Autotrophs use inorganic carbon sources such as carbon dioxide to synthesize their own organic matter. There are many examples of common carbon sources.

Autotrophs can use light or chemical energy to convert inorganic matter into organic matter. Most of their carbon sources are inorganic. Carbon dioxide is the most critical carbon source. Many photosynthetic autotrophs, such as green plants, algae, and some bacteria, absorb carbon dioxide from the air through photosynthesis. On chloroplasts or photosynthetic membranes, through a series of complex reactions, carbon dioxide and water synthesize carbohydrates and other organic matter, while storing energy.

There are also some chemoautotrophs, such as nitrifying bacteria, that live in soil and other environments. Nitrifying bacteria can use the chemical energy released during the oxidation of ammonia to nitrous acid and then to nitric acid to synthesize their own cellular matter using carbon dioxide as a carbon source. Such bacteria are of great significance to the soil nitrogen cycle.

Sulfur bacteria are also typical chemoautotrophs. They can oxidize sulfur-containing compounds such as hydrogen sulfide to obtain energy, and also use carbon dioxide as a carbon source to construct their own organic matter. These autotrophs play an important role in the material cycle and energy flow of ecosystems, and are the cornerstone of ecosystems, providing material and energy basis for heterotrophic organisms.