chp 1 reproducion in organisms n.
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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 –

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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
Asexual reproduction
  • Budding in Yeast
sexual reproduction
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
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.(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
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.