2024 Cambridge IGCSE Environmental Management (0680) 模擬試題連答案詳解

(a)
1. Find the increase in concentration: \(2496 - 156 = 2340\) particles/kg.
2. Divide the increase by the original concentration (small fish): \(\frac{2340}{156} = 15\).
3. Convert to a percentage: \(15 \times 100 = 1500\%\).

(b)
- **Bioaccumulation**: Organisms ingest microplastics from water or food. Because these plastic particles cannot be biodegraded, digested, or easily excreted, they accumulate within the organism's body tissues over its lifespan.
- **Biomagnification**: Due to inefficient energy transfer between trophic levels, a high-level predator (like tuna) must consume a massive biomass of lower-trophic-level prey (small fish) to meet its metabolic energy needs. Consequently, the accumulated microplastics from all these prey organisms are transferred to and highly concentrated in the tissues of the predator at the top of the food chain.

Part (a) [2.6 marks total]:
- [1 mark] for correct calculation of increase (2340) or showing correct formula: \(\frac{2496 - 156}{156} \times 100\).
- [1.6 marks] for the correct final answer of 1500% (allow 1.6 marks for correct answer with no working shown; deduct 0.6 marks if percentage sign is missing but value is correct).

Part (b) [4 marks total]:
Award 1 mark for each of the following points, up to a maximum of 4:
- Microplastics are ingested by consumers and cannot be digested, biodegraded, or easily excreted [1].
- Microplastics accumulate within the body tissues of individual organisms over time (bioaccumulation) [1].
- Organisms at higher trophic levels (predators/tuna) must eat large numbers of prey (small fish) to obtain enough energy [1].
- This results in the concentration of microplastics increasing at each successive trophic level up the food chain (biomagnification) [1].

(a)
Efficiency formula: \(\text{Efficiency} = \frac{\text{Useful energy output}}{\text{Total energy input}} \times 100\)
Calculation: \(\frac{175 \text{ MJ}}{500 \text{ MJ}} \times 100 = 35\%\).

(b)
1. **Acid rain**: Burning coal releases sulfur dioxide (\(\text{SO}_2\)) and nitrogen oxides (\(\text{NO}_x\)). These gases react with water vapor in the atmosphere to form sulfuric and nitric acids, falling as acid rain. This lowers the pH of lakes and rivers, killing fish and aquatic life, damaging forests, and leaching essential nutrients from the soil.
2. **Particulate matter and smog**: Coal combustion releases soot, fine dust (PM2.5), and fly ash. This creates visual smog and causes respiratory health issues (such as bronchitis and asthma) in humans and wildlife, as well as depositing toxic heavy metals (like mercury) into nearby habitats.

Part (a) [2.6 marks total]:
- [1 mark] for correct substitution into efficiency formula: \(\frac{175}{500} \times 100\).
- [1.6 marks] for correct final answer: 35% (allow 1.6 marks for correct answer with no working shown; deduct 0.6 marks if % sign is missing but value is correct).

Part (b) [4 marks total]:
Award up to 2 marks for each well-described impact (maximum of two impacts):
- **Acid Rain** [up to 2 marks]:
- Award 1 mark for identifying sulfur dioxide / nitrogen oxides release [1].
- Award 1 mark for explaining an effect, e.g., acidification of water bodies, damage to forest canopies, or weathering of limestone [1].
- **Particulate matter / Smog / Toxins** [up to 2 marks]:
- Award 1 mark for identifying the release of fly ash / soot / heavy metals (e.g., mercury) [1].
- Award 1 mark for explaining an effect, e.g., respiratory diseases, visual smog, or heavy metal toxic accumulation [1].
- *Note*: Do not accept responses focusing on carbon dioxide, greenhouse effect, global warming, or climate change, as the question specifically excludes this.

(a)
Ratio of Field A to Field B = \(45 : 3\).
Divide both sides by 3 to simplify: \(15 : 1\).

(b)
- **Field C (Ploughed down-slope)**: Furrows run directly down the gradient of the hill. These act as channels that collect rainfall and accelerate surface runoff. High-velocity runoff possesses greater kinetic energy to dislodge and wash away soil particles.
- **Field B (Contour ploughed with cover crops)**: Contour ploughing across the slope forms horizontal ridges that trap runoff, slowing it down and promoting water infiltration into the ground. Additionally, the cover crops provide foliage that intercepts direct raindrop impact (preventing rain splash erosion) and root systems that physically bind soil particles together.

(c)
- **Siltation / Sedimentation**: Soil particles settle on the beds of rivers and lakes, destroying spawning grounds of fish, blocking sunlight needed by aquatic plants, and reducing water depth, which can increase flooding risk.
- **Eutrophication**: Eroded soil often carries agricultural fertilizers (nitrates and phosphates). When these enter water bodies, they cause rapid algal growth (blooms). When the algae die, bacteria decompose them, consuming dissolved oxygen and causing fish to suffocate.

Part (a) [1.6 marks total]:
- [1 mark] for showing ratio of \(45:3\) or equivalent.
- [1.6 marks] for the correct simplified whole-number ratio: 15:1 (allow 1.6 marks for correct answer with no working shown).

Part (b) [3 marks total]:
Award up to 3 marks for comparative explanation:
- Furrows in Field C run down the slope, creating channels that speed up surface runoff [1].
- Ridges from contour ploughing in Field B run across the slope, intercepting water flow and encouraging infiltration [1].
- Cover crops in Field B provide roots that bind soil particles / vegetation intercepts raindrop impact (reducing rain splash erosion) [1].

Part (c) [2 marks total]:
Award 1 mark for each of the following, up to a maximum of 2:
- Siltation / blockages of rivers / sedimentation of lake beds [1].
- Reduced light penetration for aquatic plants due to high turbidity [1].
- Eutrophication / algal blooms caused by nutrients bound to eroded soil [1].
- Destruction of aquatic habitats / fish spawning grounds [1].

(a)(i) The student should draw a line graph with 'Depth / m' on the x-axis and 'Microplastic concentration / particles per \(m^3\)' on the y-axis. The scales must be linear and cover at least half of the grid area. All 6 points must be correctly plotted and connected with a ruled line or smooth curve.
(a)(ii) The trend is non-linear. The concentration increases rapidly from the surface to reach a maximum peak of 6.0 particles/\(m^3\) at 200 m depth. Below 200 m, the concentration consistently decreases as depth increases to 2000 m.
(b) Step 1: Find the change in concentration: \(6.0 - 2.5 = 3.5\) particles/\(m^3\). Step 2: Divide the change by the original concentration at the surface: \(\frac{3.5}{2.5} = 1.4\). Step 3: Multiply by 100 to get the percentage: \(1.4 \times 100 = 140\%\).
(c) Marine food web entry: Microplastics are tiny and easily consumed by low-trophic-level organisms like zooplankton, krill, and shellfish because they resemble natural plankton. Once ingested, they cannot be digested and remain within the organism's body (bioaccumulation). As predatory fish consume these smaller organisms, they ingest the plastics. Through biomagnification, top predators receive the highest concentrations of plastic and associated chemical toxins (such as PCBs and phthalates). This leads to severe physical blockages of digestive tracts, false feelings of fullness (starvation), tissue inflammation, and toxic effects like reproductive failure and immune suppression.

(a)(i) [3 marks]
- 1 mark: Correctly labeled axes with units (x-axis: Depth / m; y-axis: Microplastic concentration / particles per \(m^3\)).
- 1 mark: Appropriate linear scale used (covering at least half of the plotting grid).
- 1 mark: All 6 points plotted accurately and connected with a line.

(a)(ii) [2 marks]
- 1 mark: Identifies the initial increase from the surface to the peak at 200 m.
- 1 mark: Identifies the continuous decrease in concentration from 200 m down to 2000 m.

(b) [2 marks]
- 1 mark: Correct working shown: \(\frac{6.0 - 2.5}{2.5} \times 100\) or \(\frac{3.5}{2.5} \times 100\).
- 1 mark: Correct calculation of 140%.

(c) [4 marks]
- 1 mark: Ingestion by zooplankton / filter feeders at the bottom of the food web.
- 1 mark: Reference to bioaccumulation (plastics staying in the organisms' tissues over time).
- 1 mark: Reference to biomagnification (increasing concentration of plastics/toxins at higher trophic levels).
- 1 mark: Description of impact on top predators (e.g., physical starvation, gut blockage, toxic/chemical effects like reproductive failure).

(a)(i) Bar chart requirement: The vertical axis should have a linear scale starting at 0 and going to at least 45 (e.g., intervals of 5 or 10). Axes must be labeled: 'Land-use system' (x-axis) and 'Average annual soil loss / \(t/ha/year\)' (y-axis). Four distinct, equal-width bars must be drawn with gaps between them. Bar heights: Natural rainforest (0.2), Agroforestry (2.5), Pasture (12.3), Conventional arable (45.0).
(a)(ii) Calculation: \(\text{Factor} = \frac{\text{Soil loss from conventional arable}}{\text{Soil loss from natural rainforest}} = \frac{45.0}{0.2} = 225\). Therefore, conventional arable land loses 225 times more soil than natural rainforest.
(b) Explanation: Conventional arable farming involves active tillage (plowing), which breaks down the natural structure of the soil and destroys soil organic matter, leaving soil particles loose. Furthermore, row crops leave large areas of bare soil exposed to wind and heavy rain. Agroforestry, by contrast, integrates perennial trees. The tree canopies intercept rain (reducing its kinetic energy/impact on soil), and the complex root systems physically bind the soil particles, drastically reducing water and wind erosion.
(c) Sustainable practices:
- Contour plowing: Plowing across the slope (horizontally) rather than down the slope. The ridges act as micro-barriers, slowing down runoff and allowing water to infiltrate rather than wash soil away.
- Terracing: Cutting steep slopes into flat, step-like terraces. This prevents gravity-driven water runoff from building up speed and carrying soil away.
- Cover cropping: Planting fast-growing plants (like clover or legumes) in the off-season. This maintains plant cover, preventing direct wind and rain exposure on bare soil.

(a)(i) [3 marks]
- 1 mark: Correctly labeled axes with units (x-axis: Land-use system; y-axis: Average annual soil loss / \(t/ha/year\)).
- 1 mark: Appropriate linear scale on the vertical axis (extending to at least 45).
- 1 mark: All four bars plotted accurately with correct heights, equal widths, and clear spacing between them.

(a)(ii) [2 marks]
- 1 mark: Correct division expression shown: \(\frac{45.0}{0.2}\).
- 1 mark: Correct calculated factor of 225 (or "225 times larger").

(b) [2 marks]
- 1 mark: Reference to plowing/tillage in conventional arable farming breaking down soil structure or leaving soil bare/exposed to rain and wind.
- 1 mark: Reference to trees in agroforestry protecting soil (e.g., canopy intercepts rainfall / roots bind soil aggregates together).

(c) [4 marks]
- 1 mark: Identifies sustainable practice 1 (e.g., terracing, contour plowing, cover crops, windbreaks, strip cropping).
- 1 mark: Explains how practice 1 reduces erosion (e.g., terracing breaks slope length to slow surface water; cover crops protect bare soil between crop seasons).
- 1 mark: Identifies sustainable practice 2 (must be different from practice 1).
- 1 mark: Explains how practice 2 reduces erosion (e.g., contour plowing creates horizontal ridges that trap runoff).

(a)(i) Graph requirements: The x-axis must be labeled 'Year' (with equal intervals for the years). The y-axis must be labeled 'Wind electricity generation / TWh' with a linear scale starting at 0 and going to at least 110 TWh. All six coordinates: (2012, 12), (2014, 18), (2016, 28), (2018, 45), (2020, 72), (2022, 108) must be accurately plotted and joined with a neat line.
(a)(ii) The graph shows accelerating or exponential growth. In the first half of the decade (2012-2016), wind generation rose by only 16 TWh, whereas in the latter half (2018-2022), it surged by 63 TWh, showing a much steeper slope over time.
(b) Step 1: Calculate the total change in electricity generation: \(108 \text{ TWh} - 12 \text{ TWh} = 96 \text{ TWh}\). Step 2: Determine the total number of years elapsed: \(2022 - 2012 = 10\) years. Step 3: Divide the total change by the number of years: \(\frac{96 \text{ TWh}}{10 \text{ years}} = 9.6\) TWh per year.
(c) Discussion:
- Environmental Advantages: Wind turbines do not release greenhouse gases (like \(CO_2\)) or air pollutants (such as \(SO_2\)) during operation, helping to mitigate climate change and acid rain.
- Economic Advantages: Wind energy is renewable and incurs no ongoing fuel costs, insulating the grid from volatile global oil/gas prices.
- Environmental Disadvantages: Large wind farms can impact local wildlife, causing bird and bat fatalities due to blade collisions, and require large areas of land, disrupting natural habitats.
- Economic/Technical Disadvantages: High upfront capital is required to manufacture and install turbines. Furthermore, because wind is intermittent, expensive grid battery storage or backup thermal power stations are required to ensure continuous energy supply.

(a)(i) [3 marks]
- 1 mark: Correctly labeled axes with units (x-axis: Year; y-axis: Wind electricity generation / TWh).
- 1 mark: Appropriate linear scale on the vertical axis starting at 0.
- 1 mark: All points plotted accurately and connected with a neat line.

(a)(ii) [2 marks]
- 1 mark: Identifies that growth is non-linear / accelerating / exponential.
- 1 mark: Uses data from the table or graph to support (e.g., comparing early slow growth with later rapid growth).

(b) [2 marks]
- 1 mark: Correct working shown: \(\frac{108 - 12}{10}\) or \(\frac{96}{10}\).
- 1 mark: Correct answer of \(9.6\) (TWh per year).

(c) [4 marks]
- Accept up to 2 marks for advantages (1 environmental, 1 economic) and up to 2 marks for disadvantages (1 environmental, 1 economic/technical):
- 1 mark: Environmental advantage: Renewable / no greenhouse gas emissions (e.g., reduces carbon footprint).
- 1 mark: Economic advantage: No fuel costs / low operational costs / energy security.
- 1 mark: Environmental disadvantage: Threat to flying birds/bats / habitat disturbance.
- 1 mark: Economic/Technical disadvantage: Intermittency requires backup power OR high initial capital investment costs.

(a)(i) As soil salinity increases, the yield of wheat decreases. The relationship is non-linear, with the rate of decline accelerating as salinity levels rise (e.g., a small drop of 0.4 tonnes/ha from Year 1 to Year 2, compared to a major collapse of 1.4 tonnes/ha between Year 2 and Year 3, and a near-total loss by Year 5).

(a)(ii)
- Difference in yield = \(4.2 - 0.2 = 4.0\) tonnes/ha
- Percentage decrease = \(\left(\frac{4.0}{4.2}\right) \times 100 = 95.238\%\)
- Correct answer rounded to 1 decimal place = \(95.2\%\) (accept \(95\%\) or \(95.24\%\))

(b) When crops are irrigated intensively in arid climates, the irrigation water contains small amounts of dissolved salts. Due to high temperatures and low humidity, the rate of evaporation is extremely high. The water evaporates from the soil surface or is taken up by plants via transpiration, leaving the dissolved salts behind. Over time, these salts accumulate in the upper layers of the soil (root zone). Additionally, excess water from over-irrigation can cause the groundwater table to rise, bringing deep-seated natural salts up to the root zone through capillary action.

(c) Three strategies:
1. Switch to drip irrigation instead of flood irrigation to apply water directly to roots and reduce evaporation losses.
2. Install subsurface drainage (tile drains) to lower the water table and flush salts away.
3. Flush the soil with excess freshwater to leach the accumulated salts down below the root zone.

(a)(i) [Max 2 marks]
- 1 mark for identifying the negative correlation / inverse relationship (as salinity increases, wheat yield decreases).
- 1 mark for supporting with comparative data from the table (e.g., at 1.2 dS/m yield is 4.2 tonnes/ha, but at 12.5 dS/m yield drops to 0.2 tonnes/ha).

(a)(ii) [Max 2 marks]
- 1 mark for correct working: \(\frac{4.2 - 0.2}{4.2} \times 100\) or \(\frac{4.0}{4.2} \times 100\).
- 1 mark for correct calculation: \(95.2\%\) (accept \(95\%\) to \(95.24\%\)).

(b) [Max 3.5 marks]
- 1 mark for stating irrigation water contains dissolved salts.
- 1 mark for linking high temperatures/arid climate to high rates of evaporation/transpiration.
- 1 mark for explaining that salts are left behind in the topsoil/root zone as water evaporates.
- 0.5 marks for mentioning capillary action / rising water table bringing salts to the surface.

(c) [Max 3 marks]
- 1 mark for each valid management strategy, up to 3:
- Use drip irrigation / trickle irrigation / clay pots (minimises water use/evaporation).
- Install underground drainage pipes / tile drains (to lower water table).
- Flush soil with clean fresh water to leach salts downwards.
- Grow salt-tolerant crops (halophytes) to maintain cover/economic viability while remediating.
- Apply organic mulches to reduce evaporation rates from the soil surface.

(a)(i) Both energy sources showed an overall increase in generation between 2015 and 2023. However, coal remains the dominant source of electricity with a much higher absolute generation (over 10,000 TWh compared to under 2,500 TWh for wind in 2023). On the other hand, wind power experienced a much faster relative growth rate, nearly tripling its output (increasing by approx. 177%), whereas coal grew much more slowly in percentage terms (increasing by approx. 13.9%).

(a)(ii)
- Total increase in wind generation = \(2300 - 830 = 1470\) TWh
- Number of years elapsed = \(2023 - 2015 = 8\) years
- Average annual increase = \(\frac{1470}{8} = 183.75\) TWh/year (or TWh per year)

(b)
- Global climate: Wind power does not release greenhouse gases (such as carbon dioxide, \(CO_2\)) during operation, which helps reduce the enhanced greenhouse effect and combat global climate change.
- Local air quality: Unlike coal combustion, wind energy does not emit harmful air pollutants such as sulfur dioxide (\(SO_2\)), nitrogen oxides (\(NO_x\)), or particulate matter (PM), which cause smog, acid rain, and respiratory illnesses in local populations.

(c) Three reasons:
1. Visual pollution / negative aesthetic impact on natural landscapes and scenic views.
2. Noise pollution generated by the rotating turbine blades affecting nearby residents.
3. Ecological concerns, specifically the threat of bird and bat collisions with the turbine blades.
(Accept other valid points such as concerns over drop in property values, or interference with electromagnetic communications/radar).

(a)(i) [Max 3 marks]
- 1 mark for stating that both sources increased over the period.
- 1 mark for contrasting the absolute scale (coal is far larger than wind / wind is small scale compared to coal).
- 1 mark for contrasting the rate of growth (wind grew much faster proportionally / wind nearly tripled, while coal grew slowly/steadily).

(a)(ii) [Max 2 marks]
- 1 mark for correct working: \(\frac{2300 - 830}{8}\) or \(\frac{1470}{8}\).
- 1 mark for correct final value with unit: \(183.75\) TWh/year (accept \(183.8\) or \(184\) TWh/year; deduct 0.5 marks if unit is missing or incorrect).

(b) [Max 2.5 marks]
- 1.5 marks for global climate explanation: Wind does not emit greenhouse gases / carbon dioxide (1 mark), which reduces global warming / climate change / greenhouse effect (0.5 marks).
- 1 mark for local air quality explanation: Wind power does not release toxic air pollutants (like \(SO_2\) / particulate matter / \(NO_x\)), preventing localized smog/acid rain/respiratory disease.

(c) [Max 3 marks]
- 1 mark for each valid reason up to 3:
- Visual impact / spoils the landscape scenery.
- Noise disturbance from rotating blades.
- Threat to wildlife (kills birds/bats).
- Negative impact on local property values.
- Potential disruption to local tourism/recreation.
- Flicker effect (shadow flicker) on nearby homes.

An excellent response should evaluate both strategies across ecological and agricultural dimensions, concluding with a reasoned judgment.

**Strategy A: Intensive Commercial Monoculture**
* **Benefits:** It provides high crop yields in the short term, which is vital for feeding a growing population quickly. The use of machinery and standardized crops makes harvesting highly efficient and keeps food prices relatively low in the short term.
* **Drawbacks:** Cultivating a single crop repeatedly depletes specific soil nutrients, requiring heavier applications of synthetic fertilisers. Runoff from these fertilisers causes eutrophication in aquatic ecosystems. Heavy pesticide use bioaccumulates in food chains, kills beneficial pollinators, and leads to pest resistance. Intensive tillage exposes topsoil, causing severe soil erosion and desertification over time, making the land unproductive.

**Strategy B: Sustainable Agricultural Practices (Agroforestry and Organic Farming)**
* **Benefits:** Agroforestry integrates trees with crops, which reduces wind and water erosion by anchoring the soil and providing windbreaks. It also enhances biodiversity by creating microhabitats. Organic farming relies on natural compost and crop rotation, which restores soil structure, organic matter, and fertility naturally. It avoids chemical pollution, ensuring clean freshwater sources and protecting pollinator populations.
* **Drawbacks:** These methods typically have lower immediate yields compared to intensive chemical farming. They are also highly labor-intensive and require significant expertise, which can increase food production costs in the short term.

**Conclusion / Evaluation**
While Strategy A is highly effective for immediate food security, it is unsustainable because it degrades the environmental resources (soil health, water quality, and pollinators) needed for agriculture. Strategy B is far more sustainable in the long term as it maintains soil health and ecosystem stability, ensuring that the country can continue to feed its population for generations to come.

Level 3 (5-6 marks):
- Explains and evaluates both Strategy A and Strategy B in detail, covering both advantages and disadvantages of each.
- Discusses specific environmental impacts (e.g., soil erosion, biodiversity loss, eutrophication, soil structure, pesticide resistance).
- Provides a clear, reasoned conclusion on why Strategy B is more sustainable in the long term despite lower short-term yields.

Level 2 (3-4 marks):
- Discusses both strategies, but the evaluation may be unbalanced or lack depth on one of the strategies.
- Mentions environmental impacts but with limited depth or scientific detail.
- Provides a basic conclusion.

Level 1 (1-2 marks):
- Outlines simple facts about one or both strategies (e.g., 'chemicals kill pests', 'organic is natural').
- Lacks a balanced evaluation and contains no clear environmental links.
- No reasoned conclusion is provided.

Level 0 (0 marks):
- No response or response not worthy of credit.