Welcome dear students! Today we are going to learn about Reproduction_in_Plants from Class 7 Science. To produce its kind is a characteristic of all living organisms. You have already learnt this in Class Six. The production of new individuals from their parents is known as reproduction. But, how do plants reproduce? There are different modes of reproduction in plants which we shall learn in this chapter. In Class Six you learnt about different parts of a flowering plant. Try to list the 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 certain period of growth, most plants bear flowers. You may have seen the mango trees flowering in spring. It is these flowers that give rise to juicy mango fruit we enjoy in summer. We eat the fruits and usually discard the seeds. Seeds germinate and form new plants. So, what is the function of flowers in plants? Flowers perform the function of reproduction in plants. Flowers are the reproductive parts. There are several ways by which plants produce their offspring. These are categorised into two types: asexual, and sexual reproduction. In asexual reproduction plants can give rise to new plants without seeds, whereas in sexual reproduction, new plants are obtained from seeds. Paheli thought that new plants always grow from seeds. But, she has never seen the seeds of sugarcane, potato and rose. She wants to know how these plants reproduce.
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Asexual reproduction is when new plants are obtained without production of seeds. Vegetative propagation is a type of asexual reproduction in which new plants are produced from roots, stems, leaves and buds. Since reproduction is through the vegetative parts of the plant, it is known as vegetative propagation. Let us do Activity Eight point One. Cut a branch of rose or champa with a node. Bury the cutting in the soil. A node is a part of the stem or branch at which a leaf arises. Water the 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. In this setup, you will see a stem cutting of rose. The diagram shows a node and a bud in the axil. The axil is the point of attachment of the leaf at the node. You must have seen flower buds developing into flowers. Apart from flower buds, there are buds in the axil of leaves which develop into shoots. These buds are called vegetative buds. A bud consists of a short stem around which immature overlapping leaves are present. Vegetative buds can also give rise to new plants.
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Now let us try Activity Eight point Two. Take a fresh potato. Observe the scars on it with the help of a magnifying glass. You may find buds in them. These scars are also called eyes. Cut the potato into small portions, each with an eye and bury them in the soil. Water the pieces regularly for a few days and observe their progress. What do you find? You will see a potato plant sprouting from an eye. Likewise you can also grow ginger or turmeric. Bryophyllum, also known as sprout leaf plant, has buds in the margins of leaves. If a leaf of this plant falls on a moist soil, each bud can give rise to a new plant. Roots of some plants can also give rise to new plants. Sweet potato and dahlia are examples. Plants such as cacti produce new plants when their parts get detached from the main plant body. Each detached part can grow into a new plant. Boojho wants to know if there is any advantage of vegetative propagation. 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 they are produced from a single parent. Later in this chapter you will learn that plants produced by sexual reproduction have characters of both the parents. Plants produce seeds as a result of sexual reproduction.
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You have already learnt about the tiny organisms like yeast can be seen only under a microscope. These grow and 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? Activity Eight point Three is to be demonstrated by the teacher. Take a piece of yeast cake or yeast powder from a bakery or a chemist shop. Take a pinch of yeast and place it in a container with some water. Add a spoonful of sugar and shake to dissolve it. Keep it in the warm part of a room. After an hour, put a drop of this liquid on a glass slide and observe under a microscope. What do you observe? You may see the formation of new yeast cells. In the diagram showing reproduction in yeast by budding, you can see small bulb-like projections. The small bulb-like projection coming out from the yeast cell is called a bud. The bud gradually grows and gets detached from the parent cell and forms a new yeast cell. The new yeast cell grows, matures and produces more yeast cells. Sometimes, another bud arises from the bud forming a chain of buds. If this process continues, a large number of yeast cells are produced in a short time.
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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. This process continues and they cover a large area in a short period of time. The diagram shows fragmentation in spirogyra, which is an alga. Next is spore formation. In Chapter One you learnt that the fungi on a bread piece grow from spores which are present in the air. Repeat Activity One point Two. Observe the spores in the cotton-like mesh on the bread. When spores are released they keep floating in the air. As they are very light they can cover long distances. Spores are asexual reproductive bodies. Each spore is covered by a hard protective coat to withstand unfavourable conditions such as high temperature and low humidity. So they can survive for a long time. Under favourable conditions, a spore germinates and develops into a new individual. Plants such as moss and ferns also reproduce by means of spores. The diagram shows reproduction through spore formation in a fern, highlighting the sori, which are spore forming bodies. Another diagram shows reproduction through spore formation in fungus, indicating the sporangium, spores, and hypha.
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Now we move to 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. Let us do Activity Eight point Four. Take a mustard, China rose, or petunia flower and separate its reproductive parts. Study the various parts of a stamen and pistil. Flowers which contain either only pistil or only stamens are called unisexual flowers. Flowers which contain both stamens and pistil are called bisexual flowers. Corn, papaya and cucumber produce unisexual flowers, whereas mustard, rose and petunia have bisexual flowers. Both male and female unisexual flowers may be present in the same plant or in different plants. Could you identify the anther and the filament of a stamen? The anther contains pollen grains which produce male gametes. A pistil consists of stigma, style and ovary. Ovary contains one or more ovules. The female gamete or the egg is formed in an ovule. In sexual reproduction a male and a female gamete fuse to form a zygote. Boojho wants to know how the male gamete in the pollen grain reaches the female gamete present in the ovule.
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Generally, pollen grains have a tough protective coat which prevents them from drying up. Since pollen grains are light, they can be carried by wind or 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 is called pollination. If the pollen lands on the stigma of the same flower or another flower of the same plant, it is called self-pollination. When the pollen of a flower lands on the stigma of a flower of a different plant of the same kind, it is called cross-pollination. The diagrams illustrate self-pollination and cross-pollination in a flower. Boojho wants to know why flowers are generally so colourful and fragrant. Is it to attract insects? Yes, exactly. The cell which results after fusion of the gametes is called a zygote. The process of fusion of male and female gametes to form a zygote is called fertilisation. The diagram shows fertilisation and zygote formation, where a pollen grain germinates, forms a pollen tube, reaches the ovum, and leads to zygote formation. The zygote develops into an embryo.
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After fertilisation, the ovary grows into a fruit and other parts of the flower fall off. The fruit is the ripened ovary. The seeds develop from the ovules. The seed 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. The diagrams show a section of an apple and an almond. In nature same kind of plants grow at different places. This happens because seeds are dispersed to different places. Sometimes after a walk through a forest or a field or a park, you may have found seeds or fruits sticking to your clothes. Did you try to observe how these seeds were clinging to your clothes? What do you think will happen if all seeds of a plant were to fall at the same place and grow there? There would be severe competition for sunlight, water, minerals and space. As a result the seeds would not grow into healthy plants. Plants benefit by seed dispersal. It prevents competition between the plant and its own seedlings for sunlight, water and minerals. It also enables the plants to invade new habitats for wider distribution. Seeds and fruits of plants are carried away by wind, water and animals. Winged seeds such as those of drumstick and maple, light seeds of grasses or hairy seeds of aak, also known as Madar, and hairy fruit of sunflower, get blown off with the wind to far away places. Some seeds are dispersed by water. These fruits or seeds usually develop floating ability in the form of spongy or fibrous outer coat as in coconut. Some seeds are dispersed by animals, especially spiny seeds with hooks which get attached to the bodies of animals and are carried to distant places. Examples are Xanthium and Urena. Some seeds are dispersed when the fruits burst with sudden jerks. The seeds are scattered far from the parent plant. This happens in the case of castor and balsam.
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Let us quickly review the keywords. Asexual reproduction, sexual reproduction, budding, spore, embryo, pollen grain, sporangium, fertilisation, pollen tube, vegetative propagation, fragmentation, pollination, zygote, gametes, seed dispersal, ovule, hypha. 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 prevent overcrowding, avoid competition for sunlight, water and minerals and invade new habitats.
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Now let us solve the exercises together. Question one, fill in the blanks. Part a: Production of new individuals from the vegetative part of parent is called vegetative propagation. Part b: A flower may have either male or female reproductive parts. Such a flower is called unisexual flower. Part 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 pollination. Part d: The fusion of male and female gametes is termed as fertilisation. Part e: Seed dispersal takes place by means of wind, water and animals. Question two: Describe the different methods of asexual reproduction. Give examples. Answer: The different methods of asexual reproduction are vegetative propagation, budding, fragmentation, and spore formation. In vegetative propagation, new plants are produced from roots, stems, leaves, and buds, like rose, potato, ginger, and bryophyllum. In budding, a small bulb-like projection called a bud grows out from a single-celled organism like yeast, detaches, and forms a new cell. In fragmentation, an organism like algae breaks into fragments, and each fragment grows into a new individual. In spore formation, plants like fungi, moss, and ferns produce spores covered by a hard coat that survive unfavorable conditions and germinate into new individuals under favorable conditions.
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Question three: Explain what you understand by sexual reproduction. Answer: Sexual reproduction is the mode of reproduction in which new plants are obtained from seeds. It involves the fusion of male and female gametes to form a zygote, which develops into an embryo and eventually a new plant. Flowers are the reproductive parts where this occurs. Question four: State the main difference between asexual and sexual reproduction. Answer: In asexual reproduction, new plants are obtained without the production of seeds and involve only one parent, resulting in exact copies of the parent. In sexual reproduction, new plants are obtained from seeds, involve two parents, and the offspring have characters from both parents. Question five: Sketch the reproductive parts of a flower. Answer: Since we are listening, I will describe the sketch. You should draw a flower showing the stamen and the pistil. The stamen consists of a filament and an anther at the top. The pistil consists of the stigma at the top, a long style in the middle, and a swollen ovary at the base containing ovules. Question six: Explain the difference between self-pollination and cross-pollination. Answer: Self-pollination occurs when pollen grains are transferred from the anther to the stigma of the same flower or another flower of the same plant. Cross-pollination occurs when pollen grains from one flower land on the stigma of a flower of a different plant of the same kind.
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Question seven: How does the process of fertilisation take place in flowers? Answer: Pollen grains land on the stigma and germinate to form a pollen tube. The pollen tube grows down through the style and reaches the ovary. The male gametes travel through the pollen tube into the ovule. Inside the ovule, the male gamete fuses with the female gamete or egg. This fusion is called fertilisation, and it results in the formation of a zygote. Question eight: Describe the various ways by which seeds are dispersed. Answer: Seeds are dispersed by wind, water, and animals. Wind disperses winged seeds like drumstick and maple, and light or hairy seeds like grasses, aak, and sunflower. Water disperses seeds with spongy or fibrous coats that float, like coconut. Animals disperse spiny seeds with hooks like Xanthium and Urena that attach to their fur. Some seeds are dispersed by bursting fruits with sudden jerks, like castor and balsam. Question nine: Match items in Column I with those in Column II. Column I has Bud, Eyes, Fragmentation, Wings, Spores. Column II has Maple, Spirogyra, Yeast, Bread mould, Potato, Rose. The correct matches are: Bud matches with Yeast. Eyes matches with Potato. Fragmentation matches with Spirogyra. Wings matches with Maple. Spores matches with Bread mould.
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Question ten: Tick the correct answer. Part a: The reproductive part of a plant is the flower. Option four. Part b: The process of fusion of the male and the female gametes is called fertilisation. Option one. Part c: Mature ovary forms the fruit. Option four. Part d: A spore producing organism is bread mould. Option two. Part e: Bryophyllum can reproduce by its leaves. Option two. Extended Learning Activities and Projects: You are encouraged to make your own cactus garden by collecting pieces cut from different kinds of cacti and growing them in a flat container or separate pots. Visit a fruit market, collect local fruits, draw them, split them, examine seeds, and look for special characteristics. Think of ten different fruit-bearing plants, discuss their dispersal methods with teachers or farmers, and present data in a table with columns for name of plant, dispersal agent, and part helping dispersal. Finally, suppose there is one member of a particular kind of organism in a culture dish, which doubles itself in one hour through asexual reproduction. After ten hours, the number of members will be two to the power of ten, which is one thousand twenty four. Such a colony arising from one parent is called a clone. Thank you for listening! Keep revising and practicing. Goodbye! [CHAPTER_COMPLETE]