DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Coloured scanning electron micrograph (SEM) of green alga (chlorophyte) vegetative stage (Haematococcus pluvialis). A unicellular, microscopic green alga that has two flagella. It contains a single, cup-shaped chloroplast, with several pyrenoids. This alga occurs in many different aquatic environments including fresh and brackish water. It is believed to be the world's richest known source of astaxanthin. Astaxanthin is a natural carotenoid pigment and a biological antioxidant. When environmental conditions become adverse (i.e. when nutrients start becoming scarce, the water environment starts to dry out and the algae are increasingly exposed to direct sunlight), they enter a resting phase (cyst phase) that allows them to survive for prolonged periods, until the environment becomes much more favourable for growth. In the resting phase the alga accumulates high amounts of astaxanthin. Magnification: x600 when shortest axis printed at 25.
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