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Ecology
Most heterotrophs are chemoorganoheterotrophs (or simply organotrophs) that use organic compounds both as a carbon source and an energy source. The term "heterotroph" very often refers to chemoorganoheterotrophs. Heterotrophs function as consumers in food chains: they obtain organic carbon by eating autotrophs or other heterotrophs. 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.

Ecology
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.

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 CO2 and CH4, 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 CO2 and reduced wastes like H2O, H2S, or N2O into the atmosphere. Heterotrophic microbes’ respiration and fermentation account for a large portion of the release of CO2 into the atmosphere, making it available for autotrophs as a source of nutrient and plants as a cellulose synthesis substrate.

Respiration in heterotrophs is often accompanied by mineralization, the process of converting organic compounds to inorganic forms. When the organic nutrient source taken in by the heterotroph contains essential elements such as N, S, P in addition to C, H, and O, they are often removed first to proceed with the oxidation of organic nutrient and production of ATP via respiration. S and N in organic carbon source are transformed into H2S and NH4+ through desulfurylation and deamination, respectively. Heterotrophs also allow for dephosphorylation as part of decomposition. The conversion of N and S from organic form to inorganic form is a critical part of the nitrogen and sulfur cycle. H2S formed from desulfurylation is further oxidized by lithotrophs and phototrophs while NH4+ formed from deamination is further oxidized by lithotrophs to the forms available to plants. Heterotrophs’ ability to mineralize essential elements is critical to plant survival. --Yuyan Chen (talk) 06:25, 19 November 2017 (UTC)