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

Metamorphic rocks are created from existing sedimentary, igneous, or even older metamorphic rocks. This transformation process occurs under the following conditions: 1. Heat: High temperatures from nearby magma or deep burial within the Earth's crust alter the mineral composition. 2. Pressure: Intense pressure from overlying rock layers or tectonic forces squeezes and aligns the minerals. 3. Solid State: The rocks do not melt completely (otherwise they would become igneous rocks); instead, recrystallisation happens in a solid state over long periods. Common examples include marble (formed from limestone) and slate (formed from shale or clay).

Award 1 mark for each point up to a maximum of 5 marks: - formed from pre-existing sedimentary or igneous rocks [1] - subjected to high temperatures / heat [1] - subjected to high pressure [1] - occurs deep underground / tectonic activity [1] - minerals recrystallise in a solid state / without melting [1] - name of first valid metamorphic rock (e.g., marble, slate, gneiss, quartzite) [1] - name of second valid metamorphic rock [1] Max 5 marks total. Reject: sandstone, granite, basalt (examples of other rock types).

The process is known as eutrophication: 1. Runoff and leaching: Excess nitrates and phosphates from chemical fertilisers are washed from agricultural fields into the lake by rainwater. 2. Algal bloom: The high nutrient levels cause rapid, explosive growth of algae on the surface of the water. 3. Light blockage: The thick layer of algae blocks sunlight from reaching aquatic plants deeper in the lake, causing them to die due to an inability to photosynthesise. 4. Decomposition: Bacteria and other decomposers multiply rapidly as they feed on the dead plant matter. 5. Oxygen depletion (Anoxia): The respiration of these massive decomposer populations consumes almost all the dissolved oxygen in the water. This lack of oxygen causes fish and other aquatic organisms to suffocate and die, creating a 'dead zone'.

Award 1 mark for each point in the sequence, up to a maximum of 5 marks: - Rainwater washes fertilisers / nitrates / phosphates into the lake (runoff / leaching) [1] - Rapid growth of algae / algal bloom on the water surface [1] - Sunlight is blocked, leading to the death of submerged aquatic plants [1] - Bacteria / decomposers multiply rapidly as they feed on dead plants [1] - Decomposers use up dissolved oxygen during respiration, causing hypoxia / anoxia, which leads to the death of fish / aquatic animals [1]

1. Energy Transfer Efficiency: Energy is lost at each trophic level. On average, only about 10% of the energy stored in biomass at one trophic level is passed on to the next. 2. Mechanisms of Energy Loss: Energy is lost through metabolic processes, respiration as heat, movement, excretion, and because some parts of organisms are not eaten or digested. 3. Limit on Trophic Levels: Because of this cumulative energy loss, there is not enough chemical energy remaining at higher trophic levels (usually past the 4th or 5th level) to sustain a viable population of top predators. 4. Role of Decomposers: Decomposers (such as fungi and bacteria) break down dead organic matter and waste products. 5. Nutrient Cycling: This decomposition process releases inorganic nutrients (like nitrogen, phosphorus, and carbon) back into the soil or water, making them available once again for uptake by primary producers (plants).

Award 1 mark for each point up to a maximum of 5 marks: - Only about 10% of energy is transferred from one trophic level to the next [1] - Energy is lost as heat / through respiration / movement / excretion [1] - Insufficient energy remains at higher trophic levels to support another population [1] - Decomposers break down dead organic material / animal waste [1] - Decomposers release nutrients (e.g., nitrates, phosphates) back into the soil / environment for uptake by plants [1]

To manage and reduce soil erosion, farmers can implement several physical or biological soil conservation methods: 1. Contour Ploughing: Ploughing across a slope (following the contours of the land) rather than up and down. This creates ridges and furrows that act as barriers, slowing down surface runoff and allowing water to infiltrate the soil. 2. Terracing: Cutting steep slopes into a series of flat steps or platforms. This reduces the speed of rainwater flowing downhill, minimizing its ability to wash away topsoil. 3. Windbreaks / Shelterbelts: Planting rows of trees or large shrubs along the edges of fields. This reduces the velocity of wind near the ground level, preventing wind erosion of dry, loose topsoil. 4. Cover Crops: Growing fast-growing crops (like clover or rye) between main crop seasons to ensure the soil is never left bare. The roots hold the soil particles together, and the leaves protect the soil from direct rainfall impact.

Award marks for describing three farming methods and explaining how they reduce erosion, up to a maximum of 5 marks: - Method 1 identified and explained [2 marks] - Method 2 identified and explained [2 marks] - Method 3 identified only (or partially explained) [1 mark] Possible methods and explanations: - Contour ploughing [1]: ploughing across slopes creates ridges that slow down surface runoff / trap water [1]. - Terracing [1]: cutting flat steps into steep hillsides reduces the speed of downhill water flow [1]. - Windbreaks / shelterbelts [1]: planting rows of trees/shrubs reduces wind speed to prevent wind erosion [1]. - Cover crops / mulching [1]: keeping soil covered with plants or organic matter protects it from the impact of heavy rain / roots bind the soil [1]. - Bunds [1]: low walls of soil/stone built along contours slow down water flow and trap sediment [1].

**(a)**
- Decrease in \(\text{SO}_2\) concentration = \(45 - 8 = 37\,\mu\text{g/m}^3\)
- Percentage decrease = \(\frac{37}{45} \times 100 = 82.22\%\) (accept 82% or 82.2%)

**(b)**
- Both pollutants (\(\text{SO}_2\) and \(\text{PM}_{2.5}\)) show a clear, continuous downward trend from 2016 to 2021.
- \(\text{SO}_2\) fell from \(45\,\mu\text{g/m}^3\) to \(8\,\mu\text{g/m}^3\); \(\text{PM}_{2.5}\) fell from \(38\,\mu\text{g/m}^3\) to \(11\,\mu\text{g/m}^3\).
- Hospital admissions for respiratory issues declined steadily in tandem, from 820 to 290 per 100,000 people.
- The rate of decline in hospitalizations was sharpest immediately following the intervention years of 2018 and 2020.

**(c)**
- **LEZ (2018):** In the year following its introduction, \(\text{SO}_2\) fell by 14 units (42 to 28), \(\text{PM}_{2.5}\) fell by 9 units (35 to 26), and hospital admissions dropped by 180 (790 to 610). This indicates high effectiveness, likely due to reduced diesel/petrol vehicle emissions.
- **Power Station Fuel Switch (2020):** In the year following the switch, \(\text{SO}_2\) fell by 12 units (24 to 12), \(\text{PM}_{2.5}\) fell by 8 units (22 to 14), and hospital admissions dropped by 160 (540 to 380).
- **Comparison:** The LEZ resulted in a slightly higher absolute reduction in both pollutants and hospital admissions in its initial year. However, the power station switch achieved a greater relative/proportional reduction in \(\text{SO}_2\) (a 50% drop from 24 to 12) within one year. Both interventions significantly improved air quality and human health.

**(d)**
- *Strategy 1:* Expand and electrify mass transit systems (e.g., electric buses, light rail) to lower private vehicle emissions.
- *Strategy 2:* Establish urban green zones / urban forests, as foliage can intercept particulate matter and absorb some gaseous pollutants.
- *Other acceptable options:* Industrial stack scrubbers, catalytic converter mandates, promoting active travel (cycling/walking lanes).

**(a)**
- 1 mark for correct calculation setup: \(\frac{45 - 8}{45} \times 100\) or similar.
- 1 mark for correct final answer: 82% or 82.2% (accept 82.22%).

**(b)** Max 4 marks:
- 1 mark for identifying that both pollutants decreased over the time period (with data points).
- 1 mark for identifying that hospital admissions also decreased over the period (with data points).
- 1 mark for linking the reduction in hospital admissions directly to the reduction in ambient pollutants (correlation).
- 1 mark for pointing out the major drops occurring after 2018 or 2020.

**(c)** Max 5 marks:
- 1 mark for analyzing LEZ air quality changes using correct values (e.g., \(\text{SO}_2\) fell by 14, \(\text{PM}_{2.5}\) fell by 9).
- 1 mark for analyzing LEZ health impact (hospitalizations fell by 180).
- 1 mark for analyzing power station switch air quality changes (e.g., \(\text{SO}_2\) fell by 12 or 50%, \(\text{PM}_{2.5}\) fell by 8).
- 1 mark for analyzing power station switch health impact (hospitalizations fell by 160).
- 1 mark for a balanced evaluative conclusion comparing absolute vs. relative effects.

**(d)** Max 4 marks:
- Award 2 marks per strategy (1 mark for identifying the strategy, 1 mark for explaining how it reduces urban air pollution).
- Acceptable strategies: Electric vehicle subsidies, urban afforestation, catalytic converters on all vehicles, industrial scrubbers/electrostatic precipitators, car-pooling/congestion charges.

**(a)**
- Normal capacity (2018) = 92%
- Lowest capacity (2022) = 18%
- Absolute decrease = \(92 - 18 = 74\%\) (percentage points)
- Percentage decrease relative to 2018 = \(\frac{74}{92} \times 100 = 80.43\%\) (accept 80.4% or 80.43%)

**(b)**
- Year of highest economic loss: 2020 (12.8 million USD).
- Ratio to 2018: \(\frac{12.8}{1.2} = 10.67\) times larger (accept 10.7 times larger).

**(c)**
- In 2021, rainwater harvesting and drip irrigation schemes became active.
- Drip irrigation systems deliver water directly to the root zone of the crops, drastically minimizing evaporation and water runoff losses.
- Rainwater harvesting captured scarce rain from the 330mm/290mm events, providing supplementary watering that sustained crop growth despite depleted main reservoirs.

**(d)**
- *Strategy 1:* Cultivating drought-tolerant crops (e.g., millet, sorghum) or genetically modified varieties that have lower water requirements.
- *Strategy 2:* Water transfer schemes (diverting water from regions with surplus rainfall to dry farming regions via pipes/canals).
- *Strategy 3:* Conservation tillage/mulching to keep soil covered with organic residues, reducing water loss from evaporation and preserving soil structures.
- *Other options:* Desalination for coastal farms, crop insurance programs to cushion losses and encourage adaptation.

**(e)** Any two of:
- Increased risk of forest fires/wildfires.
- Soil degradation, dust storms, and desertification.
- Destruction of aquatic ecosystems and loss of wildlife/biodiversity due to drying wetlands/rivers.

**(a)**
- 1 mark for correct calculation setup: \(\frac{92 - 18}{92} \times 100\).
- 1 mark for correct final answer: 80.4% or 80.43% (also accept 74% if clearly labeled as percentage point reduction).

**(b)**
- 1 mark for identifying 2020.
- 1 mark for correct multiplier calculation: 10.7 (accept 10.67).

**(c)** Max 3 marks:
- 1 mark for linking yield recovery to the introduction of the irrigation/harvesting schemes in 2021.
- 1 mark for explaining that drip irrigation targets roots directly and reduces evaporation.
- 1 mark for explaining that rainwater harvesting buffers against depleted reservoir stocks.

**(d)** Max 6 marks:
- Award 2 marks per strategy: 1 mark for identifying the strategy, 1 mark for explaining how it mitigates agricultural drought vulnerability.
- Acceptable strategies include: drought-tolerant/GM crop cultivation, inter-basin water transfers, mulching/conservation agriculture, construction of deep wells/aquifer management.

**(e)** Max 2 marks:
- Award 1 mark for each valid environmental impact. Do not accept agricultural or socio-economic impacts (e.g., food shortage, financial loss). Accept: loss of habitats, wildfires, wind soil erosion, dry riverbeds.

**(a)**
- **(i) 2017 Malaria Rate:** \(\frac{8,400}{120,000} \times 1,000 = 70.0\) cases per 1,000 people.
- **(ii) 2021 Malaria Rate:** \(\frac{1,100}{130,000} \times 1,000 = 8.46\) cases per 1,000 people (accept 8.5).
- **Working:** Formula used: \(\frac{\text{Cases}}{\text{Population}} \times 1,000\) showing correct values substituted.

**(b)**
- There is a strong negative/inverse relationship between access to safe water and cholera cases.
- In 2017, when access to safe water was at its lowest (45%), cholera cases were at their peak (1,800 cases).
- As safe water access increased to 82% in 2019 and reached 98% by 2021, cholera cases dropped drastically to 450 (2019) and finally 15 cases (2021).
- This occurred because cholera is a water-borne disease caused by ingesting water contaminated with the *Vibrio cholerae* bacterium; safe chlorinated water eliminates the pathogen and halts transmission.

**(c)**
- ITNs provide a robust physical barrier that prevents mosquitoes (specifically the female *Anopheles* vector) from biting humans during their nocturnal feeding times.
- The chemical insecticide treated on the net kills mosquitoes that land on it, reducing the general vector population in the household.
- This prevents the transmission of the *Plasmodium* parasite from infected individuals to healthy individuals, breaking the disease life cycle.

**(d)**
- **Evaluation of Success:** Both campaigns were highly successful. Over the 5-year period, malaria cases decreased by 86.9% (8,400 to 1,100) and cholera cases decreased by 99.2% (1,800 to 15).
- **Differences in Rates of Decrease (2017–2019):** Cholera cases fell much faster (a 75% reduction from 1,800 to 450) than malaria cases (a 40.5% reduction from 8,400 to 5,000).
- **Reasons for Difference:**
- Water chlorination is a centralized utility improvement; once installed, it immediately protects all users from water-borne pathogens.
- ITNs are decentralized interventions that rely on individual behavioral compliance (correct usage every night by all family members).
- Furthermore, ITNs do not eliminate mosquito breeding grounds (stagnant water pools), meaning vector populations can persist and bite people when they are outdoors, whereas cholera bacteria in municipal water are instantly eradicated.

**(a)** Max 3 marks:
- 1 mark for correct 2017 rate: 70 per 1,000.
- 1 mark for correct 2021 rate: 8.46 per 1,000 (accept 8.5).
- 1 mark for showing valid working (fraction multiplied by 1,000).

**(b)** Max 4 marks:
- 1 mark for stating the inverse/negative relationship.
- 1 mark for quoting 2017 data (45% water access and 1,800 cases).
- 1 mark for quoting 2021 data (98% water access and 15 cases).
- 1 mark for explaining the biological reason (cholera is water-borne, caused by ingestion of contaminated water).

**(c)** Max 3 marks:
- 1 mark for physical barrier (prevents Anopheles mosquito bites at night).
- 1 mark for chemical action (insecticide kills vectors on contact, reducing vector population size).
- 1 mark for parasite containment (breaks transmission of Plasmodium parasite).

**(d)** Max 5 marks:
- 1 mark for stating that both campaigns were highly successful with supporting percentage reductions.
- 1 mark for identifying that cholera cases dropped much faster than malaria cases initially.
- 1 mark for explaining that chlorination is centralized/immediate and requires no individual compliance.
- 1 mark for explaining that ITNs require behavioral compliance (using them correctly every night).
- 1 mark for noting that ITNs do not destroy mosquito breeding habitats (water pools) so vector exposure outdoors continues.

(a) (i)
- The percentage of coal in the energy mix decreased significantly from 45% to 30%.
- The percentage of oil also decreased slightly from 30% to 25%.
- Natural gas increased its share from 15% to 25%.
- Renewables doubled their contribution to the energy mix, increasing from 10% to 20%.

(a) (ii)
- Change in emissions: \(156 - 120 = 36\) million tonnes.
- Percentage change: \(\frac{36}{120} \times 100\% = 30\%\) increase.

(b)
- Explanation for decrease in \(SO_2\): The relative use of coal (the highest sulfur-producing fossil fuel) decreased from 45% to 30%. Additionally, the country likely adopted cleaner technologies such as flue-gas desulfurization (scrubbers) in existing plants, or shifted towards low-sulfur coal and cleaner burning natural gas.
- Environmental impact: \(SO_2\) reacts with water vapour in the atmosphere to form sulfurous/sulfuric acid, leading to acid rain. This acidifies lakes and aquatic ecosystems (killing fish), leaches key nutrients from soils (damaging forests), and corrodes limestone buildings/monuments.

(c)
Arguments for banning new coal plants (Agree):
- Coal is the most carbon-intensive fossil fuel; stopping its expansion is critical to limit global temperature rise and meet climate goals.
- Coal-fired plants also emit significant local pollutants like sulfur dioxide, nitrogen oxides, and particulates, damaging public health and increasing healthcare costs.
- Rapidly falling costs of wind and solar make clean alternatives increasingly economically viable.

Arguments against a complete immediate ban (Disagree / Challenges):
- Developing nations require vast amounts of cheap, reliable baseload electricity to support industrial growth and poverty alleviation; renewables alone (without expensive battery storage) may not yet guarantee grid stability.
- Coal is often domestically abundant and secure, whereas transitioning completely to imports of technology or natural gas can threaten energy security.
- Transitioning immediately may cause economic shocks, job losses in coal mining regions, and energy shortages.

Conclusion/Evaluation:
An immediate absolute ban may be too restrictive for the poorest nations. Instead, a phased transition supported by international funding, grid modernization, and investment in gas as a transition fuel represents a more balanced and realistic pathway.

(a) (i) [Max 3 marks]
- Award 1 mark for identifying the decrease in coal and/or oil share (with data).
- Award 1 mark for identifying the increase in natural gas share (with data).
- Award 1 mark for identifying the increase/doubling of renewables (with data).

(a) (ii) [Max 2 marks]
- Award 1 mark for correct working: \(\frac{156-120}{120} \times 100\) or showing a difference of 36.
- Award 1 mark for the correct final answer: 30% (or +30%). Reject -30%.

(b) [Max 4 marks]
- Award up to 2 marks for explaining the decrease in \(SO_2\): Less reliance on coal / coal percentage dropped [1]; transition to cleaner fuels like natural gas and renewables which do not produce \(SO_2\) [1]; introduction of emission control technologies (e.g., scrubbers, coal gasification) [1].
- Award up to 2 marks for the environmental impact: Acid rain formation [1]; detail of impact (e.g., damage to trees/forests, acidification of aquatic habitats, damage to stone structures) [1].

(c) [Max 6 marks] Level of Response marking grid:

- Level 3 (5-6 marks): A comprehensive and balanced evaluation showing excellent understanding of the trade-offs between rapid decarbonisation and developmental needs. Arguments for and against are well-supported with specific environmental, economic, and social issues. A clear, reasoned conclusion is present.
- Level 2 (3-4 marks): A structured answer that addresses both sides of the argument but may lack balance or depth in places. Mentions alternatives and development issues but does not link them coherently to a justified conclusion.
- Level 1 (1-2 marks): A simple answer showing basic awareness of coal's impact or renewable alternatives. Weak, one-sided arguments with little or no evaluation.
- Level 0 (0 marks): No response or response contains no relevant environmental science content.

Part (a)
(i) Increase in population = \(24,600 - 15,000 = 9,600\).
Percentage increase = \(\frac{9,600}{15,000} \times 100 = 64\%\).
(ii) Axis: 'Year' on horizontal (x) axis, 'Population' on vertical (y) axis. Scale: Linear scale utilizing more than 50% of the grid space. Labels: Both axes fully labeled. Plotting: Points plotted accurately and connected with a continuous line.
(iii) 1. In-migration of workers seeking employment. 2. Rise of tertiary sector businesses supporting the new mine and its workforce.
(iv) Death rates fall due to improved sanitation, access to clean piped water, and improved healthcare facilities constructed near the mine. Birth rates stay high because family size remains culturally valued, children are viewed as security, and family planning programs are not yet established.

Part (b)
(i) Open-cast mining strips all vegetation, topsoil, and overburden across a massive surface area, causing complete habitat fragmentation. In contrast, shaft mining accesses deeper seams via vertical shafts, resulting in a much smaller surface footprint. Open-cast mining produces significantly more surface runoff, soil erosion, dust, and visual impacts.
(ii) Percentage concentration = \(\frac{3.75\text{ kg}}{250\text{ kg}} \times 100 = 1.5\%\).
(iii) The ore is finely ground and mixed with water and surfactant chemicals. Air is injected; the hydrophobic copper-bearing minerals cling to the rising bubbles, forming a froth at the surface which is removed. The hydrophilic waste rock (gangue) sinks.
(iv) 1. Leakage of heavy metals causing bioaccumulation in the food chain. 2. Sulfide minerals in tailings react with water and air to form sulfuric acid (acid mine drainage). 3. Structural failure of tailing dams causing catastrophic downstream mudflows.

Part (c)
(i) The company can backfill the open pit using the stored overburden and waste rock, contour/grade the surface to blend with the natural topography, spread the reserved fertile topsoil over the surface, and revegetate the area by planting native grass and tree species.
(ii) 1. Sprinkling water on unpaved mine roads and stockpiles to suppress dust. 2. Constructing physical acoustic walls or earthen berms. 3. Plant a dense green buffer zone of trees around the mine boundary. 4. Operating heavy machinery and executing blasts only during set daytime hours.

Part (a) [12 marks]
(i) [3 marks]
- 1 mark for correct subtraction: \(24,600 - 15,000 = 9,600\)
- 1 mark for correct fractional setup: \(\frac{9,600}{15,000} \times 100\)
- 1 mark for correct final calculation: 64% (Accept 64 without % sign if unit is written on the line)
(ii) [4 marks]
- 1 mark for placing 'Year' on the x-axis and 'Population' on the y-axis with linear scales.
- 1 mark for scales utilizing at least half of the grid space.
- 1 mark for complete labels on both axes.
- 1 mark for plotting all five points correctly and connecting with a clean line.
(iii) [2 marks]
- 1 mark for noting direct immigration of labor (seeking mining jobs).
- 1 mark for noting indirect growth in local supply/support businesses (multiplier effect).
(iv) [3 marks]
- 1 mark for explaining why death rate falls (e.g., medical clinics, clean water).
- 1 mark for explaining why birth rate remains high (e.g., cultural lag, kids as economic assets).
- 1 mark for linking the demographic lag to industrialization phases.

Part (b) [12 marks]
(i) [4 marks]
- 1 mark for contrasting surface area disturbed (large for open-cast, small for shaft).
- 1 mark for explaining complete habitat clearance in open-cast.
- 1 mark for open-cast generating more wind-borne dust/air pollution at surface.
- 1 mark for open-cast causing more extensive visual and noise impacts on local fauna.
(ii) [3 marks]
- 1 mark for dividing metal weight by total ore weight: \(\frac{3.75}{250}\)
- 1 mark for multiplying by 100: \(0.015 \times 100\)
- 1 mark for correct final calculation: 1.5%
(iii) [2 marks]
- 1 mark for mentioning bubbles/froth carrying valuable minerals to the surface.
- 1 mark for explaining that the heavier, non-valuable waste rock (gangue) sinks.
(iv) [3 marks]
- 1 mark for explaining acid mine drainage (acidification of local aquatic systems).
- 1 mark for explaining heavy metal bioaccumulation in food chains.
- 1 mark for explaining structural failure/dam burst hazards.

Part (c) [8 marks]
(i) [4 marks]
- 1 mark for backfilling (filling the pit with original waste rock).
- 1 mark for land shaping/contouring (to prevent erosion/recreate natural slopes).
- 1 mark for replacing topsoil (to provide nutrients for growth).
- 1 mark for revegetation (planting native trees/grasses to restore ecosystems).
(ii) [4 marks]
- 1 mark for dust control (e.g., wetting down roads, covering trucks).
- 1 mark for physical acoustic barriers (e.g., sound walls, earthen berms).
- 1 mark for vegetated buffer zone (e.g., planting tree belts to block noise/dust).
- 1 mark for operational limits (e.g., restricting blasting to daytime hours only).

(a)
1. Find the increase in energy generation: \( 1650 - 1200 = 450 \) GWh.
2. Calculate the percentage increase: \( \frac{450}{1200} \times 100 = 37.5\% \).

(b)
- Advantage 1: Providing a reliable water supply for agricultural irrigation.
- Associated conflict 1: Reduced downstream river flow leads to water shortages for downstream farmers and ecosystems.
- Advantage 2: Flood control downstream by regulating the seasonal flow of the river.
- Associated conflict 2: The lack of annual flooding prevents nutrient-rich silt from being deposited on downstream agricultural soils, reducing soil fertility.

(c)
- Seismic risks: Strong ground shaking can fracture the concrete or earth structure of the dam, leading to a catastrophic collapse. Landslides triggered by earthquakes can fall into the reservoir, creating a massive displacement wave that overtops the dam wall.
- Mitigation: Use flexible, earth-core rock-fill dam structures rather than rigid concrete structures, and install continuous seismic monitoring and early-warning systems to manage water levels.

(d)
- Clearance of a wide linear corridor of forest trees (deforestation) to construct and maintain the transmission lines.
- Habitat fragmentation, splitting wildlife populations and creating edge-effects in the forest ecosystem.
- Increased risk of forest fires caused by electrical faults, arcing, or maintenance equipment.

(a) [3 marks]
- 1 mark for finding the difference: \( 1650 - 1200 = 450 \)
- 1 mark for the correct calculation method: \( \frac{450}{1200} \times 100 \)
- 1 mark for correct final answer: 37.5 (accept 37.5%)

(b) [4 marks]
- 1 mark for each valid advantage (max 2)
- 1 mark for each corresponding conflict/disadvantage linked to the advantage (max 2)
- Acceptable advantages: Irrigation, domestic water supply, flood control, recreation/tourism, navigation.
- Acceptable conflicts: Downstream water shortage, loss of natural silt, displacement of communities, loss of terrestrial habitat under reservoir.

(c) [3 marks]
- 1 mark for each described seismic risk (max 2): e.g., dam wall structural cracking/failure, landslide causing reservoir displacement wave (overtopping), liquefaction of foundation.
- 1 mark for a valid mitigation strategy (max 1): e.g., earthquake-resistant/flexible materials, continuous seismic monitoring, avoiding active fault lines during planning, lowering reservoir level.

(d) [3 marks]
- 1 mark for each valid environmental impact (max 3):
- Deforestation/clearing of trees for the corridor.
- Habitat fragmentation / barrier to animal movements.
- Risk of electrical sparks causing forest fires.
- Bird collisions with high-voltage wires.
- Soil erosion and habitat disruption from construction of access roads.

Part (a): Subtract the yield of Treatment A from Treatment C: 3.5 - 3.2 = 0.3 t/ha. Divide this difference by the yield of Treatment A and multiply by 100: (0.3 / 3.2) * 100 = 9.375% (accept 9.4% or 9.38%). Part (b): IPM is more sustainable because: 1. It reduces the likelihood of pests developing resistance to chemicals. 2. It minimizes chemical runoff into water bodies, preventing eutrophication. 3. It reduces bioaccumulation of toxins in local ecosystems. 4. It protects non-target beneficial insects, like pollinators. Part (c): Limitations of biological control: 1. It takes longer to reduce pest populations compared to rapid chemical sprays. 2. Biological agents may migrate away from the crop fields. 3. Weather changes, such as heavy rain or temperature extremes, can kill the biological agents.

Part (a) [2.5 marks]: Award 1 mark for correct working showing the difference divided by the original: \(\frac{3.5 - 3.2}{3.2} \times 100\). Award 1 mark for calculating 9.375% (or 9.38% / 9.4%). Award 0.5 marks for correct unit (%). Part (b) [4 marks]: Award 1 mark for each valid explanation point up to a maximum of 4 marks: reduces pest resistance development, lowers chemical runoff/water pollution, prevents biomagnification/bioaccumulation in food webs, protects beneficial pollinators/non-target species, safer for agricultural workers, lower production costs. Part (c) [3 marks]: Award 1 mark for each distinct disadvantage of biological control up to a maximum of 3 marks: slower action/lag time, predators may leave the target area, climate/weather sensitivity of agents, high initial setup expertise, rarely achieves complete eradication of pests.

Part (a): 1. Calculate average Bt yield: (1200 + 1250 + 1220 + 1240 + 1230) / 5 = 1228 kg/ha. 2. Calculate average Non-Bt yield: (1100 + 950 + 800 + 750 + 680) / 5 = 856 kg/ha. 3. Calculate difference: 1228 - 856 = 372 kg/ha. Part (b): The yield of Non-Bt cotton decreased steadily over the 5 years from 1100 to 680 kg/ha. This occurs because the cotton bollworm developed genetic resistance to the chemical insecticides being applied, making the chemicals progressively less effective and leading to increased crop damage. Part (c): 1. Decreased insecticide applications lead to less chemical run-off, protecting aquatic life in nearby streams. 2. Reduces non-target damage to insect pollinators and soil micro-organisms, conserving local biodiversity.

Part (a) [3.5 marks]: Award 1 mark for correct average of Bt cotton (1228). Award 1 mark for correct average of Non-Bt cotton (856). Award 1 mark for correct difference (372). Award 0.5 marks for correct unit (kg/ha). Part (b) [3 marks]: Award 1 mark for describing the trend (yields decreased over time / decreased from 1100 to 680 kg/ha). Award 2 marks for explanation: bollworm pests developed genetic resistance to the insecticides (1 mark), leading to ineffective chemical control and greater crop destruction (1 mark). Part (c) [3 marks]: Award 1.5 marks for each fully outlined benefit (1 mark for identifying the benefit, 0.5 marks for its environmental link) up to a maximum of 3 marks: reduced chemical run-off prevents water pollution/eutrophication, less toxicity preserves beneficial non-target organisms/pollinators/biodiversity, less machinery fuel used reduces carbon emissions.

(a) To set up a pitfall trap:
1. Dig a small hole in the ground deep enough to fit a container (such as a plastic cup) so that the rim of the cup is exactly level with the soil surface.
2. Place a small amount of liquid (e.g., water with a drop of unscented dish soap) at the bottom to prevent trapped invertebrates from crawling out or escaping.
3. Support a flat cover (like a piece of wood or slate) slightly raised on small stones above the trap to keep out rain, leaves, and larger predators.
4. Leave the trap in place for a set period, such as 24 hours, before returning to collect, identify, and count the specimens.

(b) A line transect is used by stretching a long tape measure in a straight line starting perpendicular to the footpath (0 m) into the deeper woodland (15 m). It allows the student to sample systematically at fixed intervals along an environmental gradient (from highly trampled to undisturbed woodland) to study how soil compaction/human disturbance affects species distribution.

(c) Calculation:
- For Species A at 15 m: \(n = 8\), so \(n(n-1) = 8 \times 7 = 56\)
- For Species B at 15 m: \(n = 11\), so \(n(n-1) = 11 \times 10 = 110\)
- For Species C at 15 m: \(n = 9\), so \(n(n-1) = 9 \times 8 = 72\)
- Sum of \(n(n-1) = 56 + 110 + 72 = 238\)
- Total organisms \(N = 28\), so \(N(N-1) = 28 \times 27 = 756\)
- Fraction: \(\frac{238}{756} \approx 0.3148\)
- \(D = 1 - 0.3148 = 0.6852\)
- Rounded to 2 decimal places: **0.69**

(d) The Simpson's Index of Diversity is significantly higher at 15 m (0.69) compared to 0 m (0.43). This shows that human trampling on the footpath decreases invertebrate biodiversity. Near the path, soil is heavily compacted, removing micro-habitats and vegetation, which makes it hostile for most species (reducing species richness and evenness, leading to dominance by a single tolerant species, Species A). In contrast, the undisturbed woodland has a higher diversity index because the complex ecosystem structure supports a more balanced, even community of different species.

(e) Three variables to keep constant:
1. The size, shape, and depth of the containers used for the pitfall traps.
2. The length of time the traps are left open (e.g., exactly 24 hours).
3. The type and amount of preserving liquid or bait used in each trap.

Part (a) [4 marks]
- Digging a hole so that the rim of the container is flush/level with the soil surface [1]
- Adding a small amount of liquid/preservative (or detergent to break surface tension) [1]
- Placing a raised cover/shield over the trap to prevent rain/predators entering [1]
- Leaving the trap for a standardized duration / checking after a set time (e.g., 24 hours) [1]

Part (b) [2 marks]
- Tape measure is laid out in a straight line perpendicular to the pathway [1]
- Allows systematic sampling at measured, regular intervals along an environmental/disturbance gradient [1]

Part (c) [4 marks]
- Correct calculation of individual \(n(n-1)\) values and their sum (\(56 + 110 + 72 = 238\)) [1]
- Correct calculation of \(N(N-1)\) (\(28 \times 27 = 756\)) [1]
- Correct calculation of fraction (\(238 / 756 \approx 0.31\)) and subtraction from 1 [1]
- Correct final answer rounded to 2 decimal places: **0.69** [1]
*(Allow full marks for a correct final answer of 0.69 with working shown. Deduct 1 mark if correct calculation is not rounded to 2 d.p., e.g. 0.685)*

Part (d) [3 marks]
- Identifies that biodiversity is much higher deep in the woodland (0.69) than on the footpath (0.43) [1]
- Explains that trampling leads to low biodiversity due to soil compaction, lack of cover, or vegetation destruction [1]
- Mentions that undisturbed habitats provide more ecological niches/food resources, leading to a higher evenness of species [1]

Part (e) [3 marks]
- Award 1 mark for each valid constant variable (max 3):
- Same size / shape / material of trap container
- Same trapping duration (e.g., 24 hours)
- Same type/volume of fluid or bait inside the trap
- Same type/height of rain cover used
- Set up at the exact same time/day (constant weather conditions)