Carbon cycle · Year 12
In Year 12 you get fluent with: the carbon cycle; what adds and removes carbon dioxide in the air.
Carbon cycles between the air and living things. Photosynthesis takes carbon dioxide out of the air and plants use the carbon to make glucose. Animals get carbon by eating plants. Respiration by plants, animals and decomposers, and combustion of fuels, put carbon dioxide back into the air. Burning fossil fuels faster than they formed is raising the carbon dioxide in the air.
Key facts
- Photosynthesis takes carbon dioxide out of the air. Plants use the carbon to make glucose and other carbon compounds.
- Carbon passes to animals when they eat plants (feeding). Respiration by plants, animals and decomposers returns carbon dioxide to the air. Combustion of fossil fuels and wood releases carbon dioxide too.
- When plants and animals die, decomposers break them down. They respire, releasing carbon dioxide, and return mineral ions to the soil.
Worked examples
Example 1
Name the process shown by each arrow: carbon dioxide → plants; plants → animals; animals → carbon dioxide; fossil fuels → carbon dioxide.
Answer: photosynthesis; feeding; respiration; combustion
Example 2
What does photosynthesis do to the carbon dioxide in the air?
Answer: takes carbon dioxide out of the air
Example 3
What does burning wood do to the carbon dioxide in the air?
Answer: puts carbon dioxide back into the air
Example 4
Why are decomposers important in the carbon cycle?
Answer: they release carbon dioxide back into the air by respiration
Example 5
Give two processes that add carbon dioxide to the air and one that removes it. Why has the carbon dioxide in the air risen over the last 200 years?
Answer: added by respiration and combustion (and decay); removed by photosynthesis; it has risen because we burn more fossil fuels and cut down forests
Example 6
What does decay by microorganisms do to the carbon dioxide in the air?
Answer: puts carbon dioxide back into the air