l16_17_carb_ener

l16_17_carb_ener - MIT Department of Biology 7.014...

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7.014 Lectures 16 &17: The Biosphere & Carbon and Energy Metabolism Simplified Summary of Microbial Metabolism The metabolism of different types of organisms drives the biogeochemical cycles of the biosphere. Balanced oxidation and reduction reactions keep the system from “running down”. All living organisms can be ordered into two groups 1 , autotrophs and heterotrophs, according to what they use as their carbon source. Within these groups the metabolism of organisms can be further classified according to their source of energy and electrons. Autotrophs : Those organisms get their energy from light ( photoautotrophs ) or reduced inorganic compounds ( chemoautotrophs ), and their carbon from CO 2 through one of the following processes: Photosynthesis (aerobic) — Light energy used to reduce CO 2 to organic carbon using H 2 O as a source of electrons. O 2 evolved from splitting H 2 O. ( Plants, algae, cyanobacteria) Bacterial Photosynthesis (anaerobic) — Light energy used to reduce CO 2 to organic carbon (same as photosynthesis). H 2 S is used as the electron donor instead of H 2 O. ( e.g. purple sulfur bacteria ) Chemosynthesis (aerobic) — Energy from the oxidation of inorganic molecules is used to reduce CO 2 to organic carbon ( bacteria only) . e.g. sulfur oxidizing bacteria
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l16_17_carb_ener - MIT Department of Biology 7.014...

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