Question 1Multiple choice · 1 markA* challenge
Which processes release carbon dioxide into the atmosphere?
1 combustion of fossil fuels
2 photosynthesis
3 respiration
- A 1, 2 and 3
- B 1 and 3 only
- C 1 only
- D 3 only
Show answer
Answer: B
Free Nutrient cycles questions for IGCSE Biology (0610), part of Ecology & human influence. Each question has the answer and the marking points an examiner would look for.
Generate a full Nutrient Cycles worksheet →All Ecology & human influence questionsWhich processes release carbon dioxide into the atmosphere?
1 combustion of fossil fuels
2 photosynthesis
3 respiration
Answer: B
Which term is described by this statement?
“Organisms that break down dead organic matter and release nutrients.”
Answer: D
Nitrogen is cycled by microorganisms.
Describe the roles of decomposers and nitrifying bacteria.
Explain why waterlogged soils are low in nitrates.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | proteins → ammonium; ammonium → nitrate decomposers break down proteins/urea into ammonium ions B1 nitrifying bacteria convert ammonium to nitrite B1 then to nitrate B1 | 3 |
| (b) | anaerobic: denitrifying bacteria lack of oxygen B1 denitrifying bacteria convert nitrates to nitrogen gas B1 | 2 |
This question is about nutrient cycles.
Name the process that removes carbon dioxide from the air and the processes that return it.
Explain the role of decomposers in the carbon cycle.
Explain why waterlogged soils lead to a build-up of dead plant material.
Describe the roles of nitrogen-fixing, nitrifying and denitrifying bacteria in the nitrogen cycle.
Explain why plants need nitrate ions.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | photosynthesis; respiration; combustion; decomposition photosynthesis removes CO₂ B1 respiration and decomposition return it B1 combustion of fossil fuels returns it B1 | 3 |
| (b) | break down dead organic matter; respire, releasing CO₂ decomposers (bacteria and fungi) break down dead organisms and waste B1 they respire, releasing carbon dioxide B1 | 2 |
| (c) | lack of oxygen; decomposers cannot respire aerobically waterlogged soil lacks oxygen B1 so decomposers cannot respire aerobically and decomposition is slow B1 | 2 |
| (d) | fixing: N₂ to nitrogen compounds (ammonium); nitrifying: ammonium to nitrates; denitrifying: nitrates to N₂ nitrogen-fixing bacteria convert nitrogen gas into ammonium compounds (in root nodules) B1 nitrifying bacteria convert ammonium ions to nitrates B1 denitrifying bacteria convert nitrates back into nitrogen gas B1 | 3 |
| (e) | to make amino acids / proteins to make amino acids (proteins) B1 | 1 |
Water is recycled in the water cycle.
Describe the processes that return water to the atmosphere.
Describe how water vapour becomes rain.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | evaporation; transpiration evaporation (from sea/land) B1 transpiration from plants B1 | 2 |
| (b) | condenses into clouds, precipitation water vapour cools and condenses to form clouds B1 precipitation as rain B1 | 2 |
Carbon is recycled in the environment.
Describe how carbon is removed from the atmosphere.
Describe three ways carbon is returned to the atmosphere.
Explain how deforestation increases carbon dioxide in the atmosphere.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | photosynthesis photosynthesis B1 | 1 |
| (b) | respiration; combustion; decomposition respiration B1 combustion of fossil fuels/wood B1 decomposition by microorganisms B1 | 3 |
| (c) | less photosynthesis; burning/decay releases CO₂ fewer trees to absorb CO₂ by photosynthesis B1 burning or decay of trees releases CO₂ B1 | 2 |
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