Metabolic Diversity Among Organisms

Carbon Source:

Autotrophs are self-feeders and use CO₂ as a carbon source.

Heterotrophs feed on others and use organic sources of carbon.

Energy source:

Phototrophs use light as an energy source.

Chemotrophs use redox reactions of organic or inorganic compounds as an energy source.

Photoautotrophs obtain energy by photophosphorylation and fix carbon from CO₂ via the Calvin-Benson cycle to synthesize organic compounds.

Cyanobacteria are oxygenic phototrophs (noncyclic).  Green sulfur bacteria and purple sulfur bacteria are anoxygenic phototrophs (cyclic).

Photoheterotrophs use light as an energy source and an organic compound for their carbon source or electron donor – can’t fix CO₂.

Chemoautotrophs use inorganic compounds as their energy source and carbon dioxide as their carbon source.

Chemoheterotrophs use complex organic molecules as their carbon and energy sources.