Questions on Carbon Cycle
Multiple-Choice Questions: Carbon Cycle
1. What is the carbon cycle?
A) The flow of oxygen in ecosystems
B) The process of nitrogen fixation
C) The movement of carbon through Earth's systems
D) The melting and freezing of carbon compounds
E) The recycling of water vapor
2. Which process removes carbon dioxide from the atmosphere?
A) Respiration
B) Decomposition
C) Combustion
D) Photosynthesis
E) Erosion
3. Which of the following adds carbon dioxide to the atmosphere?
A) Photosynthesis
B) Combustion of fossil fuels
C) Ocean absorption
D) Cloud formation
E) Transpiration
4. Plants play a vital role in the carbon cycle by:
A) Producing fossil fuels
B) Storing heat energy
C) Releasing carbon into oceans
D) Absorbing CO₂ during photosynthesis
E) Increasing soil erosion
5. Which of the following is a carbon sink?
A) Volcanoes
B) Coal-burning plants
C) The atmosphere
D) Forests and oceans
E) Concrete buildings
6. Which organisms release carbon dioxide through respiration?
A) Only animals
B) Only humans
C) Only plants
D) Only bacteria
E) All living organisms
7. What is a major human activity that impacts the carbon cycle?
A) Planting trees
B) Burning fossil fuels
C) Drinking water
D) Using solar panels
E) Harvesting crops
8. Which carbon compound is primarily released during combustion?
A) Carbon monoxide
B) Carbon dioxide
C) Glucose
D) Methane
E) Carbonic acid
9. What happens to carbon in dead organisms over time?
A) It disappears
B) It is absorbed by sunlight
C) It becomes fossil fuels
D) It is converted into oxygen
E) It evaporates
10. Oceans absorb CO₂ through:
A) Photosynthesis in clouds
B) Direct diffusion from the atmosphere
C) Transpiration
D) Volcanic eruptions
E) Evaporation
11. What role do decomposers play in the carbon cycle?
A) They photosynthesize
B) They prevent carbon flow
C) They release stored carbon from dead matter
D) They remove carbon from the atmosphere
E) They store carbon in the soil forever
12. What is carbon sequestration?
A) Releasing carbon into the atmosphere
B) Burning fossil fuels
C) The long-term storage of carbon
D) Transferring carbon into animals
E) The process of deforestation
13. How does deforestation affect the carbon cycle?
A) It increases oxygen production
B) It reduces carbon emissions
C) It increases the carbon stored in plants
D) It reduces carbon absorption and increases CO₂ in the air
E) It creates fossil fuels
14. Fossil fuels are formed from:
A) Modern plants
B) Living animals
C) Ancient remains of plants and animals
D) Ocean salt
E) Sunlight and water
15. Which human action would most help to balance the carbon cycle?
A) Burning more oil
B) Increasing meat production
C) Planting trees
D) Expanding highways
E) Using coal
16. What form of carbon do animals obtain from plants?
A) Carbon dioxide
B) Glucose and other organic molecules
C) Fossil fuels
D) Methane
E) Charcoal
17. Carbon is transferred to the atmosphere during:
A) Photosynthesis
B) Carbon fixation
C) Respiration and combustion
D) Ocean absorption
E) Freezing
18. Which of these is not a way carbon is cycled?
A) Respiration
B) Photosynthesis
C) Erosion
D) Combustion
E) Decomposition
19. Carbon compounds in animals return to the soil when:
A) They breathe
B) They reproduce
C) They die and decompose
D) They migrate
E) They photosynthesize
20. An increase in atmospheric CO₂ levels is most directly linked to:
A) Photosynthesis
B) Water pollution
C) Burning fossil fuels
D) Ocean currents
E) Soil erosion
Answer Key with Explanations
1. C – The movement of carbon through Earth's systems
The carbon cycle describes how carbon moves through the atmosphere, biosphere, hydrosphere, and geosphere.
2. D – Photosynthesis
Plants absorb CO₂ from the atmosphere and convert it into glucose during photosynthesis.
3. B – Combustion of fossil fuels
Burning fossil fuels releases carbon dioxide, increasing atmospheric CO₂.
4. D – Absorbing CO₂ during photosynthesis
Plants use CO₂ in photosynthesis to make energy-storing molecules.
5. D – Forests and oceans
These act as carbon sinks by absorbing and storing large amounts of CO₂.
6. E – All living organisms
All organisms, including plants, animals, fungi, and microbes, respire and release CO₂.
7. B – Burning fossil fuels
This releases carbon that was previously stored underground into the atmosphere.
8. B – Carbon dioxide
CO₂ is the primary gas released when fossil fuels are combusted.
9. C – It becomes fossil fuels
Over millions of years, buried dead matter under heat and pressure forms fossil fuels.
10. B – Direct diffusion from the atmosphere
CO₂ gas naturally dissolves into ocean water from the air.
11. C – They release stored carbon from dead matter
Decomposers break down organic material, releasing carbon back into the atmosphere or soil.
12. C – The long-term storage of carbon
Carbon sequestration stores carbon underground or in vegetation, reducing atmospheric CO₂.
13. D – It reduces carbon absorption and increases CO₂ in the air
Fewer trees mean less CO₂ absorption, leading to higher atmospheric carbon.
14. C – Ancient remains of plants and animals
Fossil fuels are the carbon-rich remains of ancient organisms.
15. C – Planting trees
Trees absorb CO₂ and store it, helping regulate the carbon cycle.
16. B – Glucose and other organic molecules
Animals get carbon by consuming plants (or other animals) in the form of organic compounds.
17. C – Respiration and combustion
Both release CO₂ into the atmosphere.
18. C – Erosion
Erosion is not a major mechanism in the carbon cycle, though it may transport material containing carbon.
19. C – They die and decompose
When organisms die, decomposers return their carbon to the soil and atmosphere.
20. C – Burning fossil fuels
This is the leading cause of rising CO₂ levels and global climate change.
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