Carbon fixation or
сarbon assimilation refers to the
conversion process of inorganic carbon (
carbon dioxide) to
organic compounds by living
organisms. The most prominent example is
photosynthesis, although
chemosynthesis is another form of carbon fixation that can take place in the absence of sunlight. Organisms that grow by fixing carbon are called
autotrophs. Autotrophs include
photoautotrophs, which synthesize organic compounds using the energy of sunlight, and
lithoautotrophs, which synthesize organic compounds using the energy of inorganic oxidation.
Heterotrophs are organisms that grow using the carbon fixed by autotrophs. The organic compounds are used by heterotrophs to produce energy and to build body structures. "Fixed carbon", "reduced carbon", and "organic carbon" are equivalent terms for various organic compounds.