Carbon cycle
The circulation of carbon through its various forms in the environment. Briefly, carbon dioxide in the atmosphere is fixed (i.e., converted into solid matter) by the process of photosynthesis in plants and green algae. These then die and rot under the influence of bacteria and fungi or are consumed by higher organisms in the form of food or fuel (burning plant matter or fossil fuels). Either way, carbon is released into the atmosphere as carbon dioxide and is available again for fixation (i.e., incorporation into biomass).