Question

How is the entry of only one sperm and not many ensured into an ovum during fertilization in humans?

Answer 1

Human fertilization is the fusion of human egg and sperm. It takes place in the ampulla of the fallopian tube and leads to formation of a zygote cell, or fertilized egg.

Complete answer:
At the initial stage sperm goes into various changes because fresh male gametes are not able to fertilize.
The male gametes goes into capacitation in the female reproductive tract and then increases its motility and destabilizes its membrane, making it for the acrosome reaction.
The sperm enters the cytoplasm and the tail and the outer layer of the sperm diminish and the cortical reaction takes place.
Sperm depolarises the zona pellucida layer of ovum and also the fusion of cortical granule having an enzyme with zona pellucida layer takes place then causes blockage for the other sperms.

Additional information: When the sperm enters the vitelline space, receptors on the sperm head bind to the oocyte membrane. The cortical reaction occurs by ovastacin binding and cleaving receptors on the zona pellucida. Ampulla, corona radiata, cone of attraction, sperm preparation, and zona pellucida are the part of the ovary.In- vitro fertilization is the process by which egg cells and sperm are fertilized from outside the body.

Note: Once the sperm enters the ovum then the ovum wall becomes thick also due to which some chemicals are released into the surrounding which leads to the death of the other sperm.