Biology Asexual Reproduction - Global Indian International School PDF

Kuala Lumpur, Malaysia SEMESTER I NAME: _______________________ REF: 2024-25/ SCI /STD 10/ HO 07 CLASS: _______________ SUBJECT: Biology DATE: 15/07/2024...

Kuala Lumpur, Malaysia SEMESTER I NAME: _______________________ REF: 2024-25/ SCI /STD 10/ HO 07 CLASS: _______________ SUBJECT: Biology DATE: 15/07/2024 Topic: Asexual Reproduction Reproduction: The production of new organism from the existing organism of the same species is called reproduction. Reproduction is essential for the survival of species on this earth. The process of reproduction ensures continuity of life on earth. Reproduction give rise to more organism with the same basic characteristics as their parents. Role of DNA in reproduction: Deoxyribonucleic acid is a genetic material present in chromosomes. DNA holds the information needed to make proteins and other molecules that make a cell functional. It carries information from parent to offspring. DNA replication /copying is the process of creating similar copies of DNA during reproduction. The copies of DNA made can be similar but not 100% identical as there will be variations each time. Mutation leads to variation in DNA. Variations are useful for the survival of the species as the organisms can adapt to changes in the environmental conditions. As variations accumulate over a period they lead to formation of new species. Types of Reproduction There are two main methods of reproduction in living organisms. 1. asexual reproduction. 2. Sexual reproduction. Asexual Reproduction- The production of new organism from a single parent without the involvement of sex cells (or gametes) is called asexual reproduction. Page 1 of 13 Copyright © Global Indian International School Sexual Reproduction- The process of production of new organism from two parents by making use of sex cells or gametes. Asexual Reproduction Sexual Reproduction Number of One parent needed Two parents must mate organisms involved Cell division Cells divide by Fission, Cells divide by Meiosis budding, or regeneration Evolution There is truly little chance of Sexual reproduction leads to variation with asexual genetic variation in new reproduction. Mutations in DNA generations of offspring. This can still occur but not as often is fundamental to evolution. as in sexual reproduction. Involvement No formation or fusion of Formation and fusion of of sex cells gametes (sex cell) gametes (sex cell) occurs Found in Lower organisms Higher invertebrates and all vertebrates Unit of May be whole parent body or a Gamete reproduction bud or a fragment or a single somatic cell Time taken Asexual reproduction is Sexual reproduction can take completed in a short period of several months to complete. time. Number of Two or more One or more offspring Methods of Asexual Reproduction It takes place by 6 methods. 1) Fission 2) Budding 3) Spore formation 4) Regeneration Page 2 of 13 Copyright © Global Indian International School 5) Fragmentation 6) Vegetative Propagation 1) Fission In fission, a unicellular organism split to form two or more new organisms. It is of two types. Binary fission: In Binary Fission, the parent organism splits to form two new organisms. for example- Amoeba, Paramecium Leishmania, Bacteria reproduce by binary fission. When the amoeba cell has reached its maximum size of growth, first the nucleus of Amoeba lengthens and divide into two parts (karyokinesis) after that cytoplasm of parent amoeba divides(cytokinesis) to form two smaller daughter Amoeba. In Amoeba, fission take place in any plane but in Leihsmania splitting of parent cell during fission takes place in definite way longitudinal with respect to flagellum at its end. In case of bacteria: Bacteria reproduce through a process called binary fission. During binary fission, the genetic material in nucleoid copies itself, forming two genetically identical copies. Then, the cell enlarges and divides into two new daughter cells. The two daughter cells are identical to the parent cell. Multiple Fission In multiple fission the parent organism splits to form many new organisms at same time. Page 3 of 13 Copyright © Global Indian International School For example: Plasmodium. In some organisms during unfavourable conditions a cyst or protective wall is formed around the cell. Inside the cyst the nucleus of cell splits several times to form many daughter nuclei and then cytoplasm collects around each daughter nuclei and thin membrane are formed so that many new daughter cells are formed within a cyst. When favorable conditions return, the cyst breaks open and daughter cells are released each forming a new organism. 2. Budding In budding a small part of a body of parent organism grows out as a bud which then detaches and becomes a new organism. For Example: Hydra, yeast reproduce by budding. In Hydra a small outgrowth (bud) is formed on the sides of its body by the repeated mitotic division of its cell. This bud then grows gradually by developing mouth and tentacles and then the tiny new Hydra detaches itself from parent organism and lives as a separate organism. In some organisms like sponges and corals the bud remain attached to the parent organism permanently. The buds grow and produce their own buds. In this way they form a colony of sponges/corals as they can also reproduce by budding. 3. Spore Formation: In spore formation, the parent plant produces 100’s of microscopic reproductive units called “spores” within the spore case(sporangium). When the spore case bursts, the spores spread into the air. When these air borne spores land on food or soil, under favourable condition they germinate and produce new plants. For example: most of the Page 4 of 13 Copyright © Global Indian International School fungi such as Rhizopus (bread mould), mucor, bacteria, non-flowering plants, ferns and mosses reproduce by spores. The common bread mould plant (Rhizopus) consists of thread like hyphae and a thin stem having knob like sporangium which contains 100’s of spores enclosed in spore- case. When the spore case burst, then the spores spread into air. When these air borne spores land on food or soil, under favourable condition they germinate and produce new plants. Spores are covered by hard protective coat which enables them to survive under unfavourable conditions, like lack of food, lack of water and extreme temperature but when the conditions are favourable the spores can grow to produce new plants and thus, the reproduction by spores helps plants survive adverse conditions. 4. Regeneration: It is a method of Asexual reproduction where an organism will form a complete new individual from its body part. For example, simple animals like Hydra and Planaria show regeneration. Planaria (Flatworm) is found in freshwater ponds. If the body of Planaria somehow gets cut into number of pieces, then each body piece can regenerate into complete Planaria. Page 5 of 13 Copyright © Global Indian International School Certain specialized cells of cut body part divide rapidly to form a mass of cells. The cells present in the mass differentiate to form various organs and body parts of the organism. Q. Why complex multicellular organism cannot show power of regeneration? In complex multicellular organism, specialized cells make up tissue, different tissues make up an organ, different organs carrying out a life process makes up an organ system and finally all the organ systems together make up the entire organism. They have a high degree of organization in their body so they cannot reproduce their whole body through regeneration, but some multicellular organisms can form their body parts back again when they lose it. Eg blood cells regenerate in mammals, tail of a lizard grows back again. 5) Fragmentation: The breaking up of body of simple multicellular organism into two or more fragments on maturing, each of which subsequently grows to form a new complete organism is known as fragmentation. Spirogyra is a green filamentous alga. Spirogyra breaks into two or more fragments on maturing and each fragment then grows into new Spirogyra. Page 6 of 13 Copyright © Global Indian International School 6) Vegetative reproduction (Vegetative propagation): It is a process in which a part of the plant body gets detached and develops into a new independent plant. In lower plants it occurs through binary fission, budding, fragmentation, gemmule formation. etc. In higher plants, any part of the body is capable of vegetative propagation. Many plants produce modified stems, roots, and leaves, especially for natural vegetative propagation. At the same time, man, too has developed various methods of artificial vegetative propagation for many useful plants. The methods of vegetative propagation may be classified into the following two types: (1) Natural vegetative propagation (2) Artificial vegetative propagation 1. Natural Vegetative Reproduction: Different plant parts are variously modified for vegetative propagation. The common structures (vegetative parts) that take part in vegetative propagation are root, stem, leaves and buds. They are called as vegetative propagules. (i) Vegetative Propagation by Roots: The ordinary roots in many plants, such as, Guava, develop adventitious buds which grow to form new plants. Root tubers with adventitious buds occur in sweet potato Tapioca, Yam, Dahlia and Asparagus. Page 7 of 13 Copyright © Global Indian International School When placed in soil, the buds present on the tuberous roots grow into leafy shoots. Leafy shoots develop adventitious roots at their base and they are detached and planted to form new plants. (ii) Vegetative Propagation by Stems: This is one of the most common and prevalent methods of vegetative propagation. Different plant parts, such as bulbs, runners, rhizomes, corms, tubers, offset etc. help the plant to multiply under favourable conditions. (a) Bulb: It is a modified shoot that has a very short stem and apical and axillary buds. Some of these grow to form shoots, e.g. onion, garlic, Tulip (b) Runners: Page 8 of 13 Copyright © Global Indian International School These are creeping stems which produce roots at nodes. Runners break at places and each piece develops into an independent plant, e.g grass, Oxalis etc. (c) Rhizomes: These are underground, horizontally growing stems. They have prominent nodes, internodes and axillary buds. Aerial branches sprout from the axillary buds which get separated from the rhizome and form new plants, e.g. ginger (d) Corm: It is, in fact, a condensed rhizome that grows in vertical direction. The axillary buds, present in the axil of scale leaves, produce daughter corms which later on form new independent plants, e.g. Saffron, Colocasia (e) Tuber: It is a modification of underground stem. The “eyes” or buds present on the tuber form new independent plants. Potato is the most common example. (g) Aerial Shoots: A stem segment of Opuntia and other cacti develops into a new plant after falling on the soil (Fig. 10.13). A similar segment of sugarcane with at least one node is used in agriculture to produce new plant. (iii) Vegetative Propagation by Leaves: Leaves of a number of plants possess adventitious buds for vegetative propagation, e.g., leaf tips of walking fern. In Bryophyllum, the marginal buds sprout while the leaf is attached to the plant. In some other plants, the buds develop only when the leaf is injured or detached and fall on the moist soil, e.g., Begonia. iv) Vegetative Propagation by Bulbils: They are fleshy buds which develop into new plants after falling on the soil, e.g. Agave, Oxalis, Pineapple, Lily. Page 9 of 13 Copyright © Global Indian International School 2. Artificial Methods of Vegetative Propagation: In some plants, where vegetative reproduction by natural means is difficult to occur, special techniques can be used. We know that plant cells are more totipotent than animal cells. So, they can be forced to reproduce vegetatively. 1. Cutting: (a) It is a simple method, in which a suitable part of stem or root (about 20 to 30 cm long) is cut, and it is planted in the soil containing nutrients. This cut part soon develops new roots and develops into a new plant. Stem cuttings are very common in plants like Rose, Croton, Sugarcane, Tapioca, China rose, Bougainvillea, Lemon, Coffee and Grape etc. 2. Layering: (a) It is one of the most common methods of artificial vegetative reproduction in plants. (b) In this method, a twig (branch) of a plant is bent down, below the level of soil. This bent part is called layer. (c) A small incision is made in this layer (bent portion). Now the portion is covered with soil. Moisture is given at regular intervals. (d) Soon this covered portion develops new roots and become separated (or can be cut) from main body, giving rise to new plant. This plant then can be shifted to some new location. (e) Layering is common in plants like-jasmine, Strawberry, Grapevine and Cherry etc. Page 10 of 13 Copyright © Global Indian International School 3. Grafting: (a) It is the technique of joining parts of two different plants to from a composite plant. (b) It can be done efficiently in those plants, which are closely related and have vascular cambium. (c) One plant, which has a strong root system, is selected as stock or stump (basal part). The branch of other plant (which is to be grafted) is selected as scion. Scion is usually selected from plants which have desired or superior characters. (d) The shoot of the stock is cut 20-30 cm above the ground. Leaves and buds are removed from this part. (e) Now, complementary cuts are made in stock and scion, so that scion can be fitted exactly in the grooves of stock. (f) After this fitting, the area is tied tightly with the help of a tough thread and then it is covered with grafting wax, to avoid any infection. (g) Grafting is carried out commonly in plants like Mango, Guava, Apple, Rubber plant, Citrus and Pear etc. Advantages of Grafting: 1. It combines two plants with desirable traits. 2. It is used for breeding fruits and flowers of desired varieties. Ex: Seedless fruits Page 11 of 13 Copyright © Global Indian International School  3. A young scion can be made to produce flowers and fruits quickly by this method. Tissue culture (Micro propagation): The production of new plants from a small piece of plant tissue removed from a growing tip of plant in a suitable growth medium (culture or jelly like synthetic medium) is called tissue culture. Eg: tobacco, orchids, rubber, oil palm, papaya. Procedure: The tissue is placed on a culture medium which contain nutrients and plant hormones, which make the cells in the plant tissue to divide rapidly to form callus. This callus is transfer to another medium containing plant hormone which stimulates the callus to develop roots. Then it is put on another medium containing another plant hormone which stimulates the development of shoot. They are now called plantlets. The plantlets are then transplanted into soil where they can grow to form mature plant. This technique is used to the production of ornamental plants like orchids, carnation etc. Advantages of Tissue Culture: 1. It is a very fast technique. 2. New plant produced by tissue culture are disease free. 3. Very little space is needed. 4. By this method plants can be grown around the year irrespective of weather or seasons. Page 12 of 13 Copyright © Global Indian International School Advantages of Vegetative propagation: 1. The new plant produced by artificial vegetative propagation will be exactly like parent plant. 2. The fruit trees grown from cutting or grafting start to bear fruits much earlier. 3. Many plants can be grown from just one parent plant. 4. We can also get seedless plant by artificial propagation Disadvantages of Vegetative Propagation: 1. Disease contracted by a parent spreads to all the daughter plants. 2. Vegetative organs useful for propagation cannot be preserved for long. 3. Variation is absent. So, plants cannot adapt to changed environment. So plants gradually lose their vigour as there is no genetic variation. 4. There is no mechanism for dispersal. Vegetative multiplication causes overcrowding and hence severe competition which can damage most of the plants. Page 13 of 13 Copyright © Global Indian International School