What is the reason for the differences between male and female reproductive cells?

Female reproductive cells (eggs) are usually larger than male reproductive cells (sperm). This is due to the fact that in many animals, the eggs contain a large supply of yolk so that the embryo can feed on it. The eggs are immobile, and during maturation they are covered with egg membranes that protect the future embryo.

Spermatozoa are small enough and mobile. They have a huge mitochondrion and acrosome (Golgi apparatus), which contains special substances that are necessary for fertilization. They also have a tail with which they move. This structural feature is associated with the fact that the sperm needs to travel a certain distance in order to fertilize a motionless egg.