Question

1) distinguish between binary and multiple fission.give examples
2) why do animals exhibiting external fertilisation produce a large number of gamets?

Answer 1

• Binary fission: The unicellular splits into two equal daughter cells by cess division.
• Multiple fission: Unicellular organisms divide into many daughter cells.

Binary fission	Multiple fission
1. Nucleus and cytoplasm divide simultaneously.	1. First the nucleus divides into many nuclei and then each nuclei is surrounded by cytoplasm and the daughter nuclei are released by rupture of parent cell.
2.Many different patterns of division transverse and longitudinal.	2. No definite pattern of division.
3.Example :Amoeba.	3. Example :Malaria parasite.

2)

1. The external fertilisation is the process of fusion of male and female gametes outside the body or in outer environment.
2. As animal releases gametes in the external environment, there are the minimum chances of fertilisation and thus, large number of male gametes are produced to ensure better chances of fertilisation.

• The success rate of fertilisation is very low.
• Unlike internal fertilisation, numerous gametes need to be produced by the male and female to ensure reproductive success.
• A water body is required to initiate external fertilisation. The sperms would die on land.
• It is a reproductive disadvantage for most of the animals because most of the gametes die without being fertilized.
• External fertilisation is, however, a simple reproductive strategy which does not require the involvement of any hormones or mating rituals.