the pollen lands on the stigma of a flower
of the same kind. The transfer of pollen
from the anther to the stigma of a flower                             (a)
is called pollination If the pollen lands
          pollination.
on the stigma of the same flower it is                                                      (b)

called self-pollination When the pollen
        self-pollination.                            Fig. 12.12 (a) Section of an apple, (b) Almond
of a flower lands on the stigma of another
flower of the same plant, or that of a               gametes (to form a zygote) is called
different plant of the same kind, it is              fertilisation (Fig. 12.11). The zygote
called cross-pollination [Fig. 12.10 (a)             develops into an embryo
                                                                       embryo.
and (b)].
                        Pollen grain (germinating)
                                                     12.3 FRUITS     AND    SEED FORMATION
                                                     After fertilisation, the ovary grows into
                                                     a fruit and other parts of the flower fall
                                                     off. The fruit is the ripened ovary. The
                 Pollen tube
                                                     seeds develop from the ovules. The seed
                                        Zygote
                                        formation    contains an embryo enclosed in a
                                                     protective seed coat.
                                                         Some fruits are fleshy and juicy such
                                                     as mango, apple and orange. Some fruits
                                                     are hard like almonds and walnuts
                 Ovum                                [Fig. 12.12 (a) and (b)].

           (a)                    (b)
                                                     12.4 SEED DISPERSAL
  Fig. 12.11 Fertilisation (Zygote formation)        In nature same kind of plants grow at
                                                     different places. This happens because
Fertilisation                                                                          places.
                                                     seeds are dispersed to different places
The cell which results after fusion of               Sometimes after a walk through a forest
the gametes is called a zygote The
                          zygote.                    or a field or a park, you may have found
process of fusion of male and female                 seeds or fruits sticking to your clothes.

138                                                                                         SCIENCE
Did you try to observe how these seeds          (b)], light seeds of grasses or hairy seeds
were clinging to your clothes?                  of aak ( Madar ) and hairy fruit of
   What do you think will happen if all         sunflower [Fig. 12.14 (a), (b)], get blown
seeds of a plant were to fall at the same       off with the wind to far away places.
place and grow there? There would be            Some seeds are dispersed by water. These
severe competition for sunlight, water,         fruits or seeds usually develop floating
minerals and space. As a result the seeds       ability in the form of spongy or fibrous
would not grow into healthy plants.             outer coat as in coconut. Some seeds
Plants benefit by seed dispersal. It            are dispersed by animals, especially
prevents competition between the plant          spiny seeds with hooks which get
and its own seedlings for sunlight, water       attached to the bodies of animals and
and minerals. It also enables the plants        are carried to distant places. Examples
to invade new habitats for wider                are Xanthium (Fig. 12.15) and Urena.
distribution.                                       Some seeds are dispersed when the
   Seeds and fruits of plants are carried       fruits burst with sudden jerks. The seeds
away by wind, water and animals.                are scattered far from the parent plant.
Winged seeds such as those of                   This happens in the case of castor and
drumstick and maple [Fig. 12.13 (a) and         balsam.


                         Seed



                     Wing




       (a)                             (b)                 (a)                     (b)
    Fig. 12.13 Seeds of (a) drumstick and       Fig. 12.14 (a) The hairy fruit of sunflower and
                  (b) maple                              (b) hairy seed of madar (aak)




                                     Fig. 12.15 Xanthium

REPRODUCTION IN PLANTS                                                                     139
Keywords
      Asexual reproduction           Hypha                   Sexual reproduction
      Budding                        Ovule                   Spore
      Embryo                         Pollen grain            Sporangium
      Fertilisation                  Pollen tube             Vegetative propagation
      Fragmentation                  Pollination             Zygote
      Gametes                        Seed dispersal




      What you have learnt
         All organisms multiply or reproduce their own kind.
         In plants there are two modes of reproduction, asexual and sexual.
         There are several methods of asexual reproduction such as
         fragmentation, budding, spore formation and vegetative propagation.
         Sexual reproduction involves the fusion of male and female gametes.
         In vegetative propagation new plants are produced from different
         vegetative parts such as leaves, stems and roots.
         Flower is the reproductive part of a plant.
         A flower may be unisexual with either the male or the female reproductive
         parts.
         A bisexual flower has both the male and the female reproductive parts.
         The male gametes are found inside the pollen grains and female gametes
         are found in the ovule.
         Pollination is the process of transfer of pollen grains from the anther of
         one flower to the stigma of the same or another flower.
         Pollination is of two types, self-pollination and cross-pollination. In
         self-pollination, pollen grains are transferred from the anther to the
         stigma of the same flower. In cross-pollination, pollen grains are
         transferred from the anther of one flower to the stigma of another flower
         of the same kind.
         Pollination takes place in plants with the help of wind, water and insects.
         The fusion of male and female gametes is called fertilisation.
         Fertilised egg is called zygote. Zygote develops into an embryo.
         Fruit is the mature ovary whereas ovule develops into a seed, which
         contains the developing embryo.
         Seed dispersal is aided by wind, water and animals.
         Seed dispersal helps the plants to (i) prevent overcrowding, (ii) avoid
         competition for sunlight, water and minerals and (iii) invade new habitats.


140                                                                                    SCIENCE
Exercises
             1. Fill in the blanks:
                 (a)     Production of new individuals from the vegetative part of parent is
                         called_____________.
                 (b)     A flower may have either male or female reproductive parts. Such
                         a flower is called_____________.
                 (c)     The transfer of pollen grains from the anther to the stigma of the
                         same or of another flower of the same kind is known as
                         _____________.
                 (d)     The fusion of male and female gametes is termed as _____________.
                 (e)     Seed dispersal takes place by means of _____________,
                         _____________ and _____________.
             2. Describe the different methods of asexual reproduction. Give examples.
             3. Explain what you understand by sexual reproduction.
             4. State the main difference between asexual and sexual reproduction.
             5. Sketch the reproductive parts of a flower.
             6. Explain the difference between self-pollination and cross-pollination.
             7. How does the process of fertilisation take place in flowers?
             8. Describe the various ways by which seeds are dispersed.
             9. Match items in Column I with those in Column II:
                Column I                           Column II
                 (a)     Bud                        (i)   Maple
                 (b)     Eyes                      (ii)   Spirogyra
                 (c)     Fragmentation            (iii)   Yeast
                 (d)     Wings                    (iv)    Bread mould
                 (e)     Spores                    (v)    Potato
                                                  (vi)    Rose
            10. Tick ( ) the correct answer:
                 (a)     The reproductive part of a plant is the
                           (i)   leaf        (ii) stem    (iii) root       (iv) flower
                 (b)     The process of fusion of the male and the female gametes is called
                           (i)   fertilisation     (ii)   pollination
                         (iii)   reproduction     (iv)    seed formation




REPRODUCTION IN PLANTS                                                                         141
(c)    Mature ovary forms the
                   (i)   seed          (ii)   stamen
                 (iii)   pistil       (iv)    fruit
          (d)    A spore producing plant is
                   (i)   rose          (ii)   bread mould
                 (iii)   potato       (iv)    ginger
          (e)    Bryophyllum can reproduce by its
                   (i)   stem          (ii)   leaves
                 (iii)   roots        (iv)    flower


               Learning
      Extended Learning — Activities and Projects
      1. Make your own cactus garden by collecting pieces cut from different
         kinds of cacti. Grow the variety in one single flat container or in
         separate pots.
      2. Visit a fruit market and collect as many local fruits as possible. If many
         fruits are not available, you can collect tomatoes and cucumbers (these
         are fruits, though we use them as vegetables). Make drawings of the
         different fruits. Split the fruits and examine the seeds within. Look for
         any special characteristics in the fruits and their seeds. If possible visit
         the website:
         www.saps.plantsci.cam.ac.uk/fscfruit/dispersal.pdf
         You can visit a library also to learn about this.
      3. Think of ten different fruit-bearing plants. Remember that many
         vegetables are also fruits of the plants. Discuss with your teacher,
         parents, farmers, fruit growers and agricultural experts (if available
         nearby) and find out the manner of their dispersal. Present your data
         in the form of a table as shown below:
        S. No.       Name of fruit- Agent through which        Part of or seed which
                     bearing plant   seeds are dispersed         helps in dispersal
        1.
        2.
        3.
      4. Suppose there is one member of a particular kind of organism in a
         culture dish, which doubles itself in one hour through asexual
         reproduction. Work out the number of members of that kind of organism
         which will be present in the culture dish after ten hours. Such a colony
         of individuals arising from one parent is called a “clone”.
         You can read more on the following website:
         www.edumedia-sciences.com/a437_l2-blog-call.html


142                                                                                     SCIENCE

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7 reproduction in plants

  • 1. 12 Reproduction in Plants T o produce its kind is a and (ii) sexual reproduction. In asexual characteristic of all living reproduction plants can give rise to new organisms. You have already plants without seeds, whereas in sexual learnt this in Class VI. The production reproduction new plants are obtained reproduction, of new individuals from their parents is from seeds. known as reproduction But, how do reproduction. plants reproduce? There are different modes of reproduction in plants which Paheli thought that new we shall learn in this chapter. plants always grow from seeds. 12.1 MODES OF REPRODUCTION But, she has never seen the seeds of sugarcane, potato and rose. She In Class VI you learnt about different wants to know how these plants parts of a flowering plant. Try to list the reproduce. various parts of a plant and write the functions of each. Most plants have roots, stems and leaves. These are called the vegetative parts of a plant. After a Asexual reproduction certain period of growth, most plants In asexual reproduction new plants are bear flowers. You may have seen the obtained without production of seeds or mango trees flowering in spring. It is spores. these flowers that give rise to juicy Vegetative propagation mango fruit we enjoy in summer. We eat the fruits and usually discard the seeds. It is a type of asexual reproduction in Seeds germinate and form new plants. which new plants are produced from So, what is the function of flowers in roots, stems, leaves and buds. Since plants? The flowers perform the function reproduction is through the vegetative of reproduction in plants. Flowers are parts of the plant, it is known as the reproductive parts of a plant. A vegetative propagation. flower may have either the male part or Activity 12.1 the female part or both male and female parts. Cut a branch of rose or champa with a There are several ways by which node. This piece of branch is termed a plants produce their offspring. These are cutting Bury the cutting in the soil. A cutting. categorised into two types: (i) asexual, node is a part of the stem/branch at
  • 2. which a leaf arises (Fig. 12.1). Water the Eyes cutting every day and observe its growth. Observe and record the number of days taken for roots to come out and new leaves to arise. Try the same activity by growing money plant in a jar of water and record your observations. Fig. 12.2 Potato plant sprouting from an ‘eye’ of a potato, each with an eye and bury them in the soil. Water the pieces Node regularly for a few days and observe their progress. What do you find? Bud in the axil Fig. 12.1 Stem-cutting of rose You must have seen flower buds developing into flowers. Apart from flower buds, there are buds in the axil (point of attachment of the leaf at the node) of leaves which develop into shoots. These buds are called vegetative buds (Fig. 12.2). A bud consists of a short stem around which immature Fig. 12.3 Ginger with new plants sprouting overlapping leaves are folded. The from it vegetative buds can also give rise to new plants. Likewise you can also grow ginger or turmeric (Fig. 12.3). Activity 12.2 Bryophyllum (sprout leaf plant) has Take a fresh potato. Observe the scars buds in the margins of leaves (Fig. 12.4). on it with the help of a magnifying glass. If a leaf of this plant falls on a moist You may find bud(s) in them. These scars soil, each bud can give rise to a new are also called “eyes” Cut a few pieces “eyes”. plant. 134 SCIENCE
  • 3. multiply every few hours if sufficient nutrients are made available to them. Remember that yeast is a single-celled organism. Let us see how they reproduce? New plant Fig. 12.4 Leaf of bryophyllum with buds in the Activity 12.3 margin (To be demonstrated by the teacher) The roots of some plants can also Take a piece of yeast cake or yeast give rise to new plants. Sweet potato and powder from a bakery or a chemist shop. dahlia are examples. Take a pinch of yeast and place it in a Plants such as cacti produce new container with some water. Add a plants when their parts get detached spoonful of sugar and shake to dissolve from the main plant body. Each it. Keep it in the warm part of a room. detached part can grow into a new After an hour, put a drop of this liquid plant. on a glass slide and observe under a microscope. What do you observe? You may see the formation of new yeast cells Boojho wants to know if (Fig. 12.5). there is any advantage of Chain of buds vegetative propagation. Developing bud New bud Yeast cell Plants produced by vegetative propagation take less time to grow and bear flowers and fruits earlier than those produced from seeds. The new plants are exact copies of the parent plant, as Fig. 12.5 Reproduction in yeast by budding they are produced from a single parent. Later in this chapter you will learn that plants produced by sexual The small bulb-like projection reproduction have characters of both the coming out from the yeast cell is called parents. Plants produce seeds as a result a bud The bud gradually grows and bud. of sexual reproduction. gets detached from the parent cell and forms a new yeast cell. The new yeast Budding cell grows, matures and produces more You have already learnt about the tiny yeast cells. If this process continues, a organisms like yeast can be seen only large number of yeast cells are produced under a microscope. These grow and in a short time. REPRODUCTION IN PLANTS 135
  • 4. Fragmentation You might have seen slimy green patches in ponds, or in other stagnant water bodies. These are the algae. When water and nutrients are available algae grow and multiply rapidly by fragmentation. An alga breaks up into two or more fragments. These fragments or pieces grow into new individuals (Fig. 12.6). This process continues and Sori they cover a large area in a short period of time. Fig. 12.8 Reproduction through spore formation in fern like mesh on the bread. When spores are released they keep floating in the air. As they are very light they can cover Fig. 12.6 Fragmentation in spirogyra (an alga) long distances. The spores are asexual reproductive Spore formation bodies. Each spore is covered by a In Chapter 1 you learnt that the fungi hard protective coat to withstand on a bread piece grow from spores which unfavourable conditions such as high are present in the air. Repeat Activity temperature and low humidity. So 1.2. Observe the spores in the cotton- they can survive for a long time. Under Sporangium favourable conditions, a spore germinates and develops into a new Spores individual. Plants such as moss and ferns (Fig. 12.8) also reproduce by Hypha means of spores. 12.2 SEXUAL REPRODUCTION You have learnt earlier the structure of a flower. You know that the flowers are the reproductive parts of a plant. The stamens are the male reproductive part Fig. 12.7 Reproduction through spore formation and the pistil is the female reproductive in fungus part (Fig. 12.9). 136 SCIENCE
  • 5. Activity 12.4 Both the male and the female unisexual flowers may be present in the same plant Take a mustard/china rose/petunia or in different plants. flower and separate its reproductive Could you identify the anther and parts. Study the various parts of a the filament of a stamen? [Fig. 12.9 (a)]. stamen and pistil. Anther contains pollen grains which The flowers which contain either produce male gametes A pistil consists gametes. only the pistil or only the stamens are of stigma, style and ovary. The ovary called unisexual flowers The flowers flowers. contains one or more ovules. The which contain both stamens and pistil female gamete or the egg is formed in are called bisexual flowers Corn, flowers. an ovule [Fig. 12.9 (b)]. In sexual papaya and cucumber produce reproduction a male and a female unisexual flowers, whereas mustard, gamete fuse to form a zygote zygote. rose and petunia have bisexual flowers. Boojho wants to know how the Anther male gamete in the pollen grain reaches the female gamete present in the ovule. Filament Pollination Generally pollen grains have a tough protective coat which prevents them (a) Stamen from drying up. Since pollen grains are light, they can be carried by wind or Stigma Stigma Style Pollens Stigma Ovule Anther Ovary (b) Pistil (a) Self-pollination (b) Cross-pollination Fig. 12.9 Reproductive parts Fig. 12.10 Pollination in flower REPRODUCTION IN PLANTS 137
  • 6. Boojho wants to know why flowers are generally so colourful and fragrant. Is it to attract insects? water. Insects visit flowers and carry away pollen on their bodies. Some of the pollen lands on the stigma of a flower of the same kind. The transfer of pollen from the anther to the stigma of a flower (a) is called pollination If the pollen lands pollination. on the stigma of the same flower it is (b) called self-pollination When the pollen self-pollination. Fig. 12.12 (a) Section of an apple, (b) Almond of a flower lands on the stigma of another flower of the same plant, or that of a gametes (to form a zygote) is called different plant of the same kind, it is fertilisation (Fig. 12.11). The zygote called cross-pollination [Fig. 12.10 (a) develops into an embryo embryo. and (b)]. Pollen grain (germinating) 12.3 FRUITS AND SEED FORMATION After fertilisation, the ovary grows into a fruit and other parts of the flower fall off. The fruit is the ripened ovary. The Pollen tube seeds develop from the ovules. The seed Zygote formation contains an embryo enclosed in a protective seed coat. Some fruits are fleshy and juicy such as mango, apple and orange. Some fruits are hard like almonds and walnuts Ovum [Fig. 12.12 (a) and (b)]. (a) (b) 12.4 SEED DISPERSAL Fig. 12.11 Fertilisation (Zygote formation) In nature same kind of plants grow at different places. This happens because Fertilisation places. seeds are dispersed to different places The cell which results after fusion of Sometimes after a walk through a forest the gametes is called a zygote The zygote. or a field or a park, you may have found process of fusion of male and female seeds or fruits sticking to your clothes. 138 SCIENCE
  • 7. Did you try to observe how these seeds (b)], light seeds of grasses or hairy seeds were clinging to your clothes? of aak ( Madar ) and hairy fruit of What do you think will happen if all sunflower [Fig. 12.14 (a), (b)], get blown seeds of a plant were to fall at the same off with the wind to far away places. place and grow there? There would be Some seeds are dispersed by water. These severe competition for sunlight, water, fruits or seeds usually develop floating minerals and space. As a result the seeds ability in the form of spongy or fibrous would not grow into healthy plants. outer coat as in coconut. Some seeds Plants benefit by seed dispersal. It are dispersed by animals, especially prevents competition between the plant spiny seeds with hooks which get and its own seedlings for sunlight, water attached to the bodies of animals and and minerals. It also enables the plants are carried to distant places. Examples to invade new habitats for wider are Xanthium (Fig. 12.15) and Urena. distribution. Some seeds are dispersed when the Seeds and fruits of plants are carried fruits burst with sudden jerks. The seeds away by wind, water and animals. are scattered far from the parent plant. Winged seeds such as those of This happens in the case of castor and drumstick and maple [Fig. 12.13 (a) and balsam. Seed Wing (a) (b) (a) (b) Fig. 12.13 Seeds of (a) drumstick and Fig. 12.14 (a) The hairy fruit of sunflower and (b) maple (b) hairy seed of madar (aak) Fig. 12.15 Xanthium REPRODUCTION IN PLANTS 139
  • 8. Keywords Asexual reproduction Hypha Sexual reproduction Budding Ovule Spore Embryo Pollen grain Sporangium Fertilisation Pollen tube Vegetative propagation Fragmentation Pollination Zygote Gametes Seed dispersal What you have learnt All organisms multiply or reproduce their own kind. In plants there are two modes of reproduction, asexual and sexual. There are several methods of asexual reproduction such as fragmentation, budding, spore formation and vegetative propagation. Sexual reproduction involves the fusion of male and female gametes. In vegetative propagation new plants are produced from different vegetative parts such as leaves, stems and roots. Flower is the reproductive part of a plant. A flower may be unisexual with either the male or the female reproductive parts. A bisexual flower has both the male and the female reproductive parts. The male gametes are found inside the pollen grains and female gametes are found in the ovule. Pollination is the process of transfer of pollen grains from the anther of one flower to the stigma of the same or another flower. Pollination is of two types, self-pollination and cross-pollination. In self-pollination, pollen grains are transferred from the anther to the stigma of the same flower. In cross-pollination, pollen grains are transferred from the anther of one flower to the stigma of another flower of the same kind. Pollination takes place in plants with the help of wind, water and insects. The fusion of male and female gametes is called fertilisation. Fertilised egg is called zygote. Zygote develops into an embryo. Fruit is the mature ovary whereas ovule develops into a seed, which contains the developing embryo. Seed dispersal is aided by wind, water and animals. Seed dispersal helps the plants to (i) prevent overcrowding, (ii) avoid competition for sunlight, water and minerals and (iii) invade new habitats. 140 SCIENCE
  • 9. Exercises 1. Fill in the blanks: (a) Production of new individuals from the vegetative part of parent is called_____________. (b) A flower may have either male or female reproductive parts. Such a flower is called_____________. (c) The transfer of pollen grains from the anther to the stigma of the same or of another flower of the same kind is known as _____________. (d) The fusion of male and female gametes is termed as _____________. (e) Seed dispersal takes place by means of _____________, _____________ and _____________. 2. Describe the different methods of asexual reproduction. Give examples. 3. Explain what you understand by sexual reproduction. 4. State the main difference between asexual and sexual reproduction. 5. Sketch the reproductive parts of a flower. 6. Explain the difference between self-pollination and cross-pollination. 7. How does the process of fertilisation take place in flowers? 8. Describe the various ways by which seeds are dispersed. 9. Match items in Column I with those in Column II: Column I Column II (a) Bud (i) Maple (b) Eyes (ii) Spirogyra (c) Fragmentation (iii) Yeast (d) Wings (iv) Bread mould (e) Spores (v) Potato (vi) Rose 10. Tick ( ) the correct answer: (a) The reproductive part of a plant is the (i) leaf (ii) stem (iii) root (iv) flower (b) The process of fusion of the male and the female gametes is called (i) fertilisation (ii) pollination (iii) reproduction (iv) seed formation REPRODUCTION IN PLANTS 141
  • 10. (c) Mature ovary forms the (i) seed (ii) stamen (iii) pistil (iv) fruit (d) A spore producing plant is (i) rose (ii) bread mould (iii) potato (iv) ginger (e) Bryophyllum can reproduce by its (i) stem (ii) leaves (iii) roots (iv) flower Learning Extended Learning — Activities and Projects 1. Make your own cactus garden by collecting pieces cut from different kinds of cacti. Grow the variety in one single flat container or in separate pots. 2. Visit a fruit market and collect as many local fruits as possible. If many fruits are not available, you can collect tomatoes and cucumbers (these are fruits, though we use them as vegetables). Make drawings of the different fruits. Split the fruits and examine the seeds within. Look for any special characteristics in the fruits and their seeds. If possible visit the website: www.saps.plantsci.cam.ac.uk/fscfruit/dispersal.pdf You can visit a library also to learn about this. 3. Think of ten different fruit-bearing plants. Remember that many vegetables are also fruits of the plants. Discuss with your teacher, parents, farmers, fruit growers and agricultural experts (if available nearby) and find out the manner of their dispersal. Present your data in the form of a table as shown below: S. No. Name of fruit- Agent through which Part of or seed which bearing plant seeds are dispersed helps in dispersal 1. 2. 3. 4. Suppose there is one member of a particular kind of organism in a culture dish, which doubles itself in one hour through asexual reproduction. Work out the number of members of that kind of organism which will be present in the culture dish after ten hours. Such a colony of individuals arising from one parent is called a “clone”. You can read more on the following website: www.edumedia-sciences.com/a437_l2-blog-call.html 142 SCIENCE