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Thinka May 2023 SL (TZ1) IB Diploma Programme-Style Mock — Environmental Systems and Societies

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An original Thinka practice paper modelled on the structure and difficulty of the May 2023 SL (TZ1) IB Diploma Programme Environmental Systems and Societies paper. Not affiliated with or reproduced from IB.

Section A

Answer all questions. Answers must be written within the answer boxes provided.
3 PastPaper.question · 24 PastPaper.marks
PastPaper.question 1 · Data Response / Structured Short Answer
8 PastPaper.marks

Figure 1 represents the concentration of tropospheric ozone and nitrogen dioxide over a 24-hour period in a major metropolitan area on a hot, sunny day in July.

(a) Outline the chemical process by which tropospheric ozone is formed. [2]

(b) Describe and explain the trend in tropospheric ozone concentration from 06:00 to 15:00, referencing the relationship with traffic flow and solar radiation. [4]

(c) State two management strategies that address the source of tropospheric ozone production. [2]

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PastPaper.workedSolution

(a) Sunlight (UV light) breaks down nitrogen dioxide (NO2) into nitrogen monoxide (NO) and a free oxygen atom (O). This free oxygen atom reacts with diatomic oxygen (O2) to form ozone (O3). VOCs can also react with NO, preventing it from breaking down the ozone back into oxygen.

(b) Description: Ozone levels are low at 06:00, rise throughout the morning, and peak in the afternoon around 14:00-15:00. Explanation: Morning traffic (06:00-09:00) releases high levels of precursor emissions (NOx and VOCs). As solar radiation intensifies towards midday, it drives the photochemical reactions that convert these precursors into ozone, resulting in a delayed peak in the afternoon.

(c) 1. Promote public transportation, carpooling, or active transport (cycling/walking) to reduce vehicle usage. 2. Transition to electric vehicles (EVs) or vehicles with catalytic converters to minimize NOx emissions.

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(a) Max 2 marks:
- Award 1 mark for noting that NO2 is split by solar radiation/UV to produce a free oxygen atom (O).
- Award 1 mark for stating that the free oxygen atom (O) combines with oxygen gas (O2) to form ozone (O3).
- Accept alternative valid chemical descriptions involving VOCs preventing ozone destruction.

(b) Max 4 marks:
- Award 1 mark for describing the trend (low morning levels rising to a mid-to-late afternoon peak).
- Award 1 mark for linking early morning peak traffic to the release of primary pollutants (NOx/hydrocarbons).
- Award 1 mark for explaining that solar radiation is required to catalyze photochemical reactions.
- Award 1 mark for explaining that the accumulation of ozone takes time, leading to the afternoon peak.

(c) Max 2 marks:
- Award 1 mark per valid management strategy that targets precursors/sources (e.g., catalytic converters, electric vehicles, public transit promotion, clean-air zones). Do not accept CFC bans or stratospheric ozone strategies.

PastPaper.question 2 · Data Response / Structured Short Answer
8 PastPaper.marks

Cultural eutrophication remains a primary threat to freshwater ecosystems worldwide.

(a) Define the term biochemical oxygen demand (BOD). [2]

(b) Describe the sequence of ecological events that occurs in a freshwater lake following a sudden influx of agricultural fertilizer runoff, up to the point where fish kills occur. [4]

(c) Suggest two reasons why restoring a lake to its oligotrophic state after cultural eutrophication is highly difficult. [2]

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PastPaper.workedSolution

(a) Biochemical oxygen demand (BOD) is the amount of dissolved oxygen required by aerobic microorganisms to decompose the organic matter in a given volume of water at a specific temperature over a set time period.

(b) Agricultural runoff causes an influx of limiting nutrients (nitrates/phosphates), leading to an algal bloom. This bloom blocks sunlight, causing submerged aquatic plants to die. Large quantities of dead organic matter accumulate, prompting a population explosion of aerobic bacterial decomposers. These decomposers consume massive amounts of oxygen via respiration, dramatically increasing BOD and lowering dissolved oxygen, which leads to the suffocation and death of fish.

(c) 1. Phosphorus is bound within lake sediments and is continuously re-released into the water column even after external inputs stop (internal loading). 2. Positive feedback loops sustain eutrophication (e.g., dead fish decompose, releasing more nutrients to support further algal growth).

PastPaper.markingScheme

(a) Max 2 marks:
- Award 1 mark for mentioning the amount of dissolved oxygen required by aerobic decomposers/microorganisms.
- Award 1 mark for specifying that it is to break down organic matter in a given volume of water over a specific time/temperature.

(b) Max 4 marks:
- Award 1 mark for nutrient influx leading to algal bloom.
- Award 1 mark for light limitation causing death of deep-water plants.
- Award 1 mark for decomposition of dead organic matter by aerobic bacteria.
- Award 1 mark for bacterial respiration depleting dissolved oxygen (increasing BOD) leading to fish suffocation.

(c) Max 2 marks:
- Award 1 mark each for any two valid reasons (e.g., internal loading of phosphorus from sediments, positive feedback loops, difficulty in controlling non-point source agricultural runoff, high economic costs of physical removal/dredging).

PastPaper.question 3 · Data Response / Structured Short Answer
8 PastPaper.marks

Protected areas are vital tools for biodiversity conservation, and their spatial design is guided by ecological theory.

(a) Explain how the principles of the theory of island biogeography are applied to design terrestrial nature reserves to maximize species richness. [3]

(b) Contrast the advantages of establishing a single large reserve with those of establishing several small reserves of equal total area (the SLOSS debate). [3]

(c) Outline how habitat corridors can mitigate the negative effects of habitat fragmentation. [2]

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PastPaper.workedSolution

(a) Terrestrial reserves act as habitat islands. Larger reserves support larger populations and lower extinction rates. Reserves closer to each other or a mainland source have higher immigration/colonization rates. Circular reserves minimize the edge-to-area ratio, reducing edge effects.

(b) A single large reserve has a lower edge-to-area ratio, reducing edge effects, and can support large-ranging species (like apex predators) with more stable populations. Several small reserves can span a wider range of diverse habitats, protect localized endemic species, and minimize the risk of a single catastrophe (like fire or disease) wiping out an entire population.

(c) Habitat corridors connect isolated patches, allowing species to migrate, find resources, and colonize new areas. This increases gene flow, maintains genetic diversity, and reduces the risk of inbreeding depression.

PastPaper.markingScheme

(a) Max 3 marks:
- Award 1 mark for equating terrestrial reserves to 'islands' in an inhospitable 'sea' of human development.
- Award 1 mark for stating that larger size reduces extinction rates / supports larger populations.
- Award 1 mark for stating that proximity/closeness to other reserves increases colonization/immigration rates.
- Award 1 mark for explaining that compact/circular shapes minimize edge effects.

(b) Max 3 marks:
- Award up to 2 marks for advantages of Single Large (e.g., accommodates large home ranges, minimizes edge effects, supports higher trophic levels).
- Award up to 2 marks for advantages of Several Small (e.g., covers diverse habitats, reduces risk of catastrophe, easier to acquire in human landscapes).
Note: Must mention at least one advantage of each to achieve full marks.

(c) Max 2 marks:
- Award 1 mark for allowing migration/dispersal/recolonization of species between patches.
- Award 1 mark for facilitating gene flow / preventing genetic isolation and inbreeding.

Section B

Answer two questions from a choice of four. Each question consists of parts (a), (b), and (c).
6 PastPaper.question · 40 PastPaper.marks
PastPaper.question 1 · Part A: Outline / Terminology
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Outline the mechanism by which stratospheric ozone protects terrestrial life from ultraviolet (UV) radiation.
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PastPaper.workedSolution

1. Absorption of UV: Stratospheric ozone (O3) absorbs high-energy solar ultraviolet radiation, specifically UV-B and UV-C wavelengths. 2. Chemical Dissociation: The absorption of this energy causes the ozone molecule to split into an oxygen molecule (O2) and a free, highly reactive oxygen atom (O). 3. Energy Conversion: This reaction converts dangerous electromagnetic radiation into thermal energy (heat), warming the stratosphere rather than allowing the radiation to reach the troposphere. 4. Recombination (Chapman Cycle): The free oxygen atom (O) quickly recombines with an oxygen molecule (O2) to reform ozone (O3), maintaining the protective ozone layer through a dynamic equilibrium.

PastPaper.markingScheme

Award 1 mark for each of the following points, up to a maximum of 4 marks: [1 mark] for stating ozone absorbs UV-B and/or UV-C radiation; [1 mark] for explaining that absorption causes dissociation of O3 into O2 and O; [1 mark] for stating this process converts UV radiation into thermal energy (heat); [1 mark] for explaining that O and O2 recombine to reform O3 (dynamic equilibrium); [1 mark] for stating this prevents harmful UV from reaching the Earth's surface and damaging DNA or causing skin cancer.
PastPaper.question 2 · Part A: Outline / Terminology
4 PastPaper.marks
Outline four physical or chemical factors that can lead to a decline in the concentration of dissolved oxygen (DO) in an aquatic ecosystem.
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PastPaper.workedSolution

1. Water Temperature: As water temperature rises, the kinetic energy of water molecules increases, which reduces the solubility of gases, causing dissolved oxygen to escape into the atmosphere. 2. Organic Pollution (Eutrophication): Runoff containing organic nutrients (like agricultural fertilizers or raw sewage) promotes algal blooms. When these algae die, aerobic decomposers (bacteria) multiply rapidly, consuming dissolved oxygen through respiration (raising biological oxygen demand, or BOD). 3. Turbulency / Flow Rate: Slow-moving or stagnant waters have less surface agitation and mixing with the atmosphere, resulting in slower physical reaeration compared to fast-flowing, turbulent streams. 4. Salinity: High salt concentrations decrease the solubility of oxygen, meaning saline waters (estuaries, marine systems) naturally hold less dissolved oxygen than freshwater bodies at equivalent temperatures.

PastPaper.markingScheme

Award 1 mark for each valid factor clearly outlined, up to a maximum of 4 marks: [1 mark] for increased temperature lowering oxygen solubility; [1 mark] for organic pollution/eutrophication leading to increased bacterial respiration/high BOD; [1 mark] for reduced water turbulence/stagnant water reducing atmospheric mixing; [1 mark] for increased salinity reducing the solubility of oxygen; [1 mark] for high turbidity reducing light penetration and photosynthesis (thus reducing oxygen release by producers). Note: Do not accept 'pollution' without explaining its biological or chemical impact on oxygen levels.
PastPaper.question 3 · Part B: Explain / Describe / Systems context
7 PastPaper.marks
Explain how positive and negative feedback loops involving water (in its gaseous, liquid, or solid states) can influence global temperatures.
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PastPaper.workedSolution

To structure this 7-mark answer, students must demonstrate a clear understanding of both positive and negative feedback systems, using water in different physical states (vapor, liquid, solid) as the driving mechanism.

1. Define feedback loops briefly to set the system context: positive feedback amplifies change away from an equilibrium, whereas negative feedback counteracts change, bringing the system back towards equilibrium.
2. Discuss at least two distinct positive feedback loops:
- **Water vapor loop**: warming \(\rightarrow\) more evaporation \(\rightarrow\) more atmospheric water vapor (greenhouse gas) \(\rightarrow\) more heat trapped \(\rightarrow\) further warming.
- **Ice-albedo loop**: warming \(\rightarrow\) melting of ice/snow \(\rightarrow\) exposed darker sea/land \(\rightarrow\) lower albedo (less reflection, more absorption of solar energy) \(\rightarrow\) further warming.
3. Discuss at least one distinct negative feedback loop:
- **Cloud albedo loop**: warming \(\rightarrow\) more evaporation \(\rightarrow\) more cloud cover (condensation of water vapor) \(\rightarrow\) reflection of incoming solar radiation back into space \(\rightarrow\) cooling effect.
- **Snowpack accumulation loop**: warming \(\rightarrow\) higher atmospheric humidity \(\rightarrow\) increased precipitation as snowfall at high latitudes/altitudes \(\rightarrow\) thicker snowpack \(\rightarrow\) increased regional albedo \(\rightarrow\) cooling effect.

PastPaper.markingScheme

Award [1 mark] for each clear, well-explained mechanism up to a maximum of [7 marks]. To achieve full marks, both positive and negative feedback loops must be explained.

- Award [1 mark] for explaining that positive feedback amplifies/reinforces the initial warming trend, whereas negative feedback counteracts/stabilizes it.
- Award [1-2 marks] for the water vapor positive feedback loop: identifying that warming increases evaporation [1 mark] and that water vapor is a greenhouse gas that traps heat, further increasing temperatures [1 mark].
- Award [1-2 marks] for the ice-albedo positive feedback loop: identifying that warming melts ice/snow [1 mark] and that the resulting lower albedo leads to greater absorption of solar energy, further increasing temperatures [1 mark].
- Award [1-2 marks] for the cloud-albedo negative feedback loop: identifying that warming/evaporation creates clouds [1 mark] and that clouds reflect incoming solar radiation (increasing albedo), leading to cooling [1 mark].
- Award [1-2 marks] for the high-latitude precipitation negative feedback loop: explaining that increased evaporation can lead to increased snowfall in polar regions [1 mark], which increases reflectivity and counteracts warming [1 mark].

*Note: Do not award marks for simply stating 'positive feedback makes it warmer' without detailing the causal links/system interactions.*
PastPaper.question 4 · Part B: Explain / Describe / Systems context
7 PastPaper.marks
Explain how the discharge of agricultural run-off into a freshwater lake can lead to eutrophication, and describe the subsequent impacts on the lake's ecological community.
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PastPaper.workedSolution

This response should clearly outline the step-by-step causal chain of eutrophication (a key systems concept showing positive feedback and shift to a new degraded state) and link it directly to ecological impacts on the community.

1. Explain the source: agricultural runoff contains nutrients (nitrates/phosphates).
2. Link nutrients to the rapid exponential growth of producers (algae/phytoplankton).
3. Explain the physical barrier effect: algae blocks light, leading to the death of benthic/submerged macrophytes.
4. Explain the trophic shift/microbial role: aerobic decomposers (bacteria) proliferate to break down the dead organic mass.
5. Explain the chemical change: oxygen depletion (high BOD, low DO).
6. Describe the ecosystem-level consequence: die-offs of fish and sensitive macroinvertebrates, dominance of pollution-tolerant species, and loss of biodiversity.

PastPaper.markingScheme

Award [1 mark] for each of the following points, up to a maximum of [7 marks]:
- Runoff delivers high levels of limiting nutrients (nitrates and/or phosphates) into the lake system. [1 mark]
- Nutrients stimulate rapid growth of algae, forming an algal bloom on the surface. [1 mark]
- Algal bloom blocks sunlight, preventing photosynthesis of submerged aquatic plants, causing them to die. [1 mark]
- High volumes of dead organic matter (from dead algae and plants) accumulate. [1 mark]
- Aerobic bacteria/decomposers multiply rapidly to break down the dead organic matter. [1 mark]
- Bacterial respiration consumes dissolved oxygen, causing a drastic increase in Biochemical Oxygen Demand (BOD) / decrease in dissolved oxygen. [1 mark]
- Oxygen depletion (hypoxia/anoxia) leads to the suffocation and death of fish and other aerobic aquatic organisms. [1 mark]
- The lake community experiences a loss of biodiversity / food web disruption / shift towards anaerobic/pollution-tolerant species. [1 mark]

*Accept a labeled systems diagram if it clearly communicates these sequential steps.*
PastPaper.question 5 · Part C
9 PastPaper.marks
To what extent is climate change mitigation more effective than adaptation in securing sustainable societies? Use examples to support your argument.
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PastPaper.workedSolution

Candidates should structure their response as an evaluative essay. A high-scoring essay should include: 1. Clear definitions of mitigation and adaptation. 2. A balanced argument presenting the strengths and limitations of mitigation (e.g., addresses root causes but requires global cooperation and has delayed effects) with specific examples (e.g., carbon pricing, renewable energy transition). 3. A balanced argument presenting the strengths and limitations of adaptation (e.g., provides immediate, localized relief but does not solve the root problem and has financial/physical limits) with specific examples (e.g., flood defenses in the Netherlands, crop diversification). 4. A comparative evaluation that explains why mitigation is essential for long-term global sustainability, whereas adaptation is essential for short-term localized resilience. 5. A clear concluding statement offering a synthesis (i.e., that they are complementary strategies, not mutually exclusive).

PastPaper.markingScheme

[7–9 marks] Discussion is highly balanced, showing a deep understanding of both mitigation and adaptation. Specific, accurate examples are integrated throughout. Clear evaluation is present, leading to a reasoned conclusion. Specialist terminology is used correctly.

[4–6 marks] Explains both mitigation and adaptation with some examples, but the argument may be unbalanced or lack critical evaluation. Some terminology is used correctly.

[1–3 marks] Descriptive response with limited understanding of the difference or relationship between mitigation and adaptation. Lacks appropriate examples and evaluative conclusion.
PastPaper.question 6 · Part C
9 PastPaper.marks
Evaluate the use of alternative fresh water production technologies (such as desalination and wastewater recycling) versus demand-management strategies to resolve urban water scarcity.
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PastPaper.workedSolution

Candidates should present a balanced evaluation comparing supply-side technologies (desalination and wastewater recycling) with demand-management strategies. 1. Identify the drivers of urban water scarcity (e.g., urbanization, climate change). 2. Discuss alternative production technologies, evaluating their benefits (weather-independent, high volume) and drawbacks (energy use, brine disposal, high cost, public perception) using specific case studies (e.g., Singapore, Israel). 3. Discuss demand-management, evaluating benefits (low environmental impact, cost-effective, changes behavior) and drawbacks (limits of conservation, reliance on public cooperation, vulnerability in extreme drought) using examples (e.g., Cape Town, Australia). 4. Evaluate the two approaches comparatively, concluding that an integrated water resource management (IWRM) approach is necessary for true urban sustainability.

PastPaper.markingScheme

[7–9 marks] Balanced and detailed evaluation of both alternative water technologies and demand-management. Concrete case studies or urban examples are used effectively. Explicit comparison and evaluative conclusion are provided. Appropriate terminology is used throughout.

[4–6 marks] Explains both technological solutions and demand-management, but may focus heavily on one side or lack explicit comparative evaluation. Examples are mentioned but lack detail.

[1–3 marks] Superficial or purely descriptive response. Lacks structure, examples, and critical evaluation of the strategies.

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