STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Human sperm cells. Scanning electron micrograph (SEM) of the heads of healthy human sperm cells. These are the male sex cells, and are responsible for fertilising the female egg (ovum). A man releases millions of sperm cells in each ejaculation. The sperm travel to the egg by beating their tails (upper right). The head contains the genetic material that fuses with the female genetic material to form a new human. The tip of the head is called the acrosome. This releases enzymes that help the sperm penetrate the egg. Only one sperm may penetrate the egg: the egg membrane forms a barrier to sperm once penetrated. Magnification: x11,000 when printed 10cm wide.
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