DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Coloured scanning electron micrograph (SEM) of Scenedesmus spp., flat colony of 4 alga cells. Scenedesmus, a green alga from the Chlorophyceae group, is a small, non-motile, colonial green alga consisting of cells aligned in a flat plate. The colonies most often have two or four cells, but may have 8, 16, or 32 cells. The cells are usually cylindrical but may be more lunate (crescent-shaped), ovoid, or fusiform (wide in the middle and tapering at both ends). Often the end cells each have two long spines protruding from their outer corners (example: Scenedesmus quadricauda). Other cells may have additional spines or chitinous bristles. Each cell contains a single parietal, plate-like chloroplast with a pyrenoid (the site of CO2 fixation). The cell walls may be covered in bumps or reticulations. Scenedesmus is a photosynthetic planktonic organism that is important in the aquatic food chain. Magnification: x1,200 when shortest axis printed at 25.
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