<Li> Heterotroph <Ul> <Li> Chemoheterotroph </Li> <Li> Photoheterotroph </Li> </Ul> </Li> <Ul> <Li> Chemoheterotroph </Li> <Li> Photoheterotroph </Li> </Ul> <P> Many heterotrophs are chemoorganoheterotrophs that use organic carbon (e.g. glucose) as their carbon source, and organic chemicals (e.g. carbohydrates, lipids, proteins) as their energy and electron sources . Heterotrophs function as consumers in food chain: they obtain these nutrients from saprotrophic, parasitic, or holozoic nutrients . They break down complex organic compounds (e.g., carbohydrates, fats, and proteins) produced by autotrophs into simpler compounds (e.g., carbohydrates into glucose, fats into fatty acids and glycerol, and proteins into amino acids). They release energy by oxidizing carbon and hydrogen atoms present in carbohydrates, lipids, and proteins to carbon dioxide and water, respectively . </P> <P> They can catabolize organic compounds by respiration, fermentation, or both . Fermenting heterotrophs are either facultative or obligate anaerobes that carry out fermentation in low oxygen environments, in which the production of ATP is commonly coupled with substrate - level phosphorylation and the production of end products (e.g. alcohol, CO2, sulfide). These products can then serve as the substrates for other bacteria in the anaerobic digest, and be converted into CO and CH, which is an important step for the carbon cycle for removing organic fermentation products from anaerobic environments . Heterotrophs can undergo respiration, in which ATP production is coupled with oxidative phosphorylation . This leads to the release of oxidized carbon wastes such as CO and reduced wastes like H O, H S, or N O into the atmosphere . Heterotrophic microbes' respiration and fermentation account for a large portion of the release of CO into the atmosphere, making it available for autotrophs as a source of nutrient and plants as a cellulose synthesis substrate . </P>

Microorganisms classified as plantae obtain most of their energy by converting