chemosynthesis

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Chemosynthesis


Chemosynthesis is a metabolic pathway used by some bacteria to synthesize new organic compounds such as carbohydrates by using energy derived from the oxidation of inorganic moleculeshydrogen sulfide (H2S) or ammonia (NH3). Chemosynthesis can occur in environments such as the deep ocean around hydrothermal vents , where sunlight does not penetrate, but where chemicals like hydrogen sulfide are available. Chemosynthesis is also a critical part of the nitrogen cycle , where bacteria that live in the soil , or in special plant structures called heterocysts, utilize ammonia for energy and produce nitrates and nitrites which can subsequently be used as nutrients for plants. Some bacteria can also utilize hydrogen gas (H2) and carbon dioxide (CO2) in a chemosynthetic pathway that results in the production of new organic compounds and methane (CH4).

[Marie H. Bundy ]

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chemosynthesis, process in which carbohydrates are manufactured from carbon dioxide and water using chemical nutrients as the energy source, rather than the sunlight used for energy in photosynthesis. Most life on earth is fueled directly or indirectly by sunlight. There are, however, certain groups of bacteria, referred to as chemosynthetic autotrophs, that are fueled not by the sun but by the oxidation of simple inorganic chemicals, such as sulfates or ammonia. Chemosynthetic autotrophs are a necessary part of the nitrogen cycle. Some groups of these bacteria are well suited to conditions that would have existed on the earth billions of years ago, leading some to postulate that these are living representatives of the earliest life on earth. This view has been supported by the discovery of small ecosystems that thrive in the hot (350°C/660°F) water found around hydrothermal vents on the ocean floor. In these ecosystems, the primary producers in the food web are bacteria whose life functions are fueled by inorganic chemicals that seep up from the earth's crust. See also autotroph.

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che·mo·syn·the·sis / ˌkēmōˈsin[unvoicedth]əsəs; ˌkemō-/ • n. Biol. the synthesis of organic compounds by bacteria or other living organisms using energy derived from reactions involving inorganic chemicals, typically in the absence of sunlight. Compare with photosynthesis. DERIVATIVES: che·mo·syn·thet·ic / -sinˈ[unvoicedth]etik/ adj.

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chemosynthesis The pathway by which bacteria in hydrothermal vent communities synthesize complex organic molecules from hydrogen sulphide gas and dissolved carbon dioxide: 4H2S + CO2 + O2 → CH2O + 4S + 3H2O.

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chemosynthesis A type of autotrophic nutrition in which organisms (called chemoautotrophs) synthesize organic materials using energy derived from the oxidation of inorganic chemicals, rather than from sunlight. Most chemoautotrophs are bacteria, including Nitrosomonas, which oxidizes ammonium to nitrite; and Thiobacillus, which oxidizes sulphur to sulphate.