Question

Fertilisation of ovum occurs in
A) Fimbriae of Oviduct
2) Isthmus of the oviduct
3) Ampulla of the oviduct
4) None of the above

Answer 1

Oviduct (Fallopian tube) is divided into three regions, infundibulum (this is closer to the ovary) and this leads to the ampulla (Where fertilization occurs) and the last part is the isthmus.

Complete answer:
The correct sequence of reproductive events of a human being is:

1. Gametogenesis
2. Insemination
3. Fertilisation
4. implantation
5. gestation
6. Parturition
   Male gamete formed in the seminiferous tubule and then through Vas deferens it travels to the Urethra and then it is finally inseminated into the female vagina.
   From there, it travels to the ampulla part of the Oviduct. The egg is also released from the ovary (This process is called ovulation). This egg is picked up by the fimbriae (Finger-like projection) of the infundibulum and then it reaches the ampullary region of the oviduct.
   If sperm and ovum reach the ampullary region simultaneously, then only fertilization (fusion of sperm and ovum) occurs, Otherwise not. And this is the region why many copulations do not lead to pregnancy.
   So the correct answer is option (3).

Additional information:
Ovum has many protective layers around it. The inner layer around it is the non-cellular layer, Zona pellucida followed by perivitelline space and the outer layer is the corona radiata whose main function is to supply protein to the ovum.
Sperm comes in contact with zona pellucida and induces some change in the membrane which blocks the entry of other sperms ( protects Polyspermy) ensuring, only one sperm fertilize one egg.

Note: sperm is composed of four parts, a head, a neck, a middle piece, and a tail and it is covered by plasma membrane (as all the cells in the body are covered with plasma membrane) and they have an elongated nucleus. Their anterior portion is called acrosome (cup-like structure) which is filled with enzymes that dissolve the wall of zona pellucida and facilitate fertilization.