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PhototrophPhototrophs or photoautotrophs are photosynthetic algae, fungi, bacteria and cyanobacteria which build up carbon dioxide and water into organic cell materials using energy from sunlight. One product of this process is starch, which is a storage or reserve form of carbon, which can be used when light conditions are too poor to satisfy the immediate needs of the organism. Photosynthetic bacteria have a substance called bacteriochlorophyll, live in lakes and pools, and use the hydrogen from hydrogen-sulphide instead of from water, for the chemical process. (The bacteriochlorophyll pigment absorbs light in the extreme UV and infra-red parts of the spectrum which is outside the range used by normal chlorophyll). Purple and green sulfur bacteria use light, carbon dioxide and hydrogen sulphide from anaerobic decay, to produce carbohydrate, sulfur and water. Cyanobacteria live in fresh water, seas, soil and lichen, and use a plant-like photosynthesis which releases oxygen as a byproduct. Photolithotrophic autotroph Autotrophic organisms that use light energy, and inorganic electron source (eg. H2O, H2, H2S), and CO2 as their carbon source Examples: Photoorganotrophic heterotroph Heterotrophic microorganisms that use light energy and organic electron donors, and also employ simple organic molecules rather than CO2 as their carbon source. Examples:
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