Lesson 3.1.1.3

3.1.1.3 The carbon cycle Quiz: AQA Geography, Unit 1

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

In partnership with Revision Ninja

Lesson 3.1.1.3, The carbon cycle: 20 multiple choice questions for the AQA Geography (7037), Unit 1: Physical geography, written with Revision Ninja.

Host it live on the board and students join with a game code on their own devices, or revise alone with Free Play. The answers are revealed in the game.

Host this setFree Play

The 20 questions

  1. Which process removes carbon dioxide from the atmosphere and converts it into organic matter?

    • Decomposition, which releases carbon dioxide as microbes break down dead organic matter
    • Respiration, which releases carbon dioxide from living cells back into the atmosphere
    • Combustion, which releases carbon dioxide as fuels are burned in air at high temperature
    • Photosynthesis

  2. Which is the largest store of carbon on Earth by mass?

    • The surface ocean, which holds carbon dissolved in seawater as bicarbonate ions
    • The atmosphere, which holds carbon mostly as carbon dioxide gas and methane
    • The biosphere, which holds carbon in living vegetation, soils and animals
    • The lithosphere, mainly sedimentary rocks such as limestone

  3. Which process releases carbon dioxide as microorganisms break down dead organic matter?

    • Carbon sequestration, which removes carbon from the active cycle into long-term stores
    • Chemical weathering, which dissolves carbonate rock using carbonic acid from rainwater
    • Decomposition
    • Photosynthesis, which takes carbon dioxide from the air and locks it into plant tissue

  4. Which process stores carbon long term in ocean sediments?

    • Burial of dead organic matter and carbonate shells in deep sea-floor sediments
    • Evaporation of dissolved carbon dioxide from the sea surface into the atmosphere
    • Respiration by phytoplankton at the sea surface, which returns carbon to the water
    • Combustion of marine biomass by natural fires that spread across coastal waters

  5. Which equation summarises photosynthesis?

    • C6H12O6 + 6O2 -> 6CO2 + 6H2O, which describes the breakdown of glucose by respiration
    • 6CO2 + 6H2O -> C6H12O6 + 6O2
    • CO2 + H2O -> CH4 + O2, which describes the production of methane from carbon dioxide
    • 6CO2 + 6O2 -> 6C + 6H2O, which describes the reduction of carbon dioxide with oxygen

  6. Which process releases carbon dioxide from living organisms through metabolism?

    • Chemical weathering, which takes carbon dioxide from the air as rock is dissolved
    • Carbon sequestration, which stores carbon in long-term reservoirs away from the cycle
    • Photosynthesis, which uses carbon dioxide from the air to build sugars and plant tissue
    • Respiration

  7. What is the main way the lithosphere releases carbon to the atmosphere over geological timescales?

    • Photosynthesis by forests, which fixes carbon from the atmosphere into living tissue
    • Dissolution into deep ocean water, which removes carbon dioxide from the atmosphere
    • Volcanic outgassing
    • Precipitation of carbonate sediments, which locks carbon into rock on the sea floor

  8. Carbon in carbon dioxide has a mass fraction of 12/44. If 440 Mt of CO2 is emitted, how much carbon is released?

    • 528 Mt of carbon, which is obtained by multiplying the emissions by 12/10
    • 36.7 Mt of carbon, which is obtained by dividing the emissions by twelve
    • 120 Mt of carbon
    • 440 Mt of carbon, which is the full mass of the carbon dioxide emitted

  9. A forest stores 150 t of carbon per hectare. If 20 per cent is lost during deforestation, how much carbon is lost per hectare?

    • 120 t of carbon per hectare, which is the carbon remaining after the clearance
    • 130 t of carbon per hectare, which is the carbon remaining after adding 20 t of new growth
    • 15 t of carbon per hectare, which is obtained by halving the 30 t lost
    • 30 t of carbon per hectare

  10. A simplified annual carbon budget shows 9 Gt C from fossil fuels, 2.5 Gt C absorbed by the ocean and 4 Gt C remaining in the atmosphere. What is the implied land sink?

    • 2.5 Gt C per year
    • 0.5 Gt C per year, which is the difference between the ocean uptake and the atmospheric increase
    • 6.5 Gt C per year, which is the sum of the ocean uptake and the atmospheric increase
    • 15 Gt C per year, which is the sum of all three quantities in the budget as stated

  11. Which change would most increase atmospheric carbon dioxide?

    • Large-scale deforestation with burning of the cleared vegetation
    • Afforestation on degraded land, which removes carbon from the atmosphere as trees grow
    • Weathering of carbonate rocks in cold climates, which removes carbon dioxide from the air
    • Increased ocean uptake of carbon in cold surface water that dissolves more gas

  12. Which factor is most likely to increase carbon release from permafrost regions?

    • Lower temperatures that slow microbial decomposition and keep organic matter frozen
    • Greater ocean upwelling that draws carbon from the surface into deep water layers
    • Warming that thaws permafrost and speeds decomposition of frozen organic matter
    • Increased snow cover that insulates the ground and keeps the frozen layer intact all year

  13. Which process acts as a carbon sink at plant scale?

    • Respiration by roots during the night, which returns carbon dioxide to the soil air
    • Burning of biomass during wildfires, which releases stored carbon rapidly into the air
    • Growth of plant biomass by photosynthesis, storing carbon in trunks, roots and leaves
    • Rapid decomposition of leaf litter on the forest floor, which releases carbon dioxide

  14. Chemical weathering of carbonate rock by carbonic acid is best described as:

    • A process that releases carbon only through combustion of fossil fuels in power stations
    • A short-term source releasing carbon dioxide into the air within a few hours of rainfall
    • A long-term sink that removes carbon dioxide from the atmosphere-ocean system over millennia
    • An input reserved for living organisms, which takes carbon in only from their remains

  15. Why is the carbon budget a useful framework for climate policy?

    • It quantifies sources and sinks so that human emissions can be compared with natural absorption
    • It shows only the natural releases of carbon from volcanoes and other geological sources
    • It proves that all carbon is stored permanently in the oceans and cannot be released
    • It ignores land use change, which makes the model simpler to apply in policy settings

  16. A warmer ocean holds less dissolved carbon dioxide. What feedback does this create?

    • A positive feedback, because warming reduces ocean uptake and leaves more carbon dioxide to warm the planet further
    • A negative feedback, because warming increases ocean uptake of carbon dioxide and so reduces warming
    • No feedback, because the ocean's storage of carbon dioxide is fixed regardless of temperature
    • A closed loop with no net change in atmospheric carbon dioxide, since the ocean and air balance

  17. Burning wood releases carbon dioxide, which regrowing trees later reabsorb. Why is this often described as near carbon neutral over a rotation?

    • Combustion destroys carbon entirely, so none of the carbon released returns to the cycle
    • Regrowth absorbs more carbon than was released, so the store of carbon always rises over time
    • The released carbon dioxide is stored in sediments within a single year of the burning
    • Carbon released is roughly balanced by carbon taken up by regrowth over the regrowth period

  18. Which statement correctly contrasts short-term and long-term carbon stores?

    • Fossil fuels cycle carbon within hours, while the ocean holds carbon for only a few days at most
    • The biosphere and atmosphere cycle carbon within years to centuries, while sediments and fossil fuels hold it for millions of years
    • Sediments cycle carbon within years, while the atmosphere holds it for millions of years
    • The atmosphere holds carbon for millions of years, while the biosphere cycles it within days or weeks

  19. Cutting vegetation releases carbon dioxide, and regrowth on abandoned land takes decades. What is the most accurate conclusion?

    • Abandoned land stores carbon only in the lithosphere, so vegetation plays no part in the budget
    • Vegetation regrowth has no effect on atmospheric carbon dioxide, because the carbon is recycled within the soil
    • Land-use change always creates an immediate carbon sink, because the cut vegetation is stored in the soil
    • Land-use change can make land a net carbon source for decades before regrowth restores a sink

  20. Which combination of processes would increase oceanic carbon storage?

    • Greater ocean warming with increased outgassing of carbon dioxide from the surface water
    • Greater phytoplankton photosynthesis with export of dead organic matter to deep sediments
    • Increased acidification with reduced formation of carbonate shells and sediments on the sea floor
    • Increased respiration of sea organisms at the sea surface, which releases carbon dioxide to the air

All AQA Geography quizzes