2023 IB DP Environmental Systems and Societies Practice Paper with Answers

Part (a) Solution:
1. Human activities, primarily the combustion of fossil fuels and large-scale deforestation, release substantial quantities of carbon dioxide (\( \text{CO}_2 \)) into the atmosphere.
2. The oceans act as a carbon sink, absorbing approximately 30% of this atmospheric \( \text{CO}_2 \) to maintain chemical equilibrium at the surface interface.
3. Once dissolved in seawater, \( \text{CO}_2 \) reacts chemically with water (\( \text{H}_2\text{O} \)) to form carbonic acid (\( \text{H}_2\text{CO}_3 \)).
4. Carbonic acid is unstable and rapidly dissociates into hydrogen ions (\( \text{H}^+ \)) and bicarbonate ions (\( \text{HCO}_3^- \)). The release of these free hydrogen ions increases their concentration, thereby lowering the pH of the ocean and making it more acidic.
5. The abundance of free hydrogen ions also causes them to combine with carbonate ions (\( \text{CO}_3^{2-} \)), reducing the availability of carbonate for marine calcifying organisms that require it to build their calcium carbonate structures.

Part (b) Solution:
1. Impacts on Marine Food Webs:
- Reduced carbonate ion concentration makes it energetically difficult for calcifying organisms (e.g., corals, clams, oysters, and planktonic pteropods) to build and maintain their calcium carbonate (\( \text{CaCO}_3 \)) shells and skeletons. Under high acidity, existing shells can dissolve.
- Pteropods (sea butterflies) and coccolithophores represent key primary and secondary producers at the base of marine food webs. Their decline triggers a trophic cascade, starving higher trophic levels including commercially valuable fish species (e.g., salmon), marine mammals, and seabirds.
- Coral reefs undergo structural degradation and bleaching, destroying vital habitat and nurseries that support approximately 25% of all marine biodiversity.
2. Impacts on Human Communities:
- Economic Disruption: Declines in commercially harvested shellfish and finfish directly damage marine aquaculture and fisheries, threatening livelihoods and causing economic hardships in coastal communities.
- Food Security: Over one billion people, particularly in developing and coastal nations, rely on marine fish as their primary source of animal protein. Reduced yields threaten local nutrition and survival.
- Coastal Protection: Healthy coral reefs act as natural breakwaters, absorbing wave energy. Their degradation increases the vulnerability of coastal infrastructure, homes, and low-lying land to severe erosion and storm surges.
- Ecotourism: Damaged marine ecosystems, particularly degraded coral reefs, lose aesthetic value, causing significant declines in ecotourism and diving revenues for island and coastal nations.

Part (c) Solution:
1. Global Mitigation Strategies:
- Nature: International treaties (such as the Paris Agreement) and policy frameworks that aim to limit global warming by reducing greenhouse gas emissions through the transition to renewable energy, carbon taxes, and carbon capture and storage (CCS).
- Strengths: Mitigation directly targets the root cause of ocean acidification by stopping the rise of atmospheric \( \text{CO}_2 \) concentrations. This is the only long-term pathway to stabilize ocean chemistry globally and preserve entire ecosystems.
- Weaknesses: Achieving global consensus is slow and politically complex; many agreements lack binding enforcement mechanisms; transition costs are high; and there is a multi-decade lag time between emissions reduction and visible recovery in ocean chemistry.
2. Local Adaptation Strategies:
- Nature: Local actions designed to minimize regional damage, such as restoring seagrass meadows and kelp forests (which naturally absorb dissolved \( \text{CO}_2 \) via photosynthesis), establishing Marine Protected Areas (MPAs) to reduce non-climatic stressors (e.g., overfishing, pollution), using alkaline buffers in localized aquaculture pens, or breeding acid-resistant shellfish strains.
- Strengths: These can be designed and executed quickly by local communities or regional governments without waiting for global consensus. They protect high-value local aquaculture industries, foster local ecological resilience, and offer co-benefits such as nutrient filtration and habitat creation.
- Weaknesses: Local strategies do not address the global driver. They are geographically limited and cannot protect the open ocean or deep-sea ecosystems. Techniques like chemical buffering are resource-intensive, temporary, and impossible to scale up globally.
3. Conclusion/Synthesis:
Neither strategy is sufficient alone. Local adaptation strategies are vital in the short-to-medium term to preserve key ecosystems, support coastal livelihoods, and buy ecological time. However, they are temporary 'band-aids' that will be overwhelmed if global emissions continue to rise. Ultimately, global mitigation is absolutely necessary to prevent catastrophic global marine collapse, making a combined, multi-scale policy framework the most effective approach.

Part (a): [4 marks maximum]
- Award 1 mark for connecting human activities (e.g., fossil fuel burning) to increased atmospheric \( \text{CO}_2 \) and its absorption by ocean waters.
- Award 1 mark for explaining that dissolved \( \text{CO}_2 \) reacts with water to form carbonic acid (\( \text{H}_2\text{CO}_3 \)).
- Award 1 mark for describing the dissociation of carbonic acid into hydrogen ions (\( \text{H}^+ \)) and bicarbonate, which lowers the pH of seawater.
- Award 1 mark for explaining that excess hydrogen ions bind with carbonate ions (\( \text{CO}_3^{2-} \)), reducing their availability for calcifying organisms.

Part (b): [7 marks maximum]
- Award 1 mark for each valid explanation of impacts on marine food webs (up to 4 marks):
* Difficulty for calcifying organisms in synthesizing calcium carbonate (\( \text{CaCO}_3 \)) shells/skeletons.
* Dissolution of existing calcareous structures.
* Decline in keystone base-of-web species (e.g., pteropods) causing a trophic cascade affecting commercial fish and predators.
* Loss of coral reef structures leading to habitat and biodiversity loss.
- Award 1 mark for each valid explanation of impacts on human communities (up to 4 marks):
* Loss of jobs and revenue in the aquaculture and fishing industries.
* Threats to global food security and primary protein sources, especially in developing nations.
* Increased risk of coastal erosion and storm surge damage due to the loss of protective coral reefs.
* Decline in tourism and recreational revenues (e.g., reef diving).
Note: To achieve the maximum 7 marks, the response must address both marine food webs and human communities (max 5 marks if only one side is explained).

Part (c): [9 marks maximum]
- Award up to 4 marks for a balanced analysis of global mitigation strategies (their mechanism, strengths, and limitations).
- Award up to 4 marks for a balanced analysis of local adaptation strategies (their mechanism, strengths, and limitations).
- Award up to 2 marks for a logical, well-supported synthesis or conclusion evaluating how these strategies interact or which is more critical.

Band Descriptors for Part (c):
- 7 to 9 marks: Demonstrates a deep understanding of both global and local strategies with specific, realistic examples. Explicitly compares their effectiveness and provides a clear, balanced evaluative conclusion.
- 4 to 6 marks: Discusses both strategies but may lack detail or focus heavily on one over the other. The evaluation is present but superficial.
- 1 to 3 marks: Provides brief, unstructured descriptions of mitigation or adaptation without meaningful comparison or evaluation.

Part (a) Solution:
1. Agricultural expansion divides large, continuous ecosystems into smaller, isolated patches, reducing total available habitat area.
2. Smaller fragments support smaller population sizes, which are highly vulnerable to genetic drift, inbreeding depression, and stochastic (random) extinction events due to lack of genetic diversity.
3. Fragmentation creates barriers to species dispersal, restricting migration, colonization of new areas, and gene flow between subpopulations.
4. The process increases the perimeter-to-area ratio, leading to widespread "edge effects" where microclimates at the boundaries change (higher wind, light, lower humidity), allowing invasive species and generalist predators to displace interior specialist species.
5. Species with large home ranges or high trophic positions (such as apex predators) are often lost because fragments cannot provide sufficient resources or territory.

Part (b) Solution:
1. Island Biogeography (Size and Proximity):
- Principle: Larger islands hold more species due to lower extinction rates and higher habitat/niche diversity. Therefore, designing a Single Large reserve (rather than Several Small, i.e., SLOSS debate) is generally preferred to maintain viable populations of large predators and specialists.
- Proximity: Placing reserves close to one another or close to a "mainland" source population increases immigration rates, aiding genetic exchange and natural recolonization.
2. Shape and Edge Effects:
- Principle: To minimize edge effects, protected areas should have a low perimeter-to-area ratio. A circular design is optimal because it maximizes the interior core habitat, protecting sensitive interior species from the environmental disturbances and predation associated with edges adjacent to farmland.
3. Wildlife Corridors:
- Principle: Linear strips of natural habitat connecting isolated reserves allow species to migrate safely, find mates, search for food, and shift their ranges in response to climate change, directly overcoming the barrier effect of agricultural land-use.
4. Buffer Zones:
- Principle: Surrounding the core protected area with transitional buffer zones (where low-impact activities like organic agroforestry or eco-tourism are allowed) insulates the core habitat from the direct negative impacts of intensive farming, such as pesticide drift and nutrient runoff.

Part (c) Solution:
1. Ecocentric EVS:
- Perspective: Views nature as having intrinsic value, independent of human utility. It advocates for complete preservation of ecosystems and rights for non-human species.
- Influence on Conflict Resolution: Pushes for the creation of strict nature reserves (no-take zones) and calls for a fundamental reduction in intensive agriculture. It promotes diets that require less land (e.g., plant-based diets) and organic, low-impact farming.
- Limitations: Can lead to deadlocks in conflicts because it rejects compromises with economic developers. It may be viewed as impractical in regions facing severe poverty or food insecurity.
2. Anthropocentric EVS:
- Perspective: Believes humans are environmental managers who must conserve nature to ensure the continuous flow of critical ecosystem services (e.g., pollination, soil fertility, water filtration) that support human survival and agriculture itself.
- Influence on Conflict Resolution: Facilitates compromise through sustainable land-use zoning, environmental impact assessments (EIAs), and agricultural policies (e.g., subsidies for sustainable farming). It advocates for "land-sharing" approaches where biodiversity conservation is integrated directly into agricultural landscapes.
- Limitations: May fail to protect species or habitats that do not provide clear, quantifiable economic or survival value to humans.
3. Technocentric EVS:
- Perspective: Holds that human technology, scientific innovation, and economic growth can solve any resource or environmental limitation.
- Influence on Conflict Resolution: Promotes a "land-sparing" model where high-yield, intensive agricultural technology (such as GMOs, hydroponics, precision fertilizer application, and vertical farming) is used to produce maximum food on a minimal footprint, thereby leaving large, contiguous tracts of natural habitat untouched for conservation.
- Limitations: High-tech intensive farming can cause severe localized pollution (e.g., chemical runoff causing eutrophication), and these advanced technologies are often expensive and inaccessible to smallholders in developing countries.
4. Synthesis/Conclusion:
Environmental value systems profoundly shape how land-use conflicts are framed and resolved. While an ecocentric perspective establishes the ethical necessity of protecting biodiversity, it can be economically unviable on its own. A technocentric approach provides the technological tools to spare land, but carries risks of pollution. Therefore, the most robust resolution of agricultural-conservation conflicts occurs within an anthropocentric framework that uses technocentric efficiency tools while respecting the ecocentric value of natural systems to ensure long-term sustainability.

Part (a): [4 marks maximum]
- Award 1 mark for outlining that agricultural expansion divides continuous habitat into smaller, isolated fragments.
- Award 1 mark for explaining that smaller fragments support smaller populations, which are highly vulnerable to genetic drift and inbreeding depression.
- Award 1 mark for explaining that fragmentation prevents migration and gene flow, causing reproductive isolation.
- Award 1 mark for explaining that fragmentation increases the perimeter-to-area ratio, exacerbating edge effects and displacing interior species.
- Award 1 mark for noting that species with large home ranges or high trophic levels (like large carnivores) are lost because fragments are too small to meet their resource needs.

Part (b): [7 marks maximum]
- Award up to 2 marks for explaining how Island Biogeography is applied (preferring single large over several small to support larger populations and greater niche diversity, or placing reserves close to one another to increase immigration rates).
- Award up to 2 marks for explaining the management of Edge Effects (choosing circular reserve shapes to minimize the perimeter-to-area ratio, thereby maximizing interior core habitat).
- Award up to 2 marks for explaining the role of Corridors (strips of natural habitat connecting reserves to facilitate migration, mating, and gene flow).
- Award up to 2 marks for explaining the role of Buffer Zones (transitional zones of low-impact human activity that shield the core reserve from intensive agricultural runoff, pesticides, and human disturbance).
Note: To obtain the maximum 7 marks, at least three of these principles must be clearly explained in relation to protected area design.

Part (c): [9 marks maximum]
- Award up to 3 marks for evaluating the ecocentric perspective (prioritizing intrinsic value, proposing strict preservation/dietary changes, and identifying limitations such as ignoring human economic needs).
- Award up to 3 marks for evaluating the anthropocentric perspective (focusing on ecosystem services, mixed land-use, sustainable agriculture, and identifying limitations such as prioritizing utilitarian species).
- Award up to 3 marks for evaluating the technocentric perspective (focusing on land-sparing through high-yield GM crops/intensive farming, and identifying limitations like chemical pollution or high implementation costs).
- Award up to 2 marks for a well-reasoned synthesis/conclusion showing how these EVSs must be integrated or balanced to resolve real-world conflicts.

Band Descriptors for Part (c):
- 7 to 9 marks: Comprehensive and balanced evaluation of at least two (ideally three) EVSs in relation to the conflict. Specific strategies (e.g., land sparing vs. land sharing, GMOs, organic farming) are clearly linked to their respective EVSs. A clear, logical synthesis or conclusion is present.
- 4 to 6 marks: Shows a good understanding of EVSs and how they approach the conflict, but the discussion may be unbalanced or lack critical evaluation of their limitations.
- 1 to 3 marks: Basic identification of EVSs without clear application to the agricultural-conservation conflict, or a purely descriptive response lacking evaluation.