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The two modes of Reproduction ASEXUAL REPRODUCTION AND SEXUAL REPRODUCTION • In asexual reproduction, a new individual develops or grows from a single parent. • There is no fusion of cells from two different parents. SEXUAL REPRODUCTION • In sexual reproduction, new individuals are formed by the fusion of a male reproductive cell (male gamete) and a female reproductive cell (female gamete). • This fusion is known as fertilization. • How about asexual reproduction? • Since there is only one parent, the new individual would be identical in characteristics to the one parent which produced it. • Can you think of advantages of sexual reproduction and advantages of asexual reproduction? Asexual Reproduction Adult parent Detached portion of Parent Sexual Reproduction Adult parent Male gamete Adult parent Female gamete fertilization New Adult zygote New Adult Reproductive vs Vegetative Structures • Plant parts : roots, stem, leaves, flowers and fruits. • Reproductive Structures : – flowers and fruits • Vegetative Structures: – roots, stem and leaves • Some plants can reproduce both ways – reproductively as well as vegetatively. Vegetative Reproduction • Two types : Natural Vegetative Propagation and Artificial Vegetative Propagation • Natural Vegetative Propagation: – They are also flowering plants – But they can reproduce through underground storage organs e.g. rhizomes, bulbs, corms, tubers, roots – Or shoots e.g. runners, offsets, suckers • Essentially, same principle : – These organs have a store of food. Shoots grow from these organs bearing leaves and flowers. In the process, food is withdrawn from the underground storage organ which shrivels. As the leaves manufacture food, food is transported to the buds which gradually swell to become new underground stems. Natural Vegetative Reproduction • Rhizomes (e.g. canna, lallang, ginger) – Stem that grows horizontally above or below surface of soil Natural Vegetative Reproduction • Rhizomes (e.g. canna, lallang, ginger) Natural Vegetative Reproduction • Corms (e.g. water chestnut, cocoyam,) – Thick, short underground stem swollen with food reserves. – Protected by dry scale leaves – New corms grow on top of old corms Natural Vegetative Reproduction Natural Vegetative Reproduction • Bulbs (e.g. onion) – Flattened, disc-like stem with closely set nodes bearing fleshy scale leaves surrounded by some dry scale leaves. – Buds are in the axils of the fleshy scale leaves. Natural Vegetative Reproduction • Tubers (e.g. potato) – Swollen underground stem bearing a number of scale leaves. Natural Vegetative Reproduction • Tubers (e.g. potato) Natural Vegetative Reproduction • Runners (e.g. strawberry plant) Natural Vegetative Reproduction • Runners (e.g. strawberry plant) Natural Vegetative Reproduction • Offsets (e.g. water hyacinth and water lettuce) – Like runners but shorter and thicker Natural Vegetative Reproduction • Suckers (e.g. pineapple, banana, chrysanthemum) – A shoot arising either from the underground portion of the stem or from an adventitious bud on the root. Advantages and Disadvantages of Natural Vegetative Propagation • Advantages – No need external agencies e.g. insects, wind etc – Food is usually present in the vegetative structures, a rapid development of buds into daughter plants can take place. – New plants resemble parent plant in every way. – Involves only one parent • Disadvantages – Lack of dispersal mechanism may lead to overcrowding. – New plants are less varied – New plants may be less adaptable to changes in environmental condition.