An autotroph is an organism that synthesizes organic compounds from inorganic precursors and so sustains its own growth without consuming other organisms. The word derives from Greek roots often cited in biology; see the etymology in context: autos (self) + trophe (nutrition). Autotrophs are the foundation of most ecosystems because they convert simple raw materials into the complex molecules that heterotrophs rely on.

Characteristics and major types

Autotrophs are defined by two main capacities: a source of carbon and a source of energy. Based on energy source they are commonly grouped as:

  • Photoautotrophs: use light energy to drive synthesis (photosynthesis). Typical examples include plants, algae, and cyanobacteria.
  • Chemoautotrophs: obtain energy from inorganic chemical reactions (chemosynthesis), common among certain bacteria and archaea in soils, sediments, and extreme environments such as hydrothermal vents.

Both groups use small inorganic molecules—such as carbon dioxide, water, or reduced inorganic compounds—as their basic building blocks; see a concise concept link: simple molecules. They assemble these into carbohydrates, lipids, proteins and other organic compounds (organic compounds).

Ecological role and importance

Autotrophs function as primary producers: they fix carbon into biomass and form the base of food chains, supplying energy and organic matter to consumers. Oxygenic photoautotrophs changed Earth's atmosphere by producing free oxygen through photosynthesis, enabling aerobic life. Autotrophic activity also drives global cycles of carbon, nitrogen and other elements.

Not all organisms that make organic material are strict autotrophs; some are mixotrophs, combining autotrophy and heterotrophy. To understand how a living thing is classified, look to whether it primarily sources carbon from inorganic CO2 or from preformed organic matter; see a general reference: organism categories.

Autotrophs are important beyond ecology: they are used in agriculture, aquaculture, biotechnology and research into renewable energy (for example, biofuel production and engineered photosynthetic systems). They also thrive in environments inaccessible to heterotrophs—such as deep-sea vents—where chemoautotrophic communities form unique ecosystems.