Oviparous and Viviparous Animals: Science Cbse / Ncert Revision Notes

Based on the production of young ones, animals can be oviparous or viviparous animals.
  • Oviparous animals are the animals which lay eggs.
  • Viviparous animals are the animals which give birth to the young ones.
Most of the oviparous animals undergo external fertilisation, while viviparous animals undergo internal fertilisation.
  • External fertilisation is the process which involves the union of male and female gametes outside the body.
  • Internal fertilisation is the process which involves the union of male and female gametes  takes place inside the body.
Oviparous and Viviparous Animals, Science Cbse / Ncert Revision Notes, Class 8

Development in chick

  • Hen is said to be oviparous as it lays the egg.  But the fertilisation is internal.
  • After fertilisation, the zygote undergoes rapid division and moves down the oviduct.
  • As it travels down the oviduct, many protective layers form as a hard shell around the developing embryo.
  • Egg contains only the embryo when laid by the hen. Hen sits on the egg to provide warmth necessary for the development of chick.
  • The chick hatches from the egg after three weeks.

Life cycle of frog

There are three distinct stages in the life cycle of a frog - egg, tadpole and adult. During external fertilisation, the egg fuses with a sperm to form a zygote. The zygote further divides to form an early tadpole, which matures into a late tadpole. During metamorphosis, the tadpole transforms into an adult frog.

Development in  humans

Fertilisation is internal and human beings give birth to young ones. Almost all the organs are formed in human beings at the time of birth itself. As human beings grow, body undergoes certain changes during transformation from childhood to adolescent stage.

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