(b) CO2 in atmosphere → organic carbon in plants → organic carbon in animals → inorganic carbon in soil
Nutrient cycles circulate matter through the biosphere. The nutrients regularly alternate between living (biotic) and nonliving (abiotic) components. Hence the nutrient cycles are also called as biogeochemical cycles. The important nutrient cycles are water cycle, carbon cycle, nitrogen cycle, mineral cycle. In the carbon cycle, atmospheric carbon is fixed into organic compounds like carbohydrates by green plants during the process of photosynthesis. The organic compounds are consumed by heterotrophic organisms like animals.