The Carbon Cycle — AQA GCSE Biology
The carbon cycle recycles carbon between the atmosphere, living organisms and the environment.
Why recycle carbon?
Materials in the living world are recycled to provide the building blocks for future organisms. Carbon is constantly cycled between the air, living things and the ground.
Removing carbon dioxide from the air
- Photosynthesis in plants and algae removes CO₂ from the atmosphere and converts the carbon into glucose and other compounds.
Returning carbon dioxide to the air
- Respiration by plants, animals and microorganisms releases CO₂.
- Combustion (burning) of wood and fossil fuels releases CO₂.
- Decomposition — when decomposers (microorganisms) break down dead organisms and waste, they respire and release CO₂.
Carbon passing through food chains
When animals eat plants (or other animals), carbon compounds pass along the food chain. When organisms die, decomposers return the carbon to the air (or it may be stored in fossil fuels over millions of years).
Exam tips
- Photosynthesis removes CO₂; respiration, combustion and decomposition return it.
- Carbon passes along food chains by feeding.
- Decomposers (microorganisms) are essential for recycling carbon.
- Be able to describe the cycle as a sequence of these processes.