STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Sperm cell. Coloured scanning electron micrograph (SEM) of the head of a human sperm cell or spermatozoon. This tiny male sex cell is produced in the testes, and is responsible for fertilisation of the female egg (ovum). It has a rounded head which contains the male hereditary material (DNA), and a long tail that it uses to propel itself. Some 300 million sperm are released by the male during ejaculation, while the female usually releases one large egg at a time. Only one sperm cell can fertilise the egg. Magnification: x5600 at 6x7cm size.
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