Question

Which of the following layers of ovum undergoes changes to prevent polyspermy when sperm contacts with it?
A)Corona radiata
B)Plasma membrane
C)Zona pellucida
D)Tunica albuginea

Answer 1

The ovum, is a single cell in human physiology released from one of the female reproductive organs, the ovaries, which will evolve into a new organism when fertilised (united) with a sperm cell.

Complete answer:
Polyspermy refers to an egg fertilised by more than one sperm. Two copies of each chromosome are usually contained by diploid species, one from each parent. On the other hand, the cell that results from polyspermia has three or four copies of each chromosome, one from the egg and one from several sperm. The outcome is usually an invisible zygote. This can occur because, due to the selective pressures of sperm competition, sperm are too effective at reaching and fertilising eggs.

Polyspermy in human reproduction is very unusual. One of two methods that prevents polyspermy in humans is the reduction in the amount of sperm that swim to the oviduct. The blocking of sperm in the fertilised egg is the other process.

Cortical reaction is a mechanism caused by the release of cortical granules from the egg during fertilisation, which prevents polyspermy from combining several sperm with one egg. Unlike the rapid polyspermy block that prevents additional sperm from fertilising the egg immediately but briefly, the cortical reaction gradually forms a permanent barrier to the entry of sperm and acts in many species as the main part of the slow polyspermy block.

Hence, the correct answer is option (A)

Note: Result of Zona pellucida modification in cortical reaction of mammals blocks the polyspermy enzymes released by cortical granules, digesting the sperm receptors of the glycoproteins ZP2 and ZP3 so that the sperm can no longer attach.