2.2.22 (HL)—Photoautotrophs and chemoautotrophs

Both groups fix inorganic carbon, but photoautotrophs use light energy whereas chemoautotrophs obtain energy by oxidising chemicals.

The carbon source determines ‘auto’; the energy source determines ‘photo’ or ‘chemo’. This distinction predicts where an organism can live.

Algae at the surface use light; sulfur-oxidising bacteria near a dark vent can fix CO₂ using chemical energy.

Chemoautotroph: chemical energy plus inorganic carbon.

Dark does not automatically mean heterotrophic; inspect the carbon and energy sources separately.