2023 Cambridge IGCSE Environmental Management (0680) Practice Paper with Answers

By stopping fishing activities during the spawning season, cod are able to breed successfully, which increases recruitment (the number of young fish entering the population). It also reduces the total yearly catch, preventing the population from dropping below sustainable levels.

- 1 mark: Allows fish to reproduce/spawn without being disturbed or caught.
- 1 mark: Increases offspring survival/recruitment, helping to replenish/increase population size.
- 0.5 marks: Reduces overall annual fishing effort / total allowable catch.

Increasing the mesh size prevents the capture of juvenile fish, ensuring they grow up and reproduce. This keeps the population of lower-trophic-level species stable, which in turn ensures that apex predators have an adequate food source, preserving the balance of the food web.

- 1 mark: Enables juvenile / smaller fish to escape through the net gaps.
- 1 mark: Ensures these fish survive to reach breeding age / maintain future populations.
- 0.5 marks: Preserves the prey base for top predators, preventing food web collapse.

Subsistence arable farming is characterized by low use of advanced machinery and output being consumed directly by the household. On steep slopes, terracing is crucial because it slows down water movement, allowing water to flood the rice paddies while preventing topsoil from being washed away.

- 1 mark (0.5 marks per feature): Identify two features of subsistence arable farming (e.g., small land area, low level of technology/machinery, labor-intensive, crops grown for family consumption).
- 1.5 marks: Explain terracing (0.5 marks for creating flat steps to hold/retain water for wet rice; 1.0 mark for slowing surface run-off to prevent soil erosion on slopes).

Intensive cattle farming maximizes yield per hectare by packing many animals into a small space (high stocking density) and using expensive inputs. Extensive pastoral farming uses very few inputs per hectare and allows animals to graze over vast areas, resulting in a much lower stocking density.

- 1 mark: Intensive has high capital/chemical/feed inputs compared to extensive which has low inputs/relies on natural pasture.
- 1 mark: Intensive has a high stocking density (animals per unit area) compared to extensive which has a low stocking density.
- 0.5 marks: Correct comparative linking word used (e.g., 'whereas', 'however', 'compared to').

Forest fragmentation isolates populations, leading to inbreeding and loss of genetic diversity. A wildlife corridor acts as a physical bridge, enabling animals to travel between reserves, mate with unrelated individuals, and diversify the gene pool.

- 1 mark: Connects fragmented habitats, allowing the migration and movement of individuals between reserves.
- 1 mark: Encourages interbreeding / gene flow between previously isolated populations.
- 0.5 marks: Decreases the risk of inbreeding depression / increases genetic variation and adaptability.

To systematically sample the vegetation gradient, the researcher places a quadrat at predetermined intervals along a straight line. This ensures that the changing environmental conditions from the edge to the interior are sampled consistently without observer bias.

- 1 mark: Lay down a transect line (tape measure) straight from the forest edge into the interior.
- 1 mark: Place quadrats at fixed / regular intervals (e.g., every 5 meters).
- 0.5 marks: Identify and record the species abundance, count, or percentage cover within each quadrat.

Although fresh water exists, over two-thirds is locked away as solid ice in inaccessible regions like Antarctica and Greenland. Nearly all of the rest is groundwater, leaving only a tiny fraction (less than \(1\%\)) as easily accessible surface fresh water in rivers and lakes.

- 1 mark: State that around two-thirds (or approx. 68.7%) of fresh water is locked/frozen in ice sheets, glaciers, or permafrost.
- 1 mark: State that a large portion of the remaining fresh water is groundwater/aquifers which can be deep or difficult to extract.
- 0.5 marks: Recognize that only a tiny fraction (approx. 1.2% of fresh water) is surface water (rivers/lakes) that is easily accessible.

Cap-and-trade turns pollution reduction into a market asset. Power stations that clean up their emissions quickly through technology like flue-gas desulfurization can sell their unused permits, while those that do not must buy expensive extra permits, making high emissions financially punitive.

- 1 mark: Government sets an overall limit (cap) on total emissions and distributes tradeable pollution permits.
- 1 mark: Power stations that emit less than their allowance can sell/trade spare permits to earn revenue.
- 0.5 marks: Creates a market/financial incentive to invest in cleaner technologies (e.g., wet scrubbers) to lower emissions.

1. Closed seasons are timed to coincide with the spawning/breeding season of fish species [1 mark].
2. This prevents the harvesting of mature breeding individuals, allowing them to successfully reproduce [1 mark].
3. It increases recruit numbers / replenishes the population [0.5 marks].

Award 1 mark for identifying that closed seasons align with breeding/spawning times. Award 1 mark for explaining that this prevents capture of spawning adults / allows reproduction. Award 0.5 marks for stating this increases population recruitment / replenishes stocks.

1. Subsistence: labor is highly manual/uses family members, whereas commercial: highly mechanized/low labor input [1 mark].
2. Subsistence: crops are for consumption by the farmer/family [1 mark].
3. Commercial: crops are sold for profit/sale on the market [0.5 marks].

Award 1 mark for contrasting labor (manual/family vs. mechanized). Award 1 mark for stating subsistence crops are for family consumption. Award 0.5 marks for stating commercial crops are for market sale/profit.

1. Corridors connect isolated/fragmented habitats, allowing animals to move between them [1 mark].
2. This facilitates interbreeding between different populations / gene flow [1 mark].
3. This prevents inbreeding depression / increases genetic diversity [0.5 marks].

Award 1 mark for stating corridors allow migration/movement between fragmented areas. Award 1 mark for mentioning this enables gene flow/interbreeding between separated groups. Award 0.5 marks for linking this to prevention of inbreeding/increased genetic health.

1. Largest volume is in glaciers and ice sheets [1 mark].
2. It is frozen/solid water [1 mark].
3. It is located in remote regions (e.g., Antarctica, Greenland) far from major human populations [0.5 marks].

Award 1 mark for identifying ice sheets/glaciers as the largest freshwater store. Award 1 mark for explaining it is frozen/solid. Award 0.5 marks for noting its remote geographic location.

1. Catalytic converters use transition metal catalysts (e.g., platinum) [0.5 marks].
2. They convert toxic carbon monoxide (CO) into less harmful carbon dioxide (CO2) [1 mark].
3. They reduce nitrogen oxides (NOx) to harmless nitrogen gas (N2) [1 mark].

Award 0.5 marks for mentioning the use of catalysts/metals inside the exhaust. Award 1 mark for conversion of carbon monoxide to carbon dioxide. Award 1 mark for conversion/reduction of nitrogen oxides to nitrogen gas.

1. Percentage reduction calculation: \(\frac{120 - 90}{120} \times 100 = 25\%\) [1 mark].
2. The reduction limits total fish catch/mortality [0.5 marks].
3. This leaves more breeding adults in the sea to reproduce and recover the stock [1 mark].

Award 1 mark for the correct calculation showing a 25% reduction. Award 0.5 marks for explaining it limits extraction. Award 1 mark for explaining that more breeding stock remains to replenish the population.

1. Intensive livestock farming produces concentrated amounts of animal waste/manure in a small area [1 mark].
2. Runoff of this concentrated waste contains high levels of nitrates/phosphates, leading to eutrophication in local water bodies [1 mark].
3. Extensive farming has lower stocking density, meaning less concentrated waste runoff [0.5 marks].

Award 1 mark for identifying high concentration of waste in intensive systems. Award 1 mark for linking waste runoff to high nutrient input / eutrophication. Award 0.5 marks for contrasting with low stocking densities in extensive farming.

1. Wild relatives have not undergone selective breeding, so they retain high genetic diversity [1 mark].
2. They contain genes for resilience, such as disease resistance, pest resistance, or drought tolerance [1 mark].
3. These genes can be transferred/cross-bred into domestic crops to secure future food supplies [0.5 marks].

Award 1 mark for explaining wild relatives have higher genetic diversity. Award 1 mark for identifying useful adaptive traits/genes (drought/pest/disease resistance). Award 0.5 marks for explaining these genes can be bred into commercial crops.

A closed season protects fish when they are most vulnerable during spawning. By allowing mature fish to lay eggs and reproduce without being caught, the population can sustain itself. It also allows young fish to grow to adult size before they face fishing pressure, helping to maintain a healthy age structure in the population.

Award up to 3 marks: 1. protects fish during their breeding or spawning season [1 mark] 2. allows adult fish to reproduce / lay eggs / spawn undisturbed [1 mark] 3. allows young/juvenile fish to grow to maturity [1 mark] 4. increases/maintains the breeding stock for future years / prevents overfishing [1 mark]

System X focuses on self-sufficiency, which defines subsistence farming. System Y focuses on maximizing profit and yielding large-scale produce for trade, which defines commercial farming.

Award 1 mark for each correct identification: System X: subsistence (farming) [1 mark], System Y: commercial (farming) [1 mark].

In situ conservation keeps the species in its evolutionary context, allowing it to adapt to natural environmental pressures and interact with other species in the food web. It also preserves the physical habitat itself, protecting multiple species at once.

Award 1 mark for each valid advantage explained (up to 2), plus 1 mark for development/comparison: 1. protects species in their natural habitat / maintains the ecosystem / preserves food webs [1 mark] 2. allows species to continue evolving in response to natural selection / environmental changes [1 mark] 3. cheaper/more feasible for protecting multiple species simultaneously / protects non-target species [1 mark] 4. preserves natural behaviors / avoids adaptation to artificial environments [1 mark]

Nearly 69% of all freshwater is locked away as ice in glaciers and ice sheets (mainly in Antarctica and Greenland). About 30% is groundwater, much of which is deep in the earth and inaccessible without specialized drilling.

Award up to 2 marks: 1. the majority (approx. 68.7%) is locked/frozen in glaciers / ice sheets / ice caps [1 mark] 2. much of the remaining is deep groundwater / stored in deep aquifers which is hard to access/extract [1 mark]

In a wet scrubber, the flue gas is brought into contact with an alkaline liquid spray (such as lime or limestone slurry). The acidic sulfur dioxide gas reacts with the alkaline solution, forming a solid precipitate (calcium sulfite/sulfate) which is filtered out, leaving the clean gas to exit.

Award up to 3 marks: 1. waste/flue gases are sprayed with / passed through an alkaline mixture / slurry [1 mark] 2. slurry contains lime / limestone / calcium carbonate [1 mark] 3. sulfur dioxide reacts with lime/limestone to form a solid precipitate / calcium sulfate / gypsum [1 mark] 4. the solid is separated/removed, preventing acidic gas from entering the atmosphere [1 mark]

Sonar removes the element of chance in locating fish, making commercial fishing highly efficient. This extreme efficiency leads to overfishing because fish cannot reproduce fast enough to replace those caught, resulting in a rapid collapse of fish stocks.

Award up to 2 marks: 1. allows fleets to locate entire/large schools of fish very easily / leaves no refuge areas [1 mark] 2. leads to rapid/efficient extraction that exceeds the maximum sustainable yield / prevents fish populations from recovering/reproducing [1 mark]

In dry climates, grass and water are scarce and scattered. Staying in one place would quickly exhaust the pasture and water supply. Moving the animals continually allows the vegetation to regrow and prevents land degradation.

Award up to 3 marks: 1. low / unreliable rainfall / dry conditions mean vegetation/pasture is sparse / low carrying capacity [1 mark] 2. prevents overgrazing in one location [1 mark] 3. allows pasture / vegetation time to recover/regrow [1 mark] 4. water sources are temporary / seasonal, requiring movement to find water [1 mark]

To obtain a reliable estimate, the student must place the quadrats randomly to ensure unbiased representation of the field. Additionally, they must use a sufficient number of replicates (large sample size) to minimize the impact of anomalies.

Award up to 2 marks: 1. use random sampling / random coordinates to select quadrat locations / avoid bias [1 mark] 2. use a large number of quadrat samples / repeat the sampling many times [1 mark] 3. calculate a mean/average value from the samples [1 mark]

A closed season is a fisheries management strategy where harvesting is completely banned during certain times of the year. This period typically coincides with the species' breeding or spawning season.

1. **Protects spawning adults:** By banning fishing during the breeding season, adult fish/shellfish are not harvested before they can reproduce.
2. **Protects juveniles:** It ensures that eggs and young offspring are left undisturbed and are not accidentally caught as bycatch, allowing them to grow to maturity.
3. **Recruitment and stock recovery:** This directly increases the recruitment rate (number of fish entering the catchable population), preventing overexploitation and ensuring the fishery remains sustainable for the future.

Award up to 3 marks as follows:
- **1 mark** for stating that it protects adult species during their breeding/spawning season, allowing them to reproduce.
- **1 mark** for explaining that it protects young or juvenile fish/shellfish, enabling them to survive to breeding age / increases recruitment.
- **1 mark** for explaining that this prevents population decline / allows overexploited stocks to recover to sustainable levels.

Subsistence farming and commercial farming differ significantly in their scale, purpose, and methods:

1. **Purpose:** Subsistence farming is for family consumption/survival, while commercial farming is for generating profit through local or international trade.
2. **Inputs and Technology:** Subsistence farming relies on human/animal labor and basic tools. Commercial farming uses heavy machinery (tractors, harvesters), synthetic chemicals (fertilizers, pesticides), and high-yielding crop varieties.
3. **Scale:** Subsistence plots are typically small and fragmented, whereas commercial farms cover very large areas of land.

Award 1 mark for each valid difference stated (maximum 2 marks):
- **1 mark** for contrasting the purpose: subsistence is for family consumption / commercial is for selling/profit.
- **1 mark** for contrasting technology/labor: subsistence uses manual labor/low technology / commercial uses heavy machinery/high technology.
- **1 mark** for contrasting farm scale: subsistence involves small plots / commercial operates on a very large scale.

While zoos play a role in conservation, captive breeding programs face several distinct ecological and practical limitations:

1. **Genetic issues:** Due to the small starting population of endangered animals in captivity, the gene pool is highly restricted. This leads to inbreeding, which reduces genetic diversity and increases vulnerability to inherited diseases.
2. **Loss of natural behaviors:** Animals reared in artificial environments do not learn critical survival skills (e.g., finding food, navigating terrain, identifying threats/predators, establishing social hierarchies). This makes successful release into their native habitats very challenging.
3. **High costs and space constraints:** Captive breeding requires specialised veterinary care, facilities, and staff, making it highly resource-intensive. Zoos have finite physical capacity and cannot sustain the large population sizes needed to maintain healthy, genetically diverse species populations over multiple generations.

Award up to 3 marks (1 mark for each explained limitation):
- **1 mark** for explaining genetic limitations: small gene pool / reduced genetic diversity / risk of inbreeding depression.
- **1 mark** for explaining reintroduction challenges: loss of wild instincts/natural survival behaviors / difficulty in adapting to native habitats.
- **1 mark** for explaining resource limitations: high financial cost of maintenance / limited physical space to house a viable population.
- **1 mark** for explaining disease transmission risk: high density of animals in zoos can facilitate rapid spread of infectious diseases.

Groundwater represents a liquid source of fresh water found beneath the Earth's surface, which can be reached via aquifers in many inhabited regions.

Conversely, ice sheets and glaciers contain frozen fresh water. These are primarily located in the extreme polar zones (Greenland, Antarctica) or at the tops of high mountain ranges. This geographical isolation, combined with the solid state of the water, makes it highly impractical and expensive to exploit for daily human consumption.

Award up to 2 marks as follows:
- **1 mark** for identifying physical state: groundwater is liquid (easy to pump) while ice sheets and glaciers are solid ice.
- **1 mark** for explaining location/accessibility: groundwater is found locally beneath inhabited land (accessed via wells/aquifers) while ice sheets and glaciers are located in remote polar or high-altitude regions.

Indicative content:

Arguments in agreement with the statement (benefits of MPAs):
- MPAs protect critical habitats, such as coral reefs and mangroves, from destructive fishing practices like bottom trawling.
- They protect spawning grounds and nursery areas, allowing fish populations to reproduce and recover.
- 'Spillover effect' occurs, where fish stocks inside the MPA multiply and migrate out into adjacent zones where they can be sustainably fished.
- They conserve overall marine biodiversity and build ecosystem resilience against climate change.

Arguments in disagreement / alternative strategies (limitations of MPAs and need for other methods):
- MPAs are difficult and expensive to monitor, patrol, and enforce, often becoming 'paper parks' where illegal fishing continues.
- Many commercial fish species are highly migratory and travel long distances outside the boundaries of protected areas.
- MPAs do not address other major threats to fisheries, such as ocean acidification, marine pollution (plastics/oil), and global warming.
- Other fisheries management strategies are also highly effective and necessary, such as:
- Quotas (Total Allowable Catches) to limit the quantity of fish harvested.
- Regulation of mesh size to allow juvenile fish to escape.
- Closed seasons to ban fishing during breeding cycles.
- Restrictions on fishing effort (limiting boat numbers, engine sizes, or days at sea).
- Banning destructive gear like drift nets or explosives.

Conclusion:
Candidates should make a clear judgment on whether MPAs are the 'only' effective method, or if a combination of MPAs and other regulatory strategies is required for long-term sustainability.

Marking principles for 6-mark extended writing questions:

- Award 5–6 marks for a balanced, well-structured discussion that evaluates both the role of MPAs and alternative/complementary fisheries management strategies (such as quotas, mesh regulations, closed seasons), leading to a clear, justified conclusion.
- Award 3–4 marks for a response that discusses the benefits of MPAs but provides limited detail on other management strategies, or vice versa. May lack a clear conclusion.
- Award 1–2 marks for simple, brief points about MPAs or fishing restrictions without clear evaluation or development.

To find the number of years the water will last, divide the total volume of fresh water in the aquifer by the annual extraction rate:

\(\text{Number of years} = \frac{84000\text{ km}^3}{1050\text{ km}^3/\text{year}} = 80\text{ years}\)

Award 1 mark for correct working showing division: \(84000 \div 1050\).
Award 1 mark for correct final answer: 80 (years).

1. Compare the boat's distance to the EEZ limit: \(142\text{ nautical miles} < 200\text{ nautical miles}\), so the boat is inside the EEZ.
2. Calculate the distance from the outer limit: \(200 - 142 = 58\text{ nautical miles}\).

Award 1 mark for stating that the boat is inside/within the EEZ.
Award 1 mark for correct calculation of the distance from the outer limit: 58 (nautical miles).

The regulation of mesh size allows smaller, juvenile fish to pass through the net unharmed (1 mark). These fish are then able to reach sexual maturity, breed, and replenish the herring population, ensuring the fishery remains sustainable (1 mark).

Award 1 mark for identifying that juvenile/young fish can escape.
Award 1 mark for explaining that they can survive to breed/reproduce.

First benefit: Intensive arable farming relies heavily on chemical fertilizers and pesticides. Shifting to extensive grazing reduces chemical runoff, protecting local rivers from eutrophication (1 mark).
Second benefit: Rice paddies are kept flooded, creating anaerobic soil conditions that release significant amounts of methane. Extensive pastoral farming reduces these greenhouse gas emissions (1 mark).

Award 1 mark for each valid environmental benefit described (maximum of 2 marks).
Acceptable answers include: reduced water pollution/eutrophication, reduced methane emissions, reduced risk of soil salinisation, improvement in soil structure.

To ensure representativeness, scientists should use a random number generator to establish coordinates for the quadrats, which eliminates subjective selection bias (1 mark). Additionally, they must use a large sample size (many quadrats) to minimize the effect of anomalies and ensure an accurate average density (1 mark).

Award 1 mark for identifying random quadrat placement / use of random coordinates to avoid bias.
Award 1 mark for using a large sample size / repeating across different areas to ensure reliability.

The rapid extraction of groundwater removes hydrostatic support from the soil layers, which can cause land subsidence/sinking (1 mark). In coastal regions, lowering the freshwater table allows saltwater to migrate inland into the aquifer, causing saltwater intrusion and spoiling the drinking supply (1 mark).

Award 1 mark for each valid negative consequence suggested (maximum of 2 marks).
Acceptable answers include: land subsidence, saltwater intrusion, domestic wells running dry, increased energy costs for deep pumping.

Catalytic converters reduce emissions of nitrogen oxides (\(\text{NO}_x\)) and unburnt hydrocarbons by converting them to nitrogen, water, and carbon dioxide (1 mark). Since these emissions are the primary pollutants that react under sunlight to produce tropospheric ozone, reducing them directly decreases the formation of photochemical smog (1 mark).

Award 1 mark for stating that catalytic converters convert nitrogen oxides (\(\text{NO}_x\)) or hydrocarbons into harmless gases.
Award 1 mark for explaining that this reduces the primary reactants that combine with sunlight to form smog.

A closed season prohibits fishing during the spawning/breeding months of the cod (1 mark). This allows reproducing adults to mate and lay eggs undisturbed, ensuring successful recruitment of juvenile fish to replenish the cod stock (1 mark).

Award 1 mark for stating that it bans fishing during the spawning / breeding season.
Award 1 mark for explaining that this allows fish to reproduce successfully and replenish the population.

Unlike monoculture, crop rotation involves growing different plant species. Since different crops have different nutrient demands, it avoids depleting the soil of specific minerals (1 mark). Furthermore, incorporating nitrogen-fixing crops (like legumes) restores soil fertility naturally, and continuous soil coverage reduces erosion (1 mark).

Award 1 mark for explaining that different crops prevent specific nutrient depletion / mention of nitrogen fixation by legumes.
Award 1 mark for explaining that it maintains soil structure / reduces soil erosion / breaks pest cycles.

Wildlife corridors provide a safe passage for animals to migrate between isolated forest fragments, enabling them to find resources and mates (1 mark). This movement facilitates gene flow between populations, reducing the risks of inbreeding depression and helping to maintain overall genetic biodiversity (1 mark).

Award 1 mark for describing safe migration/access to resources between fragments.
Award 1 mark for explaining that it promotes gene flow / prevents genetic isolation / prevents inbreeding.

1. Spillover effect: As population density increases inside the protected area, adult fish migrate across the boundaries into adjacent areas where they can be harvested by fishers. 2. Larval export: The lack of disturbance allows fish inside the reserve to grow larger and produce significantly more eggs and larvae, which are carried by ocean currents to replenish surrounding fishing grounds.

Award [1] mark for identifying the spillover effect or migration of adult fish out of the reserve into surrounding waters. Award [1] mark for explaining that undisturbed breeding/spawning within the reserve provides larval or juvenile drift to replenish surrounding fished areas.

Intensive commercial arable farming is highly mechanized and inputs-heavy to maximize crop yield per unit area. Therefore, it requires substantial capital for: 1. Advanced machinery (such as tractors, combine harvesters, or automated sorting equipment). 2. Large-scale purchase of chemical inputs (such as synthetic fertilizers, pesticides, and herbicides) and the construction of advanced irrigation systems.

Award [1] mark for mentioning the high cost of purchasing or maintaining modern machinery/technology. Award [1] mark for mentioning significant expenditure on chemical inputs (fertilizers, pesticides, herbicides) or advanced irrigation infrastructure.

1. The lip of the container must be exactly level with the surface of the ground so that beetles crawling along the floor fall into the trap rather than walking around it. 2. A raised cover (such as a flat stone or piece of wood propped on twigs) must be placed over the trap to protect captured beetles from rain (drowning) or predation by birds.

Award [1] mark for stating that the top of the container must be flush or level with the soil surface. Award [1] mark for mentioning a raised cover or shield over the trap to prevent entry of rain or predators.

1. Depletion of the aquifer / falling water table: The aquifer is emptied faster than it can naturally recharge, leading to dry wells and requiring deeper, more expensive drilling. 2. Land subsidence / Saltwater intrusion: The loss of water pressure causes the overlying soil and rock layers to compact and sink, or in coastal regions, seawater flows into the freshwater aquifer, contaminating the supply.

Award [1] mark for identifying the lowering of the water table or depletion of the aquifer. Award [1] mark for identifying land subsidence (sinking of land) or saltwater intrusion.

In wet flue-gas desulfurization: 1. The exhaust gas containing sulfur dioxide is passed through a spray tower where it is washed with an alkaline slurry, usually composed of limestone (calcium carbonate) and water. 2. The acidic sulfur dioxide gas reacts chemically with the alkaline calcium compound, neutralizing it and forming calcium sulfite/sulfate (gypsum), which precipitates out as a solid residue, leaving the cleaned gas to exit.

Award [1] mark for describing how flue gases are sprayed with or passed through an alkaline slurry (such as limestone, calcium carbonate, lime, or calcium hydroxide in water). Award [1] mark for stating that sulfur dioxide reacts with the alkaline substance to form calcium sulfate or gypsum waste that is removed.

1. By ploughing horizontally across the slope (following the contours of the land) rather than up and down, the ridges and furrows act as barriers or mini-dams that slow down the downhill flow of surface water. 2. Slower-moving water has less kinetic energy to dislodge and transport soil particles, and more time to infiltrate into the ground, drastically reducing soil loss.

Award [1] mark for explaining that horizontal furrows across the slope act as barriers or mini-dams to slow down surface runoff. Award [1] mark for explaining that slower water speeds allow more infiltration into the soil, reducing the physical washing away of topsoil.

1. The regulation makes it illegal to keep lobsters below a certain size, meaning any caught juveniles must be returned to the sea alive. 2. This ensures that lobsters are allowed to grow to adulthood and reach reproductive age, giving them the chance to spawn at least once and contribute offspring to the next generation before they can be legally harvested.

Award [1] mark for stating that it prevents young/juvenile lobsters from being harvested (or ensures they are returned to the sea). Award [1] mark for explaining that this allows individuals to reach reproductive maturity and spawn at least once before they can be legally caught.

1. Pest and disease control: Monocultures are highly vulnerable to pests because they offer an uninterrupted food source. In polyculture, non-host plants disrupt the movement of pests and diseases, lowering overall crop damage naturally. 2. Soil conservation: Different crop species have varied root depths and nutrient requirements. Legumes can fix nitrogen, which benefits neighboring plants, while a more continuous ground cover prevents soil erosion and water runoff.

Award [1] mark for mentioning increased biodiversity (or reduced pest/disease outbreaks due to pest disruption). Award [1] mark for mentioning better soil nutrient utilisation (such as nitrogen fixation by legumes) or reduced soil depletion/erosion.

Turtle excluder devices (TEDs) consist of a metal grid installed inside a trawl net. Small target organisms, such as shrimp, easily pass through the bars into the codend. In contrast, larger non-target marine animals, like endangered sea turtles, cannot pass through the grid and are guided out through an escape opening. This significantly reduces bycatch and mortality rates of non-target marine species, preserving the marine food web and protecting biodiversity.

Award 1 mark for describing how the device works (e.g., larger animals are directed out of an opening or grid while target catch passes through). Award 1 mark for explaining the conservation benefit (e.g., reduces bycatch or mortality of endangered species like sea turtles, maintaining the ecosystem balance).

Mixed farming involves growing crops and raising livestock on the same farm. This provides two main economic benefits. First, it diversifies the farmer's income, meaning if crop prices drop or a disease destroys a harvest, the farmer can still earn money from livestock, reducing financial risk. Second, it creates a self-sustaining cycle that cuts input costs: animal manure is used as free organic fertilizer for the crops, and crop waste (like straw) is used as cheap animal feed or bedding.

Award 1 mark for each valid economic advantage suggested, up to a maximum of 2 marks. Accept: diversified income streams / reduced financial risk of crop failure [1]; reduced input costs for fertilizers or animal feed [1]; better utilization of labor throughout the year [1]. Reject: purely environmental advantages without an economic link.

Systematic sampling ensures that samples are taken at regular intervals to observe changes across an environmental gradient. First, the ecologist lays out a transect line (a measuring tape) across the wetland gradient. Second, a quadrat of fixed dimensions (e.g., 0.5 m by 0.5 m) is placed at pre-determined regular intervals (for example, every 5 meters) along the tape. Within each quadrat, the ecologist counts the individual reeds or estimates their percentage cover, recording the data systematically.

Award 1 mark for laying out a transect line across the gradient [1]. Award 1 mark for placing quadrats at regular or predetermined intervals along the transect line to record or count the plant species [1].

In coastal areas, fresh groundwater floats on top of denser, salty seawater, forming a delicate boundary. When groundwater is extracted too quickly, the freshwater table is lowered, and hydraulic pressure decreases. This reduction in pressure allows seawater to migrate laterally or rise vertically into the aquifer (saltwater intrusion). As a result, the water drawn from nearby wells becomes saline and unusable for drinking or irrigation.

Award 1 mark for stating that over-extraction lowers the freshwater table or reduces freshwater pressure [1]. Award 1 mark for explaining that this allows seawater to intrude or flow into the aquifer and contaminate wells [1].

To reduce urban sulfur dioxide (SO2) emissions, municipal authorities can target industrial and domestic combustion of fossil fuels. First, they can legislate that local factories and coal-fired power plants must install flue-gas desulfurization (FGD) systems, commonly known as wet scrubbers, which remove SO2 from waste gases before they are released. Second, they can transition urban energy grids away from sulfur-heavy fuels by mandating low-sulfur oil/gas for heating or incentivizing renewable energy installations.

Award 1 mark for each valid method stated, up to a maximum of 2 marks. Accept: installing scrubbers or flue-gas desulfurization in factories or power plants [1]; mandating the use of low-sulfur fuels [1]; subsidizing or transitioning to renewable energy sources [1]; relocating heavy industrial plants away from urban centers [1].

Individual Transferable Quotas (ITQs) are a market-based management strategy. First, scientists determine a sustainable Total Allowable Catch (TAC) for the season that ensures fish stocks can regenerate. This TAC is then divided into individual shares (quotas) allocated to registered fishers. Because each fisher is guaranteed a set portion of the catch, the competitive 'race to fish' is eliminated, reducing illegal fishing and bycatch while keeping the total harvest strictly within sustainable limits.

Award 1 mark for explaining that ITQs are based on a scientifically set Total Allowable Catch (TAC) limit [1]. Award 1 mark for explaining that individual allocations remove the competitive 'race to fish,' preventing fishers from exceeding sustainable thresholds [1].

Forest fragmentation isolates plant and animal populations in small habitat pockets, leading to genetic bottlenecking and local extinctions. By planting wildlife corridors—continuous strips of native vegetation—managers physically connect these isolated patches. This allows animals to move safely between areas, enabling gene flow between distinct populations, which decreases the risk of inbreeding depression. It also expands their foraging range and allows species to re-colonize areas where they had previously gone extinct.

Award 1 mark for explaining that corridors allow safe movement or migration of species between patches [1]. Award 1 mark for explaining that this increases gene flow or reduces inbreeding or helps species find food and mates [1].

Slash-and-burn farming relies on a long fallow period (often 10 to 20 years) during which the plots are left wild so that forest vegetation can grow back and restore organic matter and nutrients to the depleted soil. When the human population density increases, land becomes scarce. Farmers are forced to return to the same plots much sooner, drastically shortening the fallow period. Consequently, the soil does not have enough time to recover its fertility, leading to soil erosion, weed invasion, and permanent forest degradation.

Award 1 mark for identifying that increased population forces a reduction or shortening of the fallow period [1]. Award 1 mark for explaining that shorter fallows prevent soil nutrients or vegetation from fully recovering, causing soil degradation or erosion [1].

Award one mark for each explanation: 1. It restricts fishing during the breeding/spawning season, which allows adult fish to reproduce uninterrupted and increases the number of offspring. 2. It reduces the overall annual fishing pressure/catch, allowing juvenile rock bass to reach maturity and breed at least once before harvest.

Award 1 mark for each valid explanation, up to a maximum of 2 marks: - Protects fish during the spawning/breeding/reproduction season [1] - Allows fish to reproduce successfully / increases recruitment of young fish [1] - Reduces overall fishing effort/pressure/catch [1] - Gives juvenile fish time to grow to maturity / reach breeding age [1]

To conduct a valid investigation:
1. Lay out a tape measure to act as a transect line, running at a 90-degree angle (perpendicular) from the edge of the tourist trail into the forest.
2. Place a quadrat of standard size (e.g., $0.5\text{ m} \times 0.5\text{ m}$) at regular intervals (e.g., every 5 meters) along the transect line.
3. Count the number of individuals of the rare wildflower species (Anemone nemorosa) within each quadrat.
4. Repeat this transect survey at several randomly selected points along the tourist trail to obtain replicate data and calculate averages.

Award up to 4 marks for the following points:
- M1: Use of a transect line / tape measure extending at a right angle from the trail into the forest [1]
- M2: Placement of quadrats at regular / fixed systematic intervals along the line (e.g., every 2m or 5m) [1]
- M3: Counting the number / measuring percentage cover of the wildflower species within each quadrat [1]
- M4: Repetition of the transect at multiple locations along the trail to ensure reliability / calculate mean averages [1]
(Accept alternative valid sampling strategies, e.g., stratified sampling at set zones, provided distance from trail is controlled).

The plan should include:
1. Establishing sampling points upstream of the sheep pasture (to act as a control) and multiple points downstream at fixed distances.
2. Collecting water samples from the same depth (e.g., 10 cm below the surface) and location in the stream cross-section (e.g., the center of the flow) to avoid edge effects.
3. Collecting all samples at the same time of day (to control for natural diurnal fluctuations in dissolved oxygen caused by temperature and photosynthesis changes).
4. Repeating the sampling over several consecutive days or under similar weather conditions to minimize anomalies.

Award up to 4 marks for the following points:
- M1: Selection of sampling sites upstream (as control) and downstream (to measure runoff impact) [1]
- M2: Control of sampling depth / sampling location (e.g., mid-stream, 10 cm deep) [1]
- M3: Control of sampling time of day (to avoid diurnal variations in oxygen/temperature) [1]
- M4: Repetition of sampling over time / multiple days to identify anomalies / calculate a mean [1]

To compare soil moisture:
1. Collect multiple soil samples from randomly selected locations across both the conservation tillage and intensive tillage fields, ensuring all samples are taken from the same soil depth (e.g., 10 cm).
2. Weigh each fresh soil sample immediately using a digital balance to find the wet mass (initial mass).
3. Dry the soil samples in an oven at 105°C until a constant dry mass is achieved (repeatedly weighing until the mass stops decreasing).
4. Calculate the percentage moisture content using the formula: $$\text{Moisture Content (\%)} = \frac{\text{wet mass} - \text{dry mass}}{\text{wet mass}} \times 100$$

Award up to 4 marks for the following points:
- M1: Collection of multiple random soil samples at a standardized depth across both fields [1]
- M2: Measurement of the initial wet mass of the soil immediately after collection [1]
- M3: Drying the soil in an oven (at 100-105°C) until a constant mass is reached [1]
- M4: Accurate calculation formula: $((\text{wet mass} - \text{dry mass}) / \text{wet mass}) \times 100$ [1]

To plot the line graph:
1. Label the horizontal x-axis as 'Year' and number it from 1 to 6 with equal spacing.
2. Label the vertical y-axis as 'shrimp production / tonnes' and choose a scale from 0 to 350 (e.g., major grid lines every 50 tonnes) to ensure the data covers at least half the page.
3. Plot each coordinate accurately: (1, 120), (2, 190), (3, 240), (4, 280), (5, 310), (6, 310).
4. Connect the plotted points sequentially using a sharp pencil and a ruler.

**M1** Both axes labelled with correct units: 'shrimp production / tonnes' on the vertical axis (y-axis) and 'Year' on the horizontal axis (x-axis). [1]

**M2** Sensible linear scale chosen so that the plotted points occupy at least half of the grid area on both axes. [1]

**M3** All six points plotted accurately within \(\pm\) half a small square. [1]

**M4** Points connected with clear, straight ruled lines (no freehand sketching). [1]

To plot the bar chart:
1. Label the horizontal x-axis as 'Year' and allocate equal spacing for the 5 bars.
2. Label the vertical y-axis as 'Sulfur dioxide emissions / thousand tonnes' and choose a linear scale from 0 to 50 with regular intervals (e.g., every 5 or 10 units).
3. Draw the 5 vertical bars to their corresponding heights: 45, 40, 32, 22, and 15.
4. Ensure that all bars have the same width and are separated by equal gaps.

**M1** Both axes labelled with correct units: 'Sulfur dioxide emissions / thousand tonnes' on the vertical axis (y-axis) and 'Year' on the horizontal axis (x-axis). [1]

**M2** Sensible linear scale chosen so that the height of the bars covers at least half of the vertical grid space. [1]

**M3** All five bars plotted to the correct height within \(\pm\) half a small square. [1]

**M4** Bars drawn with equal width and equal spacing. [1]

Step 1: Calculate the volume of the net pen.
\(\text{Volume} = 45.0\text{ m} \times 20.0\text{ m} \times 6.0\text{ m} = 5400\text{ m}^3\)

Step 2: Calculate the total number of fish at maximum stocking density.
\(\text{Total number of fish} = 5400\text{ m}^3 \times 15.0\text{ fish/m}^3 = 81,000\text{ fish}\)

Step 3: Calculate the total mass of the harvested fish in kg.
\(\text{Total mass} = 81,000 \times 1.2\text{ kg} = 97,200\text{ kg}\)

Step 4: Convert the total mass to tonnes.
\(\text{Mass in tonnes} = \frac{97,200}{1000} = 97.2\text{ tonnes}\)

Award 1 mark for correct calculation of volume (\(5400\text{ m}^3\)) or total number of fish (\(81,000\)).
Award 1 mark for the correct final harvest yield of 97.2 (tonnes).

Step 1: Calculate the total energy generated by the wind turbine in a 30-day month.
\(\text{Energy per month} = 4.2\text{ MWh/day} \times 30\text{ days} = 126\text{ MWh}\)

Step 2: Convert the generated energy from MWh to kWh.
\(\text{Energy in kWh} = 126\text{ MWh} \times 1000 = 126,000\text{ kWh}\)

Step 3: Calculate the number of households that can be supported.
\(\text{Number of households} = \frac{126,000\text{ kWh}}{350\text{ kWh/household}} = 360\)

Award 1 mark for calculating the total monthly generation as \(126,000\text{ kWh}\) (or \(126\text{ MWh}\)).
Award 1 mark for the correct final number of households (360).