2024 IB DP Environmental Systems and Societies Practice Paper with Answers

By examining the vertical bars in Figure 1 representing the annual net mass balance of the Gries Glacier, the lowest bar (representing the greatest negative value/net mass loss) is located at the year 2018.

Award 1 mark for identifying '2018' (accept '2018' or 'the year 2018'). Do not accept any other year.

1. Calculate the total change in elevation: \(2,348\text{ m} - 2,300\text{ m} = 48\text{ m}\).
2. Calculate the number of decades: \(2020 - 1980 = 40\text{ years} = 4\text{ decades}\).
3. Calculate the rate per decade: \(\frac{48\text{ m}}{4\text{ decades}} = 12\text{ meters per decade}\).

Award 1 mark for the correct calculation of '12' (accept '12 m/decade' or '12 meters per decade').

By reading the horizontal axis (months) against the peak of the discharge curve on the vertical axis, the maximum runoff value occurs in the month of July.

Award 1 mark for 'July' (accept 'mid-summer' or 'July/August' if both are mentioned, but 'July' is the primary peak).

Locate the pie chart or table in Figure 4 displaying 'Electricity Generation by Source in 2021'. Identify the slice/row labeled 'Hydropower' (or 'Hydro') and read its value, which is 61.5%.

Award 1 mark for '61.5%' (accept '61.5' or answers in the range of '61% to 62%').

Increasing average temperatures in the Swiss Alps cause glaciers to retreat, which alters downstream river flows and freshwater habitats. Additionally, it drives species to migrate to higher altitudes, which reduces habitat area for specialized high-altitude species and increases competition from colonizing lower-altitude species.

Award 1 mark for each valid environmental impact identified, up to a maximum of 2 marks: - Upward shift of treeline/vegetation zones (1 mark) - Habitat loss/fragmentation for high-altitude/cold-adapted species (1 mark) - Loss of biodiversity due to increased competition from invasive or lower-altitude species (1 mark) - Altered seasonal timing of life cycle events (1 mark). Do not accept socio-economic impacts.

Initially (short-term), glacier retreat increases river runoff due to the release of stored water, which can temporarily boost water availability. However, in the long-term, as glacier volume is significantly reduced, the flow of meltwater during dry summer months will decline sharply, leading to water scarcity and reduced water security downstream.

Award 1 mark for the short-term trend and 1 mark for the long-term trend: - Short-term: Increased runoff/meltwater availability (1 mark) - Long-term: Decreased river flows during summer/dry seasons leading to water scarcity/droughts (1 mark)

Endemic high-altitude plants are adapted to harsh, cold conditions and have limited tolerance for warmer temperatures. As lower-elevation species migrate upward, they outcompete the specialists for space and nutrients. Because the mountain summit represents a physical boundary, the high-altitude specialists have nowhere higher to migrate, resulting in local extinction.

Award 1 mark for each of the following explanations up to a maximum of 2: - Outcompetition by generalist/lower-altitude species migrating upwards (1 mark) - Physical limitation of mountain summits (nowhere higher to go / summit trap) (1 mark) - Loss of specialized niche/habitat conditions due to warming (1 mark)

Technocentrics believe that technology, such as artificial snow-making and mountain grading, can overcome environmental limitations to sustain tourism and economic growth. In contrast, ecocentrics argue that these developments disrupt fragile alpine ecosystems, consume vast amounts of water and energy, and that nature has intrinsic value and should be left undisturbed.

Award 1 mark for each well-formulated conflict, up to a maximum of 2 marks: - Artificial snow production: Technocentrics view it as a technological solution to climate warming, while ecocentrics emphasize the disruption of local hydrology and high energy use (1 mark) - Infrastructure development: Technocentrics favor engineering slopes/lifts for economic benefit, while ecocentrics argue for protecting the intrinsic value of pristine alpine wilderness (1 mark) - Resource use: Technocentrics emphasize management of alpine areas for human recreational use, while ecocentrics advocate for minimal human footprint (1 mark)

Permafrost acts as a glue holding rock and soil together on steep slopes. When it melts, the loss of structural ice reduces cohesion, destabilizing the slope. Furthermore, the released meltwater saturates the overlying soil, increasing pore water pressure and causing the soil to lose shear strength, which triggers landslides and accelerates erosion.

Award 1 mark for each physical process outlined, up to a maximum of 2 marks: - Loss of structural ice/binding agent that holds soil and rock particles together (1 mark) - Increased soil saturation / high pore water pressure which reduces shear strength (1 mark) - Thawing of the active layer leading to downslope sliding/slumping (1 mark) - Runoff from melted ice washing away loose, unstable topsoil (1 mark)

High-altitude alpine lakes are highly vulnerable to acid deposition because they are often located in catchments with granitic bedrock and thin soils, which have very low buffering capacity to neutralize acids. Additionally, acidic pollutants accumulate in snow during winter and are released rapidly into the lakes in a short period during spring snowmelt, causing acid shock.

Award 1 mark for each valid reason outlined, up to a maximum of 2 marks: - Thin soils and/or granitic bedrock with low buffering capacity (1 mark) - High precipitation/snowfall rates that capture and deposit atmospheric pollutants (1 mark) - Spring snowmelt causing a sudden release of accumulated acids (1 mark) - Small volume of alpine lakes relative to watershed size, which reduces dilution potential (1 mark)

Swiss alpine municipalities face significant challenges due to the massive seasonal surge in population during winter, which creates waste volumes far exceeding the year-round capacity of local infrastructure. Additionally, the remote location and steep terrain of alpine villages make transporting heavy solid waste to lowland recycling or incineration plants logistically difficult and expensive.

Award 1 mark for each valid management challenge identified, up to a maximum of 2 marks: - Seasonal fluctuation/spikes in waste volume exceeding municipal capacity (1 mark) - Logistical difficulty/high cost of transporting waste down steep, narrow mountain roads (1 mark) - Increased littering in remote ski slopes/trails that is hard to access and clean up (1 mark) - High energy/resource requirements to process/recycle waste in isolated mountain communities (1 mark)

An ecological advantage of run-of-the-river schemes is that they do not require flooding large valleys, thereby preserving terrestrial habitats and preventing the loss of alpine biodiversity. A disadvantage is that they still alter local river flow regimes and create physical barriers that disrupt the connectivity of aquatic ecosystems, hindering the movement of fish and macroinvertebrates.

Award 1 mark for a valid ecological advantage and 1 mark for a valid ecological disadvantage: - Advantage: Avoids large-scale flooding of terrestrial habitats / preserves upstream valleys (1 mark) - Advantage: Lowers greenhouse gas emissions from flooded decomposing vegetation compared to reservoirs (1 mark) - Disadvantage: Alters natural flow rates/discharge downstream, affecting aquatic habitats (1 mark) - Disadvantage: Creates barriers that block migratory paths of fish/aquatic organisms (1 mark). Note: Do not accept purely economic advantages.

As temperatures rise, the conditions suitable for tree growth shift to higher elevations, causing the treeline to migrate upward. This process reduces the available area for traditional alpine tundra and meadow ecosystems (often referred to as a "summit trap" or "niche squeeze"). Specialized alpine plants, which are adapted to cold, open, wind-swept conditions, face habitat loss and fragmentation. Additionally, these slow-growing alpine species face intense competition from faster-growing, taller subalpine woody plants and trees encroaching from lower elevations, which can lead to a decline in local alpine biodiversity.

Award 1 mark for each valid ecological consequence outlined, up to a maximum of 2 marks.
- Accept: Habitat loss / reduction of living space for specialized high-altitude species / mountain summit trap (1 mark).
- Accept: Increased interspecific competition from encroaching subalpine/lower-altitude species (1 mark).
- Accept: Disruption of food webs / loss of alpine-specific pollinators due to changes in vegetation community structure (1 mark).
- Reject: Broad, non-ecological consequences (e.g., "global warming increases" or "tourists cannot hike").

Artificial snowmaking requires vast quantities of water, which is often extracted from alpine lakes and streams during the winter when water levels are naturally low. This extraction can severely disrupt aquatic ecosystems and lower the water table. Additionally, snowmaking requires significant energy, contributing to carbon emissions if fossil fuels are used. On the other hand, a continuous layer of artificial snow provides an important physical barrier that protects fragile alpine soils and vegetation from direct physical damage, soil compaction, and erosion caused by ski edges and groomers when natural snow cover is too thin.

Award 1 mark for a valid environmental cost and 1 mark for a valid environmental benefit, up to a maximum of 2 marks.

Environmental Cost (max 1 mark):
- Diverts/depletes local water resources from mountain streams or reservoirs during ecologically sensitive low-flow winter periods.
- High energy consumption of snow cannons, increasing greenhouse gas emissions/carbon footprint (if powered by non-renewable sources).
- Alters soil hydrology and chemistry due to additives used to freeze water at higher temperatures or delayed spring runoff.

Environmental Benefit (max 1 mark):
- Protects underlying alpine plants and soil from physical damage, erosion, or compaction by skiers and maintenance machinery.
- Provides thermal insulation for subnivean (under-snow) soil communities and plant roots when natural snow cover is insufficient to protect against extreme frost.

Note: Do not accept socio-economic impacts (e.g., "maintains tourism income" or "expensive to run").

To find the percentage decrease:

1. Calculate the absolute decrease in volume:
\(2.0 \text{ km}^3 - 1.6 \text{ km}^3 = 0.4 \text{ km}^3\)

2. Divide the decrease by the original volume and multiply by 100:
\(\frac{0.4}{2.0} \times 100 = 20\%\)

[1] Award 1 mark for the correct final answer: 20% (accept "20" or "20 percent"). Do not accept negative values (e.g., -20%).

Using the Lincoln Index formula:
\(N = \frac{n_1 \times n_2}{m_2}\)

Where:
- \(n_1 = 50\) (number of individuals marked in the first sample)
- \(n_2 = 40\) (total number of individuals in the second sample)
- \(m_2 = 10\) (number of marked individuals recaptured in the second sample)

Calculation:
\(N = \frac{50 \times 40}{10} = \frac{2000}{10} = 200\)

[1] Award 1 mark for the correct final answer: 200 (accept "200 marmots").

### Indicative Content

**Environmental Perspectives:**
* **Pros:**
* Act as a buffer for altered river flow regimes, storing excess spring/summer runoff and preventing downstream flooding.
* Provide a reliable source of renewable, low-carbon hydroelectric power, assisting Switzerland's transition away from fossil fuels and reducing greenhouse gas emissions.
* Can create new aquatic habitats, though different from native alpine streams.
* **Cons:**
* Loss of pristine alpine ecosystems, tundra, and biodiversity due to inundation.
* Disruption of natural river connectivity, affecting sediment transport downstream which can lead to coastal/delta erosion and degradation of downstream riverbeds.
* Construction activities (heavy machinery, roads) cause habitat fragmentation, noise pollution, and soil compaction in fragile alpine zones.

**Socio-Economic Perspectives:**
* **Pros:**
* Enhances water security for agriculture, domestic consumption, and industrial use during increasingly dry summers.
* Economic benefits through job creation during construction and long-term revenue from hydroelectricity generation.
* Can serve as multi-use infrastructure, supporting tourism (e.g., recreational lakes, boat tours).
* **Cons:**
* Extremely high capital investment and maintenance costs.
* Aesthetic degradation of iconic natural landscapes, potentially harming the traditional nature-based tourism industry.
* Safety hazards for downstream populations due to risks of landslide-triggered dam failures, exacerbated by permafrost degradation on surrounding slopes.

**Conclusion/Evaluation:**
* A balanced conclusion should weigh these arguments. For instance, declaring that while artificial reservoirs are an essential technocentric adaptation to secure Switzerland's water and energy future under climate change, their ecological footprint must be carefully managed through hybrid approaches, such as combining reservoirs with strict environmental flow mandates and localized conservation efforts.

Apply the following holistic marking grid:

* **[5–6 marks]**
* The response shows a broad and deep understanding of both environmental and socio-economic perspectives regarding high-altitude reservoirs.
* Explicit and balanced evaluation of both positive and negative consequences.
* Effectively synthesizes information from the resource booklet and integrates relevant own knowledge.
* Structure is logical, and a clear, reasoned conclusion/judgment is provided.

* **[3–4 marks]**
* The response shows some understanding of the environmental and/or socio-economic impacts of the reservoirs.
* Mentions both pros and cons, but the discussion may be unbalanced (e.g., focusing heavily on economic aspects while neglecting ecology, or vice-versa).
* Utilizes some information from the resources, though links to own knowledge may be limited.
* A conclusion is present but may lack depth or clear justification.

* **[1–2 marks]**
* The response shows a limited or superficial understanding of the issue.
* Points are listed without development or clear evaluation.
* Minimal or no reference to the resources or own knowledge.
* No clear conclusion is reached.

First, state the NPP formula: \(NPP = GPP - R\). Substitute the given values into the equation: \(NPP = 2.4 \times 10^4\text{ kJ m}^{-2}\text{ yr}^{-1} - 1.5 \times 10^4\text{ kJ m}^{-2}\text{ yr}^{-1} = 0.9 \times 10^4\text{ kJ m}^{-2}\text{ yr}^{-1}\), which equals \(9000\text{ kJ m}^{-2}\text{ yr}^{-1}\).

[0.5 marks] for stating the correct formula: \(NPP = GPP - R\).
[1.0 mark] for the correct final value of \(9000\text{ kJ m}^{-2}\text{ yr}^{-1}\) (or \(9.0 \times 10^3\text{ kJ m}^{-2}\text{ yr}^{-1}\)) with correct units. Deduct 0.5 marks if units are missing or incorrect.

Calculate total annual extraction: \(3.2 \times 10^6\text{ m}^3 + 1.8 \times 10^6\text{ m}^3 = 5.0 \times 10^6\text{ m}^3\). Calculate net annual change: \(\text{Recharge} - \text{Extraction} = 4.5 \times 10^6\text{ m}^3 - 5.0 \times 10^6\text{ m}^3 = -0.5 \times 10^6\text{ m}^3\) (or \(-500,000\text{ m}^3\)). This is unsustainable because extraction exceeds recharge.

[1.0 mark] for calculating the correct net annual change of \(-500,000\text{ m}^3\) (or \(-5 \times 10^5\text{ m}^3\)), showing working.
[0.5 marks] for correctly stating that this is unsustainable because the rate of extraction exceeds the rate of recharge.

First, calculate NIR: \(NIR = \frac{CBR - CDR}{10} = \frac{34 - 9}{10} = 2.5\%\). Next, calculate the doubling time using the rule of 70: \(\text{Doubling Time} = \frac{70}{NIR} = \frac{70}{2.5} = 28\text{ years}\).

[0.5 marks] for the correct calculation of NIR as \(2.5\%\).
[1.0 mark] for the correct calculation of doubling time as 28 years (must include the unit 'years').

Substitute the given values into the provided formula: \(MSY = \frac{0.15 \times 80,000}{4} = \frac{12,000}{4} = 3000\text{ metric tons per year}\).

[1.0 mark] for the correct substitution and mathematical calculation resulting in 3,000.
[0.5 marks] for the correct units (metric tons per year or tonnes \(\text{yr}^{-1}\)).

Identify days exceeding 70 ppb: 78 ppb (Day 3) and 85 ppb (Day 4) which is 2 out of 5 days. Percentage: \(\frac{2}{5} \times 100 = 40\%\). Mean calculation: \(\frac{45 + 52 + 78 + 85 + 60}{5} = \frac{320}{5} = 64\text{ ppb}\).

[0.5 marks] for the correct percentage calculation of \(40\%\).
[1.0 mark] for the correct calculation of the mean as \(64\text{ ppb}\) (0.5 marks for the number 64, 0.5 marks for the unit 'ppb').

Current stocking density: \(\frac{150\text{ LU}}{50\text{ ha}} = 3.0\text{ LU/ha}\). Maximum sustainable capacity is 2.5 LU/ha (or 125 LU total). Overstocking percentage relative to the capacity: \(\frac{3.0 - 2.5}{2.5} \times 100 = \frac{0.5}{2.5} \times 100 = 20\%\) (alternatively: \(\frac{150 - 125}{125} \times 100 = 20\%\)).

[0.5 marks] for calculating the correct current stocking density of \(3.0\text{ LU/ha}\) (or \(3.0\text{ LU ha}^{-1}\)).
[1.0 mark] for the correct calculation of the overstocking rate as \(20\%\) with working shown.

Mitigation strategies target the sources of greenhouse gases to reduce their emissions into the atmosphere. For electricity generation, this involves shifting the energy mix away from high-emission fossil fuels or capturing emissions before they escape. 1. Transition to renewable energy: Generating power from solar, wind, hydro, or geothermal systems replaces coal or gas combustion, avoiding carbon emissions entirely. 2. Carbon Capture and Storage (CCS): Retrofitting fossil-fuel power stations with chemical scrubbers can capture up to 90% of the carbon dioxide emissions, which are then compressed and injected into deep geological formations.

Award [1] for each valid strategy outlined, up to [2] marks.
- Transitioning to renewable energy sources (e.g., solar, wind, hydro, geothermal) or nuclear energy [1].
- Implementing Carbon Capture and Storage (CCS) at fossil-fuel power stations [1].
- Switching from coal to natural gas (which has lower carbon intensity) [1].
- Improving the thermodynamic efficiency of power plants so less fuel is burned per MWh [1].
Note: Do not accept demand-side reduction strategies (like turning off lights) as the question specifically asks for strategies to reduce emissions from electricity generation itself.

While both processes involve persistent, lipophilic pollutants (such as DDT or methylmercury), they occur at different scales. Bioaccumulation occurs at the individual level (organismal scale) because the rate of absorption of the toxin is greater than the rate of excretion or metabolic breakdown over time. Biomagnification occurs at the ecosystem/food chain level (trophic scale) because predators must ingest large quantities of prey from the lower trophic level, concentrating the toxins further at each successive stage.

Award [1] for a clear description of bioaccumulation and [1] for a clear description of biomagnification.
- Bioaccumulation: The accumulation of a contaminant or toxin in the tissues of an individual organism over time [1].
- Biomagnification: The increase in concentration of a contaminant/toxin up the food chain / at successive trophic levels [1].
Note: For maximum marks, the distinction must clearly contrast the individual/single-organism scale (bioaccumulation) with the food chain/trophic scale (biomagnification).

Cultural eutrophication leads to nutrient enrichment (primarily phosphorus and nitrogen), causing algal blooms, anoxia, and biodiversity loss. Restoring a lake that is already degraded requires active remediation (Level 3 of pollution management). 1. Sediment dredging: Nutrients accumulate in lakebed sediments and are recycled back into the water column; removing this sediment breaks this cycle. 2. Artificial aeration: Pumping oxygen into deep waters prevents anaerobic conditions, which stops phosphorus from dissolving out of the sediment and supports aerobic decomposers.

Award [1] for each valid restoration strategy outlined, up to [2] marks.
- Dredging or removing nutrient-rich sediments from the lake floor [1].
- Aerating the lake/pumping oxygen into deep waters to prevent anoxia [1].
- Adding chemicals (such as alum or calcium hydroxide) to precipitate and bind phosphorus in the sediment [1].
- Harvesting and physically removing dense algal mats or aquatic weeds [1].
- Biomanipulation, such as removing zooplankton-eating fish to increase zooplankton populations that graze on algae [1].
Note: Do not accept preventative measures (such as ban on phosphate detergents or reducing agricultural fertilizer runoff) because the question specifically asks to restore a lake already severely affected.

Edge effects refer to the changes in population or community structures that occur at the boundary of two or more habitats. In a nature reserve, the outer edges are exposed to different microclimatic factors (higher temperature, wind, lower humidity), invasive species, and human disturbance, making them unsuitable for interior-specialist species and reducing the effective conservation area. To minimize this, designers can: 1. Shape: Use compact/circular designs rather than long, thin shapes to keep the perimeter-to-area ratio low, maximizing the secure interior area. 2. Buffer Zones: Establish areas of transitional, semi-protected habitat around the core reserve to absorb external disturbances.

Award [1] for explaining the negative impact of edge effects, and [1] for explaining a design feature to mitigate it.
- Edge effects explanation: Boundary areas have different microclimates (more wind/sunlight) or higher rates of predation/invasion, which reduces habitat quality/survival for interior-specialist species [1].
- Mitigation design: Designing the reserve to be circular or compact (minimizing perimeter-to-area ratio) OR creating a surrounding buffer zone to shield the core habitat [1].
Note: Do not accept 'making the reserve larger' unless it is linked to increasing the ratio of interior-to-edge area.

Systems are categorized based on their interactions with the environment. An open system exchanges both matter and energy. A tropical rainforest is a classic ecological example of an open system: 1. Energy exchange: It receives solar radiation from the Sun, which drives photosynthesis, and radiates heat energy back into space. 2. Matter exchange: It receives precipitation and nutrients from the atmosphere and soils, releases water vapor via evapotranspiration, exchanges oxygen and carbon dioxide, and allows animals to migrate in and out across its boundaries.

Award [1] for identifying the system type, and [1] for the correct reasoning.
- Open system [1].
- Reason: It exchanges both matter (e.g., water, gases, organic matter) and energy (e.g., solar radiation, heat) across its boundaries [1].
Note: No mark can be awarded for the reason if the system is incorrectly identified as closed or isolated.

1. Carbon dioxide (\(\text{CO}_2\)) from the atmosphere dissolves in the surface waters of the ocean, forming carbonic acid (\(\text{H}_2\text{CO}_3\)). 2. Carbonic acid dissociates into hydrogen ions (\(\text{H}^+\)) and bicarbonate ions (\(\text{HCO}_3^-\)). 3. The release of hydrogen ions (\(\text{H}^+\)) increases the acidity of the water (lowers pH). 4. These free hydrogen ions (\(\text{H}^+\)) react with available carbonate ions (\(\text{CO}_3^{2-}\)) to form more bicarbonate ions (\(\text{HCO}_3^-\)), which decreases the concentration of carbonate ions available for marine organisms to build calcium carbonate (\(\text{CaCO}_3\)) structures.

Award [1] mark for each of the following up to a maximum of [4]: [1] for stating that dissolved carbon dioxide (\(\text{CO}_2\)) reacts with water to form carbonic acid (\(\text{H}_2\text{CO}_3\)); [1] for explaining that carbonic acid dissociates to release hydrogen ions (\(\text{H}^+\)), which lowers ocean pH; [1] for explaining that excess hydrogen ions (\(\text{H}^+\)) react with carbonate ions (\(\text{CO}_3^{2-}\)) to produce bicarbonate ions (\(\text{HCO}_3^-\)); [1] for linking this reaction to the direct depletion of free carbonate ions available for marine organisms to synthesize calcium carbonate (\(\text{CaCO}_3\)) shells.

1. Carbon dioxide (\(\text{CO}_2\)) from the atmosphere dissolves in the surface waters of the ocean, forming carbonic acid (\(\text{H}_2\text{CO}_3\)). 2. Carbonic acid dissociates into hydrogen ions (\(\text{H}^+\)) and bicarbonate ions (\(\text{HCO}_3^-\)). 3. The release of hydrogen ions (\(\text{H}^+\)) increases the acidity of the water (lowers pH). 4. These free hydrogen ions (\(\text{H}^+\)) react with available carbonate ions (\(\text{CO}_3^{2-}\)) to form more bicarbonate ions (\(\text{HCO}_3^-\)), which decreases the concentration of carbonate ions available for marine organisms to build calcium carbonate (\(\text{CaCO}_3\)) structures.

Award [1] mark for each of the following up to a maximum of [4]: [1] for stating that dissolved carbon dioxide (\(\text{CO}_2\)) reacts with water to form carbonic acid (\(\text{H}_2\text{CO}_3\)); [1] for explaining that carbonic acid dissociates to release hydrogen ions (\(\text{H}^+\)), which lowers ocean pH; [1] for explaining that excess hydrogen ions (\(\text{H}^+\)) react with carbonate ions (\(\text{CO}_3^{2-}\)) to produce bicarbonate ions (\(\text{HCO}_3^-\)); [1] for linking this reaction to the direct depletion of free carbonate ions available for marine organisms to synthesize calcium carbonate (\(\text{CaCO}_3\)) shells.

Under normal conditions, air temperature decreases with altitude, allowing warm, polluted air from urban activities to rise and disperse into the upper atmosphere. During a thermal inversion, this relationship is reversed: a layer of warmer air sits directly above a layer of cooler, denser air near the surface. The warm air layer acts as a lid or cap because the cooler air below is denser and cannot rise through it. This prevents vertical convective currents, trapping urban pollutants (such as particulate matter, sulfur dioxide, and nitrogen oxides) close to the ground, where they accumulate and can lead to severe photochemical smog.

Award 1 mark for each valid point up to a maximum of 4 marks: - Explaining normal conditions (temperature decreases with altitude, allowing vertical dispersion of pollutants) [1 mark]; - Describing inversion conditions (a warm air layer overlies a cooler air layer near the ground) [1 mark]; - Explaining the mechanism of trapping (the warm layer acts as a 'cap' or barrier, preventing convection/vertical mixing) [1 mark]; - Describing the consequence (pollutants such as PM, NOx, or smog are trapped and accumulate near the ground) [1 mark].

A drainage basin is an open system with various inputs, outputs, storages, and flows. The key physical transfers (flows) of water within this system include: 1. Infiltration: The process by which water on the ground surface enters the soil. 2. Surface run-off (overland flow): The flow of water over the land surface, occurring when soil is saturated or impermeable, moving towards river channels. 3. Throughflow: The lateral (horizontal) movement of water through the soil layer towards a stream or river. 4. Percolation: The deeper vertical downward movement of water through soil and permeable rock into the groundwater storage/aquifers. Other acceptable flows include groundwater flow, stemflow, throughfall, or evapotranspiration.

Award 1 mark for each correctly identified and described physical transfer (flow), up to a maximum of 4 marks: - Infiltration: movement of water from surface into soil [1 mark]; - Surface run-off / overland flow: water flowing across the ground surface toward channels [1 mark]; - Throughflow: horizontal/lateral movement of water through the soil [1 mark]; - Percolation: downward movement of water from soil into underlying bedrock/aquifers [1 mark]; - Groundwater flow: horizontal movement of water through rock/aquifers [1 mark]. Note: Do not award marks for identifying storages (e.g., soil moisture, groundwater, lakes) unless they are explicitly described in the context of a transfer process.

At the equator, the intense solar radiation heats the Earth's surface, warming the overlying air. This warm air becomes less dense and rises rapidly, creating a low-pressure belt known as the Intertropical Convergence Zone (ITCZ). As this warm, humid air rises, it expands and cools adiabatically. When the air cools to its dew point, water vapor condenses to form cumulus clouds, releasing latent heat which further fuels the updraft. This leads to heavy, frequent convective rainfall, which sustains the tropical rainforest biome. Once the rising air reaches the upper troposphere, it diverges and moves poleward (North and South). By the time this air reaches approximately 30 degrees latitude, it has cooled and lost most of its moisture. This dry, dense air sinks back toward the surface, creating a high-pressure subtropical belt. As the air descends, it compresses and warms adiabatically, which increases its capacity to hold water vapor and prevents condensation and cloud formation. The resulting lack of precipitation and high evaporation rates create the extremely dry, arid conditions characteristic of desert biomes.

Award 1 mark for each point up to a maximum of 7 marks: 1. Intense solar insolation at the equator heats the surface and overlying air. 2. Air expands, becomes less dense, and rises, creating a low-pressure zone. 3. Rising air cools adiabatically, leading to condensation, cloud formation, and high precipitation (forming rainforests). 4. Dry air in the upper troposphere moves poleward as part of the Hadley Cell. 5. Air cools and becomes denser, descending at approximately 30 degrees North/South. 6. Sinking air compresses and warms adiabatically, suppressing cloud formation and precipitation (creating high pressure). 7. Low rainfall and high evaporation rates in these zones lead to arid desert biomes.

The process begins with agricultural runoff carrying excess nitrates and phosphates into a freshwater lake. These nutrients act as fertilizers, stimulating a rapid increase in the population of algae and phytoplankton at the water surface, known as an algal bloom. The thick algal mat blocks sunlight from penetrating deeper into the water column. Consequently, submerged aquatic plants (macrophytes) cannot perform photosynthesis and die. When the algae exhaust the available nutrients, they also die. This massive influx of dead organic matter becomes food for aerobic decomposers, such as bacteria, whose populations multiply exponentially. The massive populations of bacteria respire aerobically, consuming the dissolved oxygen in the water at a rate much faster than it can be replenished. This leads to a severe drop in dissolved oxygen levels, creating hypoxic or anoxic conditions (a dead zone). Aquatic animals, such as fish and macroinvertebrates, suffocate and die due to the lack of oxygen. Their death adds more organic matter to the system, which sustains and increases the population of decomposers, further depleting the oxygen in a self-reinforcing positive feedback loop.

Award 1 mark for each point up to a maximum of 7 marks: 1. Runoff introduces limiting nutrients (nitrates/phosphates) to the aquatic ecosystem. 2. Excess nutrients trigger rapid proliferation of algae/surface plants (algal bloom). 3. Dense surface algae block sunlight, causing submerged plants to die due to lack of photosynthesis. 4. Large-scale die-off of algae occurs once nutrients are exhausted. 5. Populations of aerobic decomposers (bacteria) increase rapidly to feed on the abundant dead organic matter. 6. Bacterial aerobic respiration rapidly consumes dissolved oxygen, creating hypoxic/anoxic conditions. 7. Suffocation of fish/aquatic animals leads to more organic matter for decomposition, reinforcing the positive feedback loop of oxygen depletion.

An environmental value system (EVS) shapes how individuals and societies perceive and evaluate environmental issues.

Ecocentrics view nature as having intrinsic value and advocate for solutions that respect ecological limits. For climate mitigation, an ecocentric approach prioritizes reducing resource consumption, adopting plant-based diets, conserving and restoring natural carbon sinks (e.g., reforestation, peatland restoration), and shifting to decentralized, community-scale renewable energy. For adaptation, they favor ecosystem-based adaptation, such as restoring coastal mangroves to prevent flooding rather than building concrete sea walls.

Technocentrics believe that technological developments and scientific research can solve environmental problems. For mitigation, they support large-scale geoengineering projects (e.g., solar radiation management, ocean fertilization), carbon capture and storage (CCS) systems, and nuclear power. For adaptation, they favor high-tech interventions like genetically modifying crops to withstand drought, constructing massive sea barriers, and developing sophisticated weather-prediction systems.

Anthropocentrics argue that humans must sustainably manage global systems through taxes, regulations, and international agreements. For mitigation, they advocate for market-based instruments like carbon taxes, cap-and-trade systems, and international treaties like the Paris Agreement. For adaptation, they prioritize government-funded infrastructure projects and public education campaigns to improve community resilience.

In conclusion, while ecocentrics emphasize lifestyle changes and working with nature, technocentrics look to technological innovation, and anthropocentrics rely on policy and global governance. A society's chosen climate strategy is rarely pure; it usually represents a pragmatic compromise among these different value systems.

[7-9 marks]: The response shows a clear understanding of at least three EVS perspectives (ecocentric, anthropocentric, technocentric). It effectively links each perspective to specific, distinct mitigation and/or adaptation strategies. Specific, appropriate examples are provided (e.g., geoengineering, carbon taxes, lifestyle shifts, mangrove restoration). The discussion is balanced, structured, and ends with a reasoned, synthesis-driven conclusion.

[4-6 marks]: The response discusses at least two EVS perspectives and relates them to climate change strategies. There is some structure, but the discussion may be unbalanced (e.g., focusing heavily on technocentric solutions while ignoring others) or lacking specific examples. The distinction between mitigation and adaptation may be blurred.

[1-3 marks]: The response shows a limited understanding of EVSs or climate strategies. It lists concepts without linking them logically. Examples are missing or inappropriate, and there is no clear structure or conclusion.

Habitat-based conservation strategies focus on protecting entire ecosystems (e.g., through national parks, marine protected areas, and ecological corridors), whereas species-based conservation strategies target individual threatened species (e.g., through CITES, captive breeding, and flagship species initiatives).

Habitat-based strategies are highly effective because they preserve the ecological processes, food webs, and niches necessary for long-term survival. By protecting an entire habitat, we conserve not only the known endangered species but also thousands of other, often undocumented, species of plants, invertebrates, and microbes. These strategies also maintain valuable ecosystem services, such as clean water and carbon sequestration. However, habitat-based approaches can be highly expensive to establish and manage, can lead to conflicts with local communities over land rights, and may fail to protect specific species targeted by highly organized poachers if active policing is absent.

Species-based strategies, on the other hand, are highly focused and can prevent the immediate extinction of critical taxa. Programs like captive breeding and reintroduction (e.g., the California Condor) have successfully revived species on the brink of extinction. Legislative tools like CITES regulate international trade, directly addressing the pressure of overexploitation. Furthermore, using charismatic 'flagship species' (e.g., the Giant Panda) can capture public attention and generate significant conservation funding. However, species-based strategies suffer from a 'taxonomic bias' that favors mammals and birds over ecologically vital insects and fungi. They are also costly per species and fail if the underlying habitat continues to degrade.

In conclusion, while habitat-based strategies are more fundamentally effective at preserving broad-scale biodiversity and ecological integrity, they are not always sufficient on their own. Species-based strategies are essential for emergency interventions and public engagement. Therefore, the most effective approach is an integrated one, where species-specific laws and flagship campaigns are nested within broader, well-managed habitat conservation networks.

[7-9 marks]: The response provides a balanced, critical evaluation comparing habitat-based and species-based conservation strategies. It explicitly addresses the 'to what extent' part of the prompt. It details the strengths and limitations of both approaches, using specific examples (e.g., CITES, specific reserves, flagship species, SLOSS debate). It concludes with a clear synthesis showing that they are complementary rather than mutually exclusive.

[4-6 marks]: The response describes both habitat-based and species-based strategies, mentioning some strengths and limitations. There is some attempt at evaluation, but it lacks depth, balance, or specific examples.

[1-3 marks]: The response lists general conservation methods with little structure, comparison, or evaluation. Examples are absent or poorly integrated.