Question 1
Which process removes carbon dioxide from the air?
- Respiration
- Combustion
- Photosynthesis
- Decomposition
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Answer: C (1)
Question 2
Describe how carbon in the bodies of dead plants returns to the air as carbon dioxide, and how carbon in dead organisms that are buried for millions of years may later return to the air.
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- decomposers / bacteria and fungi break down the dead plants (1)
- decomposers respire (1)
- releasing carbon dioxide (into the air) (1)
- buried organisms form fossil fuels / coal, oil, gas (1)
- burning / combustion of the fossil fuel releases carbon dioxide (1)
- Max 4
Question 3
A student states that the amount of carbon dioxide in the air stays roughly constant in a natural ecosystem. (a) Name the process that removes carbon dioxide from the air. [1] (b) Name two processes that add carbon dioxide to the air. [2]
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- (a) photosynthesis (1)
- (b) any two from: respiration; combustion / burning; decomposition / decay (2)
- ignore breathing
Question 4
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanWhich process changes nitrate ions in the soil into nitrogen gas?
- Nitrification
- Denitrification
- Nitrogen fixation
- Deamination
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Answer: B (1)
Question 5
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanDescribe the roles of microorganisms in the nitrogen cycle by stating what each of the following does. (a) decomposers [1] (b) nitrifying bacteria [1] (c) nitrogen-fixing bacteria [1] (d) denitrifying bacteria [1]
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- (a) break down proteins in dead material / waste to ammonium ions (1) allow ammonia
- (b) change ammonium ions into nitrate ions (1) allow via nitrite ions
- (c) change nitrogen gas into nitrogen compounds (1) allow ammonium ions / nitrates
- (d) change nitrate ions into nitrogen gas (1)
Question 6
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanExplain how nitrogen in the air becomes part of the protein in a cow that eats grass.
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- nitrogen fixation / nitrogen gas is changed into nitrogen compounds (1)
- by lightning or by nitrogen-fixing bacteria (1)
- nitrifying bacteria change ammonium ions to nitrate ions (1)
- grass absorbs nitrate ions through its roots (1)
- grass makes amino acids and then proteins (1)
- cow eats / feeds on the grass (1)
- cow digests the protein to amino acids and uses them to make its own protein (1)
- Max 5