sperm

In biology, the male gamete of animals before fertilization in sexual reproduction. Each sperm cell has a head capsule containing a nucleus, a middle portion containing mitochondria (which provide energy), and a long tail (flagellum). In mammals sperm cells are produced in the testes of a male. They are produced by a special kind of cell division called meiosis, which halves the number of chromosomes present.

Sperm cells are highly specialized. When they are introduced into the vagina of the female by the penis of the male, they swim up the uterus and oviducts. The swimming is a result of the beating of the tail of the sperm cell. At the other end is the nucleus, but there is little else in the cell, making it fairly small and light.

The human sperm is 0.005 mm/0.0002 in long and can survive inside the female for 2–9 days. Sperm counts have fallen by 50% worldwide since 1940, according to a Danish study in 1990. This reduction may be due to increases in pollution – a number of pollutants, including some petroleum by-products and PCBs (polychlorinated biphenyls), appear to have similar effects to the female hormone oestrogen.