Question

fish and frogs lay hundreds of eggs at a time but Birds like sparrows lay only 4 or5 eggs. Why?​

Answer 1

Answer:

because fish and frogs are external fertilisation animal. but bird are internal fertilisation animals

Answer 2

Answer:

Fishes and frogs lay hundreds of eggs as compared to the hens because :

(1) External fertilization is occurring in fishes and frogs.

(2) The male releases a large number of gametes in the external medium (Water) while the female parent lays a vast number of eggs.

(3) Eggs and sperms may be carried to large distances or may be consumed by predators present in the medium thus loss of the gametes can take place.

(4) Hence in fishes and frogs, the fertilization of male and female gamete is a chance factor and it depends on nature too.  

So, to increase the chances of fertilization a large number of gametes are produced in these organisms.

While, on the other hand, egg development in the hen takes insideuterus thus loss of gamete does not take place therefore in hen the zygote formation is not controlled by nature.