A heterotroph is an organism that cannot produce its own food and instead obtains nutrition from other sources of organic carbon, mainly plant or animal matter. Heterotrophs are primary, secondary, and tertiary consumers in the food chain. They are also known as consumers, and they include all animals, fungi, and many protists and bacteria/02%3A_Cell_Biology/2.18%3A__Autotrophs_and_Heterotrophs). Heterotrophs can be subdivided according to their energy source. If they use chemical energy, they are chemoheterotrophs (e.g., humans and mushrooms), and if they use light for energy, they are photoheterotrophs (e.g., green non-sulfur bacteria) . Heterotrophs represent one of the two mechanisms of nutrition (trophic levels), the other being autotrophs. Autotrophs use energy from sunlight (photoautotrophs) or oxidation of inorganic compounds (lithoautotrophs) to convert inorganic carbon dioxide to organic carbon compounds and energy to sustain their life/02%3A_Cell_Biology/2.18%3A__Autotrophs_and_Heterotrophs).

Heterotrophs can be classified in different ways, such as by assigning them as chemotrophs or phototrophs. They can also be organotrophs or lithotrophs. Organotrophs exploit reduced carbon compounds as electron sources, like carbohydrates, fats, and proteins from plants and animals. On the other hand, lithoheterotrophs use inorganic compounds, such as ammonium, nitrite, or sulfur, to obtain electrons.

Examples of heterotrophs include herbivores, which eat plants to obtain their nutrition, and carnivores, which eat other animals. Chameleons are also an example of a heterotroph, as they consume other animals or plants to sustain themselves.