Asexual Reproduction PDF

#prachisharma Biology Chapter 8 How do organisms reproduce - **Reproduction:** The production of new organisms from pre-existing organisms of the same species is called reproduction. - **Reproduction is essential for the survival of species on earth.** - The reproduction process ensures continuity o...

#prachisharma Biology Chapter 8 How do organisms reproduce - **Reproduction:** The production of new organisms from pre-existing organisms of the same species is called reproduction. - **Reproduction is essential for the survival of species on earth.** - The reproduction process ensures continuity of life on Earth. ## Types of reproduction - **Asexual reproduction:** The production of new organisms from a single parent (without the involvement of sex cells or gametes) is called asexual reproduction. - **Sexual reproduction:** The production of new organisms by two parents by making use of their gametes is called sexual reproduction. ### Distinguish between Asexual and Sexual Reproduction | Asexual | Sexual | |---|---| | The production of new organisms from a single parent without the involvement of sex cells (gametes) | The production of new organisms by two parents by making use of their gametes | ### Asexual reproduction methods - Asexual reproduction occurs in six methods: - Fission (Binary, Multiple) - Budding - Spore formation - Regeneration - Vegetative propagation - Fragmentation **1. Fission** - In this process, a unicellular organism splits (divides) to form two or more new organisms. - Binary fission: Eg. Amoeba - Multiple fission: Eg. Plasmodium (protozoa) **2. Binary Fission** - The parent organism divides to form two organisms. (Eg. Amoeba, Paramecium) - The parent identity is lost. **3. Paramecium** - Paramecium is a unicellular animal having scent thread-like structure called cilia. - A fully grown paramecium divides its body into two parts to form two smaller paramecia, followed by the division of nucleus and cytoplasm. **4. Leishmania** - Leishmania is a unicellular animal (protozoa). - It is a parasite which causes diseases known as Kala-Azar (Black fever). - Kala-Azar is known as Leishmaniasis. **5. Multiple fission** - The parent organism divides into many new organisms at the same time (Eg. Plasmodium). - Sometimes during unfavorable conditions, a cyst or protective wall is found around the cell of a single-celled organism. - Plasmodium- a protozoan microscopic, single-celled animal. **6. Budding** - In budding, a small part of the body of the parent organism grows out as a bud, which then separates and becomes a new organism. - Eg. Hydra, Yeast **7. Spore formation** - Spore formation is an asexual reproductive process. - Spores are microscopic asexual reproductive bodies covered by a protective outer hard covering (cyst). - During favorable conditions, the cyst breaks down, and the spore unit germinates. **8. Spore formation in plants** - The parent plant produces hundreds of microscopic reproductive units called spores. - When the spore is introduced into the air, when these airborne spores land on food (soil), under favorable conditions (like warm weather), they germinate and produce a new plant. **9. Regeneration** - The process of getting back a full organism from its body parts is called regeneration. - Eg. Hydra, Planaria **10. Planaria** - Planaria is a flatworm found in freshwater ponds and slow-moving streams. - It has a great power of regeneration. **11. Regeneration from cut parts** - The regeneration of an organism from its cut body parts occurs by the process of growth and development. This happens because the cells of cut body parts make a bale of cells. - The 6% organism cells in all of the cells move to their proper places within the body, where they have to form various organs and body parts of the organism. - Eg. Bryophyllum - plant like Bryophyllum develops adventitious buds on its leaves. These buds on separation can develop into new plants. **12. Vegetative propagation** - In vegetative propagation, new plants are obtained from parts of old plants like root, stem and leaves without the help of reproductive organs. - Eg. - Green grass grows in the field after rain from the dry stems of the old grass plants. - Buds are present on the stem as well as on the leaves of the Bryophyllum plants which can develop into a new plant. - The leaves of a Bryophyllum plant have special type of buds in their margin (eggs). These buds may get seperated from the leaves, fall to the ground, and then grow to produce new Bryophyllum plants. - Money plant can also grow by vegetative propagation by using a piece of stem. - The root of sweet potato, sesame, and some other plants bear adventitious buds. The buds sprout and form a new plant. ### Artificial propagation of plants - The process of growing many plants from one plant by man-made methods is called the artificial propagation of plants. **1. Cutting** - A small part of a plant which is removed by making a cut with a sharp knife is called cutting. - Cutting may be a piece of stem, root, or even a leaf. - Eg. Rose, Bougainvillea, Chrysanthemum, grapes, sugarcane, banana, and cactus, etc. **2. Layering** - A branch of a plant is pulled towards the ground, and a part of it is covered with moist soil, leaving the tip of a branch exposed above the ground. - After some time, new roots develop from the part of the branch buried in the soil. - The branch is then cut off from the parent plant. - The part of the branch which has developed roots grows to become a new plant. **3. Grafting** - Grafting is a method in which the cut stem of two different plants (one with roots and another without roots) are joined together in such a way that the two stems join and grow as a single plant (A separate stem without root is called scion, and another stem with root is called stock). - The cut stem of scion is placed over the stock. - The surfaces of scion and stock are fitted together and bound tightly with a piece of cloth and covered properly with polythene sheets (to prevent harmful infection by bacteria or fungus, and loss of water and plant sap from the cut and joined ends of stock and scion). - The cambium layer of scion is in contact with the cambium layer of stock. ### Advantages of artificial propagation - The artificial propagation of farm and garden plants has several advantages. - The advantages of artificial propagation of plants are given below: - The new plants produced by artificial vegetative propagation will be exactly like the parent plant. - Any desirable features of the parent plant will be replicated in the new plant. **2. Fruit trees** - Fruit trees grown from seeds may take many years, but the fruit trees grown from cutting or grafting start to bear fruit much earlier. **3. Plants grown by vegetative propagation usually needs less attention in their early years than the plant grown from seeds.** **4. Many plants can been grown from just one parent by artificial propagation.** **5. We can also get seedless plants by artificial propagation**.