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Chapter-12 REPRODUCTION IN PLANTS
Introduction: • Reproduction is the process by which organisms produce young ones of their own kind. • All living things are capable of reproducing. • Reproduction is not necessary for the survival of an individual, it is essential for the survival of the kind of organism. • Plants have special organs that help them to reproduce. • The flower is the reproductive part of a plant. • Some flowers become fruits. • Fruits have seeds that help plants reproduce. • Not all plants reproduce through seeds. • Plants that do not have flowers also reproduce using different modes of reproduction.
Introduction: • Reproduction in plants is of two types. • Asexual Reproduction: The mode of reproduction in which new plants are obtained from a single parent is known as Asexual Reproduction. The offspring are exact copies of the parent. • Sexual Reproduction: The mode or reproduction in which new plants are obtained from two parent plants (one, male and one female) is known as Sexual reproduction. • The offspring are not exact copies of parents. • Seeds are formed in sexual Reproduction
Asexual Reproduction in Plants: (a) Spore Formation: • The mode of asexual reproduction in which some non flowering plants reproduce with the help of small, round bodies called spores is known as Spore formation. • Each spore is covered by a hard and thick wall, which protects it from harsh conditions like extreme temperatures and lack of water. • A spore becomes a new plant only when the temperature is correct and water is present. • Spores are produced in structures called Sporangia (singular: Sporangium). • Spore Formation can be seen in Ferns and Mosses.
Asexual Reproduction in Plants: (b) Fragmentation: • The mode of asexual reproduction in which a part of the parent organism breaks away to form a new organism is called Fragmentation. • Fragmentation kind of reproduction occurs in a freshwater alga called the Spirogyra. • Each fragment behaves as an individual organism. • Fragmentation helps an organism to multiply very fast.
Asexual Reproduction in Plants: (c) Budding: • The mode of asexual reproduction in which a small bud forms on the surface of the parent organism in order to give rise to a new organism is called Budding. • Budding kind of reproduction occurs in microorganisms such as Bacteria and Yeast. • The bud developed in budding is different from the flower bud. • The bud becomes larger and breaks off from the parent to form a new plant.
Self Assessment-1 1. What is Reproduction? 2. What is the importance of Reproduction? 3. What is Sexual Reproduction? 4. What is Asexual Reproduction? 5. Name the special organ that the plants use for Sexual Reproduction. 6. Name the type of reproduction in which seeds are formed. 7. Name the type of reproduction in which the offspring are the exact copies of their parents. 8. What is Spore Formation? 9. What is Fragmentation? 10. What is Budding? 11. Name two microorganisms which reproduce with the help of Budding. 12. Name two non flowering plants that reproduce by Spore Formation. 13. Name an organism that reproduce by Fragmentation.
Vegetative Propagation: • Vegetative Parts: The parts of the plant that help it to live and grow are called the vegetative parts of the plant. e.g. Roots, Leaves and Stem. • Vegetative Reproduction or Vegetative Propagation: The mode of asexual reproduction in which new plants are obtained from the vegetative parts of the parent plant is known as Vegetative Reproduction or Vegetative Propagation. Vegetative Propagation naturally occurs in some plants. Vegetative Propagation is also carried out artificially by humans in some cases.
Vegetative Propagation: • (a)Propagation through Roots: Some plants store food in the roots. When these roots are planted, new plants grow from them. e.g. Sweet Potato, Radish, Turnip, Carrot and Beetroot. • (b)Propagation through Stem: • (i) Stem Tubers: Stem-tubers are swollen parts of the stem that store food underground. Stem tubers has small buds on its surface called eyes. Shoots grow from these eyes. e.g Potato.
Vegetative Propagation: • (b)Propagation through Stem: • (ii) Rhizomes: Rhizomes are modified underground stems that give rise to roots. e.g. Stems Ginger, Turmeric and Water Lily spread by producing rhizomes. • (iii) Bulbs: Bulbs are modified stems surrounded by fleshy leaves that store food. When a bulb is planted, a new plant grows from it. e.g. Onion, Garlic and Lily plants reproduce through bulbs.
Vegetative Propagation: • (b)Propagation through Stem: • (iv) Corms: Corms are vertical, fleshy, underground stem that acts as a food-storage structure. Corms bear membranous or scaly leaves and buds. e.g. Plants like the Taro (Colocasia), Gladiolus and Crocus produce corms. (v) Runners: Runner is a slender stem that comes out from the parent plant. Runners grow horizontally along the ground and give rise to roots and vertical shoots at specific points on the stem called nodes, e.g. Mint, Strawberry and some grasses reproduce through runners.
Vegetative Propagation: • (c)Propagation through Leaves: In some plants, small plantlets grow along the edges of the leaves. These plantlets fall to the ground and give rise to new plants. e.g. Bryophyllum
Self Assessment-2 1. What are Vegetative parts? 2. What is Vegetative Reproduction or Vegetative Propagation? 3. Write a note on Vegetative Propagation by Roots. 4. What are Stem Tubers? 5. Name the plant that reproduces through Stem Tubers. 6. What are Rhizomes? 7. Name the plants that reproduce through Rhizomes. 8. What are Bulbs? 9. Name the plants that reproduce though Bulbs. 10. What are Corms? 11. Name the plants that reproduce through Corms. 12. How does Bryophyllum reproduce. 13. Write a note on Vegetative propagation by Leaves.
Artificial Methods of Vegetative Propagation: Plants can also be grown by artificial methods. • Layering: In Layering, a stem or a branch is bent to the ground. A small part of the stem is buried in soil so that roots develop there. Layering occurs naturally also. e.g. Grapes, Climbing Roses, Jasmine etc. • Cutting: In cutting, a small part of a stem, leaf or root is cut and planted in soil. The part of the plant which is planted is called cutting. The cutting develops roots and forms a new plant. e.g. Rose, Hibiscus, Bougainvillea etc.
Artificial Methods of Vegetative Propagation: • Grafting: Grafting is commonly used to combine the desirable characteristics to two varieties of a plant. The stem part is cut off such that its roots are still in the soil. This plant is called the Stock. The stock is chosen for its hardy roots. A stem cutting form another healthy plant named Scion is placed over the stock. The scion is usually chosen for its flowers, fruits etc. The Stock and the Scion are tied together in such a way that tissues of both the parts unite. • The Stock provides the Scion with water and minerals that it absorbs from the soil. • The resulting plant has the hardness of the Stock but the desirable fruits or flowers of the scion.
Advantages and Disadvantages of Vegetative Propagation: Advantages of Vegetative Propagation: Vegetative Propagation have many advantages. • Plants that do not produce seeds can reproduce using Vegetative Propagation. • Since only one plant is required for vegetative propagation, Pollination is not needed. • Vegetative Propagation is a fast method of reproduction. • Plants with desirable characteristics can be propagated easily because the offspring are exact copies of their parents. Disadvantages of vegetative Propagation: Vegetative Propagation have many disadvantages too. • Since the offspring are the exact copies of the parent plant, they may also carry the undesirable characteristics from the parent plant. • There is no variation between the plants produced with the help of Vegetative Propagation. • Germs may also be transmitted from the parent to the offspring in Vegetative Propagation.
Self Assessment-3 1. Name the different Artificial Methods of Vegetative Propagation. 2. Write a note on Cutting 3. Write a note on Layering. 4. Write a note of Grafting. 5. With what aim do we go for grafting? 6. What is a Scion? 7. What is a Stock? 8. Mention three advantages of Vegetative Propagation. 9. Mention three disadvantages of vegetative propagation. 10. Why is Vegetative Propagation considered as a faster method of reproduction? Comment.
Sexual Reproduction in Plants: • In most flowering plants, flowers are the main organs of reproduction. Structure of a Flower: • The colourful parts of the flower are called Petals. It is the colour of the Petals that attract insects towards the flower. • The green leafy outer covering of the flower are known as Sepals. Sepals protect the inner parts of the flower when it is in Bud stage. • The Stamen is the male part of the flower. The stamen is made up of an anther and a supporting filament. The anther contains pollen sacs that contain a fine, powdery substance called pollen. These pollen grains produce the male gametes or male sex cells • The Pistil is the female part of the flower. The Pistil consists of an Ovary, a sticky Stigma and a tube-like Style. The Ovary contains one or more Ovules. The Ovule contains the Egg Cell or the Female Gamete.
Sexual Reproduction in Plants: Types of Flowers: • Complete or Bisexual Flowers: The flowers that contain both Stamens and Pistil are known as Complete or Bisexual Flowers. e.g.: Rose, Mango, Hibiscus etc • Incomplete or Unisexual Flowers: The flowers that contain either only Stamens or only Pistils are called Incomplete or Unisexual Flowers. e.g.: Papaya, Watermelon, Maize etc. • Both Bisexual and Unisexual flowers may be found either on the same plant or on different plants.
Pollination: • When the anther matures, pollen grains are released. They are then transferred from the anther to the stigma. Pollination: The transfer of pollen from the anther to the stigma of a flower is called pollination . • Pollination is an essential step, needed for the male and female gametes to come together. • There are two kinds of pollination: (a)Self-Pollination (b)Cross-Pollination . • Self-Pollination: The pollination in which the transfer of pollen takes place from the anther of a flower to the stigma of the same flower or another flower on the same plant is known as Self-Pollination. • Cross-Pollination: The pollination in which the transfer of pollen takes place from the anther of a flower to the stigma of a flower on another plant of same type is known as Cross-Pollination.
Self Assessment-4 1. Name the reproductive organ of a flowering plant. 2. What are Sepals? What is the function of Sepals? 3. What are Petals? What is the function of Petals? 4. Name the Male Reproductive part of a flower. 5. Name the Female Reproductive part of a flower. 6. Name the parts of Stamen. 7. Name the parts of Pistil. 8. What are Pollen Grains? 9. What are Ovules? 10. Draw a neat labeled diagram of parts of a flower. 11. What are Bisexual Flowers? 12. What are Unisexual Flowers? 13. What is Pollination? 14. What is Self-Pollination? 15. What is Cross-Pollination?
Agents of Pollination: • Pollen grains are light and are carried by insects, wind or water. (a)Insect Pollination: • Insects such as bees, wasps and butterflies fly from flower to flower to drink nectar. When an insect visits a flower to drink its nectar, some pollen grains stick to its body. • When the same insect visits another flower, the pollen is transferred to the stigma of that flower. • Insect-pollinated flowers usually have colourful petals and a strong scent to attract insects.
Agents of Pollination: (b)Wind Pollination: • Plants that are pollinated by the wind produce large amounts of pollen grains. • Pollen is light and can easily be carried by the wind. • Flowers that are pollinated by the wind are usually small, not colourful and do not have a strong scent. Their petals are small so that they do not obstruct the wind. e.g. Maple, Oak and Pine trees and grasses are wind pollinated .
Agents of Pollination: (c)Water Pollination: • Plants that are pollinated by the water also produce large amounts of pollen grains. • The pollen is released into water and is carried to other flowers by water. • Water pollination is very rare as most aquatic plants are pollinated by insects. e.g. Pond Weed and Sea Grasses are water pollinated .
Self Assessment- 5 1. Name the agents of pollination. 2. Why do insects fly from flower to flower? 3. How do insects help in pollination? 4. Who attracts insects towards flowers? 5. What type of flowers are generally pollinated by wind? 6. Name three flowers that are insect pollinated. 7. Name three flowers that are wind pollinated. 8. Name two flowers that are water pollinated. 9. Write a note on Insect pollination. 10. Write a note on Water pollination. 11. Write a note on Wind pollination.
Fertilisation: • When a pollen grain reaches the stigma, a small tube grows out of it. • This tube, called the pollen tube, carries two male gametes and enters the ovule. • one of the male gametes and the female gamete (the egg cell) join to form a single cell called a zygote. • The process in which one male gamate that lands on the stigma combines with a female gamate present in the ovule to form a single cell (known as zygote) is called fertilisation.
Formation of Fruit and Seed: • In many flowers, the ovary swells after fertilisation to become the fruit. • In some plants like peas, the ovary hardens to form the pod. • The walls of the ovules become hard and the ovules become seeds. • The zygote divides repeatedly and forms the embryo inside the seed. • The petals, sepals and other parts of the flower usually dry up and fall off.
Germination: • A seed germinates into a seedling in the presence of water, air, sunlight and nutrients. • When a seed germinates, a structure called the radicle develops first. • It grows into the ground and becomes the root. • The plumule develops next. • It grows away from the ground and forms the shoot. • Once the leaves appear, they start to make food.
Self Assessment- 6 1. What is a Zygote? 2. What is Fertilisation? 3. Write a note on Fertilisation. 4. How do Fruit and Seed form? 5. What is Radicle? 6. What is Plumule? 7. When does a seed Germinate? 8. Write a note on Germination. 9. With the help of a neat labeled diagram show the different stages of Seed Germination. 10. Name the part of the flower that becomes seed. 11. Name the part of the flower that becomes fruit.
Seed Dispersal: • What will happen if all the seeds of a plant fall in the same place? • If all the seeds of a plant fall in the same place then the • Saplings will be over crowded • Saplings will get lesser nutrients • Saplings will get lesser sunlight • The action or process of distribution or spreading of seeds over a wide area by different agents is known as Seed Dispersal. • Proper dispersal of seeds prevents overcrowding and ensures that the seeds get enough nutrients and sunlight to grow into healthy plants. Seeds are dispersed in many ways. (a) Wind Dispersal: • Seeds that are dispersed by the wind are small and light. • Some seeds also have wing-like structures that help the wind to carry them to faraway places. • Some other seeds have fine hair. • The seeds of the dandelion, drumstick and maple are dispersed by wind.
Seed Dispersal: (b) Water Dispersal: • The seeds of some aquatic plants and some terrestrial plants that grow near water have waterproof outer covering or special features that help them to float on the surface of water • The coconut husk is light and helps the coconut to float. • The seeds of the lotus are carried in a seed pod that has trapped air. (c) Explosive Dispersal: • Some plants have pods that break open with force when they mature. This throws the seeds some distance away from the parent plant. • Seeds of the balsam and pea are dispersed this way.
Seed Dispersal: (d) Animal Dispersal: Animals can disperse seeds in a variety of ways. • Animals eat fleshy fruits such as mangoes and throw away the seeds, which later germinate . • Animals sometimes swallow the seeds of the fruits they eat. These seeds have hard covering and cannot be digested. They come out of the animal along with the faeces and can germinate into plants. • Ants and rodents hoard seeds in hiding places. Such seeds can later germinate into new plants. • Some seeds have hooks or spines on their surfaces. These seeds stick to the fur of animals and can be carried away from the parent plant.
Self Assessment- 7 1. What is seed Dispersal? 2. What will happen if all the seeds of a plant fall in the same place? 3. What are the advantages of proper dispersal of seeds? 4. List the features of seeds dispersed by wind. 5. Name two seeds that are dispersed by wind. 6. List the features of seeds dispersed by water. 7. Name two seeds that are dispersed by water. 8. What is explosive dispersal? 9. What is the advantage of explosive dispersal? 10. Mention three ways by which animals can disperse seeds. 11. Name three agents contributing towards seed dispersal.
