<P> In biochemistry, chemosynthesis is the biological conversion of one or more carbon - containing molecules (usually carbon dioxide or methane) and nutrients into organic matter using the oxidation of inorganic compounds (e.g., hydrogen gas, hydrogen sulfide) or methane as a source of energy, rather than sunlight, as in photosynthesis . Chemoautotrophs, organisms that obtain carbon through chemosynthesis, are phylogenetically diverse, but also groups that include conspicuous or biogeochemically - important taxa include the sulfur - oxidizing gamma and epsilon proteobacteria, the Aquificae, the methanogenic archaea and the neutrophilic iron - oxidizing bacteria . </P> <P> Many microorganisms in dark regions of the oceans use chemosynthesis to produce biomass from single carbon molecules . Two categories can be distinguished . In the rare sites at which hydrogen molecules (H) are available, the energy available from the reaction between CO and H (leading to production of methane, CH) can be large enough to drive the production of biomass . Alternatively, in most oceanic environments, energy for chemosynthesis derives from reactions in which substances such as hydrogen sulfide or ammonia are oxidized . This may occur with or without the presence of oxygen . </P>

What form of energy is used for chemosynthesis