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MO3001: Cyanobacteria also known as Blue Green Algae are sometimes considered to be photosynthetic bacteria having evolved during the Mesoproterozoic era approximately 3.5 billion years ago. They are credited with converting the earths atmosphere from a reducing atmosphere to an oxidising one. This enabled new life forms to evolve which required free oxygen. The image shows strings of cells of Nostoc, a common blue green alga. The larger cells are heterocysts which are Nitrogen fixing. This sample is beginning to decompose hence visible bacteria. Phase Contrast illumination, approximate magnification x500.

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