An autotroph is an organism that produces its own organic compounds from inorganic substances (e.g., minerals) using either light or chemical bonds as a source of energy. Plants and other organisms using photosynthesis are photoautotrophs; bacteria that utilize inorganic compounds such as hydrogen sulfide or ferric iron for energy are chemoautotrophs.

Autotrophs are a vital part of the food chain. They take energy from the sun or from inorganic sources and convert it into a form (organic molecules) that they use to carry out biological functions including cell growth; and that other organisms (called heterotrophs) can utilize as food. Thus, heterotrophs — animals, fungi, as well as most bacteria and protozoa — depend on autotrophs for energy and for the raw materials to make complex organic molecules. The heterotrophs obtain energy by breaking down organic molecules in their food. Even carnivorous animals rely on autotrophs because the energy and organic building blocks obtained from their prey comes ultimately from the autotrophs eaten by the prey.

See also: Primary nutritional groups