sperm

Fluid containing the male gametes (sperm cells) of animals. Usually, each sperm cell has a head capsule containing a nucleus, a middle portion containing mitochondria (which provide energy), and a long tail (flagellum). See sexual reproduction.

In most animals, sperm cells (sometimes called ‘sperm’ for short) are motile, and are propelled by a long flagellum, but in some (such as crabs and lobsters) they are nonmotile. The term is sometimes used for the motile male gametes (antherozoids) of lower plants. The human sperm cell is 0.0002 in/0.005 mm long and can survive inside the female for 2–9 days. Mammalian sperm cells have receptor cells identical to some of those found in the lining of the nose. These may help in navigating towards the egg.

Sperm cell counts have fallen by 50% worldwide since 1940, according to a Danish study conducted in 1990. This reduction may be due to increases in pollution as a number of pollutants, including some petroleum by-products and polychlorinated biphenyls, mimic the effects of the female hormone estrogen on cells.