IB DP · Thinka-original Practice Paper

2024 IB DP Environmental Systems and Societies Practice Paper with Answers

Thinka Nov 2024 SL (TZ2) IB Diploma Programme-Style Mock — Environmental Systems and Societies

100 marks180 mins2024

An original Thinka practice paper modelled on the structure and difficulty of the Nov 2024 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 companion resource booklet about Switzerland and the Alps.

12 Question · 26 marks

Question 1 · Direct retrieval & calculation

1.25 marks

Refer to Figure 2 in the resource booklet. In 1850, the volume of a specific Alpine glacier was estimated at \( 4.0 \text{ km}^3 \). By 2020, its volume had decreased to \( 1.2 \text{ km}^3 \). Calculate the percentage decrease in glacier volume over this period.

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Worked solution

To find the percentage decrease: \( \text{Percentage Decrease} = \frac{\text{Initial Volume} - \text{Final Volume}}{\text{Initial Volume}} \times 100 \). Substituting the values: \( \frac{4.0 - 1.2}{4.0} \times 100 = \frac{2.8}{4.0} \times 100 = 70\% \).

Marking scheme

Award [0.5 marks] for showing correct working: \( \frac{4.0 - 1.2}{4.0} \times 100 \). Award [0.75 marks] for the correct final answer: \( 70\% \) (accept '70' or '70 percent').

Question 2 · Direct retrieval & calculation

1.25 marks

Refer to the table in Figure 4. Canton Uri has a population of 36,400 residents living across a total land area of \( 1,076 \text{ km}^2 \). Calculate the population density of Canton Uri to one decimal place.

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Worked solution

Population density is calculated by dividing total population by total area: \( \text{Population Density} = \frac{36,400 \text{ people}}{1,076 \text{ km}^2} \approx 33.829 \text{ people/km}^2 \). Rounded to one decimal place, this is \( 33.8 \text{ residents per km}^2 \).

Marking scheme

Award [0.5 marks] for correct division setup: \( \frac{36,400}{1,076} \). Award [0.75 marks] for correct final answer rounded to one decimal place: \( 33.8 \text{ residents/km}^2 \) (accept '33.8' or '33.8 people per square kilometer').

Question 3 · Direct retrieval & calculation

1.25 marks

Refer to Figure 6 in the resource booklet. Switzerland's total annual electricity generation is \( 60 \text{ TWh} \). Hydroelectric power accounts for \( 36 \text{ TWh} \ of this total. Calculate the percentage of Switzerland's electricity generated by hydroelectric power.

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Worked solution

To find the percentage of electricity from hydroelectric power: \( \frac{\text{Hydroelectric Generation}}{\text{Total Generation}} \times 100 = \frac{36}{60} \times 100 = 60\% \).

Marking scheme

Award [0.5 marks] for showing correct working: \( \frac{36}{60} \times 100 \). Award [0.75 marks] for the correct final answer: \( 60\% \) (accept '60' or '60 percent').

Question 4 · Direct retrieval & calculation

1.25 marks

Refer to Figure 8 in the resource booklet. The ecological footprint of an average Swiss citizen is \( 4.5 \text{ gha} \), while Switzerland's local available biocapacity is \( 1.2 \text{ gha} \) per person. Calculate the biocapacity deficit of Switzerland in \( \text{gha} \) per person.

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Worked solution

Biocapacity deficit is the difference between the available biocapacity and the ecological footprint: \( \text{Deficit} = \text{Biocapacity} - \text{Ecological Footprint} = 1.2 \text{ gha} - 4.5 \text{ gha} = -3.3 \text{ gha} \) per person (representing a deficit of \( 3.3 \text{ gha} \) per person).

Marking scheme

Award [0.5 marks] for showing the correct subtraction step: \( 4.5 - 1.2 \) or \( 1.2 - 4.5 \). Award [0.75 marks] for the correct absolute or negative deficit: \( 3.3 \) or \( -3.3 \text{ gha per person} \) (accept '3.3 gha' or '3.3').

Question 5 · Short explanation

2 marks

Explain how the ice-albedo feedback loop contributes to the accelerated warming of alpine regions like the Swiss Alps.

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Worked solution

First, the student needs to identify the change in surface cover: melting ice and snow expose darker underlying surfaces such as rock, soil, or alpine vegetation. Second, they must connect this change to albedo: darker surfaces have a lower albedo and thus absorb more solar radiation (heat) rather than reflecting it back into space. This additional heat absorption raises local temperatures, leading to even more melting, establishing a self-reinforcing positive feedback loop.

Marking scheme

Award 1 mark for identifying that melting ice/snow exposes darker surfaces (rock/soil) which lowers the albedo (reflectivity). Award 1 mark for explaining that this lower albedo causes greater absorption of solar radiation, increasing temperatures and causing further melting (positive feedback).

Question 6 · Short description

2 marks

Describe two potential consequences of the long-term depletion of Swiss glaciers on downstream European river basins.

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Worked solution

Glaciers in the Swiss Alps act as 'water towers' that store water as ice and release it gradually. Two distinct consequences are: (1) A reduction in late summer streamflow when glacial melt is normally a primary source of river water for downstream European nations, causing water shortages for domestic, industrial, and agricultural use. (2) Increased vulnerability to seasonal hydrological extremes, with high runoff and flooding during winter/spring rains and severe drought in summer.

Marking scheme

Award 1 mark for each valid consequence described, up to a maximum of 2 marks. Acceptable points include: reduced river levels in late summer affecting shipping/navigation; loss of cooling water for downstream thermal/nuclear power plants; decreased freshwater availability for agriculture or domestic use; changes in freshwater biodiversity due to warmer river water temperatures; and increased risk of seasonal flooding.

Question 7 · Short explanation

2 marks

Describe how rising global temperatures are expected to affect the altitudinal distribution of plant communities in the Swiss Alps, and outline one ecological challenge this creates for endemic alpine species.

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Worked solution

As the climate warms, the climatic envelopes of alpine vegetation zones move upslope. Consequently, lowland and subalpine plants migrate higher. The ecological challenge for high-altitude endemics is that they are physically limited by the mountain summits; once they reach the peaks, they cannot migrate any higher. They also face competitive exclusion from more aggressive colonizing species migrating from lower altitudes.

Marking scheme

Award 1 mark for describing the upward/higher altitudinal shift of plant communities. Award 1 mark for outlining an ecological challenge (e.g., habitat loss/fragmentation, running out of space/altitude at the summit, or competitive exclusion by encroaching lower-altitude species).

Question 8 · Short description

2 marks

Outline two benefits of implementing ecological corridors, such as green bridges, to conserve large mammal populations in the highly fragmented Alpine valleys of Switzerland.

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Worked solution

Alpine valleys in Switzerland are heavily utilized for transport, agriculture, and urban development, which fragments wildlife habitats. Ecological corridors counteract this by: (1) restoring genetic connectivity, allowing individuals to mate with distant populations, thereby enhancing the gene pool; and (2) providing safe pathways across human infrastructure, which reduces roadkill and allows seasonal migration or range expansion in response to environmental shifts.

Marking scheme

Award 1 mark for each valid benefit outlined, up to a maximum of 2 marks. Acceptable points include: promotes gene flow/genetic diversity; reduces inbreeding depression; reduces wildlife-vehicle collisions/roadkill; allows seasonal migration for foraging/breeding; and assists species range shifts due to climate change.

Question 9 · Short explanation

2 marks

Explain how high-density seasonal tourism in Alpine ski resorts can lead to the degradation of local freshwater resources.

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Worked solution

High-density seasonal tourism exerts immense pressure on localized infrastructure. First, wastewater volume spikes dramatically during winter, which can lead to incomplete sewage treatment and discharge of organic pollutants/nutrients into pristine streams. Second, ski resorts rely heavily on artificial snowmaking, which extracts millions of liters of water from local reservoirs and streams, lowering water tables and altering natural winter stream hydrology.

Marking scheme

Award 1 mark for identifying a source of degradation (e.g., sewage system overload, runoff from resort infrastructure, or heavy water extraction for artificial snowmaking). Award 1 mark for explaining the impact on water quality or quantity (e.g., eutrophication, pollution of streams, or disruption of winter river flows and aquatic habitats).

Question 10 · Short explanation

2 marks

Explain how the degradation of mountain permafrost due to global warming poses a risk to both alpine ecosystems and human infrastructure in Switzerland.

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Worked solution

Permafrost acts as the 'glue' holding steep rock faces and loose scree together in cold alpine environments. As temperatures rise and permafrost thaws, the structural stability of slopes is compromised. This triggers mass wasting events (rockfalls, debris flows, landslides). For ecosystems, this causes soil erosion, loss of alpine soil profiles, and destruction of habitats like mountain forests. For humans, it threatens the structural integrity of mountain cableways, hiking trails, roads, and villages located in run-out zones.

Marking scheme

Award 1 mark for explaining the mechanism of slope destabilization (thawing permafrost loses its binding capacity, leading to structural instability). Award 1 mark for linking this instability to consequences for both ecosystems (e.g., habitat destruction, soil erosion, forest loss) and human infrastructure (e.g., damage to ski lifts, roads, railways, or alpine buildings).

Question 11 · Synthetic evaluation essay

4.5 marks

With reference to the Alps, evaluate the use of expanding protected area networks (such as national parks) versus implementing assisted migration (species translocation) to conserve vulnerable alpine flora threatened by temperature increases of up to \(2^\circ\text{C}\) due to climate change.

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Worked solution

In the Swiss Alps, climate change is shifting thermal niches upward, forcing species to migrate to higher elevations where habitable space decreases (known as the 'mountaintop extinction' effect).

**Expanding Protected Area Networks:**
- **Strengths:** By enlarging protected corridors, it maintains ecosystem integrity and facilitates natural dispersal. It protects multiple species simultaneously (holistic conservation) and safeguards ecosystem services.
- **Limitations:** It is static; as temperatures rise, species may physically run out of room to migrate upward within the boundaries of the park. It does not overcome physical barriers like alpine fragmentation (valleys, ski resorts).

**Implementing Assisted Migration:**
- **Strengths:** It allows active rescue of critically endangered endemics that cannot migrate fast enough or have reached the physical limit of their mountain range.
- **Limitations:** High ecological risk of translocated species becoming invasive or disrupting receiving communities. It is expensive, labor-intensive, and focuses on single species rather than systemic health.

**Conclusion/Synthesis:**
Expanding protected areas is a superior proactive, ecosystem-wide strategy, but for high-elevation endemic alpine plants facing immediate extinction, assisted migration represents a necessary reactive emergency measure.

Marking scheme

**Marking Scheme (Total: 4.5 Marks)**

- **Evaluation of Protected Areas (Max 2 marks):**
- Award **1 mark** for discussing a strength (e.g., protects whole-ecosystem processes, allows natural migration of multiple species).
- Award **1 mark** for explaining a limitation (e.g., ineffective if the species' climate envelope moves entirely off the top of the mountain peak).

- **Evaluation of Assisted Migration (Max 2 marks):**
- Award **1 mark** for identifying a strength (e.g., prevents immediate extinction of poor dispersers or those on isolated summits).
- Award **1 mark** for identifying a limitation (e.g., risk of disrupting receiving ecosystems, high cost, low success rate).

- **Synthesis/Conclusion (0.5 marks):**
- Award **0.5 marks** for a clear, justified comparative judgment on how both strategies should be integrated to optimize alpine conservation.

Question 12 · Synthetic evaluation essay

4.5 marks

Using the context of Swiss alpine catchments, evaluate the ecological and hydrological impacts of expanding artificial snow production as an adaptation to declining natural winter snow cover.

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Worked solution

To combat warming winters, Swiss ski resorts rely heavily on artificial snowmaking. This has complex ecological and hydrological feedbacks on alpine catchments.

**Hydrological Impacts:**
- **Water Abstraction:** Water is extracted from mountain streams or high-altitude reservoirs during low-flow winter periods. This drastically lowers stream levels, threatening aquatic invertebrates and fish species adapted to stable winter flows.
- **Altered Runoff:** Artificial snow is denser and melts later in spring. This delays the natural peak runoff, shifts the hydrological regime of downstream rivers, and can exacerbate late-spring flooding risks.

**Ecological Impacts:**
- **Soil and Vegetation:** Artificial snow contains chemical/microbial additives (to facilitate freezing at higher temperatures) which can alter soil chemistry and damage sensitive alpine meadow flora. Additionally, the heavy machinery causes soil compaction, reducing soil permeability and oxygen levels.
- **Thermal Protection:** On the positive side, a layer of artificial snow provides thermal insulation for soil and hibernating organisms during periods of winter drought when natural snowpack is absent.

**Conclusion/Synthesis:**
While artificial snow protects the soil from extreme frost and preserves local winter tourism, its high water footprint and disruption to mountain hydrology present a severe risk to alpine freshwater ecosystems.

Marking scheme

**Marking Scheme (Total: 4.5 Marks)**

- **Hydrological Impacts (Max 2 marks):**
- Award **1 mark** for explaining the impact of winter water abstraction on aquatic habitats and streamflow.
- Award **1 mark** for explaining the disruption of spring runoff regimes due to delayed melting of high-density artificial snow.

- **Ecological Impacts (Max 2 marks):**
- Award **1 mark** for explaining a negative ecological impact (e.g., soil compaction, chemical additives, vegetation delay).
- Award **1 mark** for identifying a potential ecological benefit (e.g., insulation against soil frost during snow-free periods).

- **Synthesis/Conclusion (0.5 marks):**
- Award **0.5 marks** for a balanced concluding judgment linking hydrological stress to long-term ecosystem instability.

Paper 2 Section A (Core Data Compulsory)

Answer all questions. Complete calculations and evaluations based on municipal waste, eutrophication, and kelp marine systems.

11 Question · 22 marks

Question 1 · Calculation

1 marks

In 2022, City X produced 450,000 tonnes of municipal solid waste. 30% of this total waste was identified as paper waste. Out of this paper waste, 54,000 tonnes were successfully sorted and recycled. Calculate the percentage of the generated paper waste that was recycled in City X.

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Worked solution

Step 1: Calculate the total amount of paper waste generated. \(450,000 \text{ tonnes} \times 0.30 = 135,000 \text{ tonnes}\) of paper waste. Step 2: Calculate the percentage of this paper waste that was recycled. \(\frac{54,000 \text{ tonnes}}{135,000 \text{ tonnes}} \times 100 = 40\%\).

Marking scheme

Award 1 mark for the correct final answer of 40% (or 40). Accept work showing the intermediate step of 135,000 tonnes of paper waste.

Question 2 · Retrieval

1 marks

A freshwater lake experiencing agricultural runoff is monitored for eutrophication. At a depth of 5 meters, the dissolved oxygen (DO) concentration before an algal bloom was measured at \(7.8 \text{ mg/L}\). Following the bloom, the decomposition of dead algae reduced the DO concentration at this depth to \(2.1 \text{ mg/L}\). Calculate the difference in dissolved oxygen concentration (in \(mg/L\)) at this depth before and after the bloom.

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Worked solution

Subtract the post-bloom dissolved oxygen concentration from the pre-bloom concentration: \(7.8 \text{ mg/L} - 2.1 \text{ mg/L} = 5.7 \text{ mg/L}\).

Marking scheme

Award 1 mark for the correct value of 5.7 mg/L (accept 5.7).

Question 3 · Calculation

1 marks

In a marine coastal ecosystem off California, the gross primary productivity (GPP) of a giant kelp forest is estimated to be \(22,000 \text{ kJ m}^{-2} \text{ yr}^{-1}\). The total respiratory loss (R) by the kelp community is measured at \(14,500 \text{ kJ m}^{-2} \text{ yr}^{-1}\). Calculate the net primary productivity (NPP) of this kelp forest in \(kJ m^{-2} yr^{-1}\).

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Worked solution

Use the formula: \(NPP = GPP - R\). Therefore, \(NPP = 22,000 \text{ kJ m}^{-2} \text{ yr}^{-1} - 14,500 \text{ kJ m}^{-2} \text{ yr}^{-1} = 7,500 \text{ kJ m}^{-2} \text{ yr}^{-1}\).

Marking scheme

Award 1 mark for the correct calculation of 7,500 kJ m^-2 yr^-1 (accept 7,500).

Question 4 · Calculation

1 marks

A small island nation with a population of 80,000 residents generates 29,200 tonnes of municipal solid waste per year. Calculate the per capita waste generation of this nation in kilograms (kg) per person per year. (Assume \(1 \text{ tonne} = 1,000 \text{ kg}\)).

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Worked solution

Step 1: Convert the total municipal solid waste from tonnes to kilograms: \(29,200 \text{ tonnes} \times 1,000 \text{ kg/tonne} = 29,200,000 \text{ kg}\). Step 2: Divide the total waste in kg by the population: \(\frac{29,200,000 \text{ kg}}{80,000 \text{ people}} = 365 \text{ kg/person/year}\).

Marking scheme

Award 1 mark for the correct answer of 365 (or 365 kg per person per year).

Question 5 · Ecosystem and feedback loop outlines

2.2 marks

Outline how a positive feedback loop can accelerate the process of eutrophication in a freshwater ecosystem.

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Worked solution

Step 1: Nutrient runoff triggers an algal bloom, blocking sunlight and killing submerged plants. Step 2: Aerobic decomposers break down the dead plants, consuming dissolved oxygen. Step 3: Low oxygen levels cause fish and other organisms to die. Step 4: The dead fish provide more organic matter for decomposers, which further depletes oxygen, accelerating the cycle.

Marking scheme

Award 1 mark for explaining that initial decomposition of dead biomass consumes dissolved oxygen. Award 1 mark for explaining how the resulting fish/organism deaths provide more organic biomass, which further increases decomposition and oxygen depletion, reinforcing the loop.

Question 6 · Ecosystem and feedback loop outlines

2.2 marks

Outline a positive feedback loop through which anaerobic decomposition of municipal solid waste (MSW) in a landfill contributes to global climate change, which then further accelerates decomposition.

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Worked solution

Step 1: Landfill waste undergoes anaerobic decomposition, releasing methane (\(\text{CH}_4\)), which is a potent greenhouse gas. Step 2: The accumulation of methane in the atmosphere enhances the greenhouse effect, raising global temperatures. Step 3: Increased ambient temperatures warm the landfill environment, accelerating the metabolic rate of anaerobic bacteria. Step 4: Faster bacterial activity increases the rate of decomposition, releasing more methane and further warming the climate.

Marking scheme

Award 1 mark for explaining that anaerobic decomposition of MSW releases methane (\(\text{CH}_4\)) which increases global temperatures. Award 1 mark for explaining that higher temperatures increase bacterial metabolic rates, resulting in faster decomposition and more methane release, reinforcing the loop.

Question 7 · Ecosystem and feedback loop outlines

2.2 marks

With reference to a kelp forest ecosystem, outline a negative feedback loop that maintains the stability of the sea urchin population when sea otter predation is absent.

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Worked solution

Step 1: Without sea otters to prey on them, the sea urchin population grows rapidly. Step 2: The large urchin population overgrazes and depletes the kelp forest (their food source). Step 3: The lack of food (resource limitation) leads to starvation and reduced reproduction among sea urchins. Step 4: The sea urchin population decreases, allowing the kelp to partially recover and stabilizing the system.

Marking scheme

Award 1 mark for identifying that urchin population growth leads to overgrazing and depletion of kelp (limiting resource). Award 1 mark for explaining that the resulting food shortage causes a decline in the urchin population, demonstrating a self-regulating negative feedback loop.

Question 8 · Ecosystem and feedback loop outlines

2.2 marks

Outline how the growth of macrophytes (aquatic plants) can act as a negative feedback mechanism to restore ecological balance in a shallow lake undergoing mild nutrient enrichment.

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Worked solution

Step 1: Nutrient enrichment increases the growth of macrophytes. Step 2: These plants take up and store large quantities of nitrogen and phosphorus from the water. Step 3: The absorption of these nutrients reduces the concentration of dissolved nutrients available in the lake. Step 4: This nutrient reduction limits further algal blooms and excessive plant growth, returning the lake toward its original state.

Marking scheme

Award 1 mark for explaining that macrophytes absorb and lock up the excess dissolved nutrients (nitrogen/phosphorus) from the water column. Award 1 mark for explaining how this reduction in available nutrients limits further eutrophication/algal growth, stabilizing the ecosystem (negative feedback).

Question 9 · Ecosystem and feedback loop outlines

2.2 marks

Kelp forests are highly effective marine carbon sinks. Outline a positive feedback loop that occurs when rising ocean temperatures cause the degradation of kelp marine ecosystems.

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Worked solution

Step 1: Increased ocean temperatures cause kelp forests to degrade and die. Step 2: The loss of kelp reduces overall marine photosynthesis and carbon sequestration. Step 3: More carbon dioxide (\(\text{CO}_2\)) remains in the atmosphere, accelerating global warming. Step 4: The resulting increase in global temperatures further warms the oceans, causing additional kelp mortality.

Marking scheme

Award 1 mark for linking kelp degradation to decreased carbon sequestration/higher atmospheric \(\text{CO}_2\) levels. Award 1 mark for explaining how higher atmospheric \(\text{CO}_2\) enhances global warming, further increasing ocean temperatures and causing additional kelp loss (positive feedback).

Question 10 · Strategy evaluation

3.5 marks

Evaluate the effectiveness of diverting municipal organic waste from landfills to composting facilities as a strategy to mitigate eutrophication in adjacent freshwater ecosystems.

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Worked solution

1. Strengths: Landfills produce highly concentrated leachate when organic waste decomposes anaerobically. Diverting this waste to composting reduces the volume of leachate and the quantity of nutrients like nitrogen and phosphorus that can leach into groundwater or runoff into local streams, preventing the nutrient enrichment that triggers eutrophication. 2. Limitations: If composting facilities are not properly designed (e.g., lacking impermeable liners or covered structures), rainwater can leach nutrients from compost piles, creating a new source of runoff. Furthermore, municipal waste diversion only addresses a portion of local nutrient inputs, leaving major non-point sources like agricultural fertilizer runoff unmitigated. 3. Evaluation: While highly effective at reducing localized municipal point-source pollution, the strategy must be combined with strict runoff management at composting sites and agricultural nutrient management plans to successfully mitigate regional eutrophication.

Marking scheme

Award up to 3.5 marks. Award 1 mark for explaining a strength (e.g., reducing landfill leachate volume and nutrient loading of \(\text{N}\) and \(\text{P}\) in nearby water bodies). Award 1 mark for explaining how this directly reduces the risk of freshwater eutrophication (e.g., limiting rapid algal growth). Award 1 mark for identifying a clear limitation (e.g., potential nutrient runoff from poorly managed compost sites, or the fact that it does not address agricultural sources). Award 0.5 marks for a balanced concluding evaluative judgment on its overall effectiveness relative to other pollution sources or management practices.

Question 11 · Impact explanation

3.5 marks

Explain how coastal eutrophication resulting from untreated municipal wastewater discharges can lead to the degradation of benthic kelp forest ecosystems.

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Worked solution

1. Untreated municipal wastewater contains high concentrations of limiting nutrients, specifically nitrogen (\(\text{N}\)) and phosphorus (\(\text{P}\)). 2. When discharged into coastal waters, these nutrients stimulate the rapid proliferation of phytoplankton and opportunistic ephemeral algae, creating dense algal blooms. 3. These algal blooms increase water turbidity and physically block sunlight from penetrating to the sea floor where benthic kelp is established. 4. Because kelp is a macroalgae that relies heavily on light for photosynthesis, this shading reduces its capacity to produce carbohydrates, leading to kelp die-offs. The loss of kelp (a foundation species) subsequently collapses the complex three-dimensional habitat, causing a decline in biodiversity among associated fish and marine invertebrates.

Marking scheme

Award up to 3.5 marks. Award 1 mark for linking municipal wastewater discharges to nutrient enrichment (nitrogen/phosphorus) and the subsequent formation of algal blooms. Award 1 mark for explaining that these blooms block sunlight penetration and increase water turbidity. Award 1 mark for explaining that reduced light limits photosynthesis in benthic kelp, leading to reduced growth or mortality. Award 0.5 marks for explaining the wider ecological impact (e.g., loss of kelp as a foundation species leads to habitat destruction and a decline in biodiversity/trophic structure).

Paper 2 Section B (Structured Essays)

Answer two options out of four structured questions. Each option consists of part a, b, and c.

7 Question · 49 marks

Question 1 · Part A: Key concept outline

4 marks

Outline how negative feedback mechanisms contribute to the stability of a system, using a named environmental example.

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Worked solution

Negative feedback mechanisms promote stability by counteracting any deviation from a system's set point or equilibrium. When a change occurs in a system, negative feedback processes work to reverse or minimize that change, bringing the system back to its original state. For example, in a predator-prey system (such as snowshoe hares and lynx), an increase in the hare population provides more food for the lynx. This leads to an increase in the lynx population, which subsequently increases predation on the hares. As a result, the hare population decreases, which then leads to a decline in the lynx population due to food scarcity, stabilizing both populations around a long-term average carrying capacity.

Marking scheme

Award 1 mark for each of the following up to a maximum of 4 marks: [1 mark] for defining negative feedback as a mechanism that counteracts or reverses deviation from an equilibrium/steady state. [1 mark] for explaining that negative feedback stabilizes systems and maintains dynamic equilibrium. [1 mark] for identifying a valid named environmental example (e.g., predator-prey cycles, temperature regulation in organisms, or atmospheric carbon dioxide uptake by plants). [1 mark] for explaining explicitly how the feedback loop operates in the chosen example to restore balance (e.g., increase in prey leads to predator increase, which reduces prey, returning the system to balance).

Question 2 · Part A: Key concept outline

4 marks

Outline the mechanism of the natural greenhouse effect and how it differs from the enhanced greenhouse effect.

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Worked solution

The natural greenhouse effect is a vital atmospheric process where solar (shortwave) radiation passes through the atmosphere and warms the Earth's surface. The Earth then re-emits this energy as longwave (infrared) radiation. Greenhouse gases (such as water vapor, carbon dioxide, and methane) absorb some of this outgoing infrared radiation and re-radiate it in all directions, including back toward the Earth's surface, keeping the planet warm enough to sustain life. In contrast, the enhanced greenhouse effect refers to the additional warming of the atmosphere caused by human activities (such as burning fossil fuels and deforestation) that release excess greenhouse gases. This increases the concentration of these gases, trapping more heat than normal and leading to global warming and climate change.

Marking scheme

Award 1 mark for each of the following up to a maximum of 4 marks: [1 mark] for explaining that incoming solar radiation is shortwave, which passes through the atmosphere and warms the Earth's surface. [1 mark] for explaining that the Earth re-emits this energy as longwave/infrared radiation, which is absorbed and re-radiated by greenhouse gases in the atmosphere. [1 mark] for stating that the natural greenhouse effect is essential for maintaining temperatures necessary to support life on Earth. [1 mark] for explaining that the enhanced greenhouse effect is caused by anthropogenic/human activities increasing greenhouse gas concentrations, leading to excess heat being trapped and resulting in rising global temperatures.

Question 3 · Part B

7 marks

Explain how agricultural runoff can lead to the process of eutrophication in a freshwater lake, and describe how this process can become a positive feedback loop.

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Worked solution

Agricultural activities often involve the application of synthetic fertilizers containing nitrogen and phosphorus. When it rains, surface runoff carries these excess nutrients into nearby freshwater lakes, causing nutrient enrichment. This triggers a rapid increase in the population of algae, known as an algal bloom. The dense algal layer on the water surface blocks sunlight from reaching submerged aquatic plants, preventing them from photosynthesizing and causing them to die. As both the algae (which have short lifespans) and the submerged plants die, there is a large influx of dead organic matter. Aerobic bacteria and other decomposers multiply rapidly to feed on this organic matter. The respiration of these decomposers drastically increases the Biochemical Oxygen Demand (BOD) and consumes the dissolved oxygen in the water. This results in hypoxia (extremely low oxygen levels), causing fish and other aerobic aquatic organisms to suffocate and die. The decomposition of these dead organisms adds even more organic matter to the lake, which in turn feeds more decomposers and consumes more oxygen, creating a self-reinforcing positive feedback loop that further degrades the ecosystem.

Marking scheme

Award 1 mark for each of the following points, up to a maximum of 7 marks:
- Runoff carries excess nutrients (nitrates and phosphates) from fertilizers into lakes.
- Nutrient enrichment causes rapid growth of algae / algal bloom.
- Algal bloom blocks sunlight, preventing photosynthesis of submerged plants, leading to their death.
- Increase in dead organic matter leads to rapid multiplication of aerobic decomposers/bacteria.
- Decomposers use up dissolved oxygen through respiration, leading to high Biochemical Oxygen Demand (BOD) / hypoxia.
- Hypoxia leads to death of fish and other aerobic aquatic organisms.
- Positive feedback loop explained: Death of fish/organisms leads to more dead organic matter, which increases decomposition, further depleting oxygen and killing more organisms. (Must explicitly link back to the self-reinforcing/positive feedback cycle to gain this mark).

Question 4 · Part B

7 marks

Explain how human activities and environmental factors interact to produce photochemical smog in urban areas, and suggest why this is considered a secondary pollutant.

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Worked solution

Photochemical smog is a mixture of air pollutants that forms when primary pollutants interact with sunlight. Human activities, primarily the combustion of fossil fuels in internal combustion engines (vehicles) and industrial plants, release primary pollutants such as nitrogen oxides (\(\text{NO}_x\)) and volatile organic compounds (VOCs). In the presence of sunlight, specifically ultraviolet (UV) radiation, these primary pollutants undergo a series of complex photochemical reactions. This process produces secondary pollutants, including tropospheric (ground-level) ozone (\(\text{O}_3\)), peroxyacyl nitrates (PANs), and aldehydes. It is classified as a secondary pollutant because these harmful substances are not emitted directly from a source (like a tailpipe or chimney) but are formed in the atmosphere through chemical reactions involving primary pollutants. Several environmental and meteorological factors influence the severity of smog: high levels of solar radiation and warm temperatures accelerate the chemical reactions; low wind speeds prevent the dispersion and dilution of the pollutants; and local topography, such as cities located in basins or valleys surrounded by mountains, physically traps the air. Additionally, thermal inversions (where a layer of warm air sits above a layer of cooler air) trap pollutants close to the ground, preventing them from rising and dispersing, which dramatically increases smog concentration.

Marking scheme

Award 1 mark for each of the following points, up to a maximum of 7 marks:
- Human activities (burning fossil fuels/vehicle emissions) release primary pollutants (\(\text{NO}_x\) and VOCs).
- Solar radiation (specifically UV light) drives chemical reactions among these primary pollutants.
- The reaction products include ground-level ozone, PANs, and aldehydes, which constitute photochemical smog.
- Definition of secondary pollutant: Photochemical smog/ozone is a secondary pollutant because it is formed in the atmosphere from primary pollutants and not emitted directly from a source.
- Influence of sunlight/temperature: Warm, sunny climates accelerate the chemical reactions that form smog.
- Influence of topography: Valley/basin topography physically traps pollutants and prevents horizontal dispersion.
- Influence of wind: Low wind speeds prevent the dilution and dispersion of the smog.
- Influence of thermal inversion: Thermal inversions trap cool, polluted air beneath a layer of warm air close to the ground, preventing vertical mixing.

Question 5 · essay

9 marks

To what extent can technological solutions (such as carbon dioxide removal and solar radiation management) address the global climate crisis compared to behavioral and lifestyle changes? Discuss with reference to contrasting environmental value systems.

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Worked solution

A successful essay should address the following key points:

Technocentric perspective (Technological solutions):
- Discusses Carbon Dioxide Removal (CDR) e.g., carbon capture and storage (CCS), biochar, afforestation, and Solar Radiation Management (SRM) e.g., stratospheric aerosol injection, space mirrors.
- Strengths: Can be deployed on a large scale; does not require global consensus on lifestyle changes; can potentially prevent tipping points rapidly (specifically SRM).
- Weaknesses: High cost; untested at scale; potential for unforeseen ecological consequences (e.g., disruption of monsoons with SRM); 'moral hazard' (discourages reduction of greenhouse gas emissions).
Ecocentric perspective (Behavioral/Lifestyle changes):
- Discusses reduction in resource consumption, shifting to plant-based diets, choosing public transport/active travel, localized organic agriculture.
- Strengths: Addresses the root cause of ecological degradation (unsustainable consumption); promotes holistic ecological harmony and ethical stewardship; low risk of unintended technological catastrophes.
- Weaknesses: Extremely difficult to enforce or encourage globally; slow to implement relative to the urgency of climate change; conflicts with current global economic systems focused on perpetual growth.
Anthropocentric perspective (Policy/Regulation):
- Discusses carbon taxes, cap-and-trade systems, international treaties (e.g., Paris Agreement) to incentivize both green technology and behavioral shifts.
- Acts as a bridge to balance technological innovation with public education and regulatory frameworks.
Conclusion: A balanced conclusion stating to what extent technology can solve the issue alone, usually arguing that while technology is necessary to mitigate existing committed warming, long-term sustainability is impossible without fundamental lifestyle and behavioral changes.

Marking scheme

Standard 9-mark essay marking descriptors apply:

[1–3 marks] The response is subjective, lacks specific examples, or is heavily unbalanced. There is a basic understanding of technological or lifestyle solutions but limited connection to Environmental Value Systems (EVSs).

[4–6 marks] The response is structured and attempts to compare technological and behavioral solutions. Demonstrates a clear understanding of technocentric and ecocentric EVSs. Examples of technologies (e.g., CCS, SRM) and lifestyle changes are mentioned. Shows some evaluation of both approaches, though one may be treated in more depth than the other.

[7–9 marks] The response provides a balanced, critical evaluation of both technological and behavioral solutions. Explicit and detailed links are made to contrasting EVSs (technocentrism, ecocentrism, anthropocentrism). Specific examples of geoengineering technologies and behavioral shifts are used effectively. Clear, logical structure with a well-justified conclusion/synthesis showing to what extent technological solutions can address the crisis.

Question 6 · essay

9 marks

With reference to named societies, evaluate the success of top-down conservation strategies (such as national parks and international legislation) compared to bottom-up approaches (such as community-managed reserves and traditional indigenous practices) in protecting threatened ecosystems.

Show answer & marking scheme

Worked solution

A successful essay should address the following key points with reference to named societies/ecosystems:

Top-down strategies (Government/International level):
- Examples: The creation of Yellowstone National Park (USA), CITES, or the Galapagos Marine Reserve.
- Strengths: Strong legal backing and enforcement capabilities; ability to secure large-scale funding; protection of massive, contiguous ecosystems across political boundaries.
- Weaknesses: Risk of 'fortress conservation' which excludes indigenous peoples and local communities, leading to conflicts and poaching; high administrative and enforcement costs; vulnerability to corruption or political instability.
Bottom-up approaches (Local/Community level):
- Examples: Community-based natural resource management (CBNRM) in Namibia, sacred groves in India, or indigenous management of the Amazon rainforest.
- Strengths: High level of local stakeholder buy-in and compliance; utilization of local ecological knowledge (TEK); lower management costs; integrates human development with conservation.
- Weaknesses: Limited funding and resources; difficulty in managing wide-ranging/migratory species; lack of authority to stop large-scale external threats (e.g., multinational logging, climate change).
Synthesis/Evaluation: Successful modern conservation increasingly relies on co-management, combining the regulatory and financial strength of top-down frameworks with the local legitimacy and knowledge of bottom-up initiatives.

Marking scheme

Standard 9-mark essay marking descriptors apply:

[1–3 marks] The response is descriptive with minimal evaluation. It outlines either top-down or bottom-up strategies but fails to compare them effectively. Named examples of societies or ecosystems are absent or very generic.

[4–6 marks] The response compares top-down and bottom-up strategies. Some specific examples are provided (e.g., national parks, local communities). The advantages and disadvantages of both approaches are discussed, and some connection is made to environmental value systems or conservation outcomes.

[7–9 marks] The response offers a highly structured, balanced, and critical evaluation of both strategies. Specific, well-chosen examples of named societies and ecosystems are integrated naturally. Evaluates to what extent each strategy is successful and provides a clear, justified conclusion proposing a synthesis or co-management model. Broad conceptual links to EVS (ecocentric vs. technocentric/anthropocentric) are clearly articulated.

Question 7 · essay

9 marks

Show answer & marking scheme

Worked solution

A successful essay should address the following key points with reference to named societies/ecosystems:

Top-down strategies (Government/International level):
- Examples: The creation of Yellowstone National Park (USA), CITES, or the Galapagos Marine Reserve.
- Strengths: Strong legal backing and enforcement capabilities; ability to secure large-scale funding; protection of massive, contiguous ecosystems across political boundaries.
- Weaknesses: Risk of 'fortress conservation' which excludes indigenous peoples and local communities, leading to conflicts and poaching; high administrative and enforcement costs; vulnerability to corruption or political instability.
Bottom-up approaches (Local/Community level):
- Examples: Community-based natural resource management (CBNRM) in Namibia, sacred groves in India, or indigenous management of the Amazon rainforest.
- Strengths: High level of local stakeholder buy-in and compliance; utilization of local ecological knowledge (TEK); lower management costs; integrates human development with conservation.
- Weaknesses: Limited funding and resources; difficulty in managing wide-ranging/migratory species; lack of authority to stop large-scale external threats (e.g., multinational logging, climate change).
Synthesis/Evaluation: Successful modern conservation increasingly relies on co-management, combining the regulatory and financial strength of top-down frameworks with the local legitimacy and knowledge of bottom-up initiatives.

Marking scheme

Standard 9-mark essay marking descriptors apply:

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