The Carbon Cycle
Introduced| English | Meaning |
|---|---|
| fossil fuels/ˈfɒsl ˈfjuːəlz/ | Coal, oil and natural gas formed from ancient organic matter over millions of years. |
| photosynthesis/ˌfəʊtəʊˈsɪnθəsɪs/ | The process by which plants and other organisms use light energy to make organic substances from carbon dioxide and water. |
| respiration/ˌrespɪˈreɪʃn/ | The chemical reactions in cells that release usable energy from nutrient molecules. |
| combustion/kəmˈbʌstʃn/ | An exothermic reaction of a fuel with an oxidising agent, usually oxygen. |
Carbon on the move
- Every living thing is built from carbon.
- That carbon is not made or destroyed — it is used over and over.
- It moves between the air, living things, oceans, and rocks.
- This endless journey is the carbon cycle.
Plants pull carbon in
- Carbon sits in the air as carbon dioxide gas.
- Through photosynthesis 光合作用, plants take in CO2.
- They lock the carbon into sugars and their own bodies.
- This removes carbon dioxide from the atmosphere.
Which process removes carbon dioxide from the air?
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Photosynthesis takes CO2 out of the air and stores the carbon in plants.
Life sends carbon back
- Animals eat plants, passing the carbon along the food chain.
- Through respiration 呼吸作用, living things release CO2 back into the air.
- When things die, decomposers break them down, releasing more.
- So carbon flows out of living things as well as in.
The carbon cycle
Step around the cycle - carbon moves between the air, living things, and fossil fuels.
Which process returns carbon dioxide to the air?
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Respiration (and combustion) release CO2 back into the atmosphere.
Carbon locked away for millions of years in coal, oil, and gas is stored as ____ fuels.
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Coal, oil and gas are fossil fuels — ancient carbon that combustion releases as CO2.
Burning releases stored carbon
- Some carbon gets buried and, over millions of years, becomes fossil fuels 化石燃料.
- Combustion 燃烧 — burning wood or fossil fuels — releases that carbon as CO2.
- Nature's burning was slow and balanced.
- Humans now burn fossil fuels fast, adding extra CO2 to the air.
Burning fossil fuels removes carbon dioxide from the atmosphere.
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False. Combustion releases carbon that was stored underground for millions of years, adding extra CO₂ to the atmosphere.
Select all true statements about the carbon cycle.
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Carbon constantly cycles between the air and living things. The other three are correct.
The natural carbon cycle is roughly balanced — photosynthesis removes about as much CO2 as respiration adds. Burning fossil fuels breaks that balance by releasing carbon that was locked away for millions of years, raising atmospheric CO2 far faster than nature removes it.
Follow one carbon atom:
- It starts as CO2 in the air.
- A tree takes it in by photosynthesis and builds it into wood.
- Years later the wood is burned; combustion sends the carbon straight back to the air as CO2 — one loop of the cycle.
The carbon cycle moves carbon between the air, living things, and fossil fuels. Photosynthesis removes CO2 from the air; respiration and combustion return it. Carbon buried as fossil fuels is released when we burn them — adding extra CO2 and unbalancing the natural cycle.