According to the different energy needed in the process of assimilating carbon dioxide, it can be divided into light energy autotrophic type and chemical energy autotrophic type. Photoautotrophic biological cells contain photosynthetic pigments, which can convert solar energy into chemical energy and supply life activities. In addition to green plants, a few bacteria (such as red sulfur bacteria and green sulfur bacteria) and cyanobacteria (such as ANABAENA and Tremella) are also photoautotrophic. Chemotactic autotrophs gain energy by oxidizing some inorganic substances, such as nitrifying bacteria ammonia oxide (NH3), sulfiding bacteria sulfur oxide (S) or hydrogen sulfide (H2S). Autotrophic organisms play an important role in carbon cycle, nitrogen cycle and sulfur cycle in nature.