MICHAEL WHITAKER / SCIENCE PHOTO LIBRARY MICHAEL WHITAKER / SCIENCE PHOTO LIBRARY
Fertilisation calcium wave (four images). Confocal light micrograph of a sea urchin egg after a sperm (top left) has penetrated during fertilisation. The round egg is seen 15 seconds (upper left), 25 seconds (upper right), 31 seconds (lower left) and 36 seconds (lower right) after sperm penetration. The sperm has triggered a red "calcium wave" which spreads across the cell. This calcium wave starts a chemical chain reaction that is essential to enable the egg to divide and form into an embryo. A confocal microscope scans the specimen with a laser. Fluorescent dye in the specimen is excited by the laser light, to produce this type of image. Magnification: x200 at 6x6cm size.
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