Question

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

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

Answer 1

The correct option is B

Secretions of acrosome helps one sperm enter cytoplasm of ovum through zona pellucida.

The correct option is B.

Explanation of correct option:

1. During the process of fertilization, when sperm comes into contact with the zona pellucida layer of the ovum a cortical reaction occurs that causes a modification of the zona pellucida thereby preventing polyspermy.
2. The acrosomal enzymes are released present inside the head of the sperm and start to dissolve and the actin filament comes into contact with the egg's plasma membrane causing the release of the calcium from the egg thereby raising the intracellular calcium concentration.
3. This triggers the fusion of the cortical granules membrane with the egg's plasma membrane liberating the contents of the granules to the extracellular space and thus establishing a permanent barrier to prevent polyspermy.

Explanation of incorrect options:

Option A: Only one sperm is capable of penetrating the membrane.

Option C: Since one sperm fuses with the egg, polyspermy does not occur.

Option D: Cells of zona pellucida do not allow all the sperms to enter into the ovum except one.

Final answer: During fertilization in humans, only one sperm penetrates zona pellucida and enters inside it.