If the first cleavage furrow divides the zygote completely into two,the cleavage type is

In human females,the blastocyst:

Assertion : During fertilization,only the head of the spermatozoa enters the egg.
Reason : If several spermatozoa hit the egg at the same time,all can enter the egg.

In mammals,the sperm produces an enzyme-like substance called sperm lysin. What is it called?

In humans,fertilization is possible only when,

The region where the sperm enters the egg is called: