Tiêu đề Chapter - 3 How_Do_Organisms_Reproduce.pdf ✅

ChemContent How Do Organisms Reproduce? Reproduction Reproduction is the ability of living organisms to produce living beings similar to themselves. The two modes of reproduction, i.e. asexual reproduction and sexual reproduction can be seen in animals. Importance of Variation • Sexual reproduction provides great scope for variation. • Variation is important for the survival of a species. • Variation helps a species to adapt to different environmental changes. Reproduction and its Kinds Sexual Reproduction Asexual Reproduction • It involves the formation ofspecial reproductive cells called gametes. • It does not involve the formation of gametes. • Male and female gametes fuse to form the zygote which develops into a new individual. • New organisms are formed either by the division of the parent body or by the differentiation of the parent body. Modes of Asexual Reproduction Plants and animals from lower classes reproduce by asexual methods. Method Description Example Binary Fission • Most common method in unicellular organisms. • It is division of the parent cell into two identical daughter organisms. Amoeba, Paramecium, bacterium Multiple Fission • Parent cell divides to produce many identical new individuals. Plasmodium vivax, Leishmania
ChemContent Fragmentation • Adult organisms, on maturation, break up into smaller fragments. Each fragment develops into a new individual. Spirogyra Budding • A small outgrowth called a bud arises on the parent body. • The bud grows by repeated cell divisions. • It then breaks off from the parent body and develops into a new individual. Hydra, sponges, corals, yeast Regeneration • Regeneration is the ability of organisms to generate lost or damaged body parts. • Regeneration is carried out by specialised cells. • These form a mass of cells which undergo changes to form cells specialised in different functions. • If planaria is cut into small pieces,then each piece develops into a new planaria. Lizard, starfish, planaria, hydra Spore Formation • Spores are special structures produced in sacs called sporangia. • When spores mature, sporangia burst and spores are carried by air or water to different places. • When spores fall on a suitable ground, they germinate and give rise to new plants. Moss, Fern, Fungi Vegetative Propagation Vegetative propagation in Bryophyllum • Several plants are capable of producing naturally through their roots, stems and leaves. Such type of reproduction is called vegetative propagation. Sweet potato (by roots) Bryophyllum (by leaves) Ginger (by stem)