📚 Cambridge Year 10 Science: Case Study Practice | 剑桥Year 10科学：案例分析实战演练
In Cambridge IGCSE Co-ordinated Sciences or separate Science examinations, case study questions are frequently used to assess your ability to apply scientific knowledge to real-world scenarios. This article walks you through a complete case study on acid rain, showing you how to interpret data, connect concepts across Chemistry, Biology and Physics, and write high-scoring answers. Active practice with cases like this will build your confidence and boost your exam performance.
在剑桥IGCSE综合科学或分科科学考试中，案例分析题常被用来评估你将科学知识应用于实际情境的能力。本文将通过一个完整的酸雨案例，带你一步步学习如何解读数据、将化学、生物和物理概念联系起来，并写出高分答案。积极练习类似案例将增强你的信心并提升考试成绩。
1. What Are Case Study Questions? | 什么是案例分析题？
Case study questions present a realistic scenario supported by data tables, graphs, diagrams or text. You are then asked a series of structured questions that test more than factual recall – they require you to analyze trends, draw conclusions, justify decisions using scientific principles, and sometimes suggest improvements to experiments. They appear in many Cambridge Science papers, especially Paper 4 (Theory Extended) and Paper 6 (Alternative to Practical).
案例分析题会给出一个真实情境，并配以数据表格、图表、示意图或文本。随后提出一系列结构化问题，不仅考查事实记忆，还要求你分析趋势、得出结论、用科学原理论证决策，有时还需要提出实验改进方案。这类题目广泛出现在剑桥科学试卷中，尤其是Paper 4（拓展理论）和Paper 6（实验替代）。
2. Why Acid Rain? | 为什么选择酸雨？
Acid rain is a classic interdisciplinary topic. In Chemistry, it covers acid formation, pH, neutralization and gas reactions. In Biology, you examine the effects on plants, aquatic life and soil. In Physics, you consider energy resources and the combustion of fossil fuels. Examiners love acid rain because it lets them test how well you can link ideas from different parts of the syllabus.
酸雨是一个经典跨学科主题。在化学中，它涉及酸的形成、pH值、中和反应以及气体反应；在生物中，考查对植物、水生生物和土壤的影响；在物理中，则与能源和化石燃料燃烧相关。考官偏爱酸雨正是因为能够测试你串联不同模块知识的能力。
3. The Scenario: A Forested Catchment | 情境：一个森林集水区
Imagine you are a scientist monitoring a forested catchment area over ten years. The local power station burns coal, and you have collected the following data.
假设你是一名科学家，对一个森林集水区进行了十年监测。当地发电站燃烧煤炭，你收集到如下数据。
| Year | Average Rainfall pH | Annual SO₂ Emissions (tonnes) | Tree Mortality Rate (%) |
|---|---|---|---|
| 2012 | 5.6 | 1200 | 2.1 |
| 2014 | 5.2 | 1500 | 3.4 |
| 2016 | 4.8 | 1800 | 5.2 |
| 2018 | 4.5 | 2100 | 7.8 |
| 2020 | 4.3 | 2500 | 10.5 |
Table 1: Environmental data from an area affected by acid rain.
表1：受酸雨影响地区的环境数据。
The data shows a clear correlation: as SO₂ emissions rise, rainfall pH drops and tree mortality increases. Your exam task will ask you to explain these links.
数据显示出明显相关性：随着SO₂排放量上升，降雨pH下降，树木死亡率增加。考试题目会要求你解释这些联系。
4. Linking SO₂ to Acid Rain Chemistry | 将SO₂与酸雨化学联系起来
In power stations, sulfur impurities in coal react with oxygen during combustion to form sulfur dioxide gas.
在发电站中，煤中的硫杂质在燃烧时与氧气反应，生成二氧化硫气体。
S + O₂ → SO₂
硫与氧气化合：S + O₂ → SO₂。
Once in the atmosphere, SO₂ undergoes further oxidation to sulfur trioxide, which then reacts with water to produce sulfuric acid.
进入大气后，SO₂被进一步氧化成三氧化硫，随后与水反应生成硫酸。
2SO₂ + O₂ → 2SO₃
2SO₂ + O₂ → 2SO₃。
SO₃ + H₂O → H₂SO₄
SO₃ + H₂O → H₂SO₄。
The overall process can be simplified as:
总过程可以简化为：
SO₂ + ½O₂ + H₂O → H₂SO₄
SO₂ + ½O₂ + H₂O → H₂SO₄。
Sulfuric acid is a strong acid that dissociates completely in water, releasing hydrogen ions (H⁺) and lowering the pH.
硫酸是一种强酸，在水中完全解离，释放出氢离子（H⁺），从而降低pH值。
5. Analyzing pH Data and Calculating Acidity Change | 分析pH数据并计算酸度变化
From Table 1, the pH fell from 5.6 in 2012 to 4.3 in 2020, a decrease of 1.3 units. Because the pH scale is logarithmic, a unit change of 1 corresponds to a tenfold change in hydrogen ion concentration. You can calculate the exact increase in acidity.
从表1可见，pH从2012年的5.6降至2020年的4.3，下降1.3个单位。由于pH标度是对数的，每变化1个单位，氢离子浓度将变化10倍。你可以精确计算酸度的增幅。
[H⁺] = 10⁻pH
[H⁺] = 10⁻pH。
·³ ≈ 20. Thus, the acidity increased by approximately 20 times over the eight-year period.
pH 5.6时，[H⁺] = 10⁻⁵·⁶ mol dm⁻³；pH 4.3时，[H⁺] = 10⁻⁴·³ mol dm⁻³。比值为10⁻⁴·³ ÷ 10⁻⁵·⁶ = 10¹·³ ≈ 20。因此，在这八年间酸度增加了约20倍。
6. Interpreting Graphs of SO₂ and Tree Mortality | 解读SO₂与树木死亡率的图表
If you were given a graph plotting SO₂ emissions and tree mortality against time, you would expect both lines to trend upward simultaneously. A common exam question asks you to state the relationship and support it with data points. For example, "From 2012 to 2020, SO₂ emissions rose from 1200 to 2500 tonnes, while tree mortality increased from 2.1% to 10.5%, showing a positive correlation."
如果给出SO₂排放量和树木死亡率随时间变化的图，预期两条线会同时上升。常见考题要求你指出关系并用数据点支持，例如：“2012年至2020年，SO₂排放量从1200吨升至2500吨，而树木死亡率从2.1%增加到10.5%，呈正相关。”
Always mention units and quote specific figures when referencing the graph or table – this is a key marker of a high-level answer.
提到图表时，务必注明单位并引用具体数字——这是高分答案的关键标志。
7. Impact on Ecosystems: Soil, Lakes and Trees | 对生态系统的影响：土壤、湖泊与树木
Acid rain leaches aluminum ions (Al³⁺) from the soil, which are toxic to plant roots and aquatic animals. In lakes, falling pH damages fish gills and reduces egg survival. The forest in our case shows increasing tree mortality because the acid damages leaves, weakens roots and washes away nutrients.
酸雨会从土壤中淋溶出铝离子（Al³⁺），这些离子对植物根系和水生动物有毒。在湖泊中，pH下降会损害鱼鳃并降低鱼卵存活率。案例中的森林树木死亡率上升，是因为酸雨损害叶片、削弱根系并
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