2025 Cambridge IGCSE Environmental Management (0680) Practice Paper with Answers

(a) Matches:
- Sandy soil: Has large pore spaces, drains very rapidly, and has high aeration.
- Clayey soil: Has very small pore spaces, retains high amounts of water, and has poor drainage.
- Silty soil: Has medium-sized particles, intermediate water retention, and is easily eroded by water.

(b) Adding organic matter increases the water-holding capacity of sandy soils by acting like a sponge. It also improves soil structure by binding the loose sand particles together, which helps retain essential mineral nutrients and prevents leaching.

(c) Soil pH is important because:
1. It directly affects the availability and uptake of essential plant nutrients (such as nitrogen, phosphorus, and potassium) from the soil.
2. Extremely acidic or alkaline conditions can damage root cells or limit the activity of beneficial soil microorganisms that decompose organic matter.

(a) [3 marks]
- Sandy soil matched to large pore spaces/rapid drainage [1]
- Clayey soil matched to small pore spaces/poor drainage [1]
- Silty soil matched to medium particles/intermediate retention [1]

(b) [2 marks]
- Increases water retention/helps hold soil moisture [1]
- Improves soil structure / binds sand particles together / reduces nutrient leaching [1]

(c) [2 marks]
- Affects nutrient availability/solubility/absorption [1]
- Affects soil microbial activity/decomposition of organic matter [1]
- Extreme pH causes root damage/toxicity [1]
(Any two, max 2)

(a) Matches:
- Cholera: Caused by consuming water contaminated with pathogenic bacteria from human faeces.
- Malaria: Transmitted by an insect vector that breeds in stagnant water.
- Schistosomiasis (bilharzia): Caused by an aquatic host organism (such as a snail) releasing larval parasites into water that penetrate human skin.

(b) Vector control methods:
1. Draining wetlands, swamps, or stagnant water puddles removes breeding sites for Anopheles mosquitoes.
2. Spraying residual insecticides on indoor walls or using insecticide-treated bed nets kills adult female mosquitoes, reducing insect bites.

(c) Physical symptoms of cholera include:
1. Severe, watery diarrhoea.
2. Vomiting and rapid dehydration.

(a) [3 marks]
- Cholera matched to consuming contaminated water/bacteria [1]
- Malaria matched to insect vector breeding in stagnant water [1]
- Schistosomiasis matched to aquatic host/snail releasing larvae [1]

(b) [2 marks]
- Draining stagnant water to eliminate vector breeding sites [1]
- Indoor residual insecticide spraying / use of insecticide-treated bed nets to kill or repel adult mosquitoes [1]
- Introduction of larvivorous fish (biological control) to consume larvae [1]
(Any two, max 2)

(c) [2 marks]
- (Severe/watery) diarrhoea [1]
- Vomiting [1]
- Rapid dehydration/loss of body fluids [1]
- Muscle cramps [1]
(Any two, max 2)

(a) Classification:
- Geothermal: Renewable
- Uranium (Nuclear): Non-renewable
- Wind: Renewable
- Coal: Non-renewable

(b) Cold water is pumped deep underground through injection wells into hot volcanic rock areas. The water is heated by the rocks and turns to high-pressure steam, which rises through production wells to spin a steam turbine. The turbine then drives an electrical generator to produce power.

(c) Environmental impacts of tidal barrages:
1. Disruption of fish migration paths and loss of marine organism habitats.
2. Changes in tidal range, salinity, and sedimentation patterns upstream in the estuary, which can destroy feeding mudflats for wading birds.

(a) [2 marks]
- All 4 correct: [2]
- 2 or 3 correct: [1]
- 0 or 1 correct: [0]
(Geothermal = Renewable, Uranium = Non-renewable, Wind = Renewable, Coal = Non-renewable)

(b) [2 marks]
- Cold water is pumped underground into hot rocks to produce steam [1]
- High-pressure steam turns a turbine which drives an electrical generator [1]

(c) [2 marks]
- Disruption of migratory pathways for fish/marine wildlife [1]
- Changes in estuary salinity/sedimentation/turbidity [1]
- Loss of intertidal habitats/mudflats for wading birds [1]
(Any two, max 2)

1(a)(i) National parks provide legal protection for habitats, preventing land conversion. They ban hunting, logging, and poaching, allowing populations to recover in their natural ecosystem.
1(a)(ii) Three activities: 1. Clearing land for agriculture (subsistence or commercial farming). 2. Infrastructure development (building roads, dams, or urban expansion). 3. Mining and mineral extraction.
1(b)(i) Decrease = 48 - 15 = 33 species. Percentage decrease = (33 / 48) * 100 = 68.75% (or 68.8%).
1(b)(ii) Primary forests have complex multi-layered canopies creating numerous ecological niches. They feature mature trees providing abundant food and shelter, a stable microclimate, and undisturbed soil systems with intact decomposer networks, whereas logged forests suffer from simplified structures and microclimatic stress.
1(c) Strategies: 1. Selective logging coupled with replanting (reforestation). 2. Establishing agroforestry systems to combine agriculture and forestry. 3. Implementing international forest certification schemes (e.g., FSC) to encourage sustainable consumer demand.
1(d) Fully balanced level-of-response answer showing both sides: agreement that selective logging preserves some forest structure compared to clear-cutting; disagreement because selective logging still involves heavy machinery causing soil erosion, building access roads that cause habitat fragmentation, and changing the microclimate of the understory, meaning it is not completely without impact.

1(a)(i) [3 marks]
- Legal protection / creates reserves where human development is banned (1)
- Prevention of hunting / poaching / harvesting of species (1)
- Preservation of natural habitats and food webs (1)

1(a)(ii) [3 marks]
- Clearing for farming / agriculture / livestock ranching (1)
- Infrastructure / roads / dam building / urbanisation (1)
- Mining / mineral extraction (1)

1(b)(i) [2 marks]
- Correct calculation of difference: 33 (1)
- Correct calculation of percentage: 68.75% or 68.8% (1)

1(b)(ii) [4 marks]
Any four from:
- More ecological niches / varied habitats (1)
- Multi-layered canopy / complex vertical structure (1)
- More stable microclimate (less wind/light fluctuations) (1)
- Intact food webs / more diverse plant-herbivore-predator relationships (1)
- Undisturbed soil structure / micro-organisms (1)

1(c) [3 marks]
Any three from:
- Selective logging with replanting (1)
- Agroforestry / crop-tree integration (1)
- Forest certification schemes / labelling (1)
- Creation of wildlife corridors (1)
- Debt-for-nature swaps (1)

1(d) [5 marks]
- Level 3 (5 marks): Well-balanced argument discussing both support for selective logging (canopy remains mostly intact, faster regeneration) and counter-evidence (heavy machinery compacts soil, access roads lead to fragmentation and illegal logging access, microclimate is altered). Clear conclusion.
- Level 2 (3-4 marks): Discusses both sides but lacks depth in either the ecological impacts or the management practices.
- Level 1 (1-2 marks): Simple descriptive points with limited evaluation of sustainability.

2(a)(i) 1. Generation of clean hydroelectric power. 2. Storage of water for agricultural irrigation during dry seasons. 3. Flood prevention downstream.
2(a)(ii) 1. Forced displacement of communities leading to loss of homes. 2. Loss of agricultural land or traditional livelihood areas. 3. Increased incidence of waterborne diseases like malaria due to stagnant reservoir water.
2(b)(i) Parameter: Fecal coliforms. Disease: Cholera (or typhoid/dysentery).
2(b)(ii) The high phosphate levels from agricultural run-off trigger rapid growth of algae (eutrophication/algal bloom). This algae blocks sunlight, causing plants to die. When the algae and plants die, aerobic bacteria decompose them. This decomposition process consumes large amounts of oxygen, lowering the dissolved oxygen level in the water.
2(c) 1. Installing water-efficient appliances (e.g., dual-flush toilets, low-flow showerheads). 2. Harvesting rainwater for garden use. 3. Recycling graywater from washing machines for toilet flushing.
2(d) A level-of-response answer: Disagree that it is the *only* way. While dams provide high-volume water storage and clean energy, they cause major ecosystem disruption and siltation. Alternative energy sources like solar, wind, and geothermal are highly sustainable. Alternative water security measures, such as desalination, wastewater recycling, and leak-reduction in municipal systems, can secure water futures with lower environmental costs.

2(a)(i) [3 marks]
- Hydroelectric power (HEP) / renewable energy generation (1)
- Water storage / reservoir for domestic or agricultural use (1)
- Flood control / regulation of river flow (1)

2(a)(ii) [3 marks]
Any three from:
- Dispersal / displacement of local residents (1)
- Loss of fertile farmland / ancestral land (1)
- Loss of clean river water / downstream fisheries (1)
- Health risks from vector-borne diseases in reservoir (e.g. malaria) (1)

2(b)(i) [2 marks]
- Parameter: Fecal coliforms (1)
- Disease: Cholera / Typhoid / Dysentery / gastroenteritis (1)

2(b)(ii) [4 marks]
- Phosphate run-off causes rapid growth of algae / algal bloom (1)
- Algae block sunlight, leading to death of submerged aquatic plants (1)
- Dead organic matter is decomposed by bacteria (1)
- Aerobic bacteria use up dissolved oxygen during respiration (1)

2(c) [3 marks]
Any three from:
- Dual-flush toilets / low-flow showerheads (1)
- Rainwater harvesting systems (1)
- Graywater recycling / reusing laundry water (1)
- Fixing leaks in household plumbing (1)
- Turning off taps when not in use / watering gardens at night (1)

2(d) [5 marks]
- Level 3 (5 marks): Comprehensive answer showing balanced perspective. Evaluates both the benefits of dams (long lifespan, reliable output) and the disadvantages, presenting realistic alternatives such as solar/wind power, desalination, water treatment/recycling, and demand management.
- Level 2 (3-4 marks): Good discussion of either water or energy alternatives, but lacks balanced evaluation of both.
- Level 1 (1-2 marks): Basic list of energy alternatives without link to sustainability of water security.

3(a)(i) At constructive plate boundaries, tectonic plates move away from each other, allowing magma to rise, cool, and create new oceanic crust (forming rifts/ridges). At destructive plate boundaries, plates move towards each other; the denser oceanic plate is forced downwards (subducted) into the mantle, where it melts, creating deep ocean trenches and explosive volcanoes.
3(a)(ii) 1. Tsunamis (triggered by underwater earthquakes/landslides). 2. Landslides / Lahars (mudflows of volcanic debris).
3(b)(i) Increase = 1250 - 80 = 1170 tonnes/day. Percentage increase = (1170 / 80) * 100 = 1462.5%.
3(b)(ii) As magma rises through the volcanic conduit, it fractures surrounding solid rock, generating minor seismic tremors (earthquakes). Magma also contains dissolved gases under high pressure; as it rises, pressure decreases, allowing gases (such as sulfur dioxide and carbon dioxide) to escape and vent. A rapid increase in both indicators shows that magma is rising closer to the surface, signaling an imminent eruption.
3(c) 1. Conducting emergency search, rescue, and evacuation operations. 2. Providing clean drinking water, food, and temporary medical shelters. 3. Clearing thick volcanic ash from roofs to prevent collapse and restoring transport lines.
3(d) Level-of-response evaluation: Disagree with permanent relocation. Volcanic regions offer significant economic opportunities: highly fertile soils rich in nutrients (mineral weathering), access to renewable geothermal energy, and tourism industries (scenery/hot springs). While hazards like pyroclastic flows, toxic gases, and lahars present severe risks, advanced volcano monitoring and clear hazard-mapping allow people to safely evacuate in time, making managed living near volcanoes viable and sustainable.

3(a)(i) [4 marks]
- Constructive plates move apart / drift away (1)
- Magma rises and solidifies to form new crust at constructive boundary (1)
- Destructive plates move together / collide (1)
- Subduction occurs / denser oceanic plate sinks and melts at destructive boundary (1)

3(a)(ii) [2 marks]
- Tsunamis (1)
- Landslides / mudflows / lahars (1)

3(b)(i) [2 marks]
- Correct calculation of difference: 1170 (1)
- Correct percentage calculation: 1462.5% (1)

3(b)(ii) [4 marks]
Any four from:
- Upward movement of magma cracks surrounding rocks (1)
- This generates seismic tremors / earthquakes (1)
- Frequency of tremors increases as magma nears the surface (1)
- Magma contains dissolved gases (1)
- Gases escape / vent as pressure decreases near surface (1)
- Rising gas emission rates indicate magma is close to erupting (1)

3(c) [3 marks]
Any three from:
- Search and rescue operations (1)
- Provision of emergency food, clean water, and shelter (1)
- Evacuation of affected zones (1)
- Clearing ash from roads / rebuilding infrastructure (1)
- Medical treatment for inhalation of toxic ash (1)

3(d) [5 marks]
- Level 3 (5 marks): Well-balanced evaluation of both opportunities (fertile volcanic soil, geothermal energy, tourism, mineral deposits) and risks (pyroclastic flows, ash fall, lahars). Argues effectively how monitoring/planning permits safe living without needing permanent relocation.
- Level 2 (3-4 marks): Explains opportunities and risks but lacks link to why permanent relocation might or might not be necessary, or lacks detail on monitoring.
- Level 1 (1-2 marks): Simple list of volcanic benefits or dangers with little evaluative reasoning.

**(a)(i)** Systematic sampling.
**(a)(ii)** It allows the researcher to study changes or gradients in orchid distribution as altitude/slope increases; it is highly structured and easy to replicate.
**(a)(iii)** Area of one quadrat = \(2 \text{ m} \times 2 \text{ m} = 4 \text{ m}^2\).
Total area sampled = \(10 \times 4 \text{ m}^2 = 40 \text{ m}^2\).
Orchids per \(1 \text{ m}^2 = 12 / 40 = 0.3\).
Orchids per hectare = \(0.3 \times 10000 = 3000\).

**(b)(i)** Graph with:
- Axes labeled (x-axis: Year, y-axis: Estimated Orchid Population).
- Linear scales starting at 0 or a clear break, covering at least half the grid.
- Points plotted accurately within half a small square.
- Points connected with straight, clean lines.
**(b)(ii)** Decrease = \(4500 - 1800 = 2700\).
Percentage decrease = \((2700 / 4500) \times 100 = 60.0\%\).
**(b)(iii)** Illegal logging/habitat fragmentation; agricultural encroachment/slashing-and-burning; poaching/wild collection of orchids; introduction of invasive species.

**(c)(i)** Development that meets the needs of the present without compromising the ability of future generations to meet their own needs.
**(c)(ii)** Advantages: provides funding for park management/rangers; creates conservation incentives/jobs for locals.
Disadvantages: foot traffic can trample rare flora/cause soil compaction; infrastructure development (trails/lodges) destroys habitat; tourists can introduce diseases or non-native pathogens.

**(a)(i)**
- 1 mark: Systematic (sampling).

**(a)(ii)**
- 1 mark: For identifying the presence of an environmental gradient (e.g., altitude, slope, temperature change up the mountain).
- 1 mark: For explaining that systematic sampling measures changes across this gradient systematically/unbiasedly.

**(a)(iii)**
- 1 mark: Calculate total sampled area = \(40 \text{ m}^2\).
- 1 mark: Calculate density as \(0.3 \text{ orchids/m}^2\) or show division: \(12 / 40\).
- 1 mark: Correct final calculation: \(3000\) (orchids per hectare). Accept correct calculation if there is an error carried forward from incorrect area.

**(b)(i)**
- 1 mark: Both axes labeled with units (Year on x-axis, Estimated Orchid Population on y-axis).
- 1 mark: Appropriate linear scale covering at least half of the grid.
- 1 mark: 4 to 5 points plotted correctly to within  half a small square.
- 1 mark: Points connected with a neat line.

**(b)(ii)**
- 1 mark: Correct subtraction: \(4500 - 1800 = 2700\).
- 1 mark: Correct percentage: \(60\%\) (or \(60.0\%\)).

**(b)(iii)**
- 2 marks: Any two from:
- Deforestation / logging / tree removal.
- Agriculture / crop planting / cattle grazing encroaching on the forest.
- Orchid collecting / illegal harvesting / poaching.
- Tourism / trampling by hikers.
- Pollution or introduction of invasive competitors.

**(c)(i)**
- 1 mark: Mentions meeting the needs of the present generation.
- 1 mark: Mentions not compromising/harming the ability of future generations to meet their own needs.

**(c)(ii)**
- 2 marks: Any two advantages, e.g.:
- Provides revenue to pay for forest rangers / anti-poaching patrols.
- Educates visitors about biodiversity conservation.
- Provides alternative income to locals, reducing their reliance on illegal logging.
- 2 marks: Any two disadvantages, e.g.:
- Trampling of orchids/rare plants along hiking trails.
- Soil erosion and compaction from tourist traffic.
- Construction of hotels/trails causes habitat destruction.
- Increased waste/pollution in pristine areas.

**(a)(i)** Synthetic/chemical fertilizer (or inorganic nitrogen fertilizer).
**(a)(ii)** Site B.
**(a)(iii)** At Site A (discharge point), the nitrates have just entered the water. As the water moves downstream to Site B, the high concentration of nitrates triggers a rapid growth of algae (algal bloom). When these algae die, aerobic bacteria decompose the dead organic matter. This decomposition process consumes large amounts of dissolved oxygen, leading to hypoxia (low DO) at Site B. Further downstream (Sites C–E), the nitrates are diluted or absorbed, and photosynthesis/turbulence restores oxygen levels.

**(b)(i)** Graph with:
- x-axis: Distance Downstream / km.
- y-axis: Concentration / mg/dm.
- Linear scale covering at least half the grid.
- All 5 points for Nitrate plotted and connected correctly with a line; all 5 points for Dissolved Oxygen plotted and connected with a different line/style.
- Key showing which line is Nitrate and which is Dissolved Oxygen.
**(b)(ii)** As distance downstream increases, the nitrate concentration decreases (non-linearly/rapidly at first, then leveling off).

**(c)(i)** 1. Planting buffer strips/riparian vegetation along riverbanks to absorb runoff before it enters the water.
2. Using organic fertilizers/compost which release nutrients more slowly, or practicing precision fertilizer application (applying only what crops need).
**(c)(ii)** 1. Fish suffocate/die due to lack of oxygen (fish kills).
2. Fish migrate away from the area, disrupting the local food web / reducing species biodiversity.
**(c)(iii)** 1. It helps identify how far the pollution plume travels and where the ecosystem recovers.
2. It prevents misleading conclusions from localized anomalies or point-source variations.

**(a)(i)**
- 1 mark: Synthetic / chemical / inorganic fertilizer (reject: pesticide / herbicide).

**(a)(ii)**
- 1 mark: Site B.

**(a)(iii)**
- 1 mark: Nitrate input causes rapid algal growth (algal bloom) between Site A and Site B.
- 1 mark: Algae die and sink to the bottom.
- 1 mark: Aerobic bacteria decompose the dead algae.
- 1 mark: The decomposition process uses up dissolved oxygen (aerobic respiration), causing DO to drop severely by the time water reaches Site B.

**(b)(i)**
- 1 mark: Both axes labeled with units (x-axis: Distance Downstream / km, y-axis: Concentration / mg/dm).
- 1 mark: Appropriate linear scale starting at 0, covering at least half the grid.
- 1 mark: Correct plotting of all 5 nitrate points.
- 1 mark: Correct plotting of all 5 dissolved oxygen points.
- 1 mark: Clear key distinguishing the two lines.

**(b)(ii)**
- 1 mark: Nitrate concentration decreases with distance downstream / inverse relationship.

**(c)(i)**
- 2 marks: Describe practice 1 (e.g., planting buffer strips of vegetation along the riverbank [1] which traps and absorbs fertilizer runoff [1]).
- 2 marks: Describe practice 2 (e.g., using organic fertilizers or slow-release fertilizers [1] which reduce the volume of free nitrates washed away during heavy rains [1], or drip irrigation / precision agriculture).

**(c)(ii)**
- 2 marks: Any two from:
- Fish mortality / fish kills / suffocation.
- Migration of fish to other areas.
- Reduced reproduction rates.
- Loss of sensitive fish species / shift to tolerant species (loss of biodiversity).

**(c)(iii)**
- 2 marks: Any two from:
- Shows the extent of the impact zone.
- Identifies the point of recovery.
- Detects secondary entry points of pollution downstream.
- Ensures data reliability / cross-checking.

**(a)(i)** ... forced down into the subduction zone. ... melts to form magma. ... known as lava.
**(a)(ii)** Graph with:
- x-axis: Distance West of Volcano / km.
- y-axis: Average Ash Thickness / mm.
- Linear scale covering at least half the grid.
- Points plotted accurately and connected with a smooth line or straight lines.
**(a)(iii)** As distance west increases, the average ash thickness decreases. The decrease is steep initially (between 4 and 12 km) and then becomes more gradual (between 12 and 20 km).

**(b)(i)** 1. Volcanic ash weathers to form highly fertile soil, ideal for high-yield agriculture.
2. Geothermal energy resources provide cheap, renewable electricity / volcanic landscapes attract tourism, creating jobs.
**(b)(ii)** Hot rocks underground heat water to produce steam. This high-pressure steam is piped to the surface. The steam turns a turbine, which rotates a generator to produce electricity.

**(c)(i)** 1. Seismometers to detect micro-earthquakes caused by magma moving upwards.
2. Tiltmeters/GPS to measure ground swelling or deformation as magma chambers fill.
3. Gas sensors to monitor changes in emissions of sulfur dioxide (\(\text{SO}_2\)) or carbon dioxide (\(\text{CO}_2\)).
**(c)(ii)** Hazard maps identify areas at high risk from lahars, lava flows, or pyroclastic flows based on historical eruptions. This allows governments to restrict building in high-risk zones, plan safe evacuation routes, and position emergency shelters in safe zones.

**(a)(i)**
- 1 mark: subduction
- 1 mark: magma
- 1 mark: lava

**(a)(ii)**
- 1 mark: Axes labeled correctly with units (x-axis: Distance West of Volcano / km, y-axis: Average Ash Thickness / mm).
- 1 mark: Linear scale covering at least half of the grid.
- 1 mark: All 5 points plotted correctly within  half a small square.
- 1 mark: Clean line connecting all plotted points.

**(a)(iii)**
- 1 mark: Thickness decreases as distance increases / negative relationship.
- 1 mark: Non-linear trend / rate of decrease slows down with distance.

**(b)(i)**
- 2 marks: Any two from:
- Fertile soils / high crop yields.
- Geothermal energy (heating/electricity).
- Tourism opportunities / employment.
- Extraction of valuable minerals / sulphur mining.

**(b)(ii)**
- 1 mark: Heat from underground rocks / magma warms water into steam.
- 1 mark: High-pressure steam turns a turbine.
- 1 mark: The turbine rotates a generator to generate electricity.

**(c)(i)**
- 3 marks: Any three from:
- Seismometers / seismic monitoring to detect harmonic tremors / earthquakes.
- Tiltmeters / satellite (InSAR) / GPS to measure ground deformation / swelling.
- Gas spectrometers to analyze volcanic gas composition / increasing sulfur dioxide.
- Thermal imaging to monitor changes in ground surface temperature.
- Phreatic activity / water temperature in crater lakes.

**(c)(ii)**
- 1 mark: Identifies high-risk zones (e.g., paths of lahars, pyroclastic flows).
- 1 mark: Restricts development / zoning laws to prevent building in high-risk areas.
- 1 mark: Dictates the location of evacuation routes and emergency shelters outside of hazard zones.

**(a)(i)** Graph with:
- x-axis: Month.
- y-axis: Electricity / MWh.
- Appropriate linear scale covering at least half the grid.
- Pairs of bars plotted correctly for each of the 6 months (one bar for Demand, one for Generation).
- Clear key distinguishing Demand and Generation.
**(a)(ii)** May and July.
**(a)(iii)** \((180 / 450) \times 100 = 40.0\%\).

**(b)(i)** Wind and solar energy are intermittent (weather-dependent). At night or on calm days, generation falls significantly, which would cause blackouts if there is no backup system to meet the base load demand.
**(b)(ii)** 1. Pumped-storage hydroelectricity.
2. Compressed air energy storage (or flywheel energy storage / demand-side management / interconnectors).
**(b)(iii)** 1. High and volatile cost of importing fossil fuels (economic instability).
2. Risk of supply chain disruptions due to storms/shipping delays.
3. Risk of ocean diesel spills during transport, damaging marine ecosystems and tourism.

**(c)(i)** Microscopic marine organisms (plankton) died and sank to the seabed millions of years ago. They were buried under layers of sediment (silt/mud). Over geological time, heat and high pressure in anaerobic conditions converted their remains into crude oil.
**(c)(ii)** Oil spills from tanker accidents / shipping emissions contributing to air pollution / noise pollution affecting marine mammals.

**(a)(i)**
- 1 mark: Axes labeled correctly with units (x-axis: Month, y-axis: Electricity / MWh).
- 1 mark: Linear scale on y-axis covering at least half of the grid.
- 1 mark: All 12 bars plotted to correct height (within  half a small square).
- 1 mark: Bars drawn in matching pairs for each month, with gaps between months.
- 1 mark: Clear key labeling Demand and Wind-Solar Generation.

**(a)(ii)**
- 2 marks: May AND July (1 mark for each).

**(a)(iii)**
- 1 mark: Show working: \(180 / 450 \times 100\).
- 1 mark: Correct calculation: \(40\%\) (or \(40.0\%\)).

**(b)(i)**
- 1 mark: Solar is unavailable at night / wind is variable / weather-dependent (intermittent).
- 1 mark: Demand must be met instantaneously to maintain grid frequency/prevent blackouts.
- 1 mark: Base load cannot be guaranteed without a constant backup source (e.g., diesel generator or storage).

**(b)(ii)**
- 2 marks: Any two from:
- Pumped-storage hydroelectricity.
- Compressed air storage.
- Flywheels.
- Geothermal energy backup.
- Smart grid / demand-side response.

**(b)(iii)**
- 3 marks: Any three from:
- High costs of fuel imports / improves balance of trade.
- Energy security / independence from global supply shocks.
- Risk of fuel spills during maritime transport damaging coral reefs/tourism.
- High cost of local diesel generators maintenance.
- Diversifying the energy mix.

**(c)(i)**
- 1 mark: Marine organisms / plankton die and accumulate on the ocean floor under sediments.
- 1 mark: Heat and high pressure in anaerobic conditions convert organic matter over millions of years.

**(c)(ii)**
- 1 mark: Risk of marine oil spills during shipping / greenhouse gases from tanker exhaust / noise pollution.