The region where the sperm enters the egg is called:

The fertilization membrane during fertilization is synthesized by

In placental mammals,where does the fertilization of the ovum take place?

Statement-$I$: The trophoblast layer gets attached to the endometrium and the inner cell mass gets differentiated as the embryo.
Statement-$II$: The morula becomes embedded in the endometrium of the uterus.

In humans,fertilization is only possible if:

To ensure the effectiveness of reproduction in mammals,which of the following is essential?