Carbon cycle is a biogeochemical cycle which has its reservoir pool in the atmosphere. Carbon is present as a major constituent of the body in all living organisms. All biomolecules such as carbohydrates, proteins and lipids required for life processes are made up of carbon. It is a fundamental element found in all organisms. It is found in various forms such as carbonate, carbon dioxide etc. During the plants absorb CO2 from the atmosphere due to the process of phtosynthesis and releases CO2 during night. When the animals eat plants, the carbon present in the plants get transferred into their body. When the plants die, they get converted into the fossil like coal (which contain carbon), fossil fuels, inorganic carbonates (shells) etc. Combustion of fuels also releases carbon dioxide to the atmosphere. The carbon is released into the atmosphere also by the process of respiration and decomposition of the dead remains of the animals which is further used by the plants during the process of photosynthesis and the cycle continues.
It is important as it helps in the movement of carbon through all the spheres of Earth maintaining optimum concentrations in each sphere. It also regulates climatic conditions. A minor disturbance in the concentrations of carbon in these spheres may result in serious problems like global warming.