AQA Biology (8464) 4.7.2.2 · Process
The carbon cycle
The carbon in your body was once carbon dioxide in the air, and one day it will be again. What carries it all the way round?
Combined Science · Higher tier
Start here
A fallen leaf rots away. Its carbon does not.
A leaf that drops in autumn has mostly vanished a year later. Yet the amount of carbon on Earth never changes: carbon atoms are not made or destroyed, only moved.
If you had to guess, did most of the leaf’s carbon go up into the air, or down into the soil?
Because the total amount of carbon is fixed, it has to be recycled. It sits in stores: the air, as carbon dioxide; living things, in carbohydrates, proteins, fats and DNA; dead matter and waste; and fossil fuels deep underground. Processes move it from store to store. Here, follow one atom and call each process before it happens.
Follow one carbon atom · journey 1
In the air
Step 1 of 6
The atom is in a carbon dioxide molecule, drifting past a leaf in sunlight.
Which process can take it into a living thing?
Think again · plants and carbon dioxide
“Plants take carbon dioxide in. They don't give it out.”
Your call
PredictA bean plant is sealed in a jar and left in the dark overnight. What happens to the carbon dioxide in the jar?
Your turn · name the processes
Name the process at every arrow.
0 of 9 named
For thousands of years before people burned fossil fuels on a large scale, carbon dioxide was taken out of the air about as fast as it was put back. Humans are now adding it faster than natural processes can remove it. Burning coal, oil and gas releases carbon that was locked away for millions of years. Deforestation does double damage: fewer trees are left to photosynthesise, and the felled trees are burned or rot, releasing more carbon dioxide. Cattle and rice fields add methane. Rising levels of carbon dioxide and methane contribute to global warming.
Sort the processes
What does it do to the air?
Each card is one process. Decide what it does to the carbon dioxide in the air.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Command words in this lesson
- Name
- The process at an arrow, in a word or two: photosynthesis, respiration, combustion.
- Describe
- Say what happens to the carbon, store by store, in order.
- Explain
- Give the how: decomposers respire, so carbon dioxide is released.
Key fact
Photosynthesis takes carbon dioxide out of the air. Feeding passes carbon along food chains. Respiration by every organism, including decomposers, and combustion return it to the air.
Key note · AQA 4.7.2.2 (8464)
The carbon cycle
- Photosynthesis takes carbon dioxide out of the air.
- Feeding passes carbon compounds along food chains.
- Respiration by plants, animals and decomposers returns carbon dioxide.
- Combustion of fossil fuels returns carbon locked away for millions of years.
- Deforestation and burning add carbon dioxide faster than it is removed.
Photograph this card. Tomorrow, cover it and say each line first.
Previous and next
Connects to
Ask MrBadmus
Not sure which process sits on which arrow?
The cycle shows the stores and processes AQA examines in biology. It leaves out oceans, rocks and volcanoes, which also store and release carbon and are taught in chemistry. Arrows show where carbon goes, not how much moves or how fast.