Question

What is fertilization? In which part of the Human female reproductive system does it occur? Explain diagrammatically various physical and chemical events of fertilization in humans.

Answer 1

Hint: Gametogenesis is the process by which male and female gametes are formed. The human female gamete is the ovum or egg and the human male gamete is the sperm. Sperms are transferred to the human female reproductive tract where the formation of zygote takes place. The ovum is large and non-motile and the sperm is small and motile.

Complete answer:
Fertilization is the process in which the fusion of male and females gametes takes place. A diploid zygote is formed by this process. Fertilization occurs in the fallopian tube of the human female reproductive system.
Physical and chemical events of fertilization in humans are-
- Firstly, the approximation is achieved by the fertilizin-antifertilizin reaction. Fertilizin present on the ovum reacts with antifertilizin of sperm of the same species. As a result of approximation, the sperm get stuck on the surface of the ovum. The acrosome is a highly modified lysosome consisting of lytic enzymes enclosed with the plasma membrane.
- Next, the acrosome helps the sperm to penetrate the layers around the ovum. The acrosome is a highly modified lysosome consisting of lytic enzymes enclosed with the plasma membrane.
- Capacitation of the sperm takes place as the sperm reaches the egg in the female reproductive system. Capacitation prepares the sperm to fertilize the ovum.
- Now, as the sperm cell penetrates the corona radiata layer and zona pellucida, its membrane fuses with the membrane of the ovum. Just when a sperm enters into the ovum, a fertilization membrane is formed by the zona pellucida layer of the ovum which prevents further entry of sperms. Perivitelline membrane is formed between the fertilization membrane and plasma membrane.
- As the sperm enters the egg, the secondary oocyte completes its second meiotic division thereby releasing the ovum and a second polar body. The polar body degenerates and the ovum and sperm fertilize and gives rise to a zygote.
- Syngamy is the fusion of males and female gametes. The fusion of the cytoplasm of the gametes is called plasmogamy, the mixing of pronuclei of the gametes is called karyogamy, and the fusion of their chromosomes is called amphimixis.
- Penetration of the corona radiata layer happens by hyaluronidase enzyme present in the sperm. The penetration of sperm through zona pellucida is by acrosin.

Note: Zona pellucida is an acellular layer. The fertilization membrane is formed by structural changes in zona pellucida through cortical reaction and discharge of cortical granules in the perivitelline membrane. Hyaluronidase is a lytic enzyme found in the acrosome involved in penetrating the corona radiate layer of the ovum.