Question 1 Medium
What substance is formed from decayed plant matter and used as a natural fertiliser?
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Answer: compost
- Gardeners make it in heaps.
- It is compost.
Decay, the carbon cycle and the water cycle: GCSE Combined Science Biology practice questions
A second set of questions on decay, the carbon cycle and the water cycle. They are different from the ones on the topic page. Try each, then open the answer and compare your working.
More questions
Question 2 Medium
Name the gas that aerobic decay needs in order to happen quickly.
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Answer: oxygen
- Aerobic means using oxygen.
- So decay needs oxygen.
Question 3 Medium
Name the chemicals that decomposers release onto dead material to digest it.
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Answer: enzymes
- The decomposers digest food outside their cells.
- They release enzymes.
Question 4 Hard
Why does decay slow down in very hot conditions? Give one word for what happens to the enzymes.
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Answer: denatured
- High temperature damages enzymes.
- They are denatured.
Question 5 Hard
Which process in decomposers releases carbon dioxide back to the air?
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Answer: respiration
- They release energy from their food.
- It is respiration.
Question 6 Hard
Which process in plants returns water vapour to the air?
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Answer: transpiration
- It happens through stomata.
- It is transpiration.
Question 7 Hard
Decay is faster when there is plenty of oxygen. What type of respiration do decomposers then use to release more energy?
Show answer
Answer: aerobic
- With plenty of oxygen, decomposers respire using oxygen.
- That is aerobic respiration.
Quick checks
Short questions with options. Choose one before you open the answer.
Check 1
What are decomposers?
Show answer
Bacteria and fungi that break down dead material.
Check 2
What do decomposers return to the soil?
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Mineral ions that plants can take up.
Check 3
What conditions speed up decay?
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Warmth, moisture and oxygen.
Check 4
Why does decay slow in the cold?
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Enzymes work more slowly.
Check 5
What is evaporation?
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A liquid changing to a gas, driven by the Sun.
Check 6
What is condensation?
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Water vapour cooling to make liquid droplets.
Check 7
What is precipitation?
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Water falling as rain, snow or hail.
Check 8
What is transpiration?
Show answer
Loss of water vapour from plant leaves.
Check 9
Which process removes carbon dioxide from the air?
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Photosynthesis.
Check 10
Name two processes that return carbon dioxide to the air.
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Respiration and combustion.
Check 11
How do animals get carbon?
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By eating plants and other animals.
Check 12
How are fossil fuels formed?
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From the remains of dead organisms over millions of years.
Check 13
What is compost?
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Decayed plant material used as a natural fertiliser.
Check 14
Why is decay important?
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It recycles nutrients so plants can grow.
Check 15
What is a decomposer?
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A living thing, such as a bacterium or fungus, that feeds on dead material.
Check 16
How do decomposers digest dead material?
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They release enzymes onto it, then absorb the nutrients.
Check 17
Why does decay slow in very hot conditions?
Show answer
The enzymes are damaged.
Check 18
What does the carbon dioxide in the air act as?
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The main store of carbon for living things.
Check 19
Where does the energy for the water cycle come from?
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The Sun.
Check 20
What do decomposers do to release carbon dioxide?
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They respire.
Check 21
What is combustion?
Show answer
Burning, which releases carbon dioxide.
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