STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Sperm tail. Coloured transmission electron micrograph (TEM) of a longitudinal section through the tail of a human sperm (spermatozoa). This is the middle piece, the part of the tail (flagellum) that contains mitochondria (green ovals). Mitochondria provide energy for the contraction of the microtubules (pink) that creates the tail's whiplash swimming action. Sperm are the tiny male sex cells produced in the testes that are responsible for the fertilization of the female's ovum (egg). Magnification: x27,000 at 6x7cm size.
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