Question

What is fertilization? In which part of the human female reproductive system does it occur? Explain, with the help of diagrams, various physical and chemical events of fertilization in humans.

Hint:

Sperms can remain viable in the female reproductive tract for about 48–72 hours, but the ovum is viable for only about 24 hours after ovulation.

Answer 1

Definition: Fertilization is the process of fusion of a haploid male gamete (sperm) with a haploid female gamete (ovum) to form a diploid zygote.
Site of Fertilization: It occurs in the ampullary region of the Fallopian tube (oviduct). Events of Fertilization:
Acrosomal Reaction (Chemical Event): When the sperm comes in contact with the zona pellucida layer of the ovum, the acrosome releases enzymes (hyaluronidase and acrosin). These enzymes dissolve the egg's membranes to allow sperm entry.
Cortical Reaction (Physical Event): The entry of the first sperm induces changes in the zona pellucida (depolarization), making it impervious to other sperms. This blocks polyspermy.
Completion of Meiosis II: The entry of the sperm stimulates the secondary oocyte to complete its second meiotic division, forming a haploid ovum (ootid) and a second polar body.
Karyogamy: The haploid nucleus of the sperm and that of the ovum fuse together to form a diploid zygote.