Carbon Cycle
The carbon cycle describes the movement of carbon around the environment.
Essentially carbon is in one of three forms:
organic carbon - i.e. as part of a biomolecule (carbohydrate, protein etc)
inorganic carbon - as carbonates e.g. in limestone
carbon dioxide gas - the product of respiration or combustion. Both of these processes use organic carbon as a fuel
image from http://www.geog.ouc.bc.ca/physgeog/contents/9r.html
image from http://www.chadevans.co.uk/asite/Alevel/u03/ln/cycles.html
The carbon in atmospheric carbon dioxide gas is made available by photosynthesis
Photosynthesis incorporates carbon into organic molecules which move around the ecosystem by consumption
Some of this carbon will be returned to the atmosphere as carbon dioxide by respiration
The carbon that remains in organisms when they die will be:
consumed by, and assimilated into, other living things
given off as CO2 in combustion
laid down in the soil to be turned, eventually, into
fossil fuels (which may then be combusted)
limestone rocks (carboniferous rocks)
inorganic solutions (including soluble carbonates [CO3-])
These three fates represent reservoirs of carbon which may be released at a later stage. They are therefore called carbon sinks
The role of microorganisms in the carbon cycle
Microorganisms act as decomposers breaking down dead organisms by secreting digestive enzymes on to organic material. They thus play a crucial role in recycling assimilated carbon back into the system both by incorporating the carbon into their own structures and because some of the freed carbon "leaks" into the soil