2023 Cambridge IGCSE Environmental Management (0680) 模擬試題連答案詳解

Inside the designated no-take zones, all fishing is prohibited. This allows target fish species to live longer, reach sexual maturity, and reproduce without human interference, leading to rapid population growth and larger individuals. As the density of fish inside the reserve increases, adult fish and their larvae naturally migrate or disperse outward (known as the "spillover effect") into surrounding waters where fishing is permitted, thus replenishing the depleted stocks there.

1 mark: Fish inside the zone grow, mature, and reproduce without pressure (increases spawning stock biomass).
1 mark: Spillover effect / dispersal of larvae and adult fish across boundaries into fished areas.
0.5 marks: Connection to replenishing catches for local fishers in adjacent areas.

To enforce international fishing quotas, regulatory bodies use technologies like Vessel Monitoring Systems (VMS) to track boat locations, deploy independent scientific observers on vessels to record catches, and carry out mandatory port inspections where landed fish weights are cross-checked. A primary limitation is the immense size of the high seas, which makes comprehensive physical surveillance extremely expensive and challenging, leading to non-compliance and illegal, unreported, and unregulated (IUU) fishing by flag-of-convenience vessels.

1 mark: Description of enforcement methods (e.g., satellite tracking/VMS, observers, or port inspection).
1 mark: Outline of a major limitation (e.g., vast ocean areas are hard to patrol, high cost, or illegal/unreported/unregulated (IUU) fishing).
0.5 marks: Clear and coherent explanation linking enforcement with its limitations.

Intensive subsistence farming requires high labor inputs per unit of land because operations are mostly manual or animal-assisted, and the primary objective is to produce enough food to support the household or local community with little to no surplus. In contrast, extensive commercial farming involves low labor input per unit area because it is highly mechanized and covers vast tracts of land, with the primary goal being to maximize crop yield for sale on national or global markets to generate profit.

1 mark: Labor input comparison (high labor input per unit area for intensive subsistence vs low labor input/high mechanization for extensive commercial).
1 mark: Purpose of production comparison (feeding the household/subsistence vs sale for financial profit).
0.5 marks: Use of clear comparative language to structure the response.

Mixed farming combines crop cultivation with livestock rearing. Two environmental benefits of this transition are: 1) the use of animal manure as organic fertilizer, which improves soil structure and reduces the need for synthetic chemical fertilizers, and 2) the integration of crop rotation and varied crop types which breaks weed, pest, and disease cycles. It reduces the farmer's economic risk because income is diversified. If a disease destroys the crops or if market crop prices plummet, the farmer still has livestock products (such as meat, milk, or wool) to sell, preventing total financial loss.

1 mark: Stating two environmental benefits (0.5 marks for each, e.g., manure as organic fertilizer, reduced synthetic inputs, crop rotation breaking pest cycles, improved biodiversity).
1 mark: Explaining the economic risk reduction (diversified income streams act as a safety net if one product fails/suffers market collapse).
0.5 marks: Correct use of environmental and agricultural concepts.

A Simpson's Index of Diversity close to 1 indicates high species richness (many different species present) and high species evenness (balanced abundances among species). This creates a complex network of feeding relationships and ecological niches. If a disturbance occurs (such as a disease outbreak or climatic stress), the ecosystem is resilient because multiple alternative species exist to perform similar ecological roles and maintain energy flow, preventing food web collapse. In contrast, low diversity communities are dominated by few species, making them highly vulnerable to single disturbances.

1 mark: Connects high index to high species richness and species evenness (or balanced abundance).
1 mark: Explains the stability mechanism (complex food webs / alternative pathways / species redundancy if one fails).
0.5 marks: Contrast with low-diversity systems which are prone to sudden collapse.

Habitat fragmentation divides forests into small, isolated patches, isolating wildlife populations. Wildlife corridors are strips of native vegetation that physically link these isolated fragments. They allow animals to travel safely between patches to find food, water, and nesting sites. Crucially, they facilitate interbreeding between otherwise isolated populations, promoting gene flow, increasing genetic diversity, and preventing inbreeding depression and local extinctions.

1 mark: Explaining physical connectivity (strips of habitat allowing safe movement/migration between fragments).
1 mark: Explaining genetic/demographic advantages (facilitates gene flow, maintains genetic diversity, or prevents inbreeding depression).
0.5 marks: Relating the corridor solution directly to mitigating habitat fragmentation effects.

To find the percentage of fresh water that is readily accessible liquid surface water and other usable forms, we subtract the percentages locked in glaciers and stored as groundwater from the total fresh water (100\%):

Percentage of inaccessible/less accessible freshwater = 68.7\% \text{ (glaciers)} + 30.1\% \text{ (groundwater)} = 98.8\%

Accessible freshwater = 100\% - 98.8\% = 1.2\%.

1 mark: Correct method of subtraction shown: 100 - (68.7 + 30.1).
1 mark: Correct numerical value of 1.2.
0.5 marks: Correct unit (\%) included with the final answer.

A catalytic converter contains precious metal catalysts (like platinum, palladium, and rhodium) that facilitate chemical reactions. First, it oxidizes toxic carbon monoxide (\text{CO}) and unburnt hydrocarbons (\text{HC}) into much less harmful carbon dioxide (\text{CO}_2) and water vapor (\text{H}_2\text{O}). Second, it reduces toxic nitrogen oxides (\text{NO}_x), which cause photochemical smog and acid rain, into harmless nitrogen gas (\text{N}_2) and oxygen (\text{O}_2).

1 mark: Correct identification of at least two harmful gases reduced (e.g., carbon monoxide / \text{CO}, nitrogen oxides / \text{NO}_x, or unburnt hydrocarbons).
1 mark: Correct identification of the less harmful products generated (e.g., carbon dioxide / \text{CO}_2, water / \text{H}_2\text{O}, or nitrogen gas / \text{N}_2).
0.5 marks: Describing the chemical nature of the transformation (oxidation of \text{CO}/\text{HC} or reduction of \text{NO}_x).

Catch quotas are set to limit the total allowable catch (TAC) of specific marine species, which ensures that enough mature breeding individuals remain in the population to reproduce and maintain sustainable stock levels. A major limitation of this approach is the practice of 'bycatch discarding' or 'high-grading'. Fishermen may catch non-target species or smaller/less valuable fish of the target species. To avoid exceeding their strict quota, they often dump these dead or dying fish back into the ocean, meaning the actual ecological impact and fish mortality are higher than official records suggest.

Award up to 2.5 marks: 1.0 mark for explaining how quotas promote sustainability (e.g., setting catch limits to preserve a viable breeding population and prevent population collapse). 1.0 mark for describing a valid limitation (e.g., high-grading, discarding bycatch, or the high financial/logistical costs of monitoring and enforcement at sea). 0.5 marks for linking the limitation to its negative impact on conservation or data accuracy.

As marine populations within the MPA grow due to protection from harvesting, the density of fish increases. This leads to a natural outward migration (spillover) of adult fish and larvae into adjacent, non-protected waters where fishing is permitted, improving catches for local fishers. Despite this long-term benefit, fishermen often oppose MPAs initially because the zones restrict access to their historical fishing areas, which can decrease their immediate daily income and force them to spend more time and fuel traveling to alternative sites.

Award up to 2.5 marks: 1.0 mark for explaining the spillover effect (population growth inside the MPA leading to migration of fish/larvae into harvestable zones). 1.0 mark for explaining the source of fisherman opposition (short-term loss of income, restriction of traditional fishing grounds, or increased travel costs). 0.5 marks for providing a clear contrast between short-term economic disruption and long-term ecological/economic benefit.

Intensive subsistence farming is characterized by very small farm sizes (often less than a few hectares) because land is scarce or family-owned, and it features very low capital input per unit of land, relying instead on manual labor and draft animals to maximize yields. On the other hand, extensive commercial farming involves vast tracts of land (often hundreds of hectares) with low capital and labor input spread out per unit area, even though the total farm-wide machinery cost may be high, resulting in a lower crop yield per hectare.

Award up to 2.5 marks: 1.0 mark for contrasting the land area used (intensive subsistence uses small plots of land; extensive commercial uses very large areas of land). 1.0 mark for contrasting capital input per unit of land (intensive subsistence has low capital input per unit of land, relying on high human labor; extensive commercial has low capital/labor input per unit of land despite high overall farm investment). 0.5 marks for clear comparative structure or correctly identifying the output/yield relationship relative to land size.

Overcultivation in arable farming involves growing crops continuously without fallow periods, which depletes soil nutrients and breaks down soil aggregate structure due to constant tillage, leaving the soil bare and loose. Similarly, overgrazing in pastoral farming occurs when livestock consume pasture vegetation faster than it can regenerate, removing the protective plant canopy and root networks, while their hooves compact the soil. In both cases, the soil is left unprotected and vulnerable to erosion by wind and rain, leading to a loss of fertile topsoil and desertification.

Award up to 2.5 marks: 1.0 mark for explaining how overcultivation degrades soil (continuous planting depletes nutrients, tillage breaks structure, leaves soil bare). 1.0 mark for explaining how overgrazing degrades soil (animals eat vegetation down to roots, hooves compact soil, reducing infiltration and plant growth). 0.5 marks for identifying the shared consequence (both leave soil exposed to wind and water erosion, leading to desertification or complete loss of fertility).

The most suitable sampling method for ground-dwelling invertebrates is the use of pitfall traps, which are small containers sunk into the ground so that crawling organisms fall inside. To ensure the sampling is fair and ethical, the following precautions should be taken: 1) Traps must be checked frequently (e.g., at least once every 24 hours) to minimize stress, starvation, or predation among captured invertebrates. 2) Traps should be fitted with a raised cover (such as a flat stone or leaf supported by twigs) to protect captured organisms from rain and predators, or have drainage holes to prevent drowning. Additionally, the same size of trap and active duration must be used in both forest types to keep the comparison fair.

Award up to 2.5 marks: 0.5 marks for identifying 'pitfall traps' (or 'pitfall trapping') as the correct method. 2.0 marks (1.0 mark per precaution) for two distinct, explained precautions. Acceptable precautions: checking traps regularly to prevent death/predation; using a rain cover/drainage to prevent drowning; placing some leaf litter/food inside to reduce stress; using identical trap designs and keeping them active for the same duration in both locations to ensure a fair test.

The edge effect describes the modified abiotic and biotic conditions (such as increased wind, sunlight, lower humidity, and higher predation rates) at the boundary of a habitat compared to its interior. A single large reserve has a lower perimeter-to-area ratio than several small reserves, meaning it contains a much larger protected core area unaffected by edge disturbances. Where reserves are fragmented, wildlife corridors (strips of native vegetation connecting the fragments) mitigate isolation by allowing animals to migrate safely between patches, find food, and mate with other populations, which increases genetic diversity and reduces the risk of inbreeding.

Award up to 2.5 marks: 1.0 mark for explaining the edge effect and why a single large reserve is preferred (e.g., larger undisturbed core habitat, lower perimeter-to-area ratio). 1.0 mark for describing how wildlife corridors work (e.g., physical strips of habitat connecting isolated reserves to allow migration/movement). 0.5 marks for linking these corridors to conservation benefits (e.g., preventing genetic isolation, allowing adaptation to change, or maintaining gene flow).

The majority of the Earth's fresh water (about \(68.7\%\)) is locked away and stored as ice in glaciers, ice caps, and permanent snowfields, mainly in polar regions such as Antarctica and Greenland. Approximately \(30.1\%\) is stored as groundwater, much of which is deep and expensive or difficult to extract. This leaves less than \(1.2\%\) of all fresh water as surface water (in lakes, rivers, and swamps) and atmospheric moisture, which is the only fraction easily accessible and available for direct human use.

Award up to 2.5 marks: 1.0 mark for identifying glaciers / ice caps / ice sheets as the storage location of the majority of fresh water. 1.0 mark for explaining that these resources are frozen and geographically isolated (inaccessible for direct human consumption). 0.5 marks for noting that much of the remaining portion is underground (groundwater), leaving only a tiny fraction in easily accessible surface bodies (rivers and lakes).

A catalytic converter is fitted to a vehicle's exhaust system and uses transition metals (such as platinum, palladium, or rhodium) as catalysts to facilitate chemical reduction and oxidation reactions. It targets harmful pollutant gases: it reduces toxic nitrogen oxides (\(\text{NO}_x\)) into harmless nitrogen gas (\(\text{N}_2\)), and oxidizes toxic carbon monoxide (\(\text{CO}\)) into less harmful carbon dioxide (\(\text{CO}_2\)). It also oxidizes unburnt hydrocarbons into carbon dioxide and water vapor.

Award up to 2.5 marks: 0.5 marks for explaining the mechanism (using metal catalysts to promote redox reactions within the exhaust gas flow). 1.0 mark (0.5 marks each) for identifying two harmful pollutants (e.g., carbon monoxide, nitrogen oxides, or unburnt hydrocarbons). 1.0 mark (0.5 marks each) for correctly identifying their respective converted, less harmful products (carbon dioxide, nitrogen gas, or carbon dioxide and water vapor respectively).

In marine reserves, fishing is prohibited, which allows targeted fish species to reach maturity and achieve their full reproductive potential. Larger mature fish produce exponentially more eggs. As the population within the reserve density increases, resource competition triggers a spillover effect. This causes juvenile and adult fish, as well as currents carrying larvae and eggs, to move outwards across the boundary into adjacent waters where fishing is permitted, thereby increasing the harvestable biomass.

1 mark: Explain that fish within the reserve are protected from harvesting, allowing them to grow larger and reproduce successfully. 1 mark: Explain the 'spillover effect' where increased population density inside the reserve causes adults and juveniles to migrate outward. 0.5 marks: Explain that currents carry eggs and larvae out of the reserve, enhancing recruitment in fished areas.

Setting an accurate TAC requires highly precise biological data which is difficult to gather due to the vastness of ocean habitats. Firstly, estimating the stock size of migratory fish relies on sampling and catch reports, which can have significant uncertainty or suffer from illegal, unreported, and unregulated (IUU) fishing data gaps. Secondly, external environmental variables like water temperature fluctuations, disease outbreaks, and climate phenomena (e.g., El Nino) can cause sudden changes in natural mortality and recruitment rates that stock assessment models cannot instantly predict.

1 mark: Difficulty in accurately sampling and estimating population size/biomass in massive ocean environments. 1 mark: Unpredictable natural/environmental fluctuations (temperature, food webs) affecting fish survival and reproduction rates. 0.5 marks: Inaccurate reporting of catches by commercial vessels or illegal, unreported, and unregulated (IUU) fishing.

Intensive subsistence farming is typically practiced on very small, fragmented plots of land due to high population pressures. Because farmers lack capital for machinery, they must use intensive manual and animal labour to maximize yields to feed their households. Conversely, extensive commercial farming occupies massive areas of land (such as large wheat farms or cattle ranches) and relies on high levels of mechanization (tractors, harvesters) and capital, resulting in very low human labour requirements per hectare.

1 mark: Comparison of land area (small plots for intensive subsistence vs. large, expansive tracts of land for extensive commercial). 1 mark: Comparison of labour input (high manual/animal labour per unit area for intensive subsistence vs. low labour input with high mechanization for extensive commercial). 0.5 marks: Distinct reference to the purpose of each (subsistence is for feeding family/local community, while commercial is for generating profit on the open market).

Shifting cultivation is an agricultural system where farmers clear an area of forest vegetation, burn the debris to release ash nutrients into the soil, and cultivate crops for a few seasons. Once soil fertility declines, the plot is abandoned to allow natural forest regeneration (fallow period) while the farmer moves to a new patch. With rapid population growth, land pressure increases, forcing farmers to return to abandoned plots much sooner. The fallow period is drastically shortened, meaning the soil does not recover its nutrient levels, leading to chronic soil erosion, loss of forest regeneration, and permanent land degradation.

1 mark: Clear description of the slash-and-burn/fallow cycle (clearing, burning for ash nutrients, cultivation, and abandonment). 1 mark: Explanation that population growth leads to land scarcity, which shortens the required fallow period. 0.5 marks: Linking the shortened fallow period to permanent soil nutrient depletion, land degradation, or deforestation.

Seed banks offer a highly space-efficient way to preserve the genetic material of thousands of plant species. By keeping seeds under low temperature and low moisture conditions, their metabolic rate is suspended, allowing long-term storage and protecting them against habitat destruction, natural disasters, or climate change in the wild. However, a major limitation is that 'recalcitrant' seeds (such as those from many tropical trees) lose viability when dried and frozen, meaning they cannot be stored this way. Additionally, seeds stored in banks do not undergo natural evolutionary processes and adaptation to changing pests or climates.

1 mark: Explaining benefits of space efficiency and protection from wild threats (habitat destruction, diseases). 1 mark: Explaining the mechanism of preservation (dehydration and sub-zero temperatures to suspend metabolism). 0.5 marks: Stating a valid limitation (recalcitrant seeds cannot survive the process, high maintenance costs/power vulnerability, or lack of active evolution during storage).

When a large, continuous habitat is fragmented by roads, agriculture, or urban development, the perimeter-to-area ratio increases. This creates 'edge effects' where the outer boundaries of the remaining habitat patches are exposed to different abiotic factors (increased sunlight, wind, lower humidity) and biotic pressures (higher invasion of pests, weed species, and predators), reducing the quality of the interior habitat. Wildlife corridors are strips of natural habitat that physically connect these isolated fragments, allowing animals to disperse, find food, mate with different populations to maintain genetic diversity, and escape localized disturbances.

1 mark: Explaining how fragmentation increases the perimeter-to-area ratio, exposing interior species to harsh microclimates, invasive species, or predators at the edges. 1 mark: Describing wildlife corridors as continuous strips of vegetation that physically link isolated fragments. 0.5 marks: Explaining that corridors facilitate gene flow, seasonal migrations, and access to a wider foraging range.

While around 2.5% to 3% of the water on Earth is freshwater, approximately 68.7% of this freshwater is frozen in glaciers, ice caps, and permanent snowfields, mainly in Antarctica and Greenland, making it geographically isolated and physically inaccessible. The largest accessible reservoir of liquid freshwater is groundwater, stored within underground aquifers, which accounts for approximately 30.1% of all freshwater resources.

1 mark: Explaining that the majority (approx. 68-69%) of freshwater is frozen in glaciers, ice sheets, or permanent snow. 1 mark: Correctly identifying groundwater/aquifers as the largest accessible liquid freshwater reservoir. 0.5 marks: Pointing out that easily accessible surface water (rivers and lakes) makes up less than 1% of total freshwater.

A catalytic converter is installed in a vehicle's exhaust system. It contains precious metals (such as platinum, palladium, or rhodium) which act as catalysts to speed up chemical oxidation and reduction reactions. It reduces nitrogen oxides (\(\text{NO}_x\)) into harmless nitrogen gas (\(\text{N}_2\)) and oxygen (\(\text{O}_2\)), and oxidizes toxic carbon monoxide (\(\text{CO}\)) and unburnt hydrocarbons (\(\text{HC}\)) into carbon dioxide (\(\text{CO}_2\)) and water vapour (\(\text{H}_2\text{O}\)).

1 mark: Explaining that the exhaust gases pass over precious metal catalysts (e.g. platinum) to facilitate chemical oxidation and reduction reactions. 1 mark: Stating two correct conversions (e.g., carbon monoxide to carbon dioxide, nitrogen oxides to nitrogen gas, or unburnt hydrocarbons to carbon dioxide and water). 0.5 marks: Explaining that these reactions turn highly toxic or ozone-depleting gases into less harmful atmospheric components.

Closed seasons are designated periods of the year when fishing for a specific species is banned. This protects adult fish during their spawning and breeding phases, which maximizes reproduction and recruitment. It also allows juvenile fish to grow to maturity and reproduce at least once before being harvested, helping to maintain the population above the maximum sustainable yield and preventing overexploitation.

1.0 mark for stating that closed seasons protect fish during their spawning or breeding periods to facilitate reproduction. 1.0 mark for explaining that it allows juvenile fish to reach maturity and breed before harvest. 0.5 marks for noting that it reduces overall annual fishing pressure or prevents overfishing.

Intensive subsistence wet rice farming uses a permanent, fixed plot of land, which leads to permanent habitat clearance and low biodiversity due to monoculture. Shifting cultivation, on the other hand, involves temporary land clearance (slash-and-burn) over a much larger cumulative area. However, because fields are left fallow, the forest and its biodiversity can regenerate over time, meaning the overall, long-term impact on biodiversity is lower than permanent agriculture.

1.0 mark for comparing land use: wet rice farming is intensive and permanent on the same plot, whereas shifting cultivation is extensive and rotational. 1.0 mark for comparing biodiversity: wet rice results in permanent biodiversity loss and monoculture, while shifting cultivation allows biodiversity to recover during the fallow period. 0.5 marks for identifying that shifting cultivation's slash-and-burn phase causes localized air pollution or temporary soil exposure.

First, calculate the area of one quadrat: 0.5 m x 0.5 m = 0.25 square meters. Next, calculate the total area sampled by throwing the quadrat 10 times: 10 x 0.25 = 2.5 square meters. Finally, scale up the count to the total field area: (200 square meters / 2.5 square meters) x 15 plants = 80 x 15 = 1200 plants.

0.5 marks for calculating the area of one quadrat (0.25 square meters). 1.0 mark for calculating the total sampled area (2.5 square meters) or showing the scaling factor (200 / 2.5 = 80). 1.0 mark for the correct final answer of 1200 (with or without units).

Flue gases containing acidic sulfur dioxide are passed through a spray of water mixed with an alkaline substance, such as lime or limestone slurry. The sulfur dioxide reacts with the alkaline mist and undergoes a neutralization reaction. This chemical reaction converts the harmful gas into a solid waste byproduct, such as calcium sulfate (gypsum), which can be easily separated from the gas flow, cleaned, and removed.

1.0 mark for stating that the exhaust gases are sprayed with water containing an alkaline substance (e.g., lime or limestone). 1.0 mark for explaining that the acidic sulfur dioxide reacts with or is neutralized by the alkaline slurry. 0.5 marks for stating that this process produces a solid byproduct (e.g., calcium sulfate or gypsum) which is removed from the gas stream.

Strategy A (Marine Protected Areas) creates 'no-take' zones that protect critical habitats and breeding grounds. This allows fish populations to recover, increase in size, and eventually spill over into adjacent fishing zones, boosting local yields. However, MPAs do not limit fishing outside their boundaries, which can lead to intense overfishing in surrounding areas. They also face opposition from local fishers and require high enforcement costs to patrol boundaries. Strategy B (Quotas and Mesh Sizes) directly controls the volume of fish harvested and protects juvenile fish. Setting quotas (Total Allowable Catches) based on scientific data ensures the rate of extraction does not exceed natural replenishment. Regulating net mesh sizes allows young fish to escape, grow, and reproduce. However, quotas can lead to 'high-grading' (discarding dead, lower-value fish to maximize profit within the quota limits) and require extensive monitoring at landing ports, which is difficult to police. In conclusion, a combination of both strategies is most effective. MPAs protect biodiversity and spawning nurseries, while quotas and mesh sizes regulate harvesting in open waters, ensuring a balanced, sustainable fishery.

Level 3 (5-6 marks): A comprehensive evaluation that discusses both the advantages and limitations of both Strategy A (MPAs) and Strategy B (quotas and mesh sizes). The response contains a clear, reasoned judgment or conclusion recommending a combination or a justified single approach. Environmental terminology is used accurately throughout.
Level 2 (3-4 marks): A sound explanation of both strategies, but the evaluation may lack balance (focusing more on one than the other) or lack a clear, well-supported conclusion. Some environmental terminology is used.
Level 1 (1-2 marks): A basic description of one or both strategies with little or no evaluation. The response lacks structure and contains minimal environmental terminology.
0 marks: No response or no response worthy of credit.

To find the percentage decrease: 1. Find the decrease in tonnes: \(15400 \text{ tonnes} - 11550 \text{ tonnes} = 3850 \text{ tonnes}\). 2. Divide the decrease by the original value: \(\frac{3850}{15400} = 0.25\). 3. Convert to a percentage: \(0.25 \times 100 = 25\%\).

1 mark for correct working: e.g. \(\frac{15400 - 11550}{15400} \times 100\) or \(3850 / 15400\). 1 mark for correct final answer: 25% (accept 25, do not accept -25).

Method 1: 1. Calculate the area of one quadrat: \(0.5\text{ m} \times 0.5\text{ m} = 0.25\text{ m}^2\). 2. Calculate the total area sampled by 10 quadrats: \(10 \times 0.25\text{ m}^2 = 2.5\text{ m}^2\). 3. Calculate the density per square metre: \(\frac{30 \text{ plants}}{2.5\text{ m}^2} = 12\text{ plants/m}^2\). Method 2: 1. Find the mean number of plants per quadrat: \(\frac{30}{10} = 3\text{ plants per quadrat}\). 2. Since the quadrat is \(0.25\text{ m}^2\), multiply by 4 to scale up to \(1\text{ m}^2\): \(3 \times 4 = 12\text{ plants/m}^2\).

1 mark for correct working showing either the total sampled area (\(2.5\text{ m}^2\)) or the mean plants per quadrat (3). 1 mark for the correct final answer: 12 (accept '12 plants per square metre' or '12 plants/m2').

Marine reserves protect the entire ecosystem and key habitats (such as spawning and nursery grounds) from physical disturbance like trawling. In contrast, fishing quotas only limit the landed catch, are difficult to monitor, and do not prevent the mortality of non-target fish discarded as bycatch.

Award 1 mark for each valid reason, up to a maximum of 2 marks: • Protects breeding grounds or nursery habitats from damage [1] • Harder to bypass or easier to enforce compared to monitoring quotas [1] • Eliminates bycatch or discarding issues within the designated zone [1]

The decrease in cod catch is calculated as: \(120 - 35 = 85\) tonnes. The percentage decrease is: \(\frac{85}{120} \times 100 = 70.83\%\). Accept 70.8% or 71%.

Award 1 mark for correct working showing the decrease or the fraction: \((120 - 35) / 120 \times 100\) or \(85 / 120\) [1] Award 1 mark for the correct calculation: 70.8% or 70.83% or 71% [1]

Commercial intensive farming relies on heavy financial investment (high capital) to maximize crop yield for sale on national or international markets. In contrast, subsistence farming is low-capital, utilizing traditional manual methods to grow food directly for family survival.

Award 1 mark for comparing capital input: intensive commercial has high capital or machinery investment whereas subsistence has low capital or manual tools [1] Award 1 mark for comparing purpose of production: intensive commercial is for sale, profit, or export whereas subsistence is for feeding the family or survival [1]

To avoid bias, a grid must be established using tape measures, and random coordinates should be generated to locate the quadrats. Additionally, sampling a large number of quadrats across the entire meadow ensures the data represents the true distribution of the plant.

Award 1 mark for each valid step described, up to a maximum of 2 marks: • Use of a grid or tape measures to define the area [1] • Coordinates selected using a random number generator or table to avoid bias [1] • Take a large number of samples or repeat many times to ensure a representative sample [1]

Glaciers and ice caps contain the majority of Earth's freshwater, followed by groundwater. The freshwater in glaciers is locked up as solid ice and situated in polar or high-altitude regions, making extraction and transport economically and physically unfeasible.

Award 1 mark for naming both correct reservoirs: ice caps/glaciers AND groundwater [1] Award 1 mark for explaining why the largest is unavailable: frozen state OR located in remote areas like Antarctica [1]

Catalytic converters chemically reduce nitrogen oxides (\(\text{NO}_x\)) and oxidize unburnt hydrocarbons in car exhaust. Because these substances are primary precursors that react with sunlight to form photochemical smog and ozone, removing them at the source prevents the chemical reactions that form smog.

Award 1 mark for identifying the pollutants removed: reduces emissions of nitrogen oxides (NOx) or unburnt hydrocarbons [1] Award 1 mark for explaining how this prevents smog: prevents the reaction of these primary pollutants with sunlight to form ground-level ozone or secondary pollutants [1]

A larger mesh size allows smaller, immature fish to escape capture. By allowing juvenile fish to grow to adult size, they have the opportunity to reproduce at least once, maintaining the breeding population and preventing stock collapse.

Award 1 mark for explaining the escape of young fish: allows small, young, or juvenile fish to escape the net [1] Award 1 mark for linking this to population sustainability: allows fish to reach sexual maturity and reproduce to replenish the stock [1]

Low population densities mean there is plenty of land, allowing long fallow cycles where secondary forest regrows and restores nutrients to the soil. Higher population densities force farmers to return to previously cleared plots much sooner, meaning the soil never recovers its fertility, leading to permanent land degradation.

Award 1 mark for explaining the situation at low density: long fallow periods allow forest regrowth and soil nutrient recovery [1] Award 1 mark for explaining the impact of high density: fallow periods are shortened or soil is reused too quickly, leading to nutrient depletion or soil erosion [1]

1. LED lights: These illuminate the nets, making them highly visible to non-target species like sea turtles. This allows them to detect and actively avoid the net, decreasing incidental entanglement.
2. Larger mesh size: This allows smaller, juvenile fish to pass through the gaps unharmed, ensuring they can grow and reach reproductive maturity to sustain future fish stocks.

Award 1 mark for explaining how LED lights prevent turtle/mammal bycatch (by increasing visibility/allowing avoidance).
Award 1 mark for explaining how larger mesh size allows juvenile fish to escape (ensuring survival to breeding age/reducing recruitment loss).

A seasonal ban ensures that mature cod are not caught during their critical reproductive window. By protecting the adult stock, particularly the larger, highly fecund females (which produce six times more eggs than smaller females, as shown in the table), the fishery maximizes larval recruitment to restore population levels.

Award 1 mark for: protecting adult breeding stock when they are vulnerable/aggregating to spawn.
Award 1 mark for: maximizing egg production/larval recruitment to replenish the population.

1. Diversification of risk / Food security: If rainfall is low and the maize crop fails, livestock products (such as meat, milk, or selling animals) provide an alternative source of food and income.
2. Nutrient cycling: Animal manure can be applied to the arable fields as a natural fertilizer, improving soil organic matter, structure, and nutrient levels without the cost of chemical fertilizers.

Award 1 mark for: food security / diversification of risk (livestock provides food/income when crops fail).
Award 1 mark for: soil fertility improvement (use of animal manure as a natural fertilizer for crops).

System X has high inputs of capital, chemicals, and technology, which are characteristics of intensive (or commercial intensive) farming. High use of chemical fertilizers leads to surface runoff into streams and lakes, causing nutrient enrichment (eutrophication). This results in algal blooms, oxygen depletion, and the death of aquatic organisms.

Award 1 mark for identifying System X as intensive (commercial) farming.
Award 1 mark for a correct environmental impact of chemical fertilizers: eutrophication / algal blooms / water pollution / soil acidification.

To achieve valid and unbiased sampling, the scientist must avoid choosing quadrat positions subjectively. By overlaying a coordinate grid over the plots and using a random number generator to select where to place the quadrats, every plant has an equal chance of being sampled. Additionally, repeating the quadrat drops multiple times (e.g., 10+ times per plot) ensures the calculated average is representative of the whole area.

Award 1 mark for: setting up a grid and using a random number generator to determine coordinate positions (avoiding bias).
Award 1 mark for: repeating the sampling multiple times (large sample size) to ensure the data is representative.

In situ conservation preserves the ecosystem as a whole, maintaining the orchid's natural interactions with pollinators and soil fungi. Ex situ conservation (the seed bank) acts as a secure backup under controlled conditions, protecting the genetic diversity from sudden threats such as climate extremes, diseases, or habitat destruction.

Award 1 mark for a valid in situ advantage: preserves natural habitat / maintains ecological food webs / protects natural symbiotic relationships.
Award 1 mark for a valid ex situ advantage: protects genetic material from natural disasters / safe, long-term storage under controlled conditions / prevents immediate extinction if the wild habitat is lost.

To find the percentage of total global water represented by groundwater:

\text{Groundwater as a percentage of total water} = \frac{30.1}{100} \times 3\% = 0.903\%\\

Therefore, accessible groundwater accounts for approximately \(0.9\%\) (or \(0.903\%\)) of the Earth's total water supply.

Award 1 mark for showing correct working: \(30.1\% \times 3\%\) or \(0.301 \times 3\).
Award 1 mark for correct final calculated percentage: \(0.9\%\) / \(0.90\%\) / \(0.903\%\).

Photochemical smog is managed by reducing its primary precursors (\(\text{NO}_x\) and hydrocarbons). This can be achieved by:
1. Technical solutions: Requiring catalytic converters on all combustion engine vehicles to convert harmful nitrogen oxides into harmless nitrogen gas, or setting emissions standards for industrial chimneys.
2. Transport planning: Investing in clean public transport (electric trains or buses), encouraging carpooling, creating low-emission zones, or developing bicycle infrastructure to reduce overall vehicle use.

Award 1 mark for each of two distinct urban management strategies:
- catalytic converters / engine emission controls
- promoting electric/hybrid vehicles
- improving/subsidizing public transport (buses, rail)
- establishing pedestrian zones / carpooling / congestion charges
- industrial scrubbers / regulation of factory emissions

Governments can enforce compliance with mackerel catch quotas by: 1. Mandating Vessel Monitoring Systems (VMS) or satellite GPS tracking to monitor vessel locations and detect illegal fishing in restricted areas. 2. Performing physical inspections of catches at designated landing ports or placing official scientific observers on board vessels to verify catch volumes against logbooks.

Award 1 mark for each valid monitoring method described (up to 2 marks): - Compulsory vessel tracking (VMS/GPS) [1 mark]. - Port inspections, auditing of logbooks, or onboard fishery observers [1 mark].

Step 1: Calculate the absolute decrease in bycatch: \(42 - 12 = 30\). Step 2: Calculate the percentage reduction based on the initial value: \(\frac{30}{42} \times 100 = 71.428...\%\). Rounded to one decimal place, the percentage reduction is 71.4% (accept 71% or 71.4%).

Award 1 mark for correct working showing the calculation step: \(\frac{42 - 12}{42} \times 100\) or \(\frac{30}{42}\). Award 1 mark for the correct final answer: 71% or 71.4% (accept with or without the % sign).

Transitioning to settled arable farming increases soil degradation risks because: 1. Constant cultivation and tilling break up soil aggregates, leaving bare soil exposed and highly susceptible to wind and water erosion in dry climates. 2. Intensive irrigation in semi-arid environments leads to rapid evaporation of water, leaving behind dissolved salts on the soil surface (salinisation), which prevents plant growth.

Award 1 mark for explaining the impact of cultivation/tillage (e.g., destroys soil structure, increases vulnerability to wind erosion). Award 1 mark for explaining the impact of irrigation in dry regions (e.g., high evaporation rates leading to salinisation/salt accumulation).

The inputs differ significantly between the two systems: 1. Agro-chemicals: Intensive commercial systems use large inputs of artificial/synthetic fertilisers and chemical pesticides to maximise yield, whereas extensive subsistence systems use minimal inputs, relying on organic animal manure or traditional composting. 2. Technology and labor: Commercial farming is highly mechanised, requiring high capital inputs for tractors and combine harvesters, while subsistence farming is labor-intensive, relying heavily on family labor and simple hand tools.

Award 1 mark for each valid contrasting input comparison (up to 2 marks): - Contrast of chemical fertilisers/pesticides vs. organic manure/natural methods [1 mark]. - Contrast of machinery/high capital vs. manual labor/hand tools [1 mark]. - Contrast of high-yielding GM seeds vs. saved traditional seeds [1 mark].

To ensure validity and reliability: 1. Standardise the equipment and setup: use identical trap cups, placement depth, and cover designs, and leave them open for the same duration (e.g., 48 hours) in both locations. 2. Avoid bias: use a random coordinate generator to determine placement within a grid in both forest zones, and use a sufficiently large sample size (e.g., at least 15-20 traps per area) to ensure statistical reliability.

Award 1 mark for standardisation of variables (e.g., same trap design, same number of traps, or same time duration). Award 1 mark for sampling methodology to avoid bias (e.g., random sampling using grids, or transects).

Earth's fresh water is largely unavailable because: 1. Around 68.7% is frozen solid in glaciers and ice caps, mostly situated in inaccessible locations like Antarctica and Greenland. 2. Nearly all remaining liquid fresh water (30.1%) is groundwater, which often lies deep in aquifers and requires high energy, technology, and financial investment to pump out.

Award 1 mark for explaining that the largest portion (68.7%) is frozen/solid in glaciers/ice sheets in remote polar regions. Award 1 mark for explaining that groundwater (30.1%) is stored underground and is difficult or costly to access/extract compared to surface water.

The council can implement the following traffic management strategies: 1. Restrict high-emission vehicles through the establishment of low-emission zones (LEZs) or congestion charging zones in the city center. 2. Promote alternative transport by pedestrianising streets, building segregated bicycle networks, and subsidising clean public transport (such as electric buses or trams) to decrease the total volume of private combustion-engine vehicles.

Award 1 mark for each valid traffic management strategy (up to 2 marks): - Low-emission zones / vehicle bans / congestion charging [1 mark]. - Improving/subsidising public transport / park-and-ride schemes [1 mark]. - Pedestrianisation of streets / dedicated cycle networks [1 mark]. - Vehicle plate restrictions (e.g., odd-even days) [1 mark].

Flue-gas desulfurization (FGD) works by: 1. Passing the sulfur dioxide-rich flue gases through a scrubber where they are sprayed with an alkaline slurry, typically composed of limestone (calcium carbonate) or lime (calcium oxide) mixed with water. 2. The alkaline mixture chemically reacts with and neutralizes the acidic sulfur dioxide gas, converting it into solid calcium sulfate (gypsum), which is collected and removed before the clean gas is discharged.

Award 1 mark for identifying the use of an alkaline substance / slurry of limestone / lime / calcium carbonate. Award 1 mark for describing the chemical reaction/neutralization that converts the gas into a solid byproduct (calcium sulfate / gypsum) which is removed.

By increasing the mesh size to 60 mm, smaller and younger juvenile fish are able to pass through the net and escape capture. This ensures that these young fish survive long enough to reach breeding age and reproduce, which helps sustain and replenish the fish stocks. Additionally, it reduces the overall volume of unwanted juvenile bycatch.

Award 1 mark for each distinct point, up to a maximum of 2 marks:
- Allows smaller / immature / juvenile fish to escape (through the larger mesh) [1]
- Allows juvenile fish to survive to reproductive / breeding age to replenish the population [1]
- Reduces bycatch of smaller non-target species [1]

To conduct systematic sampling along a environmental gradient (from the disturbed footpath to undisturbed forest), a transect line is appropriate rather than random sampling. Placing quadrats at regular intervals ensures that changes in species richness are measured objectively in relation to distance. Standardizing quadrat size and repeating the process at multiple sites helps control variables and increases the reliability of the collected ecological data.

Award 1 mark for each of the following points, up to a maximum of 4 marks:
- Lay out a line or belt transect starting from the edge of the footpath and extending perpendicular into the forest. [1]
- Place quadrats at regular/systematic intervals along the transect line (e.g. every 2 m). [1]
- Record the number of different plant species (species richness) inside each quadrat. [1]
- Repeat the transect at multiple locations along the footpath / calculate a mean value for each distance. [1]

A logical field investigation must establish a control (upstream of the pollution source) to compare with downstream data. Measuring dissolved oxygen at fixed intervals downstream shows the progression and recovery of the river from the organic/fertilizer input. Using a probe at a standardized depth controls physical variables that affect oxygen solubility, and replicates ensure data reliability.

Award 1 mark for each of the following points, up to a maximum of 4 marks:
- Take a baseline/control measurement of dissolved oxygen upstream of the runoff point. [1]
- Measure dissolved oxygen at fixed/regular intervals downstream from the point of entry. [1]
- Standardize the measurement method (e.g., use an electronic DO probe at a constant water depth). [1]
- Repeat the measurements at each site / sample multiple times on the same day to calculate an average. [1]

To test the hypothesis using bioindicators, the student must control for external variables that affect lichen growth, such as tree bark pH and texture (controlled by using the same tree species) and light/moisture (controlled by using the same height and trunk aspect). Measuring at regular distances along a transect away from the pollution source provides a clear gradient of data to support or reject the hypothesis.

Award 1 mark for each of the following points, up to a maximum of 4 marks:
- Establish a transect line extending away from the power station in a consistent direction. [1]
- Control tree variables by selecting trees of the same species and similar trunk size/circumference. [1]
- Standardize quadrat placement (e.g., at a fixed height on the trunk / facing the same direction) to estimate lichen percentage cover or count growth forms. [1]
- Repeat the procedure on multiple trees at each sampling distance to calculate an average / increase reliability. [1]

To construct the bar chart: Step 1: Draw the vertical axis (y-axis) and label it 'Cod catch / tonnes'. Set a linear scale from 0 to 200, with grid marks every 20 tonnes. Step 2: Draw the horizontal axis (x-axis) and label it 'Year'. Mark five evenly spaced positions for the years 2017, 2018, 2019, 2020, and 2021. Step 3: Draw a vertical bar for each year using a ruler. The heights of the bars must reach exactly 120 for 2017, 150 for 2018, 190 for 2019, 110 for 2020, and 70 for 2021. Step 4: Ensure all five bars are of equal width and that there are consistent, equal gaps between all the bars to satisfy the criteria for a bar chart.

1 mark: Axes labeled with appropriate names and units ('Year' on the x-axis, and 'Cod catch / tonnes' on the y-axis). 1 mark: Suitable linear scale on the vertical axis starting at 0, where the plotted data spans more than 50% of the grid height. 1 mark: All 5 bars plotted accurately to within +/- half a small square of the grid. 1 mark: Bars drawn with equal width and equal gaps between them using a ruler.

To construct the line graph: Step 1: Draw the vertical axis (y-axis) and label it 'Sulfur dioxide concentration / micrograms per cubic metre'. Choose a linear scale from 0 to 60, with marks every 10 units. Step 2: Draw the horizontal axis (x-axis), label it 'Month', and space out numbers 1 to 6 evenly. Step 3: Plot the points accurately at the intersection of each month and its concentration value: (1, 35), (2, 48), (3, 55), (4, 42), (5, 28), and (6, 16). Use a sharp pencil to draw small, clear crosses. Step 4: Use a ruler to connect the points sequentially with straight lines (from Month 1 to Month 2, Month 2 to Month 3, and so on).

1 mark: Axes labeled with names and units ('Month' on x-axis and 'Sulfur dioxide concentration / micrograms per cubic metre' or micrograms/m3 on y-axis). 1 mark: Linear scale on y-axis that allows the plotted data to occupy at least 50% of the available grid space. 1 mark: All 6 points plotted accurately to within +/- half a small square, using small, precise crosses or circled dots. 1 mark: Points connected sequentially with straight, neat ruled lines (reject freehand curves).

Step 1: Calculate the bycatch ratio for Year 1: \(125 \text{ tonnes} \div 500 \text{ tonnes} = 0.25\). Step 2: Calculate the bycatch ratio for Year 2: \(30 \text{ tonnes} \div 600 \text{ tonnes} = 0.05\). Step 3: Calculate the change in ratio: \(0.25 - 0.05 = 0.20\). Step 4: Calculate the percentage decrease: \((0.20 \div 0.25) \times 100 = 80\%\).

1 mark for calculating both correct ratios (0.25 and 0.05) OR for a correct substitution of values to find the percentage decrease. 1 mark for the correct final answer of 80 (accept 80%).

Step 1: Identify the values: \(n_1\) (first sample marked) = 80, \(n_2\) (second sample captured) = 64, \(m_2\) (recaptured marked) = 16. Step 2: Substitute values into the formula: \(N = \frac{80 \times 64}{16}\). Step 3: Calculate the final value: \(N = \frac{5120}{16} = 320\).

1 mark for correct substitution into the Lincoln Index formula: \((80 \times 64) \div 16\). 1 mark for the correct final answer of 320.