D. PHILLIPS / SCIENCE PHOTO LIBRARY D. PHILLIPS / SCIENCE PHOTO LIBRARY
False-colour scanning electron micrograph (SEM) of a field of mature human sperm (spermatozoa). Sperm are the motile male sex cells produced in the testis. Each sperm is about 65 micrometers long and broadly divided into head, neck and tail regions. A pear-shaped head contains the nucleus and genetic material of the male needed to ferti- lize the female egg (ovum). The head is joined to the tail by a short neck. The sperm's tail enables it to swim by whiplash movements, an action that propels it to reach the ovum. Of the millions of sperm produced by the male, only a single one will succeed in reaching, penetrating and fertilizing the egg.
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