Reproduction in organisms — BIOLOGY STD 12 Science — Question

The process of development of embryo from the zygote is called embryogenesis.Embryogenesis involves the following processes:

• Cell division (mitosis) To increase the number of cells.
• Cell differentiation For the formation of different types of tissues and organs.

Based on whether the development of the zygote takes place outside or inside the body of the female parent, animals are grouped into oviparous and viviparous.

1. Oviparous: The animals in which development of zygote takes place outside the female parent are called oviparous. They lay fertilised eggs covered with hard calcareous shell in a safe place in the environment, e.g. reptiles and birds. After a period of incubation, the young ones hatch out from the egg.
2. Viviparous: The animals in which the development of zygote into a young one takes place inside the body of the female parent, are called viviparous. After attaining a certain stage of growth, the young ones are delivered out of the body of the female organism, e.g. majority of mammals including humans. The chances of survival of young ones are greater in these organisms because of proper embryonic care and protection.