n.
or spermatozoon
Male reproductive cell .
In mammals, sperm are produced in the testes and travel through the reproductive system . At fertilization , one sperm of the roughly 300 million in an average ejaculation (see semen ) fertilizes an egg (see ovary ) to produce an offspring. At puberty , immature cells (spermatogonia) begin a maturation process (spermatogenesis). A mature human sperm has a flat, almond-shaped head, with a cap (acrosome) containing chemicals that help it penetrate an ovum. It is essentially a cell nucleus , with 23 chromosome s (including either the X or Y that determines the child's sex). A flagellum propels the sperm, which may live in a woman's reproductive tract for two to three days after sexual intercourse , to the egg. Sperm may be frozen and stored for artificial insemination .