Question

The most important significance of fertilizin and antifertilizin reaction is to
a. Preserve the sperm
b. Ensure that at least few spermatozoa encounter the egg
c. Mutually attract the gametes of opposite sexes
d. Ensure fusion gametes of same species

Answer 1

Hint: Fertilizin is a glycoprotein secreted from the egg's cortical region that helps binding the sperm to the surface of the egg. An antifertilizin is an acidic protein secreted by the plasma membrane of the sperm.

Complete answer:
Fertilizin is a glycoprotein released by the ovum that reacts with the antifertilizin of sperm. Sperm on meeting the ovum in the oviduct releases antifertilizin. Antifertilizin has acidic protein secreted by the sperm’s acrosome. The fertilizin-antifertilizin reaction is species specific. It paves the path for the sperm to fertilize the ovum. The sperm adheres to the surface of egg due to the presence of fertilizin molecules in the surface of egg cytoplasm.
Function of Fertilizin:
1. Make the surface sticky so that sperm adhere.
2. Helps sperm to reach capacitation i.e. enables sperm to penetrate the egg surface.
3. Interaction with antifertilizin ensures fertilization.
4. Prevent polyspermy in eggs.

So, the correct option is (D) Ensure fusion gametes of the same species.

Note: The fertilizin of an egg interacts with the antifertilizin of sperm of the same species. The interaction between fertilizin and antifertilizin binds the sperms to the egg surface. Post adhesion sperm acquires capacitation i.e. the capacity to fertilize the egg. In this process, the acrosome of the sperm releases the sperm lysin, a chemical substance present in the sperm’s acrosome. Lysine helps in penetrating the ovum. The ovum consists of three membranes (a) corona radiata, (b) zona pellucida (c) vitelline membranes. In the first step sperm passes through corona radiata and reaches zona pellucida. Upon reaching there it releases hyaluronidase enzyme (sperm lysin) from acrosome. Hyaluronidase enzyme dissolves zona pellucida and the sperm reaches the plasma membrane of the egg. This is called an acrosome reaction. After this at the point of contact with the sperm, the egg forms a cone of reception or fertilization cone to receive the sperm. Upon entrance of one sperm in the ovum the vitelline membrane thickens and is changed into rigid fertilization membrane. This membrane blocks the entry of other sperms. Second maturation division of the ovum is initiated and a second polar body is given off.