STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Sperm cells. Coloured scanning electron micrograph (SEM) of human sperm cells or spermatozoa. These tiny male sex cells are produced in the testes, and are responsible for fertilisation of the female egg (ovum). They have a rounded head that contains the male hereditary material (DNA), and a long tail that are used for propulsion. The sperm cell at lower right has some residual cytoplasm seen behind its head, which may affect its motility or fertility. All men have some deformed sperm, but this is not a problem unless their numbers rise. Magnification: x2150 at 6x7cm size.
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