heterotroph

thumb|300px|Cycle between autotrophs and heterotrophs. Autotrophs use light, [[carbon dioxide (CO2), and water to form oxygen and complex organic compounds, mainly through the process of photosynthesis (green arrow). Both types of organisms use such compounds via cellular respiration to generate ATP and again form CO2 and water (two red arrows).]]

A heterotroph (; from Ancient Greek ἕτερος (héteros), meaning "other", and τροφή (trophḗ), meaning "nourishment") is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly matter from other organisms. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but not producers. Living organisms that are heterotrophic include most animals, all fungi, some bacteria and protists, and many parasitic plants. The term heterotroph arose in microbiology in 1946 as part of a classification of microorganisms based on their type of nutrition. The term is now used in many fields, such as ecology, in describing the food chain. Heterotrophs occupy the second and third trophic levels of the food chain while autotrophs occupy the first trophic level.