autotrophs

Autotrophs are organisms that synthesize complex organic compounds from simple inorganic substances, using energy from light or chemical reactions. They form the base of most ecosystems by producing biomass that heterotrophs rely on for food.

There are two major kinds: photoautotrophs, which use light energy to drive photosynthesis, and chemoautotrophs, which obtain energy from chemical reactions, often involving oxidation of inorganic molecules. Photoautotrophs include plants, algae, and cyanobacteria; their chloroplasts contain pigments such as chlorophyll that capture light and fix carbon via the Calvin cycle. Chemoautotrophs include certain bacteria and archaea that live in diverse environments, such as hydrothermal vents or acidic springs; they oxidize inorganic substrates like hydrogen sulfide, ammonia, or iron to power carbon fixation via pathways like the reverse TCA cycle or the Calvin cycle.

Autotrophy enables carbon fixation, converting inorganic CO2 into organic matter. In most habitats, photoautotrophs dominate primary production in light-rich environments, while chemoautotrophs are important in dark or extreme environments where light is unavailable.

Autotrophs are contrasted with heterotrophs, which obtain fixed organic carbon by consuming or metabolizing organic matter from autotrophs or other organisms. The ecological role of autotrophs is to support food webs and influence global carbon cycles through photosynthetic and chemosynthetic processes.