1. Fish and frogs lay hundreds of eggs at a time, whereas a hen lays only one egg at a time. Explain the mechanism behind it.

In animals such as frogs and fishes, the process of fertilization takes place outside the body. This type of fertilization is known as external fertilization. In these animals large number of eggs and sperms are released at a time.In external fertilization, sperms do not have a definite route to reach the eggs. So, they are released in large amounts to increase the chances of fertilization. In addition to it the eggs to do not have protection and they can be easily destroyed by the predators. So, their large numbers enables adequate number of eggs to get fertilized even if some eggs are destroyed.

In hens the process of fertilization occurs inside the body. This type of fertilization is known as internal fertilization. Relatively lower number of eggs are produced in these animals because sperms are directed to the egg through a specific track and after fertilization the eggs are protected by a protective shell. They are released in environment after fertilization. So, there is no need to produce large number of eggs in these organism.