Mark Scheme

Section A — Structured Questions

1. (a) 58 − 34 = 24 percentage points decrease (accept −24). [1] (b) Any two comparative points using data: coal fell (from 58% to 34%); wind and solar rose sharply (from 2% to 18%); natural gas increased (20% to 28%); hydroelectric rose slightly; nuclear fell slightly. 1 mark each, must reference the data. [2] (c) Two advantages explained (1 mark for the point + 1 for development each): renewable/will not run out (unlike fossil fuels which are finite); does not release carbon dioxide/greenhouse gases when generating (reducing climate change); no air pollution from burning; free energy source once built (low running cost). [4] (d) Problem (up to 2): the supply is not constant — wind/solar only generate when it is windy/sunny, so output does not always match demand, risking shortages at peak times. Solution (up to 2): store energy (batteries/pumped storage) to use when output is low; keep other sources (gas/hydro) available to fill gaps; connect to a wider grid to share supply. [4]

2. (a) 2020 (demand 380 > supply 300; in 2010 they were equal). [1] (b) Any two: population growth (more people); higher standard of living/more water-using appliances; industrial/agricultural growth using more water; urbanisation. [2] (c) Two strategies explained: reduce leaks/repair pipes (less water lost in distribution); metering/pricing to encourage saving; educate people to use less; use water-efficient appliances; recycle/reuse greywater. 1 for method + 1 for how it reduces demand, each. [4] (d) Reduced flow (up to 4): less water/lower oxygen levels harm fish; higher concentration of pollutants (less dilution); water temperature rises, reducing dissolved oxygen; habitats such as spawning grounds dry out; less food/plants so food chains are disrupted. Any developed points. [4]

3. (a) Soil fertility = the ability of the soil to provide the nutrients needed for plants to grow well (accept: how well soil supports plant growth). [1] (b) Two reasons explained: the same crop removes the same nutrients each year, depleting them; no variation means nutrients are not replaced; monoculture allows pests and diseases specific to the crop to build up; roots may not bind the soil, increasing erosion. 1 + 1 development each. [4] (c) Two methods with how each works: crop rotation — different crops use/replace different nutrients (e.g. legumes fix nitrogen), so fertility is maintained; adding organic matter/manure — returns nutrients and improves soil structure; leaving land fallow — allows nutrients to recover; planting cover crops — reduces erosion and adds organic matter. [4] (d) Fertiliser problem (up to 3): rain washes excess fertiliser into rivers/lakes (leaching); nutrients cause eutrophication — rapid algal growth; algae block light and, when they decompose, use up oxygen; fish and other organisms die from lack of oxygen. [3]

4. (a) The catch is decreasing (falling every year, from 90 to 40 thousand tonnes). [1] (b) Overfishing (up to 3): fish are caught faster than they can reproduce/replace themselves; too many mature/breeding fish removed; the breeding population falls, so fewer young are produced; the population declines further each year. [3] (c) Two methods with how each helps: quotas — limit the amount caught so enough fish remain to breed; net mesh size — larger holes let young fish escape to grow and breed; closed seasons/areas — protect fish during breeding; banning certain methods — reduces bycatch and habitat damage. 1 + 1 each. [4] (d) Advantage (up to 2): reduces pressure on wild fish stocks, letting them recover; provides a reliable food supply. Disadvantage (up to 2): waste, uneaten food and chemicals can pollute surrounding water; disease/parasites can spread to wild fish; escaped farmed fish may harm wild populations. 1 advantage + 1 disadvantage, developed. [3]

5. (a) Natural increase = birth rate − death rate = 34 − 9 = 25 per 1000. [1] (b) Country Y is more developed; reason from data: much higher life expectancy (81 vs 58) and low birth rate, which are typical of more developed countries with better healthcare. [2] (c) Two problems explained: more demand for resources (water, energy, food) causing depletion; more land cleared for housing/farming, destroying habitats; more waste and pollution produced; overuse of resources becomes unsustainable. 1 + 1 development each. [4] (d) Two strategies with how each helps: education (especially of women) → smaller families/later childbearing; family planning/contraception access → fewer births; incentives or policies encouraging smaller families → lower birth rate; improving healthcare → lower infant mortality so families choose to have fewer children. 1 + 1 development each. [4]

Section B — Extended Response

6. (a) (up to 4) Greenhouse gases (e.g. carbon dioxide, methane) build up in the atmosphere; short-wave radiation from the Sun passes through and warms the Earth's surface; the Earth radiates long-wave (infrared) radiation back; greenhouse gases absorb and re-emit this outgoing radiation, trapping heat; so more heat is retained and global temperatures rise. Mark for a clear causal chain. [4] (b) (up to 6, two consequences developed) e.g. melting ice/rising sea levels → flooding of low-lying land and coastal cities, displacing people; changing weather patterns → more droughts/floods, reducing crop yields and causing food/water shortages; more extreme weather events → damage and loss of life; shifting habitats → some species cannot adapt and may become extinct. 3 marks per consequence (statement + explanation + impact). [6]

7. (14 marks) Levels-marked. Award for a discussion referring to energy, resources and pollution with balanced points on developing the economy while protecting the environment.

• Level 3 (10–14): Detailed, balanced discussion covering all three areas (energy, resources, pollution); explains specific strategies (e.g. switching to renewable energy, recycling and efficient resource use, controlling pollution through laws/technology); recognises tensions (development costs money, may conflict with growth) and reaches a supported judgement.
• Level 2 (5–9): Sound points on two or more areas with some explanation; strategies named and partly developed; some awareness of the balance between development and environment.
• Level 1 (1–4): Simple or general statements; limited use of the three areas; little explanation.
• 0: No relevant content. Indicative content: renewable energy and energy efficiency to cut emissions and conserve fossil fuels; sustainable management of water, forests and fish; recycling and reducing waste; pollution controls and cleaner technology; international cooperation; the idea that sustainable methods may cost more initially but protect resources for the future.

Sample Answers with Examiner Commentary

Question 3(d) — Sample Answers

Grade A response. "If a farmer uses too much artificial fertiliser, the excess is not used by the crops and is washed off the field by rain into nearby rivers and lakes. This is called leaching. The extra nutrients cause algae to grow very quickly, forming an algal bloom that covers the surface of the water. This blocks sunlight from reaching plants below, which die. When the algae and plants die, they are decomposed by bacteria that use up the oxygen dissolved in the water. With little oxygen left, fish and other animals suffocate and die. This whole process is called eutrophication."

Mark: 3/3. Examiner commentary: A complete and correctly sequenced answer that earns full marks with room to spare. The candidate names the process (eutrophication), and — more importantly — gives the causal chain in the right order: excess fertiliser → leaching into water → algal bloom → light blocked → decomposition uses oxygen → animals die. Naming the process alone would not be enough; it is the explanation of how the oxygen is depleted that secures the third mark. Precise use of terms like "leaching" and "decomposed" is exactly what examiners reward.

Grade C response. "Too much fertiliser gets into the rivers and pollutes them. It makes algae grow and this is bad for the fish, which can die."

Mark: 1/3. Examiner commentary: The candidate has the right starting point — fertiliser reaching rivers and causing algae to grow — which earns one mark. But the answer stops at "bad for the fish" without explaining the mechanism. Why do the fish die? The marks lie in the steps the candidate has missed: the algae block light, then decomposition of the dead algae uses up the dissolved oxygen, and it is the lack of oxygen that kills the fish. "Pollutes them" and "bad for the fish" are the kind of vague phrases that describe the outcome without explaining the science.

Question 6(a) — Sample Answers

Grade A response. "Greenhouse gases such as carbon dioxide and methane collect in the atmosphere. Short-wave radiation from the Sun passes through the atmosphere and heats the Earth's surface. The warmed Earth then gives off heat as long-wave infrared radiation. The greenhouse gases absorb this outgoing infrared radiation and re-emit some of it back towards the Earth, instead of letting it escape into space. This traps heat in the atmosphere, so as the concentration of greenhouse gases rises, more heat is trapped and the average global temperature increases."

Mark: 4/4. Examiner commentary: Full marks. This answer works because it distinguishes clearly between the short-wave radiation coming in and the long-wave radiation going out — the single most important idea in the greenhouse effect, and the one weaker answers blur. The candidate then explains that the gases absorb and re-emit the outgoing radiation, and links a higher concentration of gases to more trapped heat. The causal chain is complete and in the correct order.

Grade C response. "Carbon dioxide from burning fossil fuels goes into the air and makes a layer that traps the Sun's heat like a greenhouse. This makes the Earth get hotter and hotter."

Mark: 2/4. Examiner commentary: The candidate correctly identifies that carbon dioxide traps heat and that this warms the Earth, earning two marks, and the greenhouse analogy shows some understanding. But the explanation treats the atmosphere as a simple "layer" or "blanket" and does not distinguish between incoming short-wave and outgoing long-wave radiation, nor mention that the gases absorb and re-emit the radiation. Those two ideas are where the remaining marks are. The phrase "hotter and hotter" is also imprecise — the effect is a rise in average temperature, not unlimited heating.

Question 7 (14-mark discussion) — Sample Answer

Level 3 response (12/14). "A country can develop its economy while reducing environmental damage by managing energy, resources and pollution carefully.

For energy, a country can gradually shift from fossil fuels towards renewable sources such as solar, wind and hydroelectric power. Fossil fuels are finite and release carbon dioxide and other pollutants that cause climate change and acid rain, so reducing dependence on them lowers pollution while still supplying the energy that industry and homes need. Improving energy efficiency — for example, better insulation and more efficient machinery — allows the economy to grow while using less energy per unit of output. The drawback is that renewable infrastructure is expensive to build, which can slow a developing country's growth in the short term.

For resources, the country should manage water, forests, soils and fish sustainably rather than exhausting them. Sustainable forestry (replanting and selective logging), crop rotation to protect soils, and fishing quotas all allow resources to keep providing income into the future rather than being used up in one generation. Recycling and reusing materials reduce the need to extract new raw materials and cut waste. This is the essence of sustainable development: meeting present needs without preventing future generations from meeting theirs.

For pollution, the country can introduce laws and standards that limit emissions to air and water, and require industries to treat waste before releasing it. Cleaner technology, such as filters on factory chimneys and catalytic converters on vehicles, reduces pollution without stopping production. Enforcing these rules costs money and can raise business costs, which is a tension with rapid growth.

Overall, development and environmental protection can be balanced, but there are real trade-offs. Sustainable methods often cost more at first and may slow growth, yet they protect the resources, clean air and water that the economy and its people depend on in the long term. A sensible strategy is to grow the economy using renewable energy, efficient resource use and pollution controls, accepting higher short-term costs to avoid far greater long-term damage."

Mark: 12/14. Examiner commentary: A strong Level 3 answer. It covers all three required areas — energy, resources and pollution — and, crucially, does more than list strategies: each is explained (why it reduces damage) and linked back to allowing the economy to develop. The answer repeatedly acknowledges the tension between development and protection (costs, short-term slowing of growth), which is what lifts it to the top band, and it reaches a supported judgement in the conclusion. To reach full marks it could have named a specific real example or two (a particular renewable scheme or pollution law) to anchor the general points, but the reasoning is thorough and balanced throughout.