Heterotroph

The term heterotroph refers to a living organism that must ingest biomass to obtain its energy and nutrition. In contrast, autotrophs can take in inorganic sources of energy and use these to make their food. Green plants are autotrophs; they use sunlight and simple inorganic molecules to photosynthesize organic matter. All heterotrophs require the biological products of autotrophs for their sustenance—they have no other source of nourishment.

All animals are heterotrophs, as are most microorganisms (the exceptions being algae and blue-green bacteria). Heterotrophs can be classified according to the sorts of biomass that they eat. Animals that eat living plants are known as herbivores, while those that eat other animals are known as carnivores. Many animals eat both plants and animals, and these are known as omnivores. Animal parasites are a special type of carnivore that are usually much smaller than their prey, and do not usually kill the animals that they feed upon.

Heterotrophic microorganisms mostly feed upon dead plants and animals, and are known as decomposers. Some animals also specialize on feeding on dead organic matter, and are known as scavengers or detritivores. Even a few vascular plants are heterotrophic, parasitizing the roots of other plants and thereby obtaining their own nourishment. These plants, which often lack chlorophyll, are known as saprophytes.

Humans are heterotrophs. This means that humans can only sustain themselves by eating plants, or by eating animals that have, themselves, grown by eating plants. While humans can manufacture some nutrients, the raw material for the manufacture cannot be made, but must be ingested.

Bill Freedman