OxfordAQA International AS and A-level Geography (9635): 3.3.2 Ecosystems under stress – 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 3.3.2, Ecosystems under stress, of the OxfordAQA International AS and A-level Geography (9635) specification, Version 3.2. The section is Section B of Unit 3: Physical geography 2, a 1 hour 30 minute written exam in which you answer all questions in each section. All places and data in the questions are fictional; the extended questions ask you to use your own real case studies.

Revise first with the study guide and revision notes. Track your progress on the OxfordAQA A-level Geography hub and checklist.

Questions

1. Define the term “biodiversity”. [2]

2. Distinguish between a climatic climax and a plagioclimax. [3]

3. Outline two adaptations of tropical rainforest plants to their climate or soil. [4]

4. The table shows energy available at each trophic level in Marrow Pond, a fictional freshwater ecosystem.

Trophic level	Energy (kJ per m² per year)
Producers (NPP)	8,400
Primary consumers	840
Secondary consumers	76
Tertiary consumers	7

(a) Calculate the percentage of energy transferred from primary consumers to secondary consumers. Show your working. [2] (b) Explain why the energy available falls at each trophic level. [3]

5. Students surveyed a transect inland from the strand line across Carrow Sands, a fictional dune system.

Site	1	2	3	4	5	6	7	8
Distance from strand line (m)	0	20	50	90	140	200	270	350
Number of plant species	2	3	5	6	9	8	12	14
Soil pH	8.4	8.1	7.6	7.0	6.4	5.8	5.1	4.6

(a) Describe the change in soil pH along the transect. [2] (b) Calculate Spearman’s rank correlation coefficient (rs) for distance and number of plant species, using rs = 1 - (6Σd²) / (n³ - n). The critical value at the 0.05 significance level (two-tailed) for n = 8 is 0.738. State what your result shows. [3] (c) Using the data, explain the changes along the transect in terms of succession. [6]

6. The table shows nutrient stores at two fictional sites, Site X (tropical rainforest) and Site Y (savanna grassland).

Store (kg per hectare)	Site X	Site Y
Biomass	6,000	900
Litter	200	300
Soil	1,300	2,400

(a) Calculate the percentage of the total nutrient store held in the biomass at each site. [2] (b) Explain the differences in nutrient storage between the two sites. [4]

7. Explain the environmental conditions needed for coral reef development. [4]

8. Kerai Creek is a fictional mangrove estuary on the edge of a growing coastal city. Its mangrove area fell from 420 hectares in 1995 to 260 hectares in 2025. Housing and a coastal road have been built, and an introduced ornamental shrub is spreading along the landward edge.

(a) Calculate the percentage loss of mangrove area between 1995 and 2025. [2] (b) Suggest and justify two measures to manage the impacts of change at Kerai Creek. [6]

9. With reference to a named, located coral reef, assess the relative importance of natural and human factors in the health of the reef. [9]

10. With reference to a region experiencing ecological change, discuss the extent to which the economic, social and political character of its community reflects its ecological setting. [12]

11. “Agricultural extension and intensification is the greatest threat to biodiversity in the savanna grassland biome.” To what extent do you agree with this view? [12]

Answers

1. The variety of living organisms in an area [1], at genetic, species and ecosystem (habitat) levels [1]. [2] Examiner insight: “Number of species” alone gets one mark at most, because it describes species richness, not the full concept.

2. A climatic climax is the final, stable community that the regional climate allows [1]. A plagioclimax is a community where succession is held back or deflected by continuing human activity [1]. For example, grazing or cutting can keep heath where oak woodland would otherwise develop [1]. [3] Examiner insight: “Distinguish” needs a clear contrast; two separate definitions with no example or comparison cap the answer.

3. Buttress roots [1] support very tall trees in shallow, nutrient-poor soils where roots spread near the surface [1]. Drip-tip leaves [1] shed heavy, frequent rainfall quickly, reducing the growth of algae and fungi on the leaf [1]. [4] Examiner insight: Each adaptation earns its second mark only when you link it to a named climate or soil condition.

4. (a) 76 / 840 × 100 [1] = 9.0% [1]. [2] (b) Much of the energy taken in is used in respiration and lost as heat [1]. Some material is not eaten or cannot be digested and passes out as waste [1]. So each level receives only a small share, which limits the number of top consumers the pond can support [1]. [3] Examiner insight: Show the division in (a); a bare answer risks losing the method mark if it is wrongly rounded.

5. (a) Soil pH falls from 8.4 (alkaline) at the strand line to 4.6 (acidic) at 350 m [1]. pH falls between every pair of sites, a total drop of 3.8 units [1]. [2] (b) Species ranks are 1, 2, 3, 4, 6, 5, 7, 8, so Σd² = 2 [1]. rs = 1 - (6 × 2) / (512 - 8) = 0.976 [1]. This exceeds the two-tailed critical value of 0.738, so there is a significant strong positive relationship between distance and species number at the 0.05 level [1]. [3] (c) Near the strand line only 2-3 pioneer species survive salt spray, moving sand and dry, alkaline sand [1]. Pioneers such as sea couch grass, then marram, trap sand and add organic matter as they die [1]. Humus builds up inland, improving water and nutrient retention [1]. Leaching of shell-derived calcium carbonate lowers pH from 8.4 to 4.6 [1]. Shelter and better soils allow more species to arrive, so richness rises to 14 at site 8 [1]. The slight dip at site 6 (8 species) may show a local disturbance such as trampling, so the sequence is not perfectly regular [1]. [6] Examiner insight: In (c), marks go to answers that quote figures from the table, not to a general description of a psammosere.

6. (a) Site X: 6,000 / 7,500 × 100 = 80.0% [1]. Site Y: 900 / 3,600 × 100 = 25.0% [1]. [2] (b) At Site X, hot, wet conditions allow fast decomposition, so the litter store is small (200 kg/ha) [1]. Nutrients are taken up quickly by dense vegetation and held in a large biomass store [1]. At Site Y, lower biomass and a dry season slow uptake, so more nutrients stay in the soil (2,400 kg/ha) [1]. Heavy rainfall at Site X also leaches the soil, keeping the soil store small [1]. [4] Examiner insight: Use the stores’ actual values; “the rainforest has more biomass” without numbers or a reason gains little.

7. Warm water, roughly 23-29 °C [1]. Clear, shallow water so light reaches the zooxanthellae for photosynthesis [1]. Normal sea salinity, away from large freshwater outflows [1]. Low sediment and wave action that brings oxygen and nutrients [1]. [4] Examiner insight: “Explain” needs the reason, such as light for the algae, not just a list of conditions.

8. (a) 420 - 260 = 160 ha lost [1]. 160 / 420 × 100 = 38.1% [1]. [2] (b) Protect the remaining mangrove by law, with a no-build buffer zone along the landward edge [1]. This stops further loss to housing and leaves space for mangroves to migrate inland as sea level rises [1]. Remove the introduced shrub and replant native mangrove species [1]. This restores habitat for native fauna and reduces competition along the edge [1]. Justification: both measures target the two named causes in the scenario [1]. Local residents should be involved in replanting, so that protection is supported and lasts [1]. [6] Examiner insight: Measures must answer the scenario’s causes (building and the introduced shrub); generic conservation ideas score lower.

9. The real exam marks extended answers with levels of response, not point by point. Indicative content, using the Great Barrier Reef:

• Water temperature is the dominant natural stress: marine heatwaves caused mass bleaching in 2016, 2017, 2020, 2022 and 2024 [1].
• Acidification and warming are “natural” factors driven by human emissions, so the split between natural and human is blurred [1].
• Lower salinity after floods stresses inshore reefs [1].
• Algal blooms and crown-of-thorns outbreaks are linked to nutrient-rich water [1].
• Farm runoff from catchments such as the Burdekin and Fitzroy is the main source of pollution reaching the reef [1].
• Port development and dredging add local sediment [1].
• Tourism and fishing are managed by zoning, which raised highly protected zones to over a third of the park in 2004 [1].
• So local human factors are important but partly managed, while heat stress affects the whole reef [1].
• Judgement: temperature is now the most important factor, but it is human-driven, so human activity is the main cause overall [1]. [9] Examiner insight: “Assess the relative importance” needs a ranking with a reason, not a list of factors given equal weight.

10. The real exam marks extended answers with levels of response, not point by point. Indicative content, using Rondônia, Brazil:

• Rondônia’s setting is rainforest on a frontier opened by BR-364, paved in the 1980s [1].
• Tax incentives and federal investment drew settlers [1].
• The population rose from about 117,000 in 1970 to over 1.1 million in 1991 [1].
• Cleared land now supports a cattle and soy economy, so the economy reflects the ecological change, not the original forest [1].
• Clearance along side roads gave the “fishbone” pattern [1].
• Socially, the community includes settlers and Indigenous peoples [1].
• Indigenous territories such as the Uru-Eu-Wau-Wau keep forest-based ways of life [1].
• Politically, land conflict between ranchers and Indigenous groups reflects competition for forest land [1].
• The Forest Code and satellite monitoring are responses to the change [1].
• Amazon clearance fell sharply after 2004, but enforcement has varied with national politics [1].
• So the community now reflects a changed setting rather than the original rainforest [1].
• Judgement: the economic character closely reflects the setting; the political character reflects conflict over it [1]. [12] Examiner insight: Weaker answers describe deforestation only; credit goes to answers that link it to economic, social and political character as the question asks.

11. The real exam marks extended answers with levels of response, not point by point. Indicative content:

• Agricultural extension converts grassland and woodland to cropland, removing habitat [1].
• Intensification brings fertiliser, pesticides and fewer fallow years [1].
• Fencing and fields block migration routes of large grazing herds [1].
• Population growth raises demand for land and food [1].
• But overgrazing by livestock may degrade more land than cropping in drier savannas [1].
• Changes in fire regimes alter the balance of grass and trees [1].
• Firewood collection removes trees near settlements [1].
• Climate change may lengthen dry seasons and shift biome boundaries [1].
• Hunting and poaching reduce large mammal numbers even inside intact habitat [1].
• Protected areas and community conservation can reduce several threats at once [1].
• The main threat varies with rainfall, population density and land tenure [1].
• Judgement: agricultural change is often the largest single threat because it removes habitat, but it works together with grazing, fire and climate [1]. [12] Examiner insight: “To what extent” needs both sides and a reasoned judgement; agreeing outright without considering other threats limits the level.

Where marks are usually lost

• Writing definitions that miss part of the concept, such as treating biodiversity as species richness.
• Not showing working in calculations, or rounding too early.
• Giving the Spearman value without comparing it with the critical value and saying what it means.
• Describing a psammosere from memory instead of using the transect data given.
• Explaining nutrient stores without quoting the store sizes in the table.
• Calling warming and acidification purely natural with no comment on human causes.
• Giving management measures that do not match the causes in the scenario.
• Using a case study as a story with no link to the question’s focus.
• Finishing an extended answer without a clear judgement.

Next steps

Check your weaker areas with the Marlbridge diagnostics and return to the study guide for any topic you struggled with. For Section A of Unit 3, use the Water, carbon and life on Earth study guide. For paper structure and case-study routines, read the exam preparation guide. If you want help from a teacher, book a free trial class.

Official syllabus

These questions are based on the OxfordAQA International AS and A-level Geography (9635) specification, Version 3.2, section 3.3.2 Ecosystems under stress.