The Carbon Cycle Review
Carbon in the key element for living things. There is inorganic carbon (CO2) found in the atmosphere and
dissolved in oceans. This carbon is recycled into more complex organic substances. This is done through
photosynthesis! Organic carbon can also be recycled back to inorganic carbon by respiration. Organic
carbon is also held in reservoirs – the bodies of living things. However, all living things die, and
decomposition eventually returns the carbon to the cycle in inorganic form.
Photosynthesis
6CO2
+
Carbon dioxide
6H2O +
light 
C6H12O6
water
energy
sugar (glucose)
6H2O
+
+
6O2
oxygen
Respiration
C6H12O6
+
Glucose
6O2

oxygen
water
6CO2
carbon dioxide
Combustion
CH4
+
Fuel (methane)
2O2
oxygen

CO2
+
carbon dioxide
2H2O
+
energy
water
Check for Understanding:
1.
Explain why photosynthesis and cellular respiration are considered to be complementary processes of the
carbon cycle. (2 marks)
2. Explain the importance of decomposers in the carbon cycle. (2 marks)
3. Explain how the burning of fossil fuels by humans affects the carbon cycle. (2 marks)
4. Carbon cycles more quickly through some ecosystem than others. Explain why carbon is cycled more slowly in
northern ecosystems than in the tropics. (2 marks)