An original Thinka practice paper modelled on the structure and difficulty of the Nov 2023 SL (TZ2) IB Diploma Programme Environmental Systems and Societies paper. Not affiliated with or reproduced from IB.
Paper 1 (Case Study)
Answer all questions. Refer to the resource booklet which accompanies this question paper. A calculator is required.
20 PastPaper.question · 35 PastPaper.marks
PastPaper.question 1 · Short Answer
1.5 PastPaper.marks
Based on the ecosystem data in Figure 1, the Gross Primary Productivity (GPP) of a temperate forest is \( 2.4 \times 10^4 \text{ kJ m}^{-2}\text{ yr}^{-1} \) and the respiration loss (R) is \( 1.5 \times 10^4 \text{ kJ m}^{-2}\text{ yr}^{-1} \). Calculate the Net Primary Productivity (NPP) of this forest, including appropriate units.
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PastPaper.workedSolution
Net Primary Productivity (NPP) is calculated using the formula: \( \text{NPP} = \text{GPP} - \text{R} \). Here, \( \text{NPP} = 2.4 \times 10^4 \text{ kJ m}^{-2}\text{ yr}^{-1} - 1.5 \times 10^4 \text{ kJ m}^{-2}\text{ yr}^{-1} = 0.9 \times 10^4 \text{ kJ m}^{-2}\text{ yr}^{-1} \), which is equivalent to \( 9000 \text{ kJ m}^{-2}\text{ yr}^{-1} \) (or \( 9.0 \times 10^3 \text{ kJ m}^{-2}\text{ yr}^{-1} \).
PastPaper.markingScheme
Award [1 mark] for the correct numerical calculation of 9000 (or \( 9.0 \times 10^3 \)), and [0.5 marks] for providing the correct units (\( \text{kJ m}^{-2}\text{ yr}^{-1} \)).
PastPaper.question 2 · Short Answer
1.5 PastPaper.marks
Figure 2 illustrates the process of eutrophication in a freshwater lake. Explain how the death of submerged macrophytes leads to a positive feedback loop that accelerates the degradation of the lake ecosystem.
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PastPaper.workedSolution
When submerged macrophytes die, they provide a large amount of organic matter for aerobic decomposers (bacteria). These decomposers multiply rapidly and consume dissolved oxygen through respiration. The depletion of dissolved oxygen leads to the death of fish and other aquatic organisms, which further increases the organic matter available for decomposition, thus reinforcing and accelerating the cycle of oxygen depletion and ecosystem collapse.
PastPaper.markingScheme
Award [1 mark] for explaining that plant death leads to increased aerobic decomposition which reduces oxygen, and [0.5 marks] for explaining how this reduction in oxygen causes more deaths, self-reinforcing the cycle (positive feedback).
PastPaper.question 3 · Short Answer
1.5 PastPaper.marks
According to the emissions data in Figure 3, annual methane emissions from agricultural activities in Region X rose from \( 1.2 \text{ million tonnes} \) in 2010 to \( 1.8 \text{ million tonnes} \) in 2020. Calculate the percentage increase in annual methane emissions over this ten-year period, showing your working.
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PastPaper.workedSolution
First, find the absolute increase: \( 1.8 - 1.2 = 0.6 \text{ million tonnes} \). Next, divide the increase by the original 2010 value and multiply by 100 to find the percentage: \( \frac{0.6}{1.2} \times 100 = 50\% \).
PastPaper.markingScheme
Award [1 mark] for the correct final answer (50%). Award [0.5 marks] for showing correct working: \( \frac{1.8 - 1.2}{1.2} \times 100 \) or equivalent.
PastPaper.question 4 · Short Answer
1.5 PastPaper.marks
Figure 4 presents the population pyramids for two different regions. Suggest why the dependency ratio of Region A (an aging population) is higher than Region B, and state one socio-economic impact of this demographic trend on Region A's public services.
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PastPaper.workedSolution
Region A's population pyramid has a narrow base and a wide top, indicating a large proportion of elderly citizens relative to the working-age population. This increases the dependency ratio as there are fewer workers supporting more retirees. The economic impact includes an increased strain on public healthcare systems and pension funds due to higher demand and lower tax revenue.
PastPaper.markingScheme
Award [1 mark] for suggesting why Region A has a higher dependency ratio (larger proportion of non-working elderly relative to working population), and [0.5 marks] for stating a valid socio-economic impact (e.g., increased strain on healthcare, social services, or pension funding).
PastPaper.question 5 · Short Answer
1.5 PastPaper.marks
Using the principles of island biogeography shown in Figure 5, outline why a single large conservation reserve is generally preferred over several small reserves of equal total area for protecting large carnivores, and state one risk associated with the single large reserve design.
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PastPaper.workedSolution
Large carnivores require extensive home ranges to find sufficient food and mates. A single large reserve minimizes edge effects (which can increase conflict with humans) and supports a larger, contiguous gene pool. However, a single large reserve is vulnerable to catastrophic events (like disease outbreaks or wildfires) which could wipe out the entire protected population at once.
PastPaper.markingScheme
Award [1 mark] for explaining the preference based on island biogeography (larger contiguous area reduces edge effects and supports viable breeding populations of large carnivores), and [0.5 marks] for identifying a risk (e.g., a single disease or wildfire could devastate the entire population).
PastPaper.question 6 · Short Answer
1.5 PastPaper.marks
Refer to the fishery data in Figure 6. State how the concept of Maximum Sustainable Yield (MSY) is applied to determine annual catch limits, and explain why managing a fishery at exactly MSY can lead to sudden population collapse.
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PastPaper.workedSolution
Maximum Sustainable Yield represents the maximum amount of a resource that can be harvested without reducing the underlying stock's ability to regenerate. It is typically set where population growth rate is at its peak (often around half of carrying capacity, \( K/2 \)). If environmental fluctuations (such as temperature anomalies or disease) occur, they can lower the actual growth rate below the calculated MSY; continuing to harvest at this level results in rapid overexploitation and sudden collapse.
PastPaper.markingScheme
Award [1 mark] for explaining that MSY represents harvesting the surplus growth/net productivity to keep the population at its maximum growth rate, and [0.5 marks] for explaining that environmental fluctuations (e.g., disease, climate) can lower carrying capacity, making the fixed MSY harvest rate unsustainable and leading to collapse.
PastPaper.question 7 · Short Answer
1.5 PastPaper.marks
Identify one soil conservation method shown in Figure 7 that is suitable for reducing soil degradation on steep agricultural slopes, and outline how this method physically prevents soil erosion.
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PastPaper.workedSolution
Terracing involves cutting flat steps (benches) into steep slopes. This breaks the slope length and physically slows down the downhill velocity of rainwater runoff. By slowing the water down, terracing reduces its carrying capacity for soil particles and allows more water to infiltrate into the soil, thereby significantly reducing soil erosion.
PastPaper.markingScheme
Award [0.5 marks] for identifying a correct method (e.g., terracing or contour farming), and [1 mark] for explaining how it prevents erosion (e.g., by creating physical barriers/flat sections that reduce the speed of surface runoff and promote water infiltration).
PastPaper.question 8 · Short Answer
1.5 PastPaper.marks
With reference to the regional water crisis described in the resource booklet, distinguish between an ecocentric response and a technocentric response to managing the domestic water shortage.
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PastPaper.workedSolution
An ecocentric response encourages a shift in human values and behaviors to minimize water use (e.g., community-led water conservation, behavioral restrictions on water use, planting native drought-resistant gardens). In contrast, a technocentric response relies on technical and engineering solutions to bypass natural limits and increase supply (e.g., constructing desalination plants, cloud seeding, or building new reservoirs).
PastPaper.markingScheme
Award [1 mark] for describing an ecocentric approach focused on behavioral change and reducing demand (e.g., water conservation, rainwater harvesting), and [0.5 marks] for contrasting it with a technocentric approach focused on technological supply solutions (e.g., desalination plants, greywater treatment systems).
PastPaper.question 9 · Short Answer
1.5 PastPaper.marks
Based on the data in Figure 1, the energy available at the primary consumer level (herbivorous insects) is \(15,000\text{ kJ m}^{-2}\text{ yr}^{-1}\) and the energy transferred to the secondary consumer level (insectivorous birds) is \(1,200\text{ kJ m}^{-2}\text{ yr}^{-1}\). Calculate the percentage of energy lost as heat and respiration during this transfer, assuming no other pathways exist between these two levels.
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PastPaper.workedSolution
First, calculate the energy lost: \(15,000\text{ kJ m}^{-2}\text{ yr}^{-1} - 1,200\text{ kJ m}^{-2}\text{ yr}^{-1} = 13,800\text{ kJ m}^{-2}\text{ yr}^{-1}\). Next, calculate the percentage lost relative to the starting energy: \((13,800 / 15,000) \times 100 = 92\%\). Alternatively, calculate the ecological efficiency first: \((1,200 / 15,000) \times 100 = 8\%\). The percentage lost is therefore \(100\% - 8\% = 92\%\).
PastPaper.markingScheme
[0.5 marks] For showing a correct intermediate step (e.g., calculating the energy lost as \(13,800\text{ kJ m}^{-2}\text{ yr}^{-1}\) or identifying that \(8\%\) of energy is transferred). [1.0 mark] For the correct final answer of \(92\%\) (accept '92' with or without the percentage symbol).
PastPaper.question 10 · Short Answer
1.5 PastPaper.marks
State one reason why global temperature anomalies do not show a perfectly linear correlation with increasing atmospheric carbon dioxide levels, despite the long-term upward trend.
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PastPaper.workedSolution
While the long-term trend of rising carbon dioxide causes an overall increase in global average temperatures, short-term climate variability is influenced by other natural factors. For example, major volcanic eruptions release sulfur dioxide aerosols into the stratosphere, reflecting incoming solar radiation and temporarily cooling the Earth. Alternatively, ocean-atmosphere cycles like the El Nio-Southern Oscillation (ENSO) redistribute immense amounts of heat, causing some years to be warmer (El Nio) or cooler (La Nia) than the underlying greenhouse-warming trend would predict.
PastPaper.markingScheme
[0.5 marks] For identifying a valid natural climate variable (e.g., volcanic aerosols, solar activity cycles, El Nio/La Nia cycles). [1.0 mark] For explaining how this variable creates temporary cooling or warming, causing a non-linear year-to-year deviation from the steady warming trend of carbon dioxide.
PastPaper.question 11 · Short Answer
1.5 PastPaper.marks
Refer to Figure 5, which shows a hydrograph for a river basin. Outline how the transition from a forested catchment to an urban area alters the lag time and the peak discharge of the river following a heavy rainfall event.
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PastPaper.workedSolution
Replacing natural forest cover with urban infrastructure increases the surface area of impermeable materials (such as concrete, asphalt, and rooftops) and introduces artificial drainage systems. This reduces soil infiltration and water retention, leading to a rapid increase in surface runoff. Consequently, the water reaches the river channel much faster, which decreases the lag time (the time difference between peak rainfall and peak discharge) and significantly increases the peak discharge (the maximum volume of water flow).
PastPaper.markingScheme
[0.5 marks] For stating that the transition decreases the lag time and increases the peak discharge. [1.0 mark] For explaining the underlying physical mechanism: the loss of vegetation and creation of impermeable surfaces reduces soil infiltration, causing a larger volume of surface runoff to enter the river channel rapidly via storm drains.
PastPaper.question 12 · Short Answer
1.5 PastPaper.marks
In a specific region, the crude birth rate (CBR) is 24 per 1,000 people per year and the crude death rate (CDR) is 8 per 1,000 people per year. Calculate the annual natural increase rate (NIR) as a percentage and identify which stage of the demographic transition model (DTM) this region is most likely experiencing.
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PastPaper.workedSolution
First, calculate the natural increase rate (NIR) using the formula: \(NIR = (CBR - CDR) / 10\). Substituting the values: \(NIR = (24 - 8) / 10 = 16 / 10 = 1.6\%\). A crude birth rate of 24 per 1,000 is moderately declining, while the death rate of 8 per 1,000 is low and stable. This combination of a falling birth rate and a low death rate, resulting in a moderate natural increase rate of \(1.6\%\), indicates that the region is in Stage 3 of the Demographic Transition Model.
PastPaper.markingScheme
[0.5 marks] For calculating the correct NIR of \(1.6\%\) (accept '1.6' with or without the percentage symbol, provided working is shown). [0.5 marks] For correctly identifying Stage 3 of the Demographic Transition Model. [0.5 marks] For explaining that Stage 3 is characterized by falling birth rates combined with low and stable death rates, yielding moderate, slowing population growth.
PastPaper.question 13 · Short Answer
1.5 PastPaper.marks
Explain why designing a single, wide wildlife corridor is generally more effective for conserving forest interior species than establishing multiple narrow corridors of the same total area.
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PastPaper.workedSolution
Forest interior species are highly specialized and adapted to the stable microclimatic conditions (low light, high humidity, and low wind) found deep within a forest. They are sensitive to external disturbances and increased predation. A single wide corridor has a low edge-to-area ratio, preserving a central 'core habitat' that is sheltered from the outer edges. In contrast, multiple narrow corridors of the same total area are dominated by the 'edge effect', where changes in abiotic factors (light, temperature, wind) and increased access for predators or invasive species make the entire corridor unsuitable for sensitive interior specialists.
PastPaper.markingScheme
[0.5 marks] For identifying that a single wide corridor has a lower edge-to-area ratio (minimizes edge effects) or maintains a larger contiguous core habitat. [1.0 mark] For explaining that interior species require specific, stable microclimatic/sheltered conditions and are vulnerable to edge disturbances (such as invasive species, wind, or predators) which dominate narrow corridors.
PastPaper.question 14 · Short Answer
1.5 PastPaper.marks
Explain how the practice of contour ploughing reduces soil erosion on steep slopes compared to downslope ploughing.
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PastPaper.workedSolution
Ploughing along the horizontal contours of a slope (contour ploughing) creates a series of ridges and furrows that run perpendicular to the downslope flow of water. These structures act as small dams, intercepting surface runoff and slowing its movement downslope. By reducing the velocity of the water, its kinetic energy and capacity to detach and transport soil particles are greatly diminished. Additionally, the slowed water has more time to infiltrate the soil rather than washing over it. In contrast, downslope ploughing creates parallel vertical channels that accelerate runoff, increasing soil loss.
PastPaper.markingScheme
[0.5 marks] For explaining that contour ploughing creates horizontal ridges or furrows perpendicular to the slope (rather than parallel to it). [1.0 mark] For explaining how these physical barriers slow down surface runoff, thereby reducing its erosive energy to transport soil particles and allowing more time for water infiltration.
PastPaper.question 15 · Data-Based
1 PastPaper.marks
Refer to Figure 1, which shows the change in healthy Sundarbans mangrove forest cover over a thirty-year period. In 1990, the forest cover was measured at 140 square kilometers (\(140\text{ km}^2\)), and by 2020, it had decreased to 112 square kilometers (\(112\text{ km}^2\)). Calculate the percentage decrease in healthy mangrove forest cover between 1990 and 2020.
Award 1 mark for the correct answer of 20% (accept "20" or "20 percent").
PastPaper.question 16 · Data-Based
1 PastPaper.marks
Refer to Figure 2, which outlines the relationship between mean soil salinity levels (in PSU) and the survival rate (%) of Sundari tree (*Heritiera fomes*) seedlings in a monitored plot. Soil salinity values of 5 PSU, 15 PSU, 25 PSU, and 35 PSU correspond to survival rates of 85%, 60%, 30%, and 10% respectively. Describe the relationship shown between soil salinity and seedling survival rate.
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PastPaper.workedSolution
As soil salinity increases from 5 to 35 PSU, the seedling survival rate of the Sundari tree decreases from 85% to 10%, indicating a negative correlation.
PastPaper.markingScheme
Award 1 mark for identifying a negative correlation, inverse relationship, or stating that survival rate decreases as salinity increases.
PastPaper.question 17 · Data-Based
1 PastPaper.marks
Refer to Table 1, which details the daily per capita freshwater consumption in four resource-dependent districts surrounding the Sundarbans region. District A consumes 45 L/day, District B consumes 60 L/day, District C consumes 35 L/day, and District D consumes 80 L/day. Calculate the mean daily per capita freshwater consumption across these four districts.
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PastPaper.workedSolution
To calculate the mean daily per capita freshwater consumption: \(\text{Mean} = \frac{45 + 60 + 35 + 80}{4} = \frac{220}{4} = 55\text{ L/day}\).
PastPaper.markingScheme
Award 1 mark for the correct value of 55 (accept "55" or "55 L/day").
PastPaper.question 18 · Data-Based
1 PastPaper.marks
Refer to Figure 3, which displays the monthly precipitation levels in the Sundarbans. The values are: Jan: 15 mm, Feb: 22 mm, Mar: 35 mm, Apr: 80 mm, May: 200 mm, Jun: 350 mm, Jul: 400 mm, Aug: 370 mm, Sep: 290 mm, Oct: 180 mm, Nov: 40 mm, and Dec: 10 mm. Identify the month with the lowest monthly precipitation.
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PastPaper.workedSolution
Comparing all twelve months, December has the lowest precipitation value at 10 mm.
PastPaper.markingScheme
Award 1 mark for identifying "December" (accept "Dec").
PastPaper.question 19 · Extended Response
5 PastPaper.marks
With reference to the Shannon River basin case study (as described in the resource booklet), evaluate the effectiveness of two different management strategies (one targeting the source and one targeting the active pollutant) to reduce eutrophication in this aquatic ecosystem.
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PastPaper.workedSolution
Strategy 1: Reducing the use of chemical fertilizers at the source (Altering human activity) - Description: Encouraging farmers to switch to organic fertilizers, apply fertilizers only during dry periods, or adopt precision farming techniques. - Evaluation: This is highly effective as it addresses the root cause of the problem, preventing excess nutrients from entering the watershed in the first place. However, it can be difficult to enforce across many independent farms, may initially reduce crop yields, and requires extensive educational campaigns or economic incentives to be widely adopted.
Strategy 2: Planting riparian buffer zones (Regulating and blocking pollutants) - Description: Establishing strips of native vegetation, trees, or wetlands along the edges of agricultural fields and riverbanks. - Evaluation: These buffers are highly effective at absorbing nutrient runoff (nitrates and phosphates) before they reach the water body, while also providing habitat to boost local biodiversity. However, they require farmers to sacrifice arable land, can be costly to establish, and require long-term maintenance to prevent them from becoming saturated with nutrients over time.
Conclusion/Synthesis: While source-directed strategies offer the most sustainable long-term solution, combining them with riparian buffer zones provides an immediate and highly effective physical barrier to nutrient runoff, making a multi-tiered management approach the most successful strategy.
PastPaper.markingScheme
Award 1 mark for identifying and describing a valid source-directed strategy (e.g., reducing fertilizer application, precision farming). Award 1 mark for evaluating this source-directed strategy (must include at least one strength and one limitation). Award 1 mark for identifying and describing a valid pollutant-directed strategy (e.g., riparian buffer zones, sediment basins). Award 1 mark for evaluating this pollutant-directed strategy (must include at least one strength and one limitation). Award 1 mark for an overall evaluative conclusion or synthesis comparing their effectiveness in the context of the basin.
Note: Max 3 marks if only one strategy is evaluated. Max 4 marks if both strategies are evaluated but no clear comparative conclusion/synthesis is provided.
PastPaper.question 20 · Extended Response
5 PastPaper.marks
With reference to the Cordillera Blanca case study in the Andes, discuss how the melting of glaciers (as described in the resource booklet) impacts both the local hydrological cycle and the socio-economic activities of downstream communities.
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PastPaper.workedSolution
Hydrological Cycle Impacts: - Glacier melt leads to an initial temporary increase in river discharge (known as 'peak water'), followed by a long-term, permanent reduction in annual streamflow as the glacier volume shrinks. - It disrupts the seasonal regulation of water, as glaciers act as natural freshwater reservoirs that release water during the dry season. Without them, streamflow becomes highly dependent on seasonal rainfall, leading to dry-season water shortages.
Socio-economic Impacts: - Agriculture: Downstream communities face a severe reduction in water available for irrigation during the dry season, leading to lower crop yields and reduced food security. - Energy Production: Many Andean communities rely on hydroelectric power plants. Reduced and irregular river flows limit electricity generation capacity, threatening energy security and economic development. - Natural Hazards: Rapid melting increases the risk of Glacial Lake Outburst Floods (GLOFs), which can destroy downstream infrastructure, homes, and lead to loss of human lives.
Synthesis: The reduction in glacier-derived water directly translates to economic vulnerability, forcing downstream communities to seek expensive adaptation strategies (e.g., building artificial reservoirs) or face displacement.
PastPaper.markingScheme
Award 1 mark for each valid impact identified and explained, up to a maximum of 4 marks. There must be a balance of both hydrological and socio-economic impacts (at least 2 of each to achieve full marks, or 1 of one and 3 of the other).
Hydrological impacts (Max 2 marks): - Initial increase in water flow followed by long-term decrease. - Loss of seasonal water storage/buffer capacity. - Increased frequency of seasonal droughts or altered river flow regimes.
Socio-economic impacts (Max 2 marks): - Reduced agricultural yields/loss of irrigation water. - Decline in hydroelectric power generation capacity. - Threat to domestic drinking water supplies for urban areas. - Increased hazard risks from GLOFs (Glacial Lake Outburst Floods).
Award 1 mark for a synthesis/discussion point that explicitly links the hydrological changes to human vulnerability or adaptation challenges (e.g., the economic cost of replacing natural glacial storage with human-made dams).
Paper 2 Section A
Answer all questions in Section A. Write your answers in the spaces provided.
16 PastPaper.question · 25 PastPaper.marks
PastPaper.question 1 · Short Answer
1.5 PastPaper.marks
Outline how the first law of thermodynamics applies to the flow of energy through a food chain.
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PastPaper.workedSolution
The first law of thermodynamics is the law of conservation of energy. Within a food chain, the energy entering the system as solar radiation is converted into chemical energy (glucose) by producers. This energy is then transferred along trophic levels through feeding. Although energy changes form, the total energy within the system remains constant and is not destroyed.
PastPaper.markingScheme
Award 1.0 mark for explaining that energy is converted from one form to another (e.g., light to chemical energy during photosynthesis) and transferred along the food chain. Award 0.5 marks for stating that the total energy is conserved or cannot be created or destroyed.
PastPaper.question 2 · Short Answer
1.5 PastPaper.marks
Distinguish between the roles of stratospheric ozone and tropospheric ozone in relation to human health.
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PastPaper.workedSolution
Stratospheric ozone forms a protective layer high in the atmosphere that blocks harmful UV-B and UV-C radiation, reducing health risks like melanoma. Tropospheric ozone is a ground-level air pollutant formed by photochemical reactions that acts as a strong respiratory irritant, damaging lung tissues.
PastPaper.markingScheme
Award 0.75 marks for explaining that stratospheric ozone is beneficial because it absorbs UV radiation, protecting against skin cancer or cataracts. Award 0.75 marks for explaining that tropospheric ozone is a harmful ground-level pollutant causing respiratory problems or lung damage.
PastPaper.question 3 · Short Answer
1.5 PastPaper.marks
Outline why biochemical oxygen demand (BOD) is an indirect measure of organic pollution in a freshwater ecosystem.
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PastPaper.workedSolution
BOD does not measure the actual concentration of organic pollutant molecules directly. Instead, it measures the rate of oxygen consumption by decomposers. Because decomposer populations and their respiration rates increase in proportion to the organic waste available, BOD acts as an indirect indicator of organic pollution levels.
PastPaper.markingScheme
Award 1.0 mark for explaining that BOD measures the oxygen consumed by aerobic decomposers as they break down organic matter. Award 0.5 marks for explaining that higher oxygen consumption implies higher levels of organic waste, making the measure indirect.
PastPaper.question 4 · Short Answer
1.5 PastPaper.marks
Explain how contour ploughing helps to prevent soil erosion in agricultural systems.
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PastPaper.workedSolution
By plowing parallel to the contours of the land, farmers create physical barriers (ridges) that interrupt the downhill flow of water. This decreases the velocity of surface runoff, which reduces soil detachment and transport. It also increases the residence time of water on the slope, promoting infiltration.
PastPaper.markingScheme
Award 1.0 mark for explaining that plowing across the slope (along contour lines) creates ridges that slow down surface runoff. Award 0.5 marks for stating that this reduces soil wash-away or enhances water infiltration.
PastPaper.question 5 · Short Answer
1.5 PastPaper.marks
Describe one advantage and one disadvantage of using ex-situ conservation methods, such as seed banks, to protect plant species.
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PastPaper.workedSolution
Ex-situ conservation preserves species outside their natural habitats. An advantage of seed banks is their high efficiency and security; thousands of seeds can be frozen and maintained long-term in a small space. A disadvantage is that evolutionary processes are frozen, meaning the plants cannot adapt to ongoing environmental shifts, and technical failures can destroy the collection.
PastPaper.markingScheme
Award 0.75 marks for a clear, valid advantage (e.g., space efficiency, protection from wild threats like pests/natural disasters). Award 0.75 marks for a clear, valid disadvantage (e.g., lack of natural selection/evolution, technical vulnerability, potential loss of seed viability over time).
PastPaper.question 6 · Short Answer
1.5 PastPaper.marks
Explain how a population's ecological footprint relates to the carrying capacity of its local environment.
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PastPaper.workedSolution
Carrying capacity is the maximum number of individuals that an environment can sustainably support. The ecological footprint is the area of land required to support a given population. When the footprint exceeds the biocapacity/carrying capacity of the local area, the population is living unsustainably by importing resources (drawing on other areas' carrying capacity) or depleting its own natural capital.
PastPaper.markingScheme
Award 1.0 mark for defining ecological footprint as the area of land/water required to support resource use and waste assimilation. Award 0.5 marks for explaining that if the footprint exceeds the carrying capacity, it indicates unsustainable overshoot / reliance on external resources / resource degradation.
PastPaper.question 7 · Short Answer
1.5 PastPaper.marks
Distinguish between a closed system and an open system, providing an example of each in an environmental context.
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PastPaper.workedSolution
Open systems are the most common in nature, where both energy (e.g., sunlight) and matter (e.g., water, nutrients) flow across the system boundary. Closed systems only allow energy to cross their boundary, while the matter remains recycled within. Examples: Open - forest, lake, human; Closed - Earth (practically), biosphere/mesocosm (experimental).
PastPaper.markingScheme
Award 1.0 mark for distinguishing the systems: open systems exchange both energy and matter, while closed systems exchange energy but not matter. Award 0.5 marks for providing a valid example of both (e.g., forest/lake for open, Earth/biosphere for closed).
PastPaper.question 8 · Short Answer
1.5 PastPaper.marks
Explain how energy security concerns can influence a nation's choice of energy sources.
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PastPaper.workedSolution
A country seeking energy security wants to minimize vulnerability to price shocks, political instability, and supply disruptions. This leads to policy decisions prioritizing domestic energy generation (e.g., nuclear, solar, hydro) and diversification, reducing the share of energy imported from single foreign suppliers.
PastPaper.markingScheme
Award 0.5 marks for defining energy security as reliable/affordable access to energy. Award 1.0 mark for explaining how this leads to specific energy choices, such as choosing domestic/renewable resources to avoid geopolitical dependencies or diversifying the energy mix.
PastPaper.question 9 · Short Answer
1.5 PastPaper.marks
Identify one greenhouse gas released by the melting of polar permafrost, and outline how this release contributes to a positive feedback loop that accelerates global warming.
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PastPaper.workedSolution
Methane (\(CH_4\)) or carbon dioxide (\(CO_2\)) is identified as the gas released. When permafrost melts, these stored greenhouse gases are released into the atmosphere, where they absorb and re-emit longwave infrared radiation. This enhances the greenhouse effect, raising global temperatures. The elevated temperature then accelerates the melting of the remaining permafrost, leading to further gas release in a self-reinforcing positive feedback loop.
PastPaper.markingScheme
Award 0.5 marks for correctly identifying either methane (\(CH_4\)) or carbon dioxide (\(CO_2\)). Award 1.0 mark for a clear explanation of the positive feedback loop (linking increased gas concentrations to higher temperatures, which then causes further permafrost melting and gas release). Do not award marks if a negative feedback loop is described.
PastPaper.question 10 · Short Answer
1.5 PastPaper.marks
Outline how the runoff of agricultural fertilizers containing nitrates into a freshwater lake leads to the formation of anoxic 'dead zones'.
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PastPaper.workedSolution
The input of excess nitrates causes an algal bloom, which blocks sunlight from reaching submerged plants, reducing photosynthesis. When the algae eventually die, they provide a large amount of organic matter for decomposers. Aerobic bacteria decompose this dead biomass, and their rapid respiration consumes the dissolved oxygen in the water, resulting in anoxia and the death of aquatic organisms.
PastPaper.markingScheme
Award 0.5 marks for describing the nutrient enrichment leading to an algal bloom or light blockage. Award 1.0 mark for explaining that the decomposition of dead algae by aerobic bacteria depletes the dissolved oxygen levels, leading to anoxia/dead zones. Do not accept answers that suggest plants directly consume all the oxygen.
PastPaper.question 11 · Data-Based
1 PastPaper.marks
Based on the following waste management data for 2022, calculate the per capita municipal solid waste (MSW) generation for City B in tonnes per person per year. Data: City A (Population: 2.5 million; Total MSW generated: 1.25 million tonnes; Recycling rate: 40%); City B (Population: 5.0 million; Total MSW generated: 4.00 million tonnes; Recycling rate: 15%); City C (Population: 1.2 million; Total MSW generated: 0.48 million tonnes; Recycling rate: 60%); City D (Population: 8.0 million; Total MSW generated: 4.80 million tonnes; Recycling rate: 30%).
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PastPaper.workedSolution
$$\text{Per capita MSW for City B} = \frac{\text{Total MSW Generated}}{\text{Population}} = \frac{4.00\text{ million tonnes}}{5.0\text{ million people}} = 0.8\text{ tonnes per person per year}$$
PastPaper.markingScheme
Award 1 mark for the correct answer of 0.8 (accept 0.8 tonnes per person per year, or 800 kg per person per year). Do not credit incorrect units.
PastPaper.question 12 · Data-Based
1 PastPaper.marks
Based on the following waste management data for 2022, state which city recycles the greatest absolute mass of municipal solid waste (MSW) per year. Data: City A (Population: 2.5 million; Total MSW generated: 1.25 million tonnes; Recycling rate: 40%); City B (Population: 5.0 million; Total MSW generated: 4.00 million tonnes; Recycling rate: 15%); City C (Population: 1.2 million; Total MSW generated: 0.48 million tonnes; Recycling rate: 60%); City D (Population: 8.0 million; Total MSW generated: 4.80 million tonnes; Recycling rate: 30%).
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PastPaper.workedSolution
Calculate the absolute recycled mass for each city: City A: 1.25 * 0.40 = 0.50 million tonnes; City B: 4.00 * 0.15 = 0.60 million tonnes; City C: 0.48 * 0.60 = 0.288 million tonnes; City D: 4.80 * 0.30 = 1.44 million tonnes. City D recycles the largest absolute mass (1.44 million tonnes).
PastPaper.markingScheme
Award 1 mark for identifying City D (accept 'D').
PastPaper.question 13 · Data-Based
1 PastPaper.marks
Based on the following waste management data for 2022, identify the city that has the lowest per capita waste generation. Data: City A (Population: 2.5 million; Total MSW generated: 1.25 million tonnes; Recycling rate: 40%); City B (Population: 5.0 million; Total MSW generated: 4.00 million tonnes; Recycling rate: 15%); City C (Population: 1.2 million; Total MSW generated: 0.48 million tonnes; Recycling rate: 60%); City D (Population: 8.0 million; Total MSW generated: 4.80 million tonnes; Recycling rate: 30%).
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PastPaper.workedSolution
Calculate per capita waste generation (Total MSW / Population): City A: 1.25 / 2.5 = 0.50 tonnes/person; City B: 4.00 / 5.0 = 0.80 tonnes/person; City C: 0.48 / 1.2 = 0.40 tonnes/person; City D: 4.80 / 8.0 = 0.60 tonnes/person. City C has the lowest per capita generation (0.40 tonnes/person).
PastPaper.markingScheme
Award 1 mark for identifying City C (accept 'C').
PastPaper.question 14 · Data-Based
1 PastPaper.marks
Based on the following waste management data for 2022, calculate the total amount of waste (in million tonnes) that goes to disposal (non-recycled) from all four cities combined. Data: City A (Population: 2.5 million; Total MSW generated: 1.25 million tonnes; Recycling rate: 40%); City B (Population: 5.0 million; Total MSW generated: 4.00 million tonnes; Recycling rate: 15%); City C (Population: 1.2 million; Total MSW generated: 0.48 million tonnes; Recycling rate: 60%); City D (Population: 8.0 million; Total MSW generated: 4.80 million tonnes; Recycling rate: 30%).
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PastPaper.workedSolution
Calculate non-recycled waste for each city: City A: 1.25 * 0.60 = 0.75 million tonnes; City B: 4.00 * 0.85 = 3.40 million tonnes; City C: 0.48 * 0.40 = 0.192 million tonnes; City D: 4.80 * 0.70 = 3.36 million tonnes. Total non-recycled waste = 0.75 + 3.40 + 0.192 + 3.36 = 7.702 million tonnes.
PastPaper.markingScheme
Award 1 mark for the correct calculation and answer of 7.702 million tonnes (accept range 7.7 to 7.702). Do not penalize for missing units.
PastPaper.question 15 · Extended Response
3 PastPaper.marks
Explain how the melting of permafrost can lead to a positive feedback loop that accelerates global climate change.
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PastPaper.workedSolution
Increasing global temperatures lead to the warming and thawing of permafrost. When permafrost thaws, previously frozen organic matter begins to decompose. This decomposition, often under anaerobic conditions, releases significant amounts of greenhouse gases, primarily methane and carbon dioxide, into the atmosphere. These gases trap more outgoing longwave radiation (heat), enhancing the greenhouse effect. This leads to a further increase in global temperatures, which in turn causes more permafrost to melt, reinforcing the cycle.
PastPaper.markingScheme
Award 1 mark for stating that rising temperatures cause permafrost to thaw, exposing long-stored organic matter. Award 1 mark for explaining that decomposition of this organic matter releases greenhouse gases such as methane (CH4) or carbon dioxide (CO2). Award 1 mark for explaining that these greenhouse gases trap more heat in the atmosphere, raising temperatures further and accelerating the melting process, thus completing the positive feedback loop.
PastPaper.question 16 · Extended Response
3 PastPaper.marks
Outline how Net Primary Productivity (NPP) changes during the process of primary ecological succession from a pioneer community to a climax community.
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PastPaper.workedSolution
In the pioneer stage of primary succession, Net Primary Productivity (NPP) is very low because there is little soil and only sparse, simple vegetation. As succession progresses through intermediate seral stages, NPP increases rapidly due to the development of deeper, nutrient-rich soils and the colonization of fast-growing, larger plant species. In the final climax community, NPP typically stabilizes or decreases slightly. This occurs because, although Gross Primary Productivity (GPP) is high, a large proportion of this energy is consumed by the respiration (R) of the massive accumulated biomass, leaving less energy as net primary productivity.
PastPaper.markingScheme
Award 1 mark for noting that NPP is very low in the pioneer stage due to limited soil, nutrients, and small plant biomass. Award 1 mark for explaining that NPP increases rapidly during intermediate seral stages as soil conditions improve and plant density and biomass grow. Award 1 mark for explaining that NPP stabilizes or decreases in the climax community because respiration (R) increases to support the large accumulated biomass, reducing the proportion of GPP converted to NPP.
Paper 2 Section B
Answer two questions from Section B. Each question is worth 20 marks.
6 PastPaper.question · 40 PastPaper.marks
PastPaper.question 1 · Extended Essay Part A
4 PastPaper.marks
Outline the chemical process by which chlorofluorocarbons (CFCs) deplete stratospheric ozone.
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PastPaper.workedSolution
First, ultraviolet (UV) radiation breaks down CFC molecules in the stratosphere, releasing highly reactive chlorine atoms. Second, a free chlorine atom reacts with an ozone molecule (\(\text{O}_3\)) to form chlorine monoxide (\(\text{ClO}\)) and diatomic oxygen (\(\text{O}_2\)). Third, the chlorine monoxide reacts with a free oxygen atom (\(\text{O}\)) to produce another diatomic oxygen molecule and regenerate the free chlorine atom. Fourth, this regenerated chlorine atom acts as a catalyst, starting the cycle again and destroying thousands of ozone molecules.
PastPaper.markingScheme
Award 1 mark for UV radiation breaking down CFCs to release chlorine atoms. Award 1 mark for chlorine reacting with ozone (\(\text{O}_3\)) to form chlorine monoxide (\(\text{ClO}\)) and oxygen (\(\text{O}_2\)). Award 1 mark for chlorine monoxide reacting with free oxygen (\(\text{O}\)) to regenerate the chlorine atom. Award 1 mark for stating that the chlorine atom acts as a catalyst, allowing the process to repeat continuously.
PastPaper.question 2 · Extended Essay Part A
4 PastPaper.marks
Outline the differences between bioaccumulation and biomagnification of synthetic toxins in food chains.
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PastPaper.workedSolution
Bioaccumulation occurs when an individual organism absorbs a toxic substance at a rate faster than that at which the substance is lost or metabolized, leading to a build-up of the toxin within its tissues over time. On the other hand, biomagnification is the process where the concentration of a toxin increases at progressively higher trophic levels in a food web. This happens because top predators must eat many primary and secondary consumers, thereby concentrating the persistent toxins that were stored in the tissues of all those prey organisms.
PastPaper.markingScheme
Award 1 mark for defining bioaccumulation as the buildup of toxins within a single organism over its lifetime. Award 1 mark for explaining that bioaccumulation occurs because toxins are fat-soluble/persistent and absorbed faster than excreted. Award 1 mark for defining biomagnification as the increasing concentration of toxins at successive trophic levels. Award 1 mark for explaining that biomagnification occurs because predators consume multiple prey items containing the toxin, leading to high concentration at the top of the food chain.
PastPaper.question 3 · Extended Essay Part B
7 PastPaper.marks
Explain how photochemical smog is formed and suggest three pollution management strategies, at different levels of the pollution management model, to reduce its occurrence in urban areas.
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PastPaper.workedSolution
Formation of Photochemical Smog:
Primary Pollutants: Combustion of fossil fuels in motor vehicles and industries releases primary pollutants, mainly nitrogen oxides (\(NO_x\), specifically \(NO\) and \(NO_2\)) and volatile organic compounds (VOCs).
Role of Sunlight: High intensity solar ultraviolet (UV) radiation catalyzes the breakdown of nitrogen dioxide (\(NO_2 \rightarrow NO + O\)).
Ozone Formation: The freed atomic oxygen (\(O\)) rapidly reacts with molecular oxygen (\(O_2\)) to form tropospheric/ground-level ozone (\(O_3\)), a highly reactive secondary pollutant.
VOC Interaction: VOCs react with nitric oxide (\(NO\)), preventing it from reacting with and breaking down the ozone. This leads to the accumulation of tropospheric ozone.
Other Secondary Pollutants: Complex reactions between VOCs, \(NO_x\), and oxygen produce other toxic secondary pollutants like peroxyacyl nitrates (PANs).
Thermal Inversion: The accumulation is often worsened by meteorological conditions such as thermal inversions, where a layer of warm air traps cooler air and pollutants close to the ground, preventing dispersion.
Pollution Management Strategies (Three Levels):
Level 1: Altering human activity (Education/Lifestyle changes): Encourage the use of public transport, carpooling, cycling, or walking; promote the transition to electric/hybrid vehicles; raise public awareness about energy conservation to reduce overall fossil fuel burning.
Level 2: Regulating and controlling release (At source): Implement and enforce strict emission standards for vehicles (e.g., Euro emission standards); mandate the installation of catalytic converters in exhausts; require vapor recovery systems at gas stations to capture escaping VOCs; shift power generation to renewable sources.
Level 3: Clean-up and restoration (Remediation): Increase urban canopy cover/green spaces (foresting urban areas to absorb gaseous pollutants and cool the air, reducing the chemical reaction rates); use technological solutions such as titanium dioxide-coated "smog-eating" building materials that chemically neutralize smog precursors.
PastPaper.markingScheme
Award up to 4 marks for the explanation of photochemical smog formation: - Award 1 mark for identifying primary pollutants: nitrogen oxides (\(NO_x\)) and VOCs from vehicle exhausts/fossil fuel combustion. - Award 1 mark for explaining the role of UV radiation in initiating the photochemical reactions. - Award 1 mark for explaining the formation of tropospheric ozone (\(O_3\)) as a secondary pollutant. - Award 1 mark for explaining how VOCs lead to ozone accumulation OR how other secondary pollutants like PANs are formed. - Award 1 mark for mentioning the role of thermal inversions in trapping these pollutants.
Award up to 3 marks for the pollution management strategies (1 mark for each distinct level of the pollution management model): - Award 1 mark for Level 1 (Altering human activity): e.g., public transport promotion, carpooling, active transport, EV adoption. - Award 1 mark for Level 2 (Regulating/controlling release): e.g., catalytic converters, vehicle emissions tests, VOC recovery systems at pumps. - Award 1 mark for Level 3 (Clean-up/restoration): e.g., urban afforestation/greening to absorb pollutants, smog-eating architectural coatings.
[Max 7 marks]
PastPaper.question 4 · Extended Essay Part B
7 PastPaper.marks
Explain how the principles of island biogeography and edge effects influence the design of nature reserves to maximize biodiversity conservation.
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PastPaper.workedSolution
Application of Island Biogeography Principles:
Size (SLOSS debate): Larger reserves are superior to smaller reserves because they support larger population sizes, have greater habitat heterogeneity, and can sustain top predators that require large home ranges. This reduces the risk of local extinctions (similar to large islands having lower extinction rates).
Proximity/Clustering: Reserves located close together are better than reserves spaced far apart. High proximity increases the likelihood of dispersal, colonization, and gene flow between isolated sub-populations (similar to islands close to a mainland source).
Connectivity: The inclusion of habitat/wildlife corridors connecting isolated reserves allows species to migrate, find mates, and adapt to climate shifts. This mitigates the impacts of fragmentation and prevents genetic bottlenecking.
Influence of Edge Effects:
Definition of Edge Effects: The boundary (edge) of a reserve experiences different abiotic conditions (e.g., increased wind, higher light intensity, lower humidity) and biotic pressures (e.g., increased predation, poaching, and colonization by invasive species) compared to the core.
Shape of Reserve: Circular reserves are highly preferred over long, thin, or irregularly shaped reserves because a circle minimizes the perimeter-to-area ratio. This maximizes the protected "core" habitat and minimizes the proportion of the reserve impacted by edge effects.
Buffer Zones: Designing reserves with concentric buffer zones surrounding the core area helps transition from high-impact human activities to undisturbed natural areas, absorbing edge disturbances and protecting sensitive interior specialist species that cannot tolerate edge conditions.
PastPaper.markingScheme
Award up to 4 marks for explaining island biogeography principles in reserve design: - Award 1 mark for explaining why larger reserves are better than smaller reserves (e.g., lower extinction rates, supports top predators, more niches). - Award 1 mark for explaining proximity (reserves closer together facilitate colonization/dispersal). - Award 1 mark for explaining connectivity/corridors (promotes gene flow, migration, and prevents inbreeding). - Award 1 mark for referencing the SLOSS (Single Large Or Several Small) debate in the context of fragmentation.
Award up to 3 marks for explaining the influence of edge effects and shape: - Award 1 mark for defining edge effects (different abiotic/biotic conditions at the boundary compared to the core). - Award 1 mark for explaining why circular/compact shapes are preferred over thin/irregular shapes (minimizes perimeter-to-area ratio, maximizing core habitat). - Award 1 mark for explaining the role of buffer zones in mitigating edge effects for interior/specialist species.
[Max 7 marks]
PastPaper.question 5 · essay
9 PastPaper.marks
Climate change is one of the most pressing global challenges of our time. Discuss how different environmental value systems (EVSs) influence the choice and success of strategies used to mitigate climate change.
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PastPaper.workedSolution
An environmental value system (EVS) is a particular worldview that shapes the way an individual or group perceives and evaluates environmental issues. In the context of climate change mitigation, EVSs heavily influence the types of strategies chosen. Ecocentrists prioritize low-impact technology, lifestyle changes, and the intrinsic value of nature. They advocate for mitigation strategies such as reducing energy consumption, localizing food production, and massive reforestation or rewilding projects. The strength of ecocentric strategies is that they address the root cause of climate change—namely, overconsumption and ecological degradation—promoting long-term sustainability. However, their success is often limited because they require significant behavioral and cultural shifts, which are difficult to implement globally in a growth-oriented capital economy. Anthropocentrists focus on human health, social justice, and economic stability. They favor strategies like international treaties (such as the Paris Agreement), national carbon taxes, and cap-and-trade schemes. These strategies aim to manage human behavior through regulation and economic incentives. The strength of anthropocentric strategies is their ability to mobilize global governments and corporations, creating legally binding frameworks. However, their success is often hindered by political disagreements, slow policy implementation, and the challenge of balancing economic development with emissions reductions. Technocentrists believe that technological developments can solve environmental problems. They champion strategies such as carbon capture and storage (CCS), large-scale geoengineering (such as solar radiation management), nuclear energy, and renewable energy grids. The strength of technocentric strategies is that they allow economic growth and current lifestyles to continue while actively reducing atmospheric carbon. However, their success is limited by high financial costs, potential unintended ecological side-effects (especially with geoengineering), and the risk of creating a moral hazard where society delays reducing emissions in hopes of a future technological fix. In conclusion, no single EVS provides a complete solution. The most successful mitigation pathway requires a synthesis: technocentric innovations provide the tools, anthropocentric policies provide the regulatory frameworks, and ecocentric shifts provide the grass-roots behavioral change needed for long-term ecological balance.
PastPaper.markingScheme
For 7-9 marks: The response shows a deep understanding of EVSs (ecocentric, anthropocentric, and technocentric) and explicitly links them to specific climate change mitigation strategies. Arguments are balanced, presenting both strengths and limitations of each EVS-driven strategy. There is a clear, structured conclusion that synthesizes the perspectives. For 4-6 marks: The response describes different EVSs and mentions mitigation strategies, but links may be weak or unbalanced. The discussion of strengths and limitations is superficial, and the conclusion may be missing or weak. For 1-3 marks: The response is brief, lacks structure, or fails to connect EVSs directly to mitigation strategies. Accept: Valid alternative examples of mitigation strategies (such as energy efficiency or public transit investments) when clearly linked to an EVS.
PastPaper.question 6 · essay
9 PastPaper.marks
With the increasing collapse of global fish stocks, evaluate the effectiveness of combining top-down international agreements with bottom-up community-led management strategies to ensure the sustainable harvesting of marine wild fisheries.
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PastPaper.workedSolution
The sustainable harvesting of marine wild fisheries is a complex global challenge due to the 'tragedy of the commons' in international waters. To address this, management can be divided into top-down and bottom-up strategies. Top-down strategies involve international agreements, national policies, and global frameworks. Examples include the UN Convention on the Law of the Sea (UNCLOS), the Convention on International Trade in Endangered Species (CITES), and regional fishing quotas such as the EU Common Fisheries Policy. The primary strength of top-down agreements is their ability to manage migratory fish stocks across national borders and regulate international markets. They can establish large Marine Protected Areas (MPAs) and impose legally binding sanctions on non-compliant nations. However, their effectiveness is often limited by weak enforcement in the high seas, political lobbying by commercial fishing industries, and a lack of local community buy-in, which can lead to illegal, unreported, and unregulated (IUU) fishing. On the other hand, bottom-up strategies are driven by local communities, traditional fishers, and indigenous groups. Examples include community-managed marine reserves, traditional marine tenure systems (such as in the South Pacific), and local co-management agreements. The strength of these strategies lies in high local compliance, as stakeholders are directly involved in decision-making and have a vested interest in the long-term health of the fishery. These systems also utilize valuable traditional ecological knowledge (TEK) and are highly adaptive to local environmental changes. However, bottom-up management is limited by its small geographical scale, making it vulnerable to external threats such as commercial fleets poaching from outside the managed area, climate-induced species migration, and global market pressures that local communities cannot control. Ultimately, neither approach is fully effective on its own. The most successful management framework combines both: top-down international agreements must provide the legal protection, scientific funding, and regional enforcement needed to keep large commercial fleets in check, while bottom-up community-led groups must be empowered to manage local coastal zones, ensuring that rules are culturally appropriate and locally respected.
PastPaper.markingScheme
For 7-9 marks: The response provides a balanced evaluation of both top-down international agreements and bottom-up community-led strategies, with specific examples of each. The strengths and limitations of both approaches are clearly discussed in relation to sustainable fishery harvesting. A clear, evaluative conclusion synthesizes how the two levels of management must interact. For 4-6 marks: The response describes top-down and bottom-up approaches with some examples, but the evaluation of their strengths and limitations is unbalanced or lacks depth. The conclusion is simple or lacks synthesis. For 1-3 marks: The response is descriptive, listing general fishing management techniques without clearly distinguishing or evaluating top-down versus bottom-up approaches. Accept: Specific regional examples of fisheries (such as the Grand Banks cod collapse or Icelandic quota system) as supporting evidence.