OxfordAQA International A-level Geography (9635): 3.3.1 Water, carbon and life on earth – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover section 3.3.1, Water, carbon and life on earth (3.3.1.1 to 3.3.1.6), of the OxfordAQA International AS and A-level Geography (9635) specification, Version 3.2. The section is Section A of Unit 3: Physical geography 2, a 1 hour 30 minute written exam with 40 marks in Section A and 40 in Section B, all questions compulsory. All places and data in Questions 5 to 8 are fictional; Question 7 uses illustrative figures of a realistic size.

Revise first with the study guide for this unit and the revision notes for this unit. The 9635 geography hub and the 9635 checklist show where this section fits.

Questions

1. Outline what is meant by the cryosphere and name one process that transfers water out of it. [2]

2. Explain how rising air leads to cloud formation. [3]

3. Distinguish between infiltration-excess and saturation-excess overland flow. [2]

4. Outline two processes that transfer carbon from the atmosphere to the ocean. [4]

5. The fictional River Wenlow drains a catchment of 48 km². In one year, catchment-average precipitation was 1,150 mm and evapotranspiration was 430 mm. The gauging station at the basin outlet recorded 33.6 million m³ of runoff.

(a) Convert the runoff into millimetres of water over the catchment. Show your working. [2] (b) Use the water balance equation to calculate the change in storage, and state what it shows. [2] (c) Suggest two reasons why the share of precipitation leaving as runoff might rise if forest in the upper catchment were cleared for grazing. [4]

6. Two fictional streams received the same 42 mm storm. Peak rainfall on both was at 10:00.

	Fellside Beck	Ashby Brook
Area (km²)	9	11
Basin	Steep moorland, thin peat over impermeable rock, many drainage ditches	Gentle slopes, mixed woodland, permeable sandstone
Baseflow before storm (m³/s)	1.2	1.5
Peak discharge (m³/s)	18.6	7.2
Time of peak discharge	14:00	21:00

(a) Calculate the lag time for each stream. [2] (b) Using the data, explain the differences between the two hydrographs. [6]

7. Illustrative figures for one year: fossil fuel emissions 36.7 gigatonnes of carbon dioxide; land use change emissions 4.0 gigatonnes of carbon dioxide; ocean uptake 2.9 GtC; land uptake 3.3 GtC.

(a) Convert total emissions to GtC. Use 12/44. [2] (b) Calculate the increase in the atmospheric store in GtC and in ppm (1 ppm = 2.12 GtC), and the share of emissions that stayed in the atmosphere. [3] (c) Explain why ocean uptake of carbon may weaken as the climate warms. [2]

8. A student measured infiltration rates (mm per hour) at five points on each of three surfaces in a fictional catchment.

Surface	Readings (mm/h)
Woodland	62, 75, 58, 81, 69
Grazed pasture	24, 31, 19, 28, 23
Footpath	4, 7, 3, 6, 5

(a) Calculate the mean and range for grazed pasture. [2] (b) A storm brings rain at 30 mm per hour for one hour. Using the data, explain the likely effect on overland flow at each surface. [4] (c) Suggest one limitation of the student’s sampling and how to reduce it. [2]

9. Explain the relationship between the water cycle and the carbon cycle in the atmosphere. [6]

10. With reference to a local river catchment you have studied, analyse the impact of heavy precipitation on drainage basin stores and transfers. [8]

11. With reference to a tropical rainforest you have studied, assess the extent to which human activity has changed its water and carbon cycles. [16]

12. Evaluate the effectiveness of human interventions in the carbon cycle designed to mitigate climate change. [16]

Answers

Questions 10 to 12 are extended responses. The real exam marks extended answers with levels of response, not point by point; the [1]s below show indicative creditworthy points.

1. The cryosphere is the frozen part of Earth’s water: ice sheets, glaciers, sea ice, snow and permafrost [1]. Any one transfer out: melting, sublimation or calving [1]. [2] Examiner insight: “ice” alone is too vague for the definition; list at least two named forms of frozen water.

2. Air rises by convection, over relief or at a front, and cools adiabatically as pressure falls [1]. When it cools to its dew point it is saturated [1], and water vapour condenses on condensation nuclei such as dust or salt to form cloud droplets [1]. [3] Examiner insight: the dew point and the nuclei are the two ideas most often left out; each is a separate mark.

3. Infiltration-excess flow happens when rain falls faster than the soil’s infiltration rate [1]; saturation-excess flow happens when the soil is already full of water, so any further rain runs off [1]. [2] Examiner insight: “distinguish” needs both sides in one answer; defining only one type caps you at half marks.

4. Carbon dioxide dissolves in surface water, especially cold water [1], which sinks at high latitudes and carries it to the deep ocean (the physical pump) [1]. Phytoplankton take in carbon by photosynthesis [1], and their remains and shells sink to the deep ocean and sea-floor sediments (the biological pump) [1]. [4] Examiner insight: each process has two marks, one for the uptake and one for where the carbon goes next.

5. (a) 33,600,000 m³ ÷ 48,000,000 m² = 0.7 m [1] = 700 mm [1]. [2] (b) ΔS = 1,150 − 430 − 700 = +20 mm [1]. Storage rose slightly, so the catchment gained water in soil and groundwater that year [1]. [2] (c) Grazing removes the canopy, so interception and evapotranspiration fall and more water reaches the ground [1], leaving more to become runoff rather than return to the air [1]. Livestock compact the soil, cutting infiltration [1], so more rain moves quickly as overland flow to the channel [1]. [4] Examiner insight: in (a), convert km² to m² before dividing; most lost marks here come from a missing factor of a million.

6. (a) Fellside Beck: 14:00 − 10:00 = 4 hours [1]. Ashby Brook: 21:00 − 10:00 = 11 hours [1]. [2] (b) Fellside’s peak of 18.6 m³/s is about 2.6 times Ashby’s 7.2 m³/s, despite its smaller area [1]. Steep slopes move water quickly downslope [1]. Thin peat over impermeable rock saturates fast, so rain becomes overland flow [1], and ditches speed water to the channel, giving a short 4-hour lag [1]. At Ashby, woodland intercepts rain and slows its arrival [1], and permeable sandstone lets water percolate to groundwater, released slowly as throughflow and baseflow, giving an 11-hour lag [1]. [6] Examiner insight: quote figures from the table and pair each factor with the process it controls; a list of factors with no process gains little.

7. (a) 36.7 + 4.0 = 40.7 gigatonnes of carbon dioxide [1]; 40.7 x 12/44 = 11.1 GtC [1]. [2] (b) 11.1 − (2.9 + 3.3) = 4.9 GtC [1]; 4.9 ÷ 2.12 = 2.3 ppm [1]; 4.9 ÷ 11.1 = 44% stayed in the atmosphere [1]. [3] (c) Warmer water dissolves less carbon dioxide [1]. Warmer surface water is also less dense, so it mixes less with deep water and carries less carbon down [1]. [2] Examiner insight: write the unit at every step; a correct number labelled as carbon dioxide when it is carbon loses the mark.

8. (a) Mean = 125 ÷ 5 = 25 mm/h [1]; range = 31 − 19 = 12 mm/h [1]. [2] (b) Woodland’s mean of 69 mm/h is well above 30 mm/h, so almost all rain infiltrates and overland flow is minimal [1]. Pasture’s mean of 25 mm/h is just below 30, so about 5 mm in the hour may run off as infiltration-excess flow, more where readings were as low as 19 [1]. The footpath’s mean of 5 mm/h means about 25 mm of the 30 mm becomes overland flow [1]. Compaction by trampling and grazing has reduced pore space, which explains the pattern [1]. [4] (c) Five readings per surface is a small sample, so one unusual point affects the mean [1]; take more readings using stratified or systematic sampling across each surface [1]. [2] Examiner insight: “using the data” in (b) means comparing each mean with the 30 mm rain rate, not just ranking the surfaces.

9. Water vapour and carbon dioxide are both greenhouse gases [1]. More carbon dioxide warms the atmosphere [1], which increases evaporation [1]. Warmer air holds more water vapour, which traps more heat, a positive feedback [1]. Plants link the cycles: stomata open to take in carbon dioxide for photosynthesis and lose water by transpiration at the same time [1]. Carbon dioxide dissolves in rain to form weak carbonic acid, which weathers rock and removes carbon from the atmosphere over long timescales [1]. [6] Examiner insight: the question asks for a relationship, so every point must link one cycle to the other rather than describe each separately.

10. Indicative content (River Eden, Cumbria):

• Heavy rain exceeds interception storage quickly, so throughfall and stemflow rise [1].
• Infiltration fills the soil water store; once full, saturation-excess overland flow dominates [1].
• In December 2015 (Storm Desmond), nearly 36 hours of continuous rain affected Carlisle [1], so soil stores filled and transfers to the channel were rapid [1].
• Channel storage rose until the Eden, Caldew and Petteril overtopped and defences in Carlisle were breached [1].
• In January 2005, up to 180 mm in a day upstream flooded about 2,700 Carlisle homes [1].
• Groundwater and reservoir stores, such as Haweswater, refill after heavy rain, which supports later water supply [1].
• Analysis: antecedent conditions matter as much as rainfall total, because a full soil store turns rain directly into runoff [1]. [8] Examiner insight: name the stores and flows in order from canopy to channel, and back each step with a detail from your catchment.

11. Indicative content (the Amazon):

• Introduce the forest as a large water and carbon store: about 5.5 million km², about 110 billion tonnes of carbon [1].
• Natural cycles: high interception and evapotranspiration; about half of rainfall is recycled from the forest [1].
• Deforestation reached 27,772 km² in the Brazilian Amazon in 2004 [1], about 80% linked to cattle ranching [1].
• Water cycle change: less interception and evapotranspiration [1]; compacted soils increase overland flow and erosion [1]; less moisture for rain downwind [1].
• Carbon cycle change: burning releases biomass carbon to the atmosphere [1], and soil carbon is lost once the litter supply stops [1].
• Gatti and colleagues (2021) reported that the south-eastern Amazon had become a net carbon source [1].
• Feedback: a drier forest burns more easily, so the two cycles reinforce each other [1].
• By 2022 about 20% had been deforested [1], close to a suggested tipping point of 20 to 25% [1].
• Counter-evidence: deforestation fell to 4,571 km² in 2012, so change is not one-way [1].
• Much of the basin is still forested, and the effects vary from place to place [1].
• Judgement: human activity has changed both cycles greatly at regional scale, with the largest change where clearance is concentrated [1]. [16] Examiner insight: higher-level answers judge “extent” with scale and place, rather than assuming the whole forest has changed equally.

12. Indicative content:

• Define mitigation as reducing carbon transfers to the atmosphere or increasing them out of it [1].
• Set criteria: scale of carbon removed, cost, permanence and side effects [1].
• Afforestation increases photosynthesis and biomass storage [1], but carbon is lost again if trees burn or are felled [1].
• Forest protection: Brazilian Amazon clearance fell from 27,772 km² in 2004 to 4,571 km² in 2012, alongside measures such as the Soy Moratorium and the Amazon Fund [1], but the fall was not sustained [1].
• Carbon capture and storage: Sleipner has injected about 1 million tonnes of carbon dioxide a year since 1996 [1], but this is tiny beside global emissions of tens of billions of tonnes [1].
• Farming changes such as reduced tillage keep carbon in the soil [1] but can be reversed by later ploughing [1].
• Peatland restoration stops drained peat oxidising [1].
• Cutting fossil fuel use tackles the largest flow at its source [1], supported by agreements such as the Paris Agreement (2015) [1], though pledges depend on national action [1].
• Interventions work best together; none alone matches the size of fossil emissions [1].
• Judgement: emissions cuts are most effective; storage-based methods help but are slower, smaller or less permanent [1]. [16] Examiner insight: evaluation needs criteria; judge each intervention against scale and permanence, not just describe it.

Where marks are usually lost

• Calculations with no working or no units, especially when converting km² to m².
• Mixing up GtC and gigatonnes of carbon dioxide.
• Lag time measured from the start of rain instead of peak rainfall.
• Hydrograph answers that list basin features without the process (infiltration, throughflow) they control.
• Data questions answered without quoting figures from the table.
• Catchment answers with general flood facts and no named stores and flows.
• Rainforest essays that describe deforestation but never measure its scale.
• Evaluation of interventions with no criteria and no overall judgement.

Next steps

Go back to any weak areas in the study guide, then check your progress with the Marlbridge diagnostics. For exam timing across units, read OxfordAQA A-level Geography exam preparation, and practise the other half of Unit 3 with the Ecosystems under stress guide. If you would like a teacher to go through your answers, Book a free trial class.

Official syllabus

These questions follow the OxfordAQA International AS and A-level Geography (9635) specification, Version 3.2, section 3.3.1 (Water, carbon and life on earth), sections 3.3.1.1 to 3.3.1.6, assessed in Unit 3: Physical geography 2, Section A.