Operational definition
Classification axis.
The classification of an organism according to the principal source of the carbon incorporated into its biomass.
The primary categories are:
- autotroph — biomass carbon comes principally from inorganic carbon, especially carbon dioxide or bicarbonate;
- heterotroph — biomass carbon comes principally from organic compounds;
- mixotroph — both inorganic-carbon fixation and organic-carbon acquisition contribute materially.
Autotrophy is a carbon classification, not a synonym for phototrophy.
13.1 Autotroph
Biomass carbon comes principally from inorganic carbon:
- COâ‚‚
- bicarbonate
- related dissolved inorganic carbon
13.2 Heterotroph
Biomass carbon comes principally from preexisting organic compounds.
13.3 Mixotroph
Both autotrophic and heterotrophic carbon acquisition contribute materially.
Mixotrophy can include photosynthesis plus prey ingestion, dissolved-organic-carbon uptake, parasitism, or acquired photosynthetic capacity. It is widespread among aquatic protists and also occurs in bacteria. (PubMed Central (PMC))