CNRI / SCIENCE PHOTO LIBRARY CNRI / SCIENCE PHOTO LIBRARY
False-colour transmission electron micrograph (TEM) of a single human spermatozoon, the motile, male sex cell, showing its division into a head and tail section. The sperm's tail enables it to swim, an essential action in reaching the female ovum. The mature male sex cell (male gamete) is located in the arrow-like head, the tip of which is capped by the acrosome, which releases enzymes that assist in the penetration of the egg during fertilisation. Only a single sperm succeeds in fertilisation; rapid chemical changes cause the outer membrane surrounding the ovum to thicken and form a barrier to competing sperm. Magnification: X 2,100 at 35mm size.
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