Reproduction in Plants PDF

8 Reproduction in Plants T o produce its kind is a reproduction, new plants are obtained characteristic of all living from seeds. organisms. You have already learnt this in Class VI. The production of new individuals from their...

8 Reproduction in Plants T o produce its kind is a reproduction, new plants are obtained characteristic of all living from seeds. organisms. You have already learnt this in Class VI. The production of new individuals from their parents is known as reproduction. But, how do Paheli thought that new plants reproduce? There are different plants always grow from seeds. modes of reproduction in plants which But, she has never seen the seeds we shall learn in this chapter. of sugarcane, potato and rose. She wants to know how these plants 8.1 MODES OF REPRODUCTION reproduce. In Class VI you learnt about different parts of a flowering plant. Try to list the various parts of a plant and write the Asexual reproduction functions of each. Most plants have In asexual reproduction new plants are roots, stems and leaves. These are called obtained without production of seeds. the vegetative parts of a plant. After a certain period of growth, most plants Vegetative propagation bear flowers. You may have seen the It is a type of asexual reproduction in mango trees flowering in spring. It is which new plants are produced from these flowers that give rise to juicy roots, stems, leaves and buds. Since mango fruit we enjoy in summer. We eat reproduction is through the vegetative the fruits and usually discard the seeds. parts of the plant, it is known as Seeds germinate and form new plants. vegetative propagation. So, what is the function of flowers in plants? Flowers perform the function of Activity 8.1 reproduction in plants. Flowers are the Cut a branch of rose or champa with a reproductive parts. node. This piece of branch is termed a There are several ways by which cutting. Bury the cutting in the soil. A plants produce their offspring. These are node is a part of the stem/branch at categorised into two types: (i) asexual, which a leaf arises (Fig. 8.1). Water the and (ii) sexual reproduction. In asexual cutting every day and observe its reproduction plants can give rise to new growth. Observe and record the number plants without seeds, whereas in sexual of days taken for roots to come out and Reprint 2024-25 new leaves to arise. Try the same activity by growing money plant in a jar of water and record your observations. Node Fig. 8.2 Potato plant sprouting from an ‘eye’ Likewise you can also grow ginger (Fig. 8.3) or turmeric. Bud in Bryophyllum (sprout leaf plant) has the axil buds in the margins of leaves (Fig. 8.4). If a leaf of this plant falls on a moist Fig. 8.1 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. 8.2). A bud consists of a short stem around which immature overlapping leaves are present. Vegetative buds can also give rise to new plants. Activity 8.2 Fig. 8.3 Ginger with new plants sprouting from it Take a fresh potato. Observe the scars on it with the help of a magnifying glass. soil, each bud can give rise to a new You may find bud(s) in them. These scars plant. are also called “eyes”. Cut the potato Roots of some plants can also give into small portions, each with an eye rise to new plants. Sweet potato and and bury them in the soil. Water the dahlia are examples. pieces regularly for a few days and Plants such as cacti produce new observe their progress. What do you find? plants when their parts get detached REPRODUCTION IN PLANTS 83 Reprint 2024-25  Activity 8.3 (To be demonstrated by the teacher) Take a piece of yeast cake or yeast powder from a bakery or a chemist shop. New plants Take a pinch of yeast and place it in a Fig. 8.4 Leaf of Bryophyllum with buds in the container with some water. Add a margin spoonful of sugar and shake to dissolve it. Keep it in the warm part of a room. from the main plant body. Each After an hour, put a drop of this liquid detached part can grow into a new on a glass slide and observe under a plant. microscope. What do you observe? You may see the formation of new yeast cells (Fig. 8.5). Boojho wants to know if there is any advantage of Chain of buds Developing bud vegetative propagation. Yeast cell New bud Plants produced by vegetative propagation take less time to grow and bear flowers and fruits earlier than those produced from seeds. The new plants Fig. 8.5 Reproduction in yeast by budding are exact copies of the parent plant, as they are produced from a single parent. The small bulb-like projection Later in this chapter you will learn coming out from the yeast cell is called that plants produced by sexual a bud. The bud gradually grows and reproduction have characters of both the gets detached from the parent cell and parents. Plants produce seeds as a result forms a new yeast cell. The new yeast of sexual reproduction. cell grows, matures and produces more yeast cells. Sometimes, another bud Budding arises from the bud forming a chain of You have already learnt about the tiny buds. If this process continues, a large organisms like yeast can be seen only number of yeast cells are produced in a under a microscope. These grow and short time. multiply every few hours if sufficient nutrients are made available to them. Fragmentation Remember that yeast is a single-celled You might have seen slimy green organism. Let us see how they patches in ponds, or in other stagnant reproduce? water bodies. These are the algae. When 84 SCIENCE Reprint 2024-25 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. 8.6). This process continues and they cover a large area in a short period of time. Sori (Spore forming bodies) Fig. 8.8 Reproduction through spore formation in fern Fig. 8.6 Fragmentation in spirogyra (an alga) air. As they are very light they can cover long distances. Spore formation Spores are asexual reproductive In Chapter 1 you learnt that the fungi bodies. Each spore is covered by a on a bread piece grow from spores which hard protective coat to withstand are present in the air. Repeat Activity unfavourable conditions such as high 1.2. Observe the spores in the cotton- temperature and low humidity. So like mesh on the bread. When spores they can survive for a long time. Under are released they keep floating in the favourable conditions, a spore germinates and develops into a new Sporangium individual. Plants such as moss and Spores ferns (Fig. 8.8) also reproduce by means of spores. Hypha 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. Stamens are the male reproductive part and pistil is the female reproductive part (Fig. 8.9). Fig. 8.7 Reproduction through spore formation in fungus REPRODUCTION IN PLANTS 85 Reprint 2024-25 Activity 8.4 male and female unisexual flowers may be present in the same plant or in Take a mustard/China rose/petunia 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. 8.9 (a)]. stamen and pistil. Anther contains pollen grains which Flowers which contain either only produce male gametes. A pistil consists pistil or only stamens are called of stigma, style and ovary. Ovary unisexual flowers. Flowers which contains one or more ovules. The contain both stamens and pistil are female gamete or the egg is formed in called bisexual flowers. Corn, papaya an ovule [Fig. 8.9 (b)]. In sexual and cucumber produce unisexual reproduction a male and a female flowers, whereas mustard, rose and gamete fuse to form a zygote. petunia have bisexual flowers. Both 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 Stigma light, they can be carried by wind or Stigma Style Pollens Stigma Anther Ovary Ovule (b) Pistil (a) Self-pollination (b) Cross-pollination Fig. 8.9 Reproductive parts Fig. 8.10 Pollination in flower 86 SCIENCE Reprint 2024-25  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 (b) on the stigma of the same flower or another flower of the same plant, it is Fig. 8.12 (a) Section of an apple, (b) Almond called self-pollination. When the pollen of a flower lands on the stigma of a flower gametes (to form a zygote) is called of a different plant of the same kind, it fertilisation (Fig. 8.11). The zygote is called cross-pollination [Fig. 8.10 (a) develops into an embryo. and (b)]. Pollen grain (germinating) 8.3 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 Zygote seeds develop from the ovules. The seed formation contains an embryo enclosed in a protective seed coat. Some fruits are fleshy and juicy such as mango and orange. Some fruits are hard like almonds and walnuts Ovum [Fig. 8.12 (a) and (b)]. (a) 8.4 SEED DISPERSAL (b) Fig. 8.11 Fertilisation (Zygote formation) In nature same kind of plants grow at different places. This happens because Fertilisation 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 or a field or a park, you may have found process of fusion of male and female seeds or fruits sticking to your clothes. REPRODUCTION IN PLANTS 87 Reprint 2024-25 Did you try to observe how these seeds seeds of grasses or hairy seeds of aak were clinging to your clothes? (Madar) and hairy fruit of sunflower What do you think will happen if all [Fig. 8.14 (a), (b)], get blown off with the seeds of a plant were to fall at the same wind to far away places. Some seeds are place and grow there? There would be dispersed by water. These fruits or seeds severe competition for sunlight, water, usually develop floating ability in the minerals and space. As a result the seeds form of spongy or fibrous outer coat as would not grow into healthy plants. in coconut. Some seeds are dispersed by Plants benefit by seed dispersal. It animals, especially spiny seeds with prevents competition between the plant hooks which get attached to the bodies and its own seedlings for sunlight, water of animals and are carried to distant and minerals. It also enables the plants places. Examples are Xanthium to invade new habitats for wider (Fig. 8.15) 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 drumstick This happens in the case of castor and and maple [Fig. 8.13 (a) and (b)], light balsam. Seed Wing (a) (b) (a) (b) Fig. 8.13 Seeds of (a) drumstick and Fig. 8.14 (a) The hairy fruit of sunflower and (b) maple (b) hairy seed of madar (aak) Fig. 8.15 Xanthium 88 SCIENCE Reprint 2024-25  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. REPRODUCTION IN PLANTS 89 Reprint 2024-25  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 90 SCIENCE Reprint 2024-25  (c) Mature ovary forms the (i) seed (ii) stamen (iii) pistil (iv) fruit (d) A spore producing organism is (i) rose (ii) bread mould (iii) potato (iv) ginger (e) Bryophyllum can reproduce by its (i) stem (ii) leaves (iii) roots (iv) flower 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. 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”. REPRODUCTION IN PLANTS 91 Reprint 2024-25