📚 KS3 WJEC Science: Case Study Practice | KS3 WJEC 科学：案例分析实战演练
Case studies are a key feature of KS3 WJEC Science, designed to test your ability to apply scientific knowledge to unfamiliar, real-life situations. Instead of simply recalling facts, you will need to interpret data, evaluate evidence, and justify conclusions. This article provides a series of worked examples and strategies to help you tackle case study questions confidently.
案例学习是 KS3 WJEC 科学课程的一大特色，旨在考查你将科学知识应用于陌生、真实情境的能力。你不仅需要回忆事实，更要解读数据、评价证据并论证结论。本文通过一系列演练案例和实用策略，帮助你自信应对案例分析题。
1. What Is a Case Study? | 什么是案例分析？
A case study in WJEC Science is a structured scenario based on a real-world problem, such as an environmental investigation, a health concern, or a product design challenge. You are given background information, data tables, graphs or diagrams, and then asked a series of questions that often progress from simple recall to higher-order evaluation.
WJEC 科学中的案例分析是一个围绕真实问题构建的情境，例如环境调查、健康议题或产品设计挑战。题目会提供背景信息、数据表格、图表或示意图，然后逐步设问，通常从简单回忆上升到高阶评价。
The mark scheme rewards clear, logical explanations and use of scientific terminology. It is vital to read the scenario carefully, identify relevant science concepts, and always relate your answers back to the given context.
评分标准重视清晰、有逻辑的解释以及科学术语的使用。仔细阅读情境、识别相关科学概念，并始终将答案与给定情境相联系，这一点至关重要。
2. How to Approach a Case Study | 案例分析方法
Always begin by scanning the entire case study, including any data tables, graphs and diagrams. Underline or highlight key pieces of information, such as units, control variables and trends. This will help you avoid misreading the question.
始终先通览整个案例，包括所有数据表格、图表和示意图。划出或高亮关键信息，如单位、控制变量和趋势。这有助于避免误读题目。
Next, break down each question: identify the command word (e.g. ‘describe’, ‘explain’, ‘evaluate’) and decide what type of answer is needed. For ‘explain’ questions, use the ‘because’ structure to link cause and effect. For ‘evaluate’ questions, present both sides of an argument before giving your justified conclusion.
接着，拆解每个问题：识别指令词（如“描述”“解释”“评价”），并确定所需答案的类型。对于“解释”类问题，使用“因为”结构联系因果；对于“评价”类问题，先呈现论点的两面，再给出有理有据的结论。
3. Case Study 1: Investigating a Local Pond Ecosystem | 案例一：调查当地池塘生态系统
A group of students surveyed the number of different invertebrate species in two ponds: Pond A near a farm and Pond B in a woodland. They used kick-sampling and identified the species using a key. The table below shows their findings.
一组学生调查了两个池塘中不同无脊椎动物的数量：池塘 A 靠近农场，池塘 B 位于林地。他们采用踢采法采集样本，并用检索表鉴定物种。下表展示了他们的发现。
| Species | Pond A (farm) | Pond B (woodland) | Pollution tolerance |
|---|---|---|---|
| Mayfly nymph | 3 | 18 | Very sensitive |
| Caddisfly larva | 6 | 15 | Sensitive |
| Freshwater shrimp | 12 | 9 | Moderate |
| Bloodworm | 24 | 2 | Very tolerant |
The students concluded that Pond A was more polluted than Pond B. Explain why the data supports this conclusion.
学生们得出结论：池塘 A 比池塘 B 污染更严重。请解释为什么数据支持这一结论。
The number of pollution-sensitive species, such as mayfly nymphs and caddisfly larvae, is much lower in Pond A. Meanwhile, the very tolerant bloodworm dominates Pond A with 24 individuals, compared to only 2 in Pond B. Since bloodworms thrive in polluted water, their high count suggests a higher level of pollution, likely from farm run-off containing fertilisers or pesticides.
对污染敏感的物种，如蜉蝣稚虫和石蛾幼虫，在池塘 A 中的数量少得多。同时，极耐污染的红虫在池塘 A 占据优势，有 24 只，而池塘 B 仅有 2 只。由于红虫在污染水体中大量繁殖，其高计数表明污染水平更高，污染源可能来自含有肥料或农药的农场径流。
4. Case Study 2: Forces in a Sports Injury | 案例二：运动损伤中的力
During a rugby match, a player running at 5 m/s is tackled. His body comes to a stop in 0.2 seconds. The coach wants to understand why the injury was less severe when the player wore extra padding.
在一场橄榄球比赛中，一名以 5 m/s 奔跑的球员被擒抱，他的身体在 0.2 秒内停下。教练想了解为什么球员穿戴额外护具时受伤更轻。
Using ideas about momentum and force, explain how the padding reduces injury risk. Momentum is calculated as mass × velocity. When the player stops, his momentum changes to zero. The force experienced is equal to the rate of change of momentum (force = change in momentum ÷ time taken).
运用动量和力的知识，解释护具如何降低受伤风险。动量等于质量 × 速度。当球员停下时，他的动量变为零。受到的力等于动量变化率（力 = 动量变化 ÷ 所用时间）。
The padding increases the time taken for the player to come to a stop during the tackle. Because the change in momentum is the same with or without padding, increasing the time reduces the force experienced by the player’s body. A smaller force means less damage to tissues, thus reducing injury severity.
护具延长了擒抱过程中球员身体停下来的时间。由于无论有无护具，动量变化相同，增加时间便减小了球员身体承受的力。力越小，对组织的损伤越小，从而降低了受伤严重程度。
5. Case Study 3: Food Chains and Bioaccumulation | 案例三：食物链与生物积累
Scientists monitored the concentration of a toxic chemical (PCB) in the tissues of organisms from a lake food chain. The results are shown below.
科学家监测了某湖泊食物链中生物组织内有毒化学物质（多氯联苯）的浓度，结果如下所示。
| Organism | Trophic level | PCB concentration (mg/kg) |
|---|---|---|
| Phytoplankton | Producer | 0.01 |
| Zooplankton | Primary consumer | 0.05 |
| Small fish | Secondary consumer | 1.2 |
| Large fish | Tertiary consumer | 8.4 |
| Osprey (bird) | Top predator | 25.0 |
Describe the trend in PCB concentration and explain why the osprey is most at risk.
描述多氯联苯浓度的变化趋势，并解释为什么鹗（鱼鹰）面临的风险最大。
The trend shows that PCB concentration increases as you go up the food chain, a process called biomagnification. Phytoplankton absorb the chemical from polluted water, but the concentration is low. Each consumer eats many organisms from the level below, storing the PCB in its fatty tissues and excreting very little. Because ospreys eat many large fish over their lifetime, the PCB accumulates to levels that can cause reproductive failure and death.
趋势表明，随着食物链层级上升，多氯联苯浓度不断增加，这一过程称为生物放大。浮游植物从污染水体中吸收该化学物质，但浓度较低。每个消费者会吃掉许多下一营养级的生物，将多氯联苯储存在脂肪组织中，几乎不排出。由于鹗一生中吃掉大量大型鱼类，多氯联苯积累到可导致繁殖失败和死亡的水平。
6. Case Study 4: Acid Rain and Historic Buildings | 案例四：酸雨与历史建筑
A local council is concerned about the erosion of a limestone statue. Data shows the average pH of rainwater in the area has dropped from 5.6 to 4.2 over 50 years. The statue is made of calcium carbonate (CaCO₃).
某地方议会关注一尊石灰岩雕像的侵蚀问题。数据显示，该地区雨水的平均 pH 在 50 年间从 5.6 降至 4.2。雕像由碳酸钙（CaCO₃）构成。
Explain the chemical reaction causing the damage and suggest how the council could test the prediction that the damage is caused by acid rain.
解释造成损坏的化学反应，并建议议会可以如何验证损坏确由酸雨导致的预测。
Acid rain contains sulfuric acid and nitric acid, formed when sulfur dioxide and nitrogen oxides from burning fossil fuels dissolve in rainwater. The acid reacts with calcium carbonate: CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂. Calcium sulfate is slightly soluble and can be washed away, causing the statue to wear down. The lower the pH, the faster the reaction. To test the link, the council could compare the mass loss of identical limestone samples placed in areas with different rainfall pH or expose samples to normal rainwater (pH 5.6) and acidified rainwater in the lab, measuring mass change over time.
酸雨含有硫酸和硝酸，它们是燃烧化石燃料产生的二氧化硫和氮氧化物溶解在雨水中形成的。酸与碳酸钙反应：CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂。硫酸钙微溶，可被冲刷，导致雕像磨损。pH 越低，反应越快。为检验因果关系，议会可以比较放置在降雨 pH 不同区域的相同石灰岩样品的质量损失，或在实验室中将样品分别暴露于普通雨水（pH 5.6）和酸化雨水中，测量质量随时间的变化。
7. Case Study 5: Designing a Thermos Flask Experiment | 案例五：设计保温瓶实验
A company claims its new thermos flask keeps water above 60 °C for 12 hours. You are asked to plan a fair test investigation to verify the claim.
某公司声称其新款保温瓶可使水温在 12 小时内保持 60 °C 以上。请你设计一个公平测试调查方案以验证该说法。
First, identify independent, dependent and control variables. Independent variable: the type of flask (new thermos vs a standard flask or no flask). Dependent variable: water temperature measured every hour for 12 hours. Controlled variables: volume of water (e.g. 500 cm³), starting temperature (e.g. 95 °C), room temperature, and position of the flask. Use a thermometer or data logger to record temperatures. Repeat the test three times to ensure reliability, and calculate mean values. Plot a line graph with time on the x-axis and temperature on the y-axis. The conclusion must state whether the water remained above 60 °C and compare with the control.
首先，明确自变量、因变量和控制变量。自变量：保温瓶类型（新保温瓶与标准保温瓶或无瓶对照）。因变量：在 12 小时内每小时测量的水温。控制变量：水的体积（如 500 cm³）、起始温度（如 95 °C）、室温和保温瓶的放置位置。使用温度计或数据记录器记录温度。重复测试三次以确保可靠性，计算平均值。绘制折线图，时间置于 x 轴，温度置于 y 轴。结论必须说明水温是否保持在 60 °C 以上，并与对照组进行比较。
8. Case Study 6: Identifying Evidence of a Chemical Reaction | 案例六：识别化学反应的证据
A student mixes two colourless solutions in a test tube. The test tube becomes warm, and a white solid slowly appears at the bottom. Bubbles are not observed. The student claims a chemical reaction has occurred.
一名学生将两种无色溶液在试管中混合。试管变热，底部缓慢出现白色固体，未见气泡。学生断言发生了化学反应。
Evaluate the student’s claim using evidence of chemical reactions.
运用化学反应的证据评价该学生的断言。
The observation that the test tube becomes warm indicates an exothermic reaction, where energy is transferred to the surroundings. Temperature change is a strong sign of a chemical reaction. The appearance of a white solid suggests a precipitation reaction, where an insoluble salt is formed. Even without gas production, these two observations together provide robust evidence that a new substance has been made, so the student’s claim is scientifically valid. However, it would be stronger if the student had checked for a change in pH or confirmed the precipitate had different properties from the reactants.
试管变热的观察表明发生了放热反应，能量传递给了周围环境。温度变化是化学反应的有力信号。白色固体的出现提示发生了沉淀反应，生成了不溶性盐。即便没有气体产生，这两项观察已足够有力地证明有新物质生成，因此学生的断言在科学上是成立的。不过，若学生能进一步检查 pH 变化或确认沉淀物拥有不同于反应物的性质，证据将更加充分。
9. Common Mistakes and Top Tips | 常见错误与高分提示
Many students lose marks by writing generic answers that do not link back to the case study. Always use the names of organisms, chemicals or variables from the given scenario. For example, write ‘the osprey accumulated PCB’ rather than ‘the animal got more poison’.
许多学生因给出不结合具体案例的泛泛答案而失分。务必使用题目情境中的生物、化学物质或变量名称。例如，应写“鹗积累了多氯联苯”而不是“动物获得了更多毒素”。
When asked to ‘evaluate’, never give a one-sided answer. You must weigh up advantages and disadvantages, or discuss reliability of data, before reaching a reasoned conclusion. Use phrases like ‘this data is reliable because…’, or ‘a limitation is that…’.
遇到“评价”类问题时，切勿给出片面答案。必须权衡利弊，或讨论数据的可靠性，再得出有依据的结论。使用诸如“该数据可靠，因为……”或“一个局限是……”等表述。
In calculations, always show your working clearly and include units. Check if any unit conversions are needed. For instance, if time is given in milliseconds, convert to seconds before using it in a formula.
在计算题中，务必清晰展示演算步骤并写明单位。检查是否需要换算单位。例如，若时间以毫秒给出，在使用公式前先转换为秒。
10. Putting It All Together | 总结与综合运用
Case study practice is about thinking like a scientist in context. The WJEC exam will often blend topics, so you might see a question linking chemistry and environmental science, or physics and biology. The more you practise applying your knowledge to unfamiliar situations, the more skilled you become at identifying the relevant principles quickly.
案例分析的实战演练要求你在具体情境中像科学家一样思考。WJEC 试卷经常融合多个主题，你可能会遇到将化学与环境科学联系起来，或将物理与生物联系起来的问题。你越多练习将知识应用于陌生情境，就能越快识别出相关原理。
Work through the six case studies above, then create your own by collecting news articles about science in the real world. Write the scenario, design data tables and think of the questions an examiner might ask. This active revision method is extremely effective for long-term retention.
先仔细完成上述六个案例，然后自己收集现实中的科学新闻来创编案例。写出情境、设计数据表格，并思考考官可能提出的问题。这种主动复习法对长期记忆极为有效。
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