Spermatozoa, also referred to as sperm, are male reproductive cells. Sperm occur in several different forms, and are essential components for reproduction. Sperm vary slightly in physical composition, but have distinct body shapes, characterized by heads and long singular tails.
Sperm occur in males of many species, including plants, animals and humans. Some sperm move, while others are largely immobile. Sperm cells that move are called spermatozoon; these cells have long, singular flagellum that act as tails and rudders. Non-mobile sperm, in contrast, are called spermatium and have shorter tails. Sperm cells do not divide and have relatively short life spans. Upon coupling with and fertilizing female eggs, sperms transfer critical genetic information and data to new offspring, which in turn bear traits of both parents. Sperm have distinct anatomical structures, and have the same basic physical structures. All sperm bodies contain a head, neck, mid-piece, principal piece and end piece. In their heads lie condensed nuclei, which are covered by a cap-like structure called an acrosome, which protects the nuclei and allows for the transport of fluids. Sometimes, errors and defects occur in sperm cells, which gives them abnormal appearances and may interfere with their functions. Sperm may have heads that are too small, too narrow or have multiple heads and tails.