An organism that derives its carbon for building body tissues from carbon dioxide (CO₂₎ or carbonates and obtains its energy for bodily functions from radiant sources, such as sunlight, or from the oxidation of certain inorganic substances. The leaves of green plants and the bacteria that oxidize sulfur, iron, ammonium, and nitrite are examples of autotrophs. The oxidation of ammonium to nitrite, and of nitrite to nitrate, a process called nitrification, is a critical part of the nitrogen cycle. Moreover, the creation of food by photosynthetic organisms is largely an autotrophic process.