Depending on which classification system is being used, biologists divide life up into either five or six kingdoms. In the five kingdom system, prokaryotes count as one kingdom. In the six kingdom system, they are divided into bacteria and archaea. The other kingdoms are animals, plants, fungi and protists. Of these, only animals and fungi are universally heterotrophic, meaning they obtain their carbon from organic sources. Plants are always autotrophic, meaning they obtain their own carbon from the atmosphere. The other kingdoms are divided: some species are autotrophs, some are heterotrophs.
Definition of Heterotroph
The word heterotroph comes from the Greek "heteros," which means "other" or "different," and "trophe," which means "nutrition." Heterotrophs get their food from organic sources in their environment. This means eating or absorbing sources of organic carbon. All animals and fungi are heterotrophs.
Definition of Autotroph
An autotroph is an organism that creates its own food by fixing carbon. In other words, autotrophs get their carbon directly from carbon dioxide, which they use to create organic carbon compounds for use in their own cells. All plants are autotrophs. Some bacteria, some archaea and some protists are autotrophs.
Types of Heterotrophs
Heterotrophs are divided into two basic categories: photoheterotrophs and chemoheterotrophs. Photoheterotrophs still get their carbon from organic sources, but they get energy from sunlight. They include certain types of green bacteria and purple bacteria. Chemoheterotrophs, also called organotrophs, get both their energy and their carbon from organic sources. Animals and fungi fall into this category.
Types of Autotrophs
Likewise, autotrophs are split into photoautotrophs and chemoautotrophs. The former, including plants and algae, perform photosynthesis using the energy from light to fix carbon. Chemoautotrophs, which are mostly bacteria and archaea living in extreme environments such as near volcanic vents on the ocean floor, get the energy to fix carbon from inorganic sources like hydrogen sulfide or ammonia.