Nutrition: Autotrophy
PHOTOSYNTHESIS: Microbes must be at or close to the surface of a body of water to photosynthesise. At the surface they gain adequate solar radiation that triggers photosynthesis, while remaining moist. However, the surface of a body of water is also likely to be affected by wind. Waves wash algae onto surfaces where they risk dehydrating. Protists (algae) have overcome desiccation in a variety of ways including:
- larger multicellular structures which are anchored to the sea floor;
- symbioses with other organisms such as fungi. In lichens the fungus provides protection against desiccation; Indeed, cyanobacteria are thought to have formed symbioses with eukaryotic cells; the symbiosis then evolved into what we now call plants.
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animation of division under light (212 Kb).
CHEMOSYNTHESIS: Chemotrophs are rare, though widely distributed. In soil, many of the stages of the Nitrogen, Sulphur and Iron cycles are based on chemosynthesis. Unique prokaryotic communities based on chemosynthesis are found at thermal vents on the ocean floor, and in hypersaline or extremely hot bodies of water. In deep-sea vents, chemotrophs are found singly in the waters, and in symbiosis with worms, clams and various other invertebrates.
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