1 Organisms that can grow with carbon dioxide as the main carbon source in nature-autotrophs, including most plants and a few bacteria (such as purple sulfur bacteria and nitrifying bacteria). These microorganisms all use carbon dioxide as the main carbon source and inorganic nitride as the nitrogen source. Carbon dioxide is mainly fixed by calvin cycle (i.e. photosynthetic carbon cycle) and is converted into carbohydrates through a series of complicated processes under the condition of energy demand. The energy required for growth varies according to microbial groups, and is obtained by photosynthesis or chemical synthesis.

The concept of heterotrophy: You can only take in organic matter from the outside to synthesize your own organic matter. Such as: people, animals, most fungi and most bacteria.

Judging from the metabolic types, not all animals are heterotrophs. For example, the protozoan euglena is a unicellular organism with no cell wall and only chloroplasts. Under the condition of no light, it can absorb the organic matter in the environment to maintain its life activities. Under the condition of light, it can make sugar and other organic matter and its own nutrition through the photosynthesis of chloroplasts.

As mentioned above, most bacteria are heterotrophs and a few are autotrophs.