1. Obtaining nourishment from exogenous organic material; a reference to organisms unable to synthesize organic compounds from inorganic substrates.
2. A reference to plants occurring in a wide range of habitats on a wide variety of soil types, and of protistans (algae, fungi, and protozoans) utilizing a wide variety of food materials: "There are some organisms that require organic compounds as a source of carbon, but which are able to use light or inorganic compounds as sources of energy; and so, such organisms are not defined as autotrophic, but rather as heterotrophic."
3. The ability or requirement to synthesize all metabolites from organic compounds.