heterotroph

Heterotrophs are organisms that cannot fix carbon dioxide to synthesize organic molecules and therefore must obtain carbon by consuming preformed organic compounds produced by other organisms. This contrasts with autotrophs, such as plants and many algae, which build organic matter from inorganic sources.

Heterotrophs derive energy by breaking down organic molecules. Most are chemoheterotrophs, obtaining both carbon and energy from organic compounds. Some can also use light to supplement energy intake as photoheterotrophs, but many organisms—animals, fungi, and most bacteria—rely on chemical energy alone. Heterotrophs include a diverse range of lifestyles, such as herbivores, carnivores, omnivores, and decomposers (saprotrophs) that digest dead organic matter.

Ecologically, heterotrophs depend on autotrophs or other heterotrophs for organic carbon and energy. They play key roles in nutrient cycling, energy transfer within food webs, and decomposition, helping to recycle carbon and other elements. Parasites—heterotrophs that obtain nutrients from living hosts—also contribute to ecosystem dynamics.

In microbiology and broader biology, the term heterotroph is often used alongside autotroph and is further subdivided by energy source into chemo-heterotrophs and photo-heterotrophs. This classification emphasizes the distinction between carbon source (organic versus inorganic) and energy source (chemical versus light) in microbial metabolism, and it applies broadly to many eukaryotic and prokaryotic organisms.