Question

why do fish and frog lay more eggs .where as cow and human beings usually give birth to one at a time?

Answer 1

this is because Organisms having internal fertilization, like hen, produce one egg at a time. This is so because here there is less chance of failure of fusion between male and female gamete. After the gametes are fertilized there is just the need of development of animal in the form of egg. Frog like aquatic organisms who shows external mode of reproduction have to lay egg in hundred. The first reason behind this is the single egg is so small in size that it will not be possible to stay to definite position and which in turns make hard for sperm to found and fuse them. Whereas, when large number of eggs make them stick together this makes fertilization possible. Another reason behind this is there is a lot of organisms who feed on these eggs, so larger number of eggs gives more possibility of giving birth to young ones

Answer 2

The success rate in offsprings of surving is more in humans and cows than fishes and frog
reason:
Fishes and frog lay theirs eggs in water where there is a big chance of risking the eggs as there r many other animals who will eat it called predators therefore mothernature designed it in such a way that as the number of offspring increase the number of survivors alo increase.
Still we see only 2 or 5 survive the plethora of hazards