Question

Select the correct set of conditions that block polyspermy.

I. Change in the electrical potential of the plasma membrane of oocyte
II. Cortical granule reaction enzymes
III. Fertilisation membrane
IV. Corona radiata

• A. I and III only
• B. I, II and III
• C. I, II and IV
• D. I and IV only

Answer 1

The correct option is B I, II and III

Polyspermy refers to the entry of more than one sperm into the oocyte. This can be prevented by a number of mechanisms.

The depolarisation of the membrane of the oocyte due to the increased permeability to sodium ions brings about the fast block to polyspermy.

The depolarisation also triggers the intracellular release of calcium ions, which stimulates the cortical granule reactions.

In the cortical granule reaction, the secretory vesicles located just inferior to the oocyte membrane are released outside the plasma membrane of the oocyte. These secretory vesicles release cortical enzymes which react with the zona pellucida and harden it. They also inactivate the sperm receptors present on the zona pellucida. This is the slow block to polyspermy.