CHP.-1.REPRODUCION IN ORGANISMS CLASS- XII

Life span – The period from birth to natural death of an organism. Reproduction – a biological process in which an organism gives rise to young ones similar to itself. Types of reproduction – Asexual reproduction – offspring is produced by a single parent with or without formation of gametes. Sexual reproduction – When two parents participate in reproductive process & also involve fusion of male & female gametes.

Asexual reproduction Budding in Yeast

Binary fission - Amoeba

Zoospores of Chlamydomonas

Conidia of Penicillium

Buds in Hydra

Gemmules in sponge

Vegetative propagation in plants (Eyes of potato)

Rhizome of ginger

Bulbil of Agave

Leaf buds of Bryophyllum

Offset of Water hyacinth

Sexual reproduction Events in sexual reproduction – 1.Pre-fertilisation events – (i) Gametogenesis (ii) Gamete transfer 2. Fertilisation 3.Post-fertilisation events – (i) Zygote (ii) Embryogenesis

Pre-fertilisation events 1.Gametogenesis It is the process of formation of male & female gametes. Homogametes – morphologically similar. Heterogametes – morphologically different.

Bisexual – male & female reproductive structures in the same plant Bisexual – male & female reproductive structures in the same plant.(Homothallic & Monoecious ). Unisexual – male & female reproductive structures on different plants. (Heterothllic & Dioecious). Gametes are haploid. In diploid organisms specialised cells called meiocytes ( gamete mother cell ) undergo meiosis.

2.Gamete transfer – In most of the organisms male gamete is motile & the female gamete is stationary. In aquatic plants gamete transfer takes place through Water. Male gametes are produced in very large number because a large number of male gametes are lost during transport.

3. Fertilisation – Fusion of gametes is known as syngamy which results in the formation of Zygote. External fertilisation – syngamy occurs outside the body of the organism. Eg. Algae, Fishes, Amphibians. Internal fertilisation – syngamy occurs inside the body of organism. Eg. Reptiles, Birds, Mammals, most of the plants.

Post-fertilisation events 1. The Zygote 2. Embryogenesis It is the process of development of embryo from the Zygote. Zygote undergo cell division (Mitosis) & cell differentiation. Oviparous animals –lay eggs Eg. Reptiles, birds. Viviparous animals- zygote develop into a young one inside the body of female organism.