Question

What happens during fertilization in humans after many sperms reach close to the ovum?

• A. Secretions of acrosome help one sperm enter cytoplasm of ovum through zona pellucida
• B. all sperms except the one nearest to the ovum lose their tails.
• C. cells of corona radiata trap all the sperms except one
• D. only two sperms nearest the ovum penetrate zona pellucida.

Answer 1

The correct option is A Secretions of acrosome help one sperm enter cytoplasm of ovum through zona pellucida

During the process of fertilisation of the male and the female gametes (i.e the sperm and the egg) in humans, the sperm cells reach the egg, binds through the corona radiata and reach the zona pellucida layer of the egg. Here a molecule on the sperm binds with a glycoprotein in the zona pellucida layer of the egg. This causes the acrosome to burst, releasing an enzyme that helps the sperm cells to cross the zona pellucida. Now the cortical granules in the secondary oocyte release their content. this causes the zona pellucida to cross-link and harden, thus preventing the fertilisation of the egg by more than one sperm by preventing the entry of the sperm. Therefore, only a single sperm cell penetrates the zona pellucida. So, the correct option is 'Secretions of acrosome help one sperm enter the cytoplasm of ovum through zona pellucida'.