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

(a) First, calculate the total emissions: \(150 + 75 + 12 + 13 = 250\) thousand tonnes.
Next, calculate the percentage contributed by electricity generation: \(\frac{150}{250} \times 100 = 60\%\).

(b) Strategies to reduce \(\text{SO}_2\) from power stations include:
- Flue-gas desulfurization (scrubbers) to remove sulfur dioxide gas from chimneys before it enters the atmosphere.
- Switching fuel sources from high-sulfur coal to low-sulfur coal or natural gas.
- Implementing renewable energy sources (such as wind or solar power) to replace coal combustion entirely.

(c) Mechanism of lake acidification:
- Sulfur dioxide emitted into the atmosphere reacts with moisture/water droplets, oxygen, and other oxidants.
- This reaction forms sulfuric acid dissolved in clouds/moisture.
- The acid falls as wet deposition (acid rain).
- Runoff washes this acidic water from the land into surrounding lakes, lowering their pH and disrupting aquatic life.

**(a)**
M1: Correct calculation of total emissions (250 thousand tonnes) OR correct formula setup: \(\frac{150}{\text{Total}} \times 100\) [1]
M2: Correct final answer: 60 (%) [1]

**(b)**
Award 1 mark for each valid strategy up to a maximum of 2:
- installation of flue-gas desulfurization / scrubbers [1]
- switching to low-sulfur coal / low-sulfur fuel [1]
- replacing coal with natural gas [1]
- transitioning to renewable energy sources (e.g., wind, solar, tidal) [1]
- energy conservation measures to reduce electricity demand [1]

**(c)**
Award 1 mark for each valid point up to a maximum of 3:
- sulfur dioxide reacts with water vapor / droplets / clouds in the atmosphere [1]
- forms sulfuric acid [1]
- falls as acid rain / acid precipitation / acid deposition [1]
- acidic runoff flows into / enters lakes, lowering the pH [1]

(a) (i) The highest flow rate of water measured in a river channel during or after a storm event is called the peak discharge.
(ii) The interval of time between the occurrence of peak rainfall and the peak discharge is defined as the lag time.

(b) Urban development increases river flood risk because:
- Impermeable surfaces: Replacing natural vegetated soil with concrete, tarmac, and buildings prevents precipitation from infiltrating the ground. This substantially increases surface runoff.
- Artificial drainage: Gutters, underground pipes, and storm drains carry runoff directly and rapidly into nearby river systems, causing the water level to rise much faster and shortening the lag time.

(c) Soft engineering methods use natural systems to mitigate flooding:
- Afforestation: Planting trees in the upper catchment increases interception and transpiration, reducing surface runoff.
- Floodplain zoning: Restricting construction on flood-prone flat land adjacent to the river ensures water can spread naturally without damaging property.
- Creating wetlands or retention basins: Diverting water into designated wetland storage zones during heavy rain reduces downstream peak flows.

**(a)**
(i) peak discharge [1]
(ii) lag time [1]

**(b)**
Award 1 mark for each explanation (up to a maximum of 2):
- concrete / tarmac / built-up areas are impermeable, which prevents infiltration / increases surface runoff [1]
- storm drains / gutters transport rainwater directly to rivers, speeding up the runoff rate / reducing lag time [1]
- deforestation / removal of trees to build houses reduces interception [1]

**(c)**
Award 1 mark for each valid soft engineering strategy (up to a maximum of 3):
- afforestation / planting trees [1]
- floodplain zoning / restricting development on floodplains [1]
- wetland restoration / creation of retention ponds / reservoirs [1]
- river restoration / allowing rivers to return to their natural meandering courses [1]
- soil conservation / building small debris dams in upper tributaries [1]

(a)(i) 74% - 5% = 69%. (a)(ii) The overall electricity demand of the island increased, so wind's fixed capacity represented a smaller proportion of the total. Also, wind is intermittent and may have experienced lower wind speeds in 2023. (b) Cold water is pumped deep underground into hot rocks. The water is heated by geothermal energy to produce steam. The high-pressure steam rises to the surface and turns a turbine, which drives a generator to produce electricity. (c) Geothermal is a renewable resource that does not deplete. It reduces carbon emissions and air pollution compared to burning diesel. It is a reliable base-load power source, unlike solar or wind. It reduces the island's dependency and economic cost of importing expensive diesel fuel. (d) Agree to some extent: Renewables reduce greenhouse gas emissions, mitigating global climate change which threatens all ecosystems. They reduce local air and water pollution from fossil fuels. Disagree to some extent: Construction of geothermal plants can cause localized habitat destruction, soil erosion, and release toxic underground gases. Wind turbines can harm birds and bats. Large solar farms require clearing significant areas of land, destroying habitats.

(a)(i) 69% [1]. (a)(ii) Any two from: total electricity demand/generation increased [1]; wind is intermittent/unreliable [1]; weather variations/less wind in 2023 [1]. (b) Water pumped underground heated by hot rocks [1]; steam produced turns a turbine [1]; turbine drives/spins a generator to produce electricity [1]. (c) Any four from: geothermal is renewable/will not run out [1]; produces fewer greenhouse gases/less CO2 [1]; provides a constant/reliable/base-load energy supply [1]; reduces air pollution/acid rain precursors [1]; saves money on importing expensive diesel fuel [1]; increases energy security for the island [1]. (d) Level 3 (5 marks): Balanced evaluation showing deep understanding of both positive global impacts and negative local ecological impacts of renewables, with clear supporting examples and a reasoned conclusion. Level 2 (3-4 marks): Discusses both advantages and disadvantages but lacks depth or balanced evaluation. Level 1 (1-2 marks): Simple points, mostly agreeing or disagreeing with limited ecological detail.

(a)(i) As distance from the forest edge increases, the mean number of native wildflower species per quadrat increases. The rate of increase is slow at first (from 0 to 20m) and then becomes more rapid. (a)(ii) Edge effects: higher wind speeds/temperatures/sunlight near the edge dry out the soil. Higher density of Invasive Vine X near the edge outcompetes native wildflowers for light/space/nutrients. (b) Lay a tape measure (transect line) from the forest edge extending 50 meters into the forest. Place a quadrat at regular fixed intervals (e.g., every 5 meters) along the tape. Count and record the number of different native wildflower species inside each quadrat. (c) Forests provide ecosystem services like carbon sequestration and oxygen production. They maintain soil stability and prevent erosion. They provide resources like timber, medicines, and potential genetic material for crops. (d) Seed banks: Pros: occupy very little space, cost-effective for long-term storage, protects seeds from pests/diseases/natural disasters. Cons: cannot save species that do not produce seeds, does not protect the natural habitat, species do not evolve in response to changing environments. National parks: Pros: conserves the entire ecosystem and food webs, allows natural evolution, promotes ecotourism. Cons: expensive to manage, vulnerable to poaching, climate change, and invasive species.

(a)(i) Mean number of wildflower species increases with distance [1]; data quote showing this trend (e.g., 2 species at 0m to 13 species at 50m) [1]. (a)(ii) Any two from: edge effects/more wind/sunlight/higher evaporation [1]; competition from invasive species/Invasive Vine X [1]; human disturbance near forest edges [1]; soil compaction/degradation near the edge [1]. (b) Lay out a tape measure from the forest edge into the forest [1]; place quadrats at regular/systematic intervals [1]; identify and count native wildflower species in each quadrat [1]. (c) Any three from: carbon sink/reduces greenhouse gases [1]; prevents soil erosion/stabilizes soil [1]; source of medicines/useful genes [1]; maintains food webs/ecological balance [1]; ecotourism/aesthetic value [1]. (d) Level 3 (5 marks): Well-structured comparison addressing both seed banks (ex-situ) and national parks (in-situ), highlighting pros and cons of each, concluding with a balanced evaluation of their roles. Level 2 (3-4 marks): Describes both methods but lacks a clear comparative evaluation or misses key advantages/disadvantages. Level 1 (1-2 marks): Simple descriptive statements about one or both methods with no real evaluation.

(a)(i) 380 - 150 = 230 m3/s. (a)(ii) Lag time is the time interval between peak rainfall and peak river discharge. (a)(iii) Urbanization creates impermeable surfaces like concrete and asphalt, which prevent rainwater from infiltrating the ground. This leads to increased surface runoff. Human-made drainage systems and storm drains transport this runoff directly and rapidly into the river, reducing the lag time and dramatically increasing the peak discharge. (b) Tree canopies intercept rainfall, reducing the volume of water hitting the soil directly. Tree roots improve soil structure, increasing infiltration rates and soil water storage capacity. Trees also transpire water back into the atmosphere, overall reducing and delaying runoff into the river. (c) Damage to homes and infrastructure, displacing families. Financial losses for businesses due to flooding of premises and disrupted transport networks. Contamination of drinking water supplies, leading to outbreaks of water-related diseases. (d) Hard engineering is highly effective at physically controlling water flows and protecting specific areas, but it is very expensive, visually intrusive, and disrupts natural river ecosystems. Soft engineering is cheaper, works with natural processes, and is ecologically sustainable, but it restricts land development on floodplains and does not active prevent water from rising.

(a)(i) 230 m3/s (accept 230) [1]. (a)(ii) Time between peak rainfall and peak discharge [1]. (a)(iii) Impermeable surfaces/concrete prevent infiltration [1]; increases surface runoff [1]; artificial drains/gutters speed up water delivery to the river [1]; this reduces lag time and increases peak flow/discharge [1]. (b) Interception by leaves/canopy reduces run-off [1]; roots increase infiltration/absorb water [1]; transpiration removes water from the system [1]. (c) Any three from: damage to property/homes [1]; business closures/loss of income [1]; cost of repairs/insurance increases [1]; water contamination/spread of disease [1]; disruption to transport/roads [1]; loss of life/injury [1]. (d) Any three from: hard engineering physically controls/stops water whereas soft engineering manages land use [1]; hard engineering is more expensive to build/maintain than soft engineering [1]; hard engineering can disrupt ecosystems/cause erosion downstream [1]; soft engineering (e.g. zoning) restricts where people can build/live [1].

(a)(i) There is a negative correlation: as soil pH increases (becoming less acidic), the canopy loss percentage decreases. For example, at pH 4.1 canopy loss is 55%, while at pH 5.6 it is only 8%. (a)(ii) Sulfur dioxide gas is released into the atmosphere from burning coal. It reacts with water vapor, oxygen, and other chemicals in the atmosphere to form sulfuric acid. This falls as acid precipitation (acid rain), which directly adds hydrogen ions to the soil, lowering its pH. (b) Acid rain dissolves and washes away essential nutrients (like calcium and magnesium) from the soil, depriving trees of nourishment. It also releases toxic aluminum ions into the soil, which damage tree roots and reduce water uptake. Additionally, it directly damages leaf cuticles, reducing photosynthesis. (c) Installing flue-gas desulfurization (FGD) systems, also known as scrubbers, which neutralize sulfur dioxide using alkaline slurries like lime. Switching to low-sulfur coal or transitioning to renewable energy sources like wind and solar. (d) Agree: Acid rain is a transboundary pollutant; emissions from one country are carried by winds and fall as acid rain in another. Therefore, international treaties (like the UNECE Convention on Long-range Transboundary Air Pollution) are essential to enforce emission cuts across borders. Disagree: Local and national actions are also highly effective, such as national laws mandating scrubbers or liming affected lakes and soils locally to neutralize acidity. Transitioning to green domestic energy policies reduces emissions at the source without relying solely on international consensus.

(a)(i) As soil pH increases, canopy loss decreases/negative correlation [1]; data reference comparing two plots (e.g., plot A has pH 4.1 and 55% loss, plot E has pH 5.6 and 8% loss) [1]. (a)(ii) SO2 gas is released into the atmosphere [1]; reacts with atmospheric water/oxygen to form sulfuric/sulfurous acid [1]; falls as acid rain/deposition, lowering soil pH [1]. (b) Any two from: leaches/removes essential nutrients (calcium/magnesium) from soil [1]; releases toxic aluminum ions which damage roots [1]; damages waxy cuticle on leaves, reducing photosynthesis [1]; weakens trees making them vulnerable to pests/diseases [1]. (c) Any two from: install flue-gas desulfurization (FGD) / scrubbers [1]; use low-sulfur coal [1]; switch to renewable energy sources/nuclear [1]; coal gasification/cleaning coal before burning [1]. (d) Level 3 (5-6 marks): Comprehensive and balanced discussion of the transboundary nature of acid rain, the role of international agreements, balanced against the critical importance of national regulations, industrial technologies, and local remediation strategies. Level 2 (3-4 marks): Explains the importance of international agreements but with limited comparison to national/local solutions, or lacks detail. Level 1 (1-2 marks): Simple points agreeing or disagreeing, with little ecological or political context.

This is a level-marked question. To score 5–6 marks (Level 3), the candidate must provide a coherent, structured, and balanced evaluation that develops both sides of the argument before reaching a clear conclusion. Precise scientific terms such as 'greenhouse gas emissions', 'baseload power', 'decommissioning', and 'radioactive waste' should be used.

For a Level 2 response (3–4 marks), the candidate should develop their points but the evaluation may lack balance or detail, focusing heavily on either benefits or limitations.

For a Level 1 response (1–2 marks), the response will be descriptive, simple, or presented as a basic list of advantages and disadvantages without critical evaluation.

Level 3 [5–6 marks]
A coherent response is given that develops and supports the candidate's conclusion using relevant details and examples. Indicative content and subject-specific vocabulary are generally used precisely and accurately. Good responses are likely to present a balanced evaluation of the statement.

Level 2 [3–4 marks]
Development and support of the conclusion is evident, though the response may lack some coherence and/or detail. Irrelevant detail may be present. Indicative content and subject-specific vocabulary are used but may lack some precision and/or accuracy. Responses contain evaluation of the statement, but this may not be balanced.

Level 1 [1–2 marks]
The response may be limited in development and/or support. Contradictions and/or irrelevant detail may be present. Indicative content and subject-specific vocabulary may be limited or absent. Responses may lack structure or be in the form of a list. Evaluation may be limited or absent.

No response or no creditable response [0 marks]

Indicative content:
Reasons why nuclear power is the best solution:
- High energy density / can meet large global energy demand (reliable baseload power).
- No greenhouse gas (carbon dioxide) emissions during generation, helping to limit global warming.
- Not weather-dependent, providing continuous electricity compared to wind/solar.
- Reduces acid rain and smog by decreasing reliance on coal/gas (no SO2 or NOx emissions during operation).

Reasons why nuclear power is not the best solution / alternatives are better:
- High construction, maintenance, and decommissioning costs.
- Long-term disposal of radioactive waste remains an unresolved hazard.
- Catastrophic risks from accidents/leaks (e.g., Fukushima, Chernobyl).
- Public opposition and safety concerns.
- Renewable energy (solar, wind, hydro) is safer, increasingly cheap, and completely infinite.
- Reduction in energy consumption and improved efficiency can also lower emissions.

Difference in water use = \(4200 - 3444 = 756\text{ m}^3/\text{ha}\).
Percentage decrease = \(\frac{756}{4200} \times 100 = 18\%\).

M1 for showing correct method to find the decrease or percentage: \(\frac{4200 - 3444}{4200} \times 100\) [1]
A1 for \(18\%\) [1]

Net population change = \(\text{births} - \text{deaths} + \text{immigrants} - \text{emigrants}\)
Net change = \(4500 - 1200 + 1500 - 800 = 4000\).

M1 for correct working showing additions and subtractions: \(4500 - 1200 + 1500 - 800\) or equivalent [1]
A1 for \(4000\) [1]

Total maximum capacity = \(25 \times 3.2\text{ MW} = 80\text{ MW}\).
Average power generated = \(80\text{ MW} \times 0.30 = 24\text{ MW}\).

M1 for calculating total capacity: \(25 \times 3.2 = 80\text{ MW}\) OR for showing the correct multiplication by capacity factor: \(80 \times 0.30\) [1]
A1 for \(24\) (accept with unit \(\text{MW}\)) [1]

\(N = \frac{120 \times 150}{30} = 600\)

M1 for correct substitution of values into the formula: \(\frac{120 \times 150}{30}\) [1]
A1 for \(600\) [1]

Difference in peak discharge = \(45 - 18 = 27\text{ m}^3/\text{s}\).
Catchment B has a shorter lag time and higher peak discharge, making it more vulnerable to flash flooding.

M1 for calculating the difference in peak discharge: \(27\text{ m}^3/\text{s}\) [1]
A1 for identifying Catchment B as more vulnerable [1]

Difference in yield = \(7.35 - 4.2 = 3.15\text{ tonnes/hectare}\).
Percentage increase = \(\frac{3.15}{4.2} \times 100 = 75\%\).

M1 for correct calculation step showing the difference (3.15) or correct fractional setup: \(\frac{3.15}{4.2} \times 100\) [1]
A1 for \(75\%\) [1]

Ratio = \(85 : 17\).
Dividing both sides by the greatest common divisor (17):
\(85 / 17 = 5\)
\(17 / 17 = 1\)
Ratio = \(5 : 1\).

M1 for showing correct initial ratio comparison: \(85 : 17\) or intermediate simplification [1]
A1 for \(5 : 1\) [1]

Maximum TAC = \(45\,000 \times 0.12 = 5400\text{ tonnes}\).

M1 for showing correct method to calculate percentage: \(45\,000 \times \frac{12}{100}\) [1]
A1 for \(5400\) (accept with unit tonnes) [1]

Increase in solar generation: \(39\text{ GWh} - 15\text{ GWh} = 24\text{ GWh}\). Percentage increase: \(\frac{24}{15} \times 100 = 160\%\).

1 mark for showing correct working: \(\frac{39 - 15}{15} \times 100\) or equivalent. 1 mark for the correct final answer: \(160\%\).

Natural increase = \(14.5 - 7.2 = 7.3\) per 1000. Net migration = \(5.3 - 2.1 = 3.2\) per 1000. Overall growth rate = \(7.3 + 3.2 = 10.5\) per 1000.

1 mark for calculating either natural increase (\(7.3\) per 1000) or net migration (\(3.2\) per 1000). 1 mark for the correct final answer of \(10.5\) per 1000.

Area of the meadow: \(80\text{ m} \times 50\text{ m} = 4000\text{ m}^2\). Mean number of plants per quadrat: \(\frac{45}{25} = 1.8\text{ plants/m}^2\). Estimated population: \(1.8 \times 4000 = 7200\text{ plants}\).

1 mark for calculating the total area of the meadow (\(4000\text{ m}^2\)) or the mean number of plants per quadrat (\(1.8\)). 1 mark for the correct final answer of \(7200\).

Combined usage: \(40\text{ l} + 35\text{ l} = 75\text{ l}\). Total household usage: \(160\text{ l}\). Combined percentage: \(\frac{75}{160} \times 100 = 46.875\%\).

1 mark for dividing the combined usage of 75 by the total usage of 160. 1 mark for the correct final answer of \(46.9\%\) (accept \(46.88\%\) or \(47\%\)).

Absolute decrease: \(48.0 - 31.2 = 16.8\ \mu\text{g/m}^3\). Percentage decrease: \(\frac{16.8}{48.0} \times 100 = 35\%\).

1 mark for showing correct working: \(\frac{48.0 - 31.2}{48.0} \times 100\) or equivalent. 1 mark for the correct final answer: \(35\%\).

Yield per hectare for Plot A: \(\frac{12.5}{2.5} = 5.0\text{ tonnes/ha}\). Yield per hectare for Plot B: \(\frac{18.0}{2.5} = 7.2\text{ tonnes/ha}\). Difference: \(7.2 - 5.0 = 2.2\text{ tonnes per hectare}\).

1 mark for calculating individual yields per hectare (\(5.0\) and \(7.2\)) or dividing the yield difference (\(5.5\)) by \(2.5\). 1 mark for the correct final answer of \(2.2\text{ tonnes per hectare}\) (accept \(2.2\text{ t/ha}\)). Reject answers without correct units.

To construct the bar chart:
1. Label the x-axis as 'Renewable energy source' and list the five sources: biomass, geothermal, hydroelectric, solar, and wind.
2. Label the y-axis as 'Annual electricity generated / MWh'.
3. Choose a linear scale for the y-axis that starts at 0 and goes up to at least 450 MWh (e.g., 50 MWh per major grid division) so that the data covers more than half of the grid space.
4. Draw five bars of equal width representing each energy source: biomass at 150 MWh, geothermal at 80 MWh, hydroelectric at 310 MWh, solar at 240 MWh, and wind at 420 MWh. Ensure there are equal gaps between the bars.

Award 1 mark for each of the following criteria (maximum 4 marks):
- **M1**: Both axes fully labeled with units on the y-axis ('Annual electricity generated / MWh' and 'Renewable energy source').
- **M2**: Suitable linear scale on the y-axis (e.g., 50 or 100 MWh divisions) so that the plotted bars occupy at least half of the vertical grid area.
- **M3**: All five bars plotted accurately within +/- half a small square of the grid.
- **M4**: Bars are drawn with equal width and separated by equal gaps.

Geothermal energy is a continuous, non-intermittent source of power that does not depend on weather conditions, unlike wind energy which fluctuates with wind speed. By combining them, geothermal acts as a baseload supply, ensuring that electricity is still generated when there is little to no wind, thus preventing power shortages or blackouts.

Award up to 3 marks for the following points:
- M1: Geothermal energy is a reliable/constant/baseload source of electricity (does not depend on weather/wind) [1]
- M2: Wind energy is intermittent/variable/unreliable [1]
- M3: Geothermal power can meet energy demands during calm/windless periods, preventing power blackouts/shortages [1]

A wildlife corridor facilitates the safe movement of organisms between isolated forest fragments. This movement increases genetic diversity by allowing gene flow between previously separated populations, reducing inbreeding. Additionally, it helps species migrate to find resources or mates, and provides an escape route during localized disasters, maintaining overall species richness.

Award up to 3 marks for the following points:
- M1: Allows movement/migration/dispersal of species between the isolated woodland fragments [1]
- M2: Promotes gene flow / increases genetic variation / prevents inbreeding depression [1]
- M3: Allows species to escape localized threats (e.g., disease, fire) OR find new food sources/mates (reducing extinction risk) [1]

Permeable pavements and bioswales mimic natural soil conditions by allowing rainwater to percolate into the ground rather than running off concrete surfaces immediately. This slows down the rate at which water reaches the local river channel, spreading the volume of runoff over a longer time period and reducing the maximum river level (peak discharge).

Award up to 3 marks for the following points:
- M1: Bioswales/permeable pavements increase water infiltration into the ground (reducing surface runoff) [1]
- M2: Slows down the rate/speed at which rainwater reaches the river / increases the lag time [1]
- M3: Decreases the peak discharge/maximum water level of the river (preventing it from overflowing) [1]

Underground aquifers provide a secure storage medium that prevents water from evaporating in hot, dry environments. They also filter and protect water from surface pollutants like pesticides or sewage, and they eliminate the need to flood large valleys, avoiding land loss and community displacement.

Award up to 3 marks for three distinct advantages:
- M1: Minimizes/prevents loss of water through evaporation (which is very high in hot/arid regions) [1]
- M2: Protects water from surface pollutants/contamination/pathogens/algal blooms [1]
- M3: Does not require land to be flooded (avoids loss of agricultural land / avoids displacement of local populations) [1]
- Accept: Reduces breeding grounds for water-borne vectors (e.g., mosquitoes) [1]

Financial incentives like free childcare and paid parental leave make raising children more affordable, driving up the birth rate. In the long term, these children will enter the workforce, ensuring a stable tax base to fund healthcare and pensions for the elderly, while decreasing the dependency ratio.

Award up to 3 marks for the following points:
- M1: Reduces the financial cost of raising children, encouraging families to have more babies / raising the birth rate [1]
- M2: Increases the size of the future workforce/working-age population (which supports tax revenues and pensions) [1]
- M3: Lowers the future dependency ratio (fewer elderly dependents per active worker) [1]

Drip systems feed water directly to the plant's roots through a network of pipes and emitters. This prevents water from being wasted on empty spaces between crops or evaporating from the hot soil surface. By providing precise quantities of water, it keeps roots aerated and prevents the accumulation of harmful salts at the surface, which is common with flood irrigation.

Award up to 3 marks for the following points:
- M1: Water is applied directly to the base/root zone of the plants (minimizing waste on non-crop areas) [1]
- M2: Reduces water loss from evaporation and surface runoff [1]
- M3: Prevents overwatering/waterlogging/soil salinisation, keeping roots aerated and healthy [1]

Catalytic converters utilize precious metal catalysts to promote reduction and oxidation reactions. Toxic carbon monoxide (\(\text{CO}\)) is oxidized to carbon dioxide (\(\text{CO}_2\)). Harmful nitrogen oxides (\(\text{NO}_x\)), which are primary causes of acid rain and urban smog, are reduced to harmless nitrogen gas (\(\text{N}_2\)). Unburnt hydrocarbons (volatile organic compounds) are also fully oxidized to water and carbon dioxide.

Award up to 3 marks for the following points:
- M1: Converts toxic carbon monoxide (\(\text{CO}\)) into less harmful carbon dioxide (\(\text{CO}_2\)) [1]
- M2: Reduces nitrogen oxides (\(\text{NO}_x\)) into harmless nitrogen gas (\(\text{N}_2\)) [1]
- M3: This reduction in \(\text{NO}_x\) prevents the formation of acid rain / photochemical smog OR converts unburnt hydrocarbons to water and carbon dioxide [1]

Relying on chemical pesticides alone often leads to rapid resistance in pest populations. IPM uses a combination of biological controls, crop rotation, and physical barriers, which prevents resistance. Since fewer chemicals are sprayed, helpful predatory insects are saved, and the contamination of nearby freshwater ecosystems via agricultural runoff is greatly reduced.

Award up to 3 marks for three distinct benefits:
- M1: Reduces the risk of pests developing resistance to chemical treatments [1]
- M2: Protects non-target / beneficial organisms (such as natural predators of pests and pollinating insects) [1]
- M3: Decreases pesticide runoff into water systems, reducing water pollution / bioaccumulation / harm to aquatic life [1]
- Accept: Reduces chemical residues on food crops (healthier for consumers) OR lowers long-term input costs for chemical purchase [1]

Cold water is pumped deep underground into hot rock layers where it is heated to form steam. The steam is extracted under high pressure and directed onto the blades of a turbine, causing it to spin. The spinning turbine is connected to a generator, which generates electricity. The cooled water is often condensed and returned underground to repeat the cycle.

Award up to 3 marks for the following points:
- cold water is pumped down into hot rocks OR hot water/steam is extracted from underground [1]
- steam under high pressure turns a turbine [1]
- the turbine rotates a generator which produces electricity [1]

Wildlife corridors connect isolated patches of habitat, allowing animals to move freely to find sufficient food, resources, and mates. This movement increases gene flow between populations, reducing the risks of inbreeding and genetic depletion. Additionally, it allows species to migrate and recolonize areas where local extinctions may have occurred, enhancing overall ecosystem stability and biodiversity.

Award up to 3 marks for any three of the following points:
- allows animals to migrate/move between isolated habitats to find food/water/resources [1]
- increases gene flow / prevents inbreeding / increases genetic diversity [1]
- allows recolonisation of areas where species became locally extinct [1]
- provides shelter/protection from predators while moving across open/agricultural land [1]

Permeable paving blocks have gaps or porous materials that allow rainwater to infiltrate into the ground instead of running off. By increasing infiltration, the volume of surface runoff is greatly reduced. This slows down the rate at which water reaches storm drains and local rivers, lowering the peak discharge and preventing urban drainage systems from becoming overwhelmed.

Award up to 3 marks for the following points:
- increases infiltration / allows rainwater to soak into the soil [1]
- reduces the volume/speed of surface runoff [1]
- reduces the load on stormwater drains / lowers peak discharge in local rivers [1]

Rainwater harvesting improves water availability by storing rainwater during periods of heavy rainfall for use during dry seasons, reducing the need to travel long distances for water. It improves water quality because rainwater is a clean source that is free from underground pollutants like high levels of salt, fluoride, or arsenic commonly found in regional wells. Storing it in sealed underground taankas also prevents contamination from pathogens and animal waste.

Award up to 3 marks, with at least 1 mark for availability and 1 mark for quality:
- Availability: stores water during the wet season to use during dry periods / provides a reliable local source of water [1]
- Quality: rainwater is free from underground chemical contaminants e.g. fluoride/arsenic/salts [1]
- Quality: closed storage prevents contamination from surface runoff/pathogens/animal waste [1]

An aging population poses several economic challenges. First, a shrinking working-age population leads to labor shortages, which can slow down economic growth and productivity. Second, the government faces increased financial strain due to the high cost of providing state pensions and elderly care. Third, there is a significant rise in healthcare costs and demand on medical services, which must be funded by a smaller pool of taxpayers, leading to potential fiscal deficits.

Award 1 mark for each described economic challenge, up to a maximum of 3 marks:
- labor shortage / smaller working-age population leading to lower productivity [1]
- increased government expenditure on state pensions/retirement benefits [1]
- increased cost of healthcare services / higher demand on hospitals and medical staff [1]
- reduced government tax revenue due to fewer working individuals paying income tax [1]

Drip irrigation increases water conservation by applying water slowly and directly to the soil surface around the plant roots. This targeted application minimizes water loss through evaporation, as the water is not exposed to the air over a large surface area like in flood irrigation. It also prevents water from running off the fields or being wasted on uncultivated soil between crop rows, reducing overall water consumption.

Award up to 3 marks for the following points:
- water is applied directly to the plant root zone rather than flooding the entire field [1]
- minimizes water loss through evaporation [1]
- prevents surface runoff / reduces water wastage on uncropped soil [1]

Photochemical smog is formed by the reaction of primary pollutants, mainly nitrogen oxides (NOx) and volatile organic compounds (hydrocarbons), in the presence of sunlight. Catalytic converters chemically reduce nitrogen oxides into harmless nitrogen gas (N2) and oxidize unburnt hydrocarbons into carbon dioxide (CO2) and water (H2O). By significantly decreasing the emissions of these key precursor pollutants, the reactions that produce ground-level ozone and photochemical smog are prevented.

Award up to 3 marks for the following points:
- catalytic converters reduce nitrogen oxides (NOx) into harmless nitrogen gas (N2) [1]
- they oxidize unburnt hydrocarbons / carbon monoxide (CO) into carbon dioxide (CO2) and water (H2O) [1]
- reducing these precursor gases prevents the photochemical reaction (with sunlight) that forms ground-level ozone / smog [1]

Integrated Pest Management (IPM) offers several advantages. Environmentally, it minimizes the use of synthetic chemicals, which reduces chemical runoff into waterways, preventing water pollution and the bioaccumulation of toxins in aquatic food chains. It also preserves local biodiversity by targeting only the pest species and sparing beneficial predators. Economically, IPM reduces farmers' long-term operational costs because they spend less money purchasing expensive chemical pesticides, and it prevents pests from rapidly developing chemical resistance.

Award up to 3 marks for any three of the following points:
- reduces the risk of pests developing resistance to chemical pesticides [1]
- avoids killing non-target beneficial insects / predators / preserves biodiversity [1]
- reduces chemical runoff into water bodies, preventing water pollution / bioaccumulation [1]
- lowers input costs for farmers as they buy fewer expensive chemicals [1]