Question

First step in activation of ovum during fertilisation is
A) Formation is fertilisation membrane
B) Fertilizin and antifertilizin reaction
C) Penetration of sperm into ovum
D) Formation of fertilisation cone

Answer 1

Hint: The process of fusion of two gametes of opposite sex is called as fertilisation or gamete fusion. In humans, fertilisation is seen between sperm and ovum. Sperm is the male gamete carrying X/Y chromosome as a sex chromosome and ovum is the female gamete caring X/X chromosome.

Complete answer:
Fertilisation is seen after maturation of gamete that is after spermatogenesis and oogenesis. The first event in activation of ovum during Fertilisation is thought to be the interaction between fertilizin and antifertilizin, fertilizin is a helu coat of an echinoderm that later elicits Acrosomal reaction in spermatozoa. In the first step sperm makes contact with the egg at its head. In acrosomal reaction the Enzymes in the acrosome is expelled. When spermatozoa comes in contact with the membrane of the egg there undergoes several structural changes and forms acrosomal vesicles. The burst of acrosomal vesicle releases lysine which can break down eggs vitelline coat and forms a gateway to the entry of sperms, before the formation of passage the point of contact on egg bulges to form a cone like structure called Fertilisation cone. Later this cone invaginates and allows the head of spermatozoa to insert within the ovum this step releases calcium and there is a wave of calcium induced within the egg and this is the final step of egg activation during Fertilisation.

Hence, the correct answer is Option ‘B’.

Note:Interaction of fertilizin and antifertilizin is a chemotactic process where the release of fertilizin from egg interacts with the antifertilizin of spermatozoa of same species this maintains species specificity. This attraction makes sperms bind eggs, this process is called capacitation.