Microorganisms are decomposers of many organic compounds in nature. Without their function, various elements and substances in nature cannot be repeatedly recycled, ecological balance will be disrupted, the entire living world will be extinct, and humans will naturally be unable to survive.

Carbon is the most fundamental element that constitutes various living organisms, and the carbon cycle includes the fixation and regeneration of CO2. Plants, algae, and photosynthetic microorganisms fix CO2 in nature through photosynthesis, synthesize organic carbon compounds, and then convert them into various organic carbon compounds. Animals feed on plants and release CO2 through biological oxidation. After the corpses of animals and plants are completely degraded by microorganisms (i.e. mineralization), one of the main products is also CO2. Coal, oil, and other materials buried underground have been developed and utilized by humans, such as being used as fuel. After combustion, they also produce CO2 and are reintroduced into the carbon cycle. The CO2 produced through these biological and non biological processes is then utilized by plants and photosynthetic microorganisms, initiating a new carbon cycle.