Question

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

• A. Cells of corona radiata trap all sperms except one.
• B. Only two sperms nearest the ovum penetrate zona pellucida.
• C. Secretions of acrosome helps one sperm enter cytoplasm of ovum through zona pellucida.
• D. All sperm except the one nearest to ovum loose their tails.

Answer 1

The correct option is C Secretions of acrosome helps one sperm enter cytoplasm of ovum through zona pellucida.

In acrosomal reaction, sperms that are capacitated release chemicals contained in the acrosome called sperm lysins. Sperm lysins include hyaluronidase, corona penetrating enzyme and zona lysin or acrosin. Zona lysin digest the zona pellucida of the secondary oocyte.

Due to this reaction, a fusion of plasma membrane of the sperm with the plasma membrane of the secondary oocyte takes place so that sperm contents enter the oocyte which induces depolarization of the oocyte plasma membrane. Depolarization prevents entry of more than one sperm into the oocyte which is called as polyspermy. It ensures entry of only one sperm into the secondary oocyte i.e. monospermy.