CBSE Class 10 Answered

Even though millions of sperms are released during an ejaculation, only a few hundred will survive to make the arduous trip to the egg. Of the few hundred sperm which reach the egg, only one will successfully fertilise it. The sperm which fertilises the ovum comes in contact with the zona pellucida layer of the ovum and induces changes in the membrane that block the entry of additional sperms.

Thus, it ensures that only one sperm can fertilise an ovum.

The sperm which reaches the ovum first and comes in contact with the zona pellucida layer is the one which will fertilise the ovum.