DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Darkfield light micrograph (LM) of Green alga, desmid (Micrasterias sp.). Desmids are a common group of freshwater unicellular, green algae that have intricate cell walls. Micrasterias species are placoderm desmids that have the cell wall divided into two symmetrical halves (semi-cells). The semi-cells are joined by a narrow central region called the isthmus. Visible in this image is a transparent nucleus (grey) that is located in the isthmus region. Each semi-cell contains a single large chloroplast which possess chlorophyll A and B pigments that are used in photosynthesis. Synthesized sugars are stored in small pyrenoids located in the chloroplast. The bright transparent edge is the algal cell wall, with an inner cellulose layer and an outer pectin layer. Micrasterias is the most important genus of desmids for indicating water quality they are extremely sensitive. Magnification: x80 when shortest axis printed at 25 millimetres.
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