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

At a constructive plate boundary, two tectonic plates move apart from each other. Magma rises from the mantle to fill the gap, which can result in volcanic eruptions, lava flows, or ash clouds.

Award 1 mark for describing the movement: plates move away from each other / diverge / pull apart. Award 1 mark for naming an associated hazard: volcanic eruption / lava flow / ash fall / toxic gas emission / earthquake.

Upwelling winds push warm surface water away, allowing cold, nutrient-rich water to rise from the deep ocean to the surface. These nutrients stimulate the rapid growth of phytoplankton, which forms the base of the marine food web, providing abundant food for fish populations to grow.

Award 1 mark for explaining that deep, nutrient-rich / nitrate-rich / phosphate-rich water is brought to the surface. Award 1 mark for linking this to increased growth of phytoplankton / algae / producers, which increases the food supply for fish.

By ploughing across the slope along the natural contour lines, the ridges and furrows act as mini-dams. This physical barrier slows down the speed of rainwater running downslope, reducing its power to wash away topsoil and allowing more time for the water to soak into the ground.

Award 1 mark for explaining that ridges/furrows are created across the slope (perpendicular to water flow) to trap water. Award 1 mark for explaining that this slows surface run-off and increases water infiltration/absorption.

Transpiration is the process where plants lose water vapour through their leaves into the atmosphere. This rate is increased by environmental factors such as high temperature, strong wind, high light intensity, or low air humidity.

Award 1 mark for defining transpiration: loss of water vapour from the leaves / stomata of plants. Award 1 mark for stating one factor: high temperature / wind / low humidity / high light intensity.

Malaria is spread by female Anopheles mosquitoes. Vector control can be achieved by draining stagnant pools of water to eliminate mosquito breeding grounds, and by sleeping under insecticide-treated bed nets to prevent mosquitoes from biting people.

Award 1 mark for each valid vector control method up to a maximum of 2 marks: draining stagnant water / swamps, spraying insecticide / larvicides, using biological controls (e.g., introducing predator fish that eat larvae), using insecticide-treated bed nets / window screens, applying oil to water surfaces to suffocate larvae.

Large piles of waste rock create visual pollution and destroy natural habitats. Rainwater can also percolate through these waste heaps, leaching out toxic heavy metals or acids that contaminate local groundwater systems.

Award 1 mark for each valid environmental problem up to a maximum of 2 marks: habitat destruction / loss of vegetation, visual pollution / scarring of the landscape, leaching of toxic chemicals / heavy metals / acid mine drainage into soils or groundwater, dust pollution.

Seed banks preserve a wide variety of plant seeds in controlled, frozen conditions, which maintains genetic diversity. This ensures that endangered species can be grown and reintroduced into the wild if they face extinction due to habitat loss or climate change.

Award 1 mark for each valid reason up to a maximum of 2 marks: protects/preserves genetic diversity, safeguards species against extinction in the wild / climate change / habitat loss, occupies very little space compared to entire ecosystems, keeps seeds viable for long periods at relatively low cost.

1. Identify Year 2 yield: 8.0 tonnes per hectare.
2. Identify Year 3 yield: 4.8 tonnes per hectare.
3. Calculate the decrease: \(8.0 - 4.8 = 3.2\) tonnes per hectare.
4. Calculate the percentage decrease: \(\frac{3.2}{8.0} \times 100 = 40\%\).

1 mark for showing correct calculation method: \(\frac{8.0 - 4.8}{8.0} \times 100\) or equivalent.
1 mark for the correct final answer: 40 [\%].

1. Identify the dependent age groups: 0–14 years and 65+ years.
2. Add the percentages of these two groups together: \(28\% + 10\% = 38\%\).

1 mark for identifying and adding the dependent groups: \(28 + 10\).
1 mark for the correct final answer: 38 [\%].

1. Calculate the total seafood production: \(150 + 50 = 200\) thousand tonnes.
2. Calculate aquaculture's share of this total: \(\frac{50}{200} \times 100 = 25\%\).

1 mark for calculating the total production of 200 thousand tonnes or showing the fraction \(\frac{50}{200}\).
1 mark for the correct final answer: 25 [\%].

1. Dead vegetation accumulates in swampy, oxygen-poor areas, preventing complete decay and leading to the formation of peat.
2. Over time, layers of sand, mud, and other sediments build up on top of the peat.
3. The weight of the overlying sediments subjects the peat to immense pressure and heat.
4. This compression squeezes out water and gases, increasing the carbon concentration and gradually transforming the peat into lignite and eventually hard coal.

Award up to 4 marks:
- 1 mark for dead vegetation accumulating in wet/swampy conditions to form peat.
- 1 mark for burial of organic material under layers of sediments (mud/sand).
- 1 mark for the application of high pressure and temperature over geological time / millions of years.
- 1 mark for the compression squeezing out water/gases, increasing carbon concentration to form coal.

1. Rainwater washes agricultural fertilizers (containing nitrates and phosphates) into a nearby lake.
2. The sudden influx of nutrients triggers rapid growth of algae on the surface of the water, forming an algal bloom.
3. The thick layer of algae blocks sunlight from reaching aquatic plants deeper in the lake, preventing photosynthesis and causing them to die.
4. Decomposing bacteria multiply rapidly as they feed on the dead organic matter.
5. These bacteria use up dissolved oxygen in the water during aerobic respiration, causing hypoxia, which suffocates and kills fish and other aquatic organisms.

Award up to 4 marks:
- 1 mark for agricultural runoff bringing nitrates/phosphates into the lake, causing an algal bloom.
- 1 mark for algae blocking sunlight, causing submerged plants to die due to lack of photosynthesis.
- 1 mark for decomposers/bacteria feeding on dead plants and rapidly increasing in number.
- 1 mark for bacteria using up dissolved oxygen in respiration, leading to the death of fish/aquatic animals.

1. Cold water is pumped deep underground through an injection well into hot, permeable volcanic rocks.
2. The natural heat from the Earth's mantle warms the water, turning it into high-pressure steam.
3. The steam rises to the surface through a production well and is directed onto the blades of a turbine.
4. The force of the steam spins the turbine, which is connected to a generator that converts the mechanical energy into electricity.

Award up to 3 marks:
- 1 mark for pumping water down to hot rocks deep underground to be heated by geothermal energy.
- 1 mark for steam being produced and rising to the surface under pressure.
- 1 mark for steam turning a turbine, which drives/powers an electrical generator.

1. Plant roots naturally bind soil particles together and anchor the soil layers to the underlying bedrock.
2. When vegetation is cleared, the soil becomes loose and highly vulnerable to erosion and infiltration.
3. During heavy rainfall, water rapidly saturates the soil, significantly increasing its weight and reducing the friction between the soil layer and bedrock.
4. The sheer weight of the wet soil, combined with gravity and reduced friction, causes the entire slope to fail and slide downwards as a landslide.

Award up to 3 marks:
- 1 mark for noting that roots normally bind/anchor the soil (so clearing vegetation leaves it loose/unstable).
- 1 mark for heavy rain saturating the soil, increasing its weight and reducing friction between soil and rock.
- 1 mark for gravity pulling the heavy, lubricated soil down the steep slope.

1. Seawater is collected and undergoes pre-filtration to remove large suspended solids and impurities.
2. The filtered seawater is then subjected to extremely high pressure using electric pumps.
3. This pressure forces the water against a semi-permeable membrane, overcoming the natural osmotic pressure.
4. The pores of the membrane are small enough to allow only water molecules to pass through, leaving behind dissolved salts, bacteria, and other contaminants.
5. The purified freshwater is collected for distribution, while the concentrated salty brine is discharged.

Award up to 4 marks:
- 1 mark for pre-treatment/filtration of seawater to remove large particles.
- 1 mark for applying high pressure to the water to overcome natural osmotic pressure.
- 1 mark for forcing water molecules through a semi-permeable membrane.
- 1 mark for separating dissolved salts/impurities from freshwater, leaving behind concentrated brine.

1. Farmers or scientists identify and select individual plants from a population that naturally exhibit the highest tolerance to dry/drought conditions.
2. These selected plants are deliberately cross-pollinated (bred) with each other under controlled conditions.
3. The resulting seeds are grown, and the offspring are exposed to dry conditions to assess their resistance.
4. The most drought-resistant offspring are selected, and the breeding process is repeated over many successive generations until a stable, highly resistant crop variety is established.

Award up to 3 marks:
- 1 mark for selecting parent plants with high natural drought resistance.
- 1 mark for breeding/cross-pollinating these selected plants together.
- 1 mark for growing the offspring, selecting the most resistant individuals, and repeating this process over multiple generations.

1. Human activities such as burning fossil fuels, industrial processes, and deforestation release large amounts of greenhouse gases (like carbon dioxide and methane) into the atmosphere.
2. These gases accumulate and increase in concentration in the atmosphere.
3. Short-wave solar radiation from the Sun passes through these gases and warms the Earth's surface.
4. The warmed Earth radiates this heat back toward space as long-wave infrared radiation.
5. Greenhouse gases absorb this outgoing infrared radiation and re-emit it in all directions, trapping heat in the lower atmosphere and raising global temperatures.

Award up to 4 marks:
- 1 mark for human activities (burning fossil fuels/deforestation) releasing greenhouse gases (like carbon dioxide/methane).
- 1 mark for short-wave solar radiation passing through the atmosphere to warm the Earth's surface.
- 1 mark for the Earth re-emitting energy back as long-wave infrared radiation.
- 1 mark for greenhouse gases absorbing and re-radiating this infrared heat back to Earth, trapping heat.

1. Microscopic marine organisms (producers) absorb the non-biodegradable toxin from polluted seawater.
2. Because the toxin cannot be broken down or excreted, it accumulates within the organism's fat tissues over time (bioaccumulation).
3. Primary consumers eat large quantities of these producers, absorbing and storing all the toxins they contained.
4. As this process continues up the food chain, predators at each higher trophic level must consume massive quantities of prey to survive, causing the concentration of the toxin to multiply at each step (biomagnification), leading to toxic levels in top predators.

Award up to 3 marks:
- 1 mark for explaining that non-biodegradable toxins are absorbed by small organisms/producers and stored in tissues (bioaccumulation).
- 1 mark for explaining that predators must eat large quantities of contaminated prey organisms.
- 1 mark for explaining that the toxin concentration increases/multiplies at each successive trophic level up the food chain (biomagnification).

1. Emissions of \(\text{SO}_2\) and \(\text{NO}_x\) enter the atmosphere and are transported by wind currents.
2. Chemical reactions occur in the atmosphere where these gases combine with moisture (water vapor) and oxygen.
3. This reaction forms sulfuric and nitric acids.
4. The acids dissolve in water droplets and fall to the ground as acid precipitation (wet deposition).
5. Acidic runoff enters rivers and drains into distant freshwater lakes, lowering the water pH.

Award [1 mark] for each of the following points up to a maximum of [4 marks]:
- M1: Combustion releases sulfur dioxide / nitrogen oxides which rise and are transported by winds [1]
- M2: These gases react with atmospheric water vapor / moisture / oxygen [1]
- M3: (Chemical reaction) forms sulfuric acid / nitric acid [1]
- M4: The acids fall to the Earth as acid rain / snow / sleet / precipitation [1]
- M5: Acidic runoff enters lakes and lowers their pH [1]

1. Runoff of fertilizers (containing nitrates/phosphates) leads to nutrient enrichment in the water.
2. This enrichment triggers rapid growth of algae (algal bloom) at the surface, blocking sunlight.
3. Sub-surface plants die due to lack of light for photosynthesis.
4. Decomposers (bacteria) feed on the dead plant matter and multiply rapidly, using up dissolved oxygen through respiration.
5. Severe oxygen depletion causes fish and other aquatic life to suffocate and die.

Award [1 mark] for each of the following points up to a maximum of [3 marks]:
- M1: High nutrient input (nitrates/phosphates) causes rapid algal growth / algal bloom on the surface [1]
- M2: Algal bloom blocks sunlight, preventing photosynthesis and causing sub-surface aquatic plants to die [1]
- M3: Bacteria / decomposers break down dead plant matter and multiply rapidly [1]
- M4: Bacterial respiration depletes dissolved oxygen levels in the water, causing fish / aquatic organisms to suffocate and die [1]

Candidates should discuss both sides of the statement:

**Arguments for national parks / protected areas:**
- Legal protection restricts habitat destruction, commercial logging, and mining within boundaries.
- Protects food webs, biodiversity, and rare or endangered species in their natural habitats.
- Can generate revenue through regulated ecotourism, which can fund further conservation efforts.
- Preserves crucial ecosystem services, such as carbon storage, water cycle regulation, and soil erosion prevention.

**Arguments against / Limitations of national parks:**
- Poaching and illegal logging can still occur if funding is insufficient to employ enough rangers to patrol large boundaries ('paper parks').
- Excluding local populations can lead to conflicts, loss of traditional livelihoods, and displacement of indigenous communities.
- Climate change can shift species' ranges, rendering static park boundaries ineffective.
- Habitat fragmentation can isolate species within the park, causing inbreeding and reducing genetic diversity unless ecological corridors are established.

**Other effective forest management strategies:**
- Sustainable harvesting/selective logging, where only mature trees are cut, leaving the forest canopy intact.
- Agroforestry, which integrates crops with trees, reducing the need to clear pristine forests.
- Community forestry, giving local people stewardship over forest resources, which encourages sustainable use.
- International agreements, such as REDD+ (reducing emissions from deforestation and forest degradation) and CITES, to regulate trade in endangered timber species.
- Debt-for-nature swaps, where a nation's foreign debt is reduced in exchange for environmental protection commitments.

**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 used precisely and accurately. Evaluates both the strengths and weaknesses of protected areas and discusses alternative strategies, presenting a balanced view.

**Level 2 [3–4 marks]**
Development and support of the conclusion is evident, though the response may lack some coherence and/or detail. Some subject-specific vocabulary is used but may lack precision. The response contains an evaluation of the statement but may be unbalanced (focusing heavily on either protected areas or alternative strategies).

**Level 1 [1–2 marks]**
The response is limited in development and/or support. Contradictions or irrelevant details may be present. Subject-specific vocabulary is limited or absent. May be unstructured or in the form of a simple list.

**0 marks**
No response or no creditable response.

To construct the line graph: 1. Label the horizontal x-axis as 'Year' and the vertical y-axis as 'Maximum consecutive dry days'. 2. Establish a uniform linear scale on the vertical axis (e.g., from 0 to 250 in intervals of 50) so that the data occupies at least half of the available grid space. 3. Plot the nine data points accurately: (2015, 120), (2016, 145), (2017, 180), (2018, 95), (2019, 210), (2020, 240), (2021, 160), (2022, 135), and (2023, 225). 4. Use a ruler to connect adjacent points chronologically with straight, clean lines.

M1: Axes correctly labeled with names (x-axis: Year, y-axis: Maximum consecutive dry days). [1] M2: Suitable linear scale on the vertical axis covering at least half of the grid space. [1] M3: All nine points plotted correctly within a tolerance of plus or minus half a small square. [1] M4: Points connected with a straight ruled line in chronological sequence. [1]

To construct the line graph: 1. Label the horizontal x-axis as 'Distance downstream / m' and the vertical y-axis as 'Dissolved oxygen / mg/L'. 2. Establish uniform linear scales on both axes (e.g., x-axis from 0 to 600 in steps of 100; y-axis from 0 to 8 in steps of 1 or 2) so that the data covers at least half of the grid. 3. Plot the seven points precisely: (0, 7.6), (100, 4.2), (200, 1.8), (300, 2.5), (400, 4.8), (500, 6.5), and (600, 7.4). 4. Draw neat, straight ruled lines connecting successive points.

M1: Axes correctly labeled with units (x-axis: Distance downstream / m, y-axis: Dissolved oxygen / mg/L). [1] M2: Suitable linear scales on both axes covering at least half of the grid. [1] M3: All seven points plotted accurately within plus or minus half a small square tolerance. [1] M4: Points connected with straight, ruled lines. [1]

To construct the line graph: 1. Label the horizontal x-axis as 'Nitrogen application / kg/ha' and the vertical y-axis as 'Corn yield / tonnes/ha'. 2. Choose linear, uniform scales (e.g., x-axis from 0 to 200 with steps of 40; y-axis from 0 to 10 with steps of 2) such that the data occupies more than 50% of the grid area. 3. Plot the six data points accurately: (0, 4.2), (40, 6.8), (80, 8.5), (120, 9.4), (160, 9.6), and (200, 9.5). 4. Use a ruler to join consecutive points with clean, straight lines.

M1: Both axes labeled with appropriate names and units (Nitrogen application / kg/ha and Corn yield / tonnes/ha). [1] M2: Uniform linear scales chosen so that the plotted data covers at least half of the graphing grid. [1] M3: All six points plotted accurately within a tolerance of plus or minus half a small square. [1] M4: Adjacent points joined in sequence with clean, straight, ruled lines. [1]

To construct the line graph: 1. Label the horizontal x-axis as 'Year' and the vertical y-axis as 'Population index'. 2. Apply suitable linear scales (e.g., x-axis with 8 divisions for Years 1 to 8; y-axis from 0 to 100 with steps of 20) such that the graph fills at least half of the grid space. 3. Plot the eight data points accurately: (Year 1, 45), (Year 2, 38), (Year 3, 29), (Year 4, 35), (Year 5, 52), (Year 6, 68), (Year 7, 80), and (Year 8, 76). 4. Use a ruler to connect consecutive points with straight lines.

M1: Axes correctly labeled with names (x-axis: Year, y-axis: Population index). [1] M2: Suitable linear scales on both axes so that the graph occupies at least half of the grid space. [1] M3: Correct plotting of all eight data points within plus or minus half a small square tolerance. [1] M4: Points connected with neat, straight, ruled lines. [1]

To ensure a fair test, the student must control other variables that could affect plant growth. This includes using seeds of the same species/cultivar from the same source, placing all pots in the same location to ensure identical light and temperature conditions, and watering all pots with the same volume of water at the exact same frequency.

Award [1] for each control variable identified (maximum of 2):
- same species / type / source of mung bean seeds
- same volume / mass / type of soil
- same watering regime (volume and frequency of water)
- same light / temperature conditions (placing in the same location)
- same size / material of pots

To properly monitor the effect of the discharge, a baseline must be established by sampling upstream of the sewage pipe. Downstream samples should then be taken at equal, systematic intervals (e.g., every 50 meters) from the source of the discharge to track the change in dissolved oxygen over distance, while keeping the sampling depth and distance from the bank constant.

Award [1] for each point:
- take a sample upstream of the discharge pipe (as a control / baseline)
- take samples downstream at regular / fixed distance intervals
- sample at the exact same depth / distance from the river bank at each site
- repeat sampling at each site and calculate a mean

To avoid bias, the ecologist should use a grid system. Two tape measures are laid out at right angles along the edges of the study area to act as axes. A random number generator is then used to produce pairs of coordinates, and the quadrats are placed at these coordinates.

Award [1] for each point:
- lay out two tape measures at right angles to create a coordinate grid / axes
- use a random number generator / random number table to generate coordinates
- place the quadrat at the intersection of the generated coordinates

To isolate the effect of chlorine concentration, other physical and chemical factors must be kept constant. These include the volume of water sample being tested, the temperature of the water, the duration of exposure to chlorine (contact time), and the initial concentration of bacteria in the samples.

Award [1] for each constant variable identified (maximum of 2):
- volume of water samples
- temperature of the water
- contact time / duration of exposure to chlorine
- initial concentration / strain of bacteria in the water
- pH of the water

The dependent variable is seed germination. This can be quantified by counting the number of seeds that have successfully sprouted (showing a visible radicle or shoot) after a specified time frame (e.g., 7 days) and calculating the germination percentage. Alternatively, the length of the emerging shoots can be measured with a ruler to assess growth rate.

Award [1] for each point:
- count the number of seeds that have germinated / sprouted / developed visible roots
- calculate the percentage of seeds germinated relative to the total number planted
- measure the length of the radicle / shoot using a ruler after a fixed number of days

To ensure valid comparison, the traps must be identical in design (size, depth, container material) and placed under equivalent conditions. The same number of traps must be deployed in each woodland site, and they must be left open for the exact same duration of time (e.g., 24 hours) to standardise the sampling effort.

Award [1] for each point (maximum of 2):
- use the same number of traps at each woodland site
- leave traps active for the exact same duration / period of time
- use identical traps (same size / depth / materials)
- place traps at standardized grid intervals or along a transect line
- use a standard cover / lid to protect traps from rain or predators

To measure water-holding capacity, place equal masses (e.g., 50g) of dry soil samples in separate funnels lined with filter paper. Place a measuring cylinder beneath each funnel. Pour a known volume of water (e.g., 100 cm³) slowly over each soil sample. After a set time (e.g., 15 minutes) when drainage stops, record the volume of water collected in each cylinder. Subtract this collected volume from the initial volume to determine the amount of water retained by each soil type.

Award [1] for each point:
- place equal masses / volumes of dry soil into identical funnels lined with filter paper
- pour a known, constant volume of water over each soil sample
- collect the drained water in a measuring cylinder over a fixed time period
- calculate water retained by subtracting the drained volume from the initial volume

Visual measurements are subject to individual bias and environmental variations. To minimize these errors, the same person should take all the readings, looking vertically straight down into the tube. Readings should be taken under consistent, indirect lighting (avoiding bright direct glare or deep shadows). Repeating the measurement three times for each water sample and calculating a mean further increases reliability.

Award [1] for each point:
- take readings under consistent lighting conditions (e.g., indirect daylight / avoid direct glare)
- have the same observer take all readings to ensure consistency
- look vertically straight down into the tube from the same distance
- repeat the test three times for each sample and calculate a mean

To ensure a fair test, the student must control other factors that can influence germination. These include environmental conditions such as temperature, the volume of solution applied to each seed batch, the type of soil or planting medium used, and using seeds from the same batch/species.

Award 1 mark for each correct variable identified (max 2). Accept: temperature, volume of liquid fertiliser/water, type of soil / growth medium, seed variety / type of seed, light level / intensity. Reject: 'soil' on its own, 'water' on its own (must specify volume/frequency).

The ecologist should first set up a coordinate grid over the study area using tape measures. Then, they should use a random number generator to obtain pairs of coordinates. The quadrats should be placed at these exact grid intersections to eliminate human bias.

Award 1 mark for laying out a grid using tape measures. Award 1 mark for using a random number generator/table to select coordinates. Reject: throwing the quadrat over the shoulder.

The independent variable is the factor that is changed by the investigator, which is the distance downstream from the waste pipe. The dependent variable is the factor being measured or observed, which is the turbidity of the water.

Award 1 mark for correctly identifying the independent variable as the distance downstream. Award 1 mark for correctly identifying the dependent variable as the turbidity / water clarity.

The sample with no chlorine serves as an experimental control. It allows the scientist to establish a baseline bacterial count of the untreated pond water, proving that any decrease in bacterial colonies in the other samples is directly caused by the chlorine treatment rather than external factors.

Award 1 mark for stating it acts as a control / baseline. Award 1 mark for explaining it is used for comparison to prove that the chlorine caused the change in bacteria levels.

First, find the absolute increase in population: \( 52,200 - 45,000 = 7,200 \). Next, divide this increase by the original population and multiply by 100 to get the percentage: \( \frac{7,200}{45,000} \times 100 = 16\% \).

M1: For correct calculation of population increase (7200) or correct substitution: \( \frac{52200 - 45000}{45000} \times 100 \) [1]
M2: Correct final answer of 16 (%) [1]

Calculate the total catch and the bycatch percentage for each year. For 2019: \( 300 / (1500+300) = 16.7\% \). For 2020: \( 400 / (1200+400) = 25.0\% \). For 2021: \( 400 / (800+400) = 33.3\% \). For 2022: \( 300 / (900+300) = 25.0\% \). Comparing these values, 2021 has the highest percentage of bycatch.

M1: Correct calculation of total catch for at least two years (e.g., 1200 tonnes for 2021) [1]
M2: Correct percentage calculation shown for 2021 (33.3% or 1/3) [1]
M3: Correctly identifies 2021 [1]

Looking at the data, as distance increases (100 m to 2000 m), the PM10 concentration drops from 150 to 42. The concentration falls below the safe limit of 50 micrograms per cubic meter at 2000 m.

M1: States that as distance from the mine increases, PM10 concentration decreases (negative correlation) [1]
M2: Identifies 2000 m as the minimum distance where the concentration is within safe levels (under 50 micrograms per cubic meter) [1]

First, calculate the threshold: 20% below 320 mm is \( 320 \times (1 - 0.20) = 256 \) mm. Next, identify how many years had rainfall less than 256 mm. These years are 2019 (190 mm), 2020 (150 mm), and 2023 (250 mm), making a total of 3 years.

M1: Correct calculation of the drought threshold: \( 320 \times 0.8 = 256 \) mm [1]
M2: Correct identification of the years below the threshold (2019, 2020, 2023) [1]
M3: Correct total count of 3 years [1]

Calculate the total generation: Dry season generation = \( 6 \times 45 = 270 \) MWh. Wet season generation = \( 6 \times 15 = 90 \) MWh. Total annual generation = \( 270 + 90 = 360 \) MWh. Since 360 MWh is less than the demand of 420 MWh, the system does not meet the demand.

M1: Calculates the total annual solar generation correctly: \( 6 \times 45 + 6 \times 15 = 360 \) MWh [1]
M2: States 'No' with reference to 360 MWh being less than the 420 MWh demand [1]

Percentage change is calculated as \( \frac{\text{After} - \text{Before}}{\text{Before}} \times 100 = \frac{30 - 120}{120} \times 100 = -75\% \). The ecological reason is the fragmentation of the habitat, leading to less deep forest cover and more edge effects from the highway.

M1: Correct calculation of the decrease in individuals: 90 [1]
M2: Correct percentage change calculation: -75% or 75% decrease [1]
M3: Valid ecological explanation such as habitat fragmentation, increased noise/edge effects, or loss of interior breeding sites [1]

Identify the values: Station A = 3.6 mg/L, Station C = 0.9 mg/L. Divide the concentration at Station A by the concentration at Station C: \( 3.6 / 0.9 = 4 \). Thus, the concentration decreases by a factor of 4.

M1: Correctly identifies phosphate levels of 3.6 mg/L and 0.9 mg/L from the text [1]
M2: Correctly calculates the factor of decrease: 4 (or by a factor of 4 / 4 times) [1]

Average damage for Category 3–4: \( 750 / 5 = 150 \) million USD per cyclone. Average damage for Category 1–2: \( 240 / 12 = 20 \) million USD per cyclone. Comparing the two averages, the Category 3–4 average is \( 150 / 20 = 7.5 \) times larger than Category 1–2 (or is 130 million USD higher).

M1: Correctly calculates average damage for Category 3–4: 150 million USD [1]
M2: Correctly calculates average damage for Category 1–2: 20 million USD [1]
M3: Provides a correct quantitative comparison (e.g., 7.5 times higher, or 130 million USD more) [1]

1. Marine reserves protect critical habitats and spawning grounds, allowing mature fish to reproduce and raise offspring without disturbance. 2. As the fish population density increases inside the protected reserve, individuals migrate out of the reserve into the fished areas (the spillover effect). 3. This continuous outward movement of adult fish and planktonic larvae replenishes depleted fish stocks in the surrounding unmanaged waters.

Award up to 3 marks: - Protects critical habitats / breeding / spawning grounds allowing undisturbed reproduction [1 mark] - Spillover effect / adult fish migrate into fished zones [1 mark] - Dispersal of larvae by currents replenishes adjacent areas [1 mark]

1. Terracing breaks a continuous steep slope into a series of flat, level steps. This physically obstructs and slows down the downhill velocity of surface runoff. 2. Slower water movement increases the contact time between water and land, promoting greater infiltration and percolation of water into the soil. 3. Consequently, the reduced runoff volume and speed prevent the washing away of fertile topsoil and plant nutrients, preserving soil structure and moisture.

Award up to 3 marks: - Breaks a long slope into flat steps, slowing the speed of surface runoff [1 mark] - Increases infiltration / absorption of water into the soil [1 mark] - Prevents soil and nutrients from washing downslope [1 mark]

1. Double glazing traps a layer of air or vacuum between two glass panes, and loft insulation traps air within fibers, acting as poor conductors of heat. This significantly reduces heat loss from homes by conduction and convection. 2. Because less heat escapes, homeowners require less fuel or electricity to maintain comfortable indoor temperatures. 3. Reduced demand for heating leads to less burning of fossil fuels, lowering the emissions of carbon dioxide and other greenhouse gases, which mitigates global climate change.

Award up to 3 marks: - Trapped air/vacuum acts as an insulator / reduces domestic heat loss [1 mark] - Less fossil fuel / electricity is consumed to heat homes [1 mark] - Decreases emissions of greenhouse gases / carbon dioxide, mitigating global warming [1 mark]

1. Bioremediation utilizes naturally occurring microbes (bacteria/fungi) that metabolize the hydrocarbons, turning the oil into harmless end-products like carbon dioxide and water. 2. Chemical dispersants introduce synthetic chemicals that can be highly toxic to sensitive wetland vegetation, fish, and macroinvertebrates, potentially biomagnifying up the food chain. 3. Dispersants only break oil into smaller droplets, causing it to sink and contaminate benthic sediments, whereas bioremediation actually removes the oil molecules from the ecosystem entirely.

Award up to 3 marks: - Bioremediation uses natural microbes to degrade oil into harmless carbon dioxide and water [1 mark] - Dispersants are synthetic chemicals that can be toxic to marine/wetland organisms [1 mark] - Dispersants only disperse/sink the oil, whereas bioremediation permanently removes hydrocarbons from the environment [1 mark]

1. A riparian buffer zone consists of deep-rooted native plants and trees along the water's edge. 2. The extensive root systems of these plants actively absorb dissolved nitrogen and phosphorus from the subsurface groundwater, using them for plant growth. 3. Additionally, the physical barrier of dense ground vegetation slows down surface runoff water, causing suspended soil sediments (which carry bound phosphorus) to settle out on land before entering the lake, thus preventing eutrophication.

Award up to 3 marks: - Plant root systems absorb dissolved nutrients (nitrogen and phosphorus) from groundwater [1 mark] - Physical vegetation slows surface runoff, trapping sediment-bound nutrients [1 mark] - Reduces nutrient loading into the lake, preventing algal blooms / eutrophication [1 mark]

1. Community-based ecotourism provides alternative, sustainable livelihoods (such as tour guides, lodge operators, and artisans) for local residents, decreasing their financial reliance on poaching or clearing forest for agriculture. 2. A portion of the tourism revenue (e.g., entrance fees) can be directly allocated to fund conservation management, such as hiring rangers to patrol the forest against illegal activities. 3. It fosters a sense of local ownership and pride, raising awareness about the economic and ecological value of preserving biodiversity.

Award up to 3 marks: - Provides alternative sustainable income for local residents, reducing poaching/clearing [1 mark] - Generates revenue directly used to fund conservation / forest ranger patrols [1 mark] - Raises environmental awareness and promotes local stewardship of natural resources [1 mark]

1. Standing water left by floods should be drained or filled in to eliminate potential breeding sites where mosquitoes lay their eggs. 2. Biological control agents, such as larvivorous fish (e.g., Gambusia), can be introduced into ponds and ditches to eat mosquito larvae. 3. Physical barriers, including the widespread distribution of insecticide-treated bed nets (ITNs) and fitting windows with fine mesh screens, physically block mosquitoes from biting humans, disrupting the disease transmission cycle.

Award up to 3 marks: - Draining or filling in standing water / puddles to eliminate breeding sites [1 mark] - Introducing biological predators (e.g., mosquito-eating fish) to water bodies [1 mark] - Using physical barriers such as insecticide-treated bed nets or window screens [1 mark]

1. The mining company must backfill the open pit using accumulated overburden and waste rock, grading the surface to match the natural contours of the surrounding terrain. 2. The original topsoil, which should have been stripped and stockpiled at the start of mining, must be spread evenly over the graded land to provide nutrients and organic matter. 3. Fast-growing native pioneer plants and trees must be planted to anchor the soil with their roots, preventing wind and water erosion while initiating ecological succession.

Award up to 3 marks: - Backfill the mining pit with overburden and shape/grade the landscape to natural contours [1 mark] - Replace saved topsoil to provide a fertile layer for plant growth [1 mark] - Plant native pioneer vegetation to bind soil particles and prevent erosion [1 mark]

Three effective methods for managing an oil spill are: 1. Dispersants: Spraying chemical dispersants breaks the oil slick into small droplets, increasing the surface area for natural microbial degradation. 2. Skimmers: Specialized boats or rotary devices physically vacuum or scoop floating oil from the water surface into holding tanks. 3. Bioremediation: Introducing specialized oil-degrading bacteria or applying nutrients (nitrogen and phosphorus) to stimulate existing microorganisms speeds up the natural breakdown of hydrocarbons.

Award 1 mark for each valid method described, up to a maximum of 3 marks. Acceptable responses include: - Dispersants: chemicals used to break down the oil into smaller droplets to accelerate biodegradation. - Skimmers: mechanical devices that remove oil from the water surface. - Bioremediation: using microorganisms/bacteria or adding nutrients to accelerate the natural decomposition of oil. - In-situ burning: igniting oil on the surface (under controlled conditions when fresh). - Sorbents: using materials that absorb the oil from the water surface. Do not accept 'booms' as it is excluded in the question.

The farmers can implement several strategies: 1. Terracing: Converting the steep slope into a series of flat steps reduces the speed of surface runoff and increases water infiltration. 2. Contour ploughing: Ploughing horizontally across the slope rather than up and down creates ridges that trap water and soil, preventing downslope erosion. 3. Afforestation or planting vegetation: Growing trees, shrubs, or cover crops on vulnerable areas binds soil particles together with their root systems, physically stabilizing the slope.

Award 1 mark for each clearly described strategy, up to a maximum of 3 marks. - Terracing: cutting flat steps into hillsides to slow runoff / increase infiltration. - Contour ploughing: ploughing across the slope along contours to trap water/soil. - Vegetation cover / Afforestation: planting trees/shrubs/cover crops so roots bind the soil together. - Strip cropping: alternating crop types in rows across the slope to interrupt water flow. - Mulching: covering bare ground with organic matter to protect against raindrop impact.

Three measures to manage cholera are: 1. Chemical disinfection / chlorination: Distributing chlorine tablets or setting up centralized water treatment to kill the Vibrio cholerae bacteria in drinking water. 2. Improving sanitation: Building emergency pit latrines located far from water bodies and ensuring safe disposal of sewage to prevent further contamination of water sources. 3. Hygiene education and handwashing promotion: Teaching residents to wash hands with soap or ash after using latrines and before food preparation.

Award 1 mark for each valid point, up to a maximum of 3 marks. - Chlorination / chemical treatment of water: adding chlorine to disinfect the water supply. - Safe sanitation infrastructure: constructing latrines away from water sources / safe sewage disposal to prevent fecal-oral contamination. - Hygiene education: promoting handwashing with soap / safe food handling. - Oral cholera vaccination: administering vaccines to immunize the population. - Safe water storage: using closed containers to prevent contamination during storage. Do not accept 'boiling water' as it is excluded in the question.

The government can adopt the following strategies: 1. Smart metering and time-of-use pricing: Charging higher rates during peak hours and lower rates off-peak encourages consumers to shift electricity usage to times of lower demand. 2. Financial incentives or subsidies: Providing tax credits, rebates, or subsidies for citizens purchasing highly rated energy-efficient appliances (such as LED bulbs or smart thermostats). 3. Education and public awareness campaigns: Launching informative programs on television, radio, and in schools to teach simple daily energy-saving habits like turning off appliances on standby.

Award 1 mark for each valid strategy, up to a maximum of 3 marks. - Time-of-use tariffs: introducing smart meters or peak-pricing to shift usage. - Subsidies / financial incentives: lowering the cost of energy-efficient appliances or insulation. - Public education / awareness campaigns: distributing tips on turning off lights / standby power. - Appliance energy labeling: mandating clear efficiency rating labels on sold goods. - Building codes/regulations: enforcing insulation, double-glazing, or solar panel integration on new residential builds.