In ecology, an organism that is unable to synthesize organic compounds from inorganic substances for food and so must consume other organisms or their organic products for survival: Such life forms, like any animal or fungus, or almost any bacterium are considered to be heterotrophs.

An organism, such as an animal, some bacteria, and certain plants, that depend, either directly or indirectly, on other organisms for food because of their inability to manufacture proteins and carbohydrates from inorganic sources: Heterotrophs, such as animals, fungi, as well as most bacteria and protozoa, all depend on autotrophs for energy and for the raw materials to make complex organic molecules.

Heterotrophs obtain energy by breaking down organic molecules obtained in their food."