The Carbon Cycle

Science 20F
The Carbon Cycle
Carbon is the key element for living things.
Each year, about 50 to 70 billion tonnes of carbon from inorganic carbon dioxide are
recycled into more complex organic substances. This is done through
Photosynthesis Chemical Process
Carbon dioxide + water + light energy
CO2 + H2O + light
sugar + oxygen
C6H12O6 + O2
Balanced Photosynthesis Equation:
Some of the organic carbon is released back to the environment through cellular
respiration as carbon dioxide. (opposite to photosynthesis)
Cellular Respiration Chemical Process
Glucose + oxygen
water + carbon dioxide
C6H12O6 + O2
H2O + CO2
Balanced Cellular Respiration Equation:
Carbon cycle:
The matter cycle in which, through the processes of photosynthesis, digestion,
cellular respiration, decomposition, and combustion, carbon atoms move from an
inorganic form in the air, water, or soil, to an organic form in living things, and then
back to an inorganic form; all organic compounds contain carbon.
Carbon Cycle Delay
Under certain conditions the decay process is delayed and the organic mater may be
converted into rock or fossil fuels such as coal, petroleum, and natural gas.
Carbon can be found in three main reservoirs (storage areas):
Atmosphere – smallest reservoir of carbon dioxide.
Oceans – Tremendous amount of inorganic carbon is held as dissolved carbon dioxide
in the oceans, where it is available to algae and other water plants for
Earth’s Crust – limestone (Calcium Carbonate; CaCO3) is made from the discarded
shells and bones of living things discarded in the oceans. This sedimentary rock
comprises the largest reservoir of inorganic carbon. Bogs and areas of ocean floors
contain organic carbon stored as a result of decaying aquatic animals and plants
trapped by sediment.
Carbon Dioxide increases due to Human Influence
Humans have released carbon from organic reservoirs faster than would normally
occur, by mining and burning fossil fuels trapped in Earth’s crust, and by burning
By clearing away vegetation for farming, the lack of vegetation reduces the amount
of carbon dioxide removed from the atmosphere. As a result, the amount of carbon
dioxide in the atmosphere is rising.
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