📚 Year 8 CIE Science: Case Study Practical Drills | Year 8 CIE 科学：案例分析实战演练
Case studies are a brilliant way to connect classroom science to real-world situations. In Year 8 CIE Science, you will often be asked to interpret data, identify patterns and apply your knowledge to unfamiliar scenarios. This article walks you through a series of case studies covering physics, chemistry and biology, each designed to sharpen your analytical skills. By the end, you will feel confident tackling any case study question that comes your way.
案例研究是将课堂科学与现实世界连接起来的绝佳方式。在 Year 8 CIE 科学中，你经常需要解读数据、识别规律并将所学知识应用到陌生的情境里。本文将通过一系列涵盖物理、化学和生物的案例，逐一锻炼你的分析能力。读完后，你将能自信地应对任何案例研究类题目。
1. What is a Case Study in Science? | 科学中的案例分析是什么？
A case study is a detailed investigation of a specific scientific situation or problem. It often includes a short scenario, a set of data (e.g. measurements, observations or a table), and several questions that test your understanding. Instead of simple recall, you must apply concepts, analyse evidence and draw conclusions.
案例分析是针对某个具体的科学情境或问题展开的详细探究。它通常包含一段简短的情景、一组数据（如测量值、观察结果或表格）以及若干检验你理解力的问题。你需要运用概念、分析证据并得出结论，而不仅仅是回忆知识。
For example, you might be given the results of an experiment on dissolving salt at different temperatures and asked to explain why solubility changes. The challenge is to link the data to particle theory and energy. This is exactly the type of reasoning you practice in these drills.
例如，你可能会得到一组关于食盐在不同温度下溶解的实验结果，并被要求解释溶解度为何会变化。难点在于将数据与粒子理论和能量概念联系起来。这正是你在这些演练中要练习的推理类型。
2. Key Skills for Analysing Case Studies | 案例分析的关键技巧
Before we dive into the examples, let’s establish a toolkit. Successful case study answers rely on four core skills: (1) reading the scenario carefully to identify the variables and the question asked; (2) extracting information from tables, graphs or text; (3) performing simple calculations where needed; and (4) explaining your reasoning using scientific vocabulary.
在进入实例之前，我们先建立一个工具箱。成功回答案例分析题依赖于四项核心技能：（1）仔细阅读情景，识别变量和所问的问题；（2）从表格、图表或文字中提取信息；（3）必要时进行简单计算；（4）运用科学词汇解释你的推理过程。
Whenever you see numbers, think about units and what they represent. When you spot a trend, describe it in words (e.g. “as temperature increases, the rate of reaction also increases”). And always refer back to the data to support your conclusion.
每当你看到数字，想想单位及其含义。当你发现一种趋势，用语言描述它（例如“随着温度升高，反应速率也增加”）。并且始终引用数据来支撑你的结论。
A strong answer often uses a structure: state your finding, support it with specific evidence and then link it to a scientific principle. We will model this throughout the examples.
一个强有力的答案常采用这样的结构：陈述你的发现，用具体证据支持，然后将其与科学原理联系起来。我们将在所有案例中示范这一做法。
3. Case Study 1: Buoyancy and Density | 案例1：浮力与密度
A student tested two solid blocks, A and B, by placing them in a tank of water. She recorded her observations in the table below.
一名学生将两块固体 A 和 B 放入水槽中进行测试，并将观察结果记录在下表中。
| Block | Mass (g) | Volume (cm³) | Observation |
|---|---|---|---|
| A | 50 | 20 | Sank to the bottom |
| B | 30 | 40 | Floated |
Question: Use the data to calculate the density of each block and explain why one sank while the other floated.
问题：利用数据计算每个物块的密度，并解释为什么一个沉而另一个浮。
Step 1 – Calculate density. Density (g/cm³) = mass ÷ volume. For Block A: 50 g ÷ 20 cm³ = 2.5 g/cm³. For Block B: 30 g ÷ 40 cm³ = 0.75 g/cm³.
步骤1——计算密度。密度（g/cm³）= 质量 ÷ 体积。物块 A：50 g ÷ 20 cm³ = 2.5 g/cm³。物块 B：30 g ÷ 40 cm³ = 0.75 g/cm³。
Step 2 – Compare with water. The density of water is about 1 g/cm³. Block A (2.5 g/cm³) is denser than water, so it sinks. Block B (0.75 g/cm³) is less dense than water, so it floats.
步骤2——与水比较。水的密度约为 1 g/cm³。物块 A (2.5 g/cm³) 比水密度大，因此下沉。物块 B (0.75 g/cm³) 比水密度小，因此上浮。
Conclusion: An object sinks if its density is greater than that of the fluid; it floats if its density is less. This case shows that volume alone does not decide floating – mass must also be considered.
结论：物体的密度大于液体密度时下沉；密度小于液体密度时上浮。本案例表明，仅凭体积并不能决定浮沉——还必须考虑质量。
4. Case Study 2: Acid Rain and Limestone | 案例2：酸雨与石灰石
A school investigated the effect of acid rain on building materials. They placed identical pieces of limestone, marble and granite in dilute sulfuric acid (pH 3) for 24 hours. The mass loss of each sample is shown below.
一所学校研究了酸雨对建筑材料的影响。他们将完全相同的石灰石、大理石和花岗岩试样放入稀硫酸（pH 3）中 24 小时。每个样品的质量损失如下所示。
| Material | Initial mass (g) | Final mass (g) | Mass lost (g) |
|---|---|---|---|
| Limestone | 20.0 | 15.8 | 4.2 |
| Marble | 20.0 | 16.4 | 3.6 |
| Granite | 20.0 | 19.9 | 0.1 |
Question: Explain why limestone and marble lost much more mass than granite, using your knowledge of chemical reactions.
问题：利用你的化学反应知识，解释为何石灰石和大理石的质量损失远大于花岗岩。
Limestone and marble are both forms of calcium carbonate (CaCO₃). Calcium carbonate reacts with acids to produce a salt, water and carbon dioxide gas. The reaction is:
CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂
石灰石和大理石都是碳酸钙 (CaCO₃) 的不同形态。碳酸钙与酸反应生成盐、水和二氧化碳气体。反应方程式为：
CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂
Because the carbon dioxide escapes into the air, the solid loses mass. This explains why the limestone and marble samples became lighter. The reaction is a neutralisation as well as a gas-producing reaction.
由于二氧化碳逸出到空气中，固体质量减少。这就解释了为何石灰石和大理石样品变轻了。该反应既是中和反应也是产气反应。
Granite, on the other hand, is made mainly of silicate minerals that do not react easily with dilute sulfuric acid. Hence, it showed very little mass loss – only 0.1 g, likely from surface impurities.
另一方面，花岗岩主要由硅酸盐矿物构成，很难与稀硫酸反应。因此，它的质量损失极小——仅 0.1 克，可能来自表面杂质。
Conclusion: Acid rain can severely damage buildings made of carbonate rocks, but granite is far more resistant. This is why many historical monuments use granite or need protective coatings.
结论：酸雨会严重腐蚀由碳酸盐岩石建造的建筑，但花岗岩的抗腐蚀能力强得多。这就是许多历史遗迹使用花岗岩或需要保护涂层的原因。
5. Case Study 3: Photosynthesis Rate Investigation | 案例3：光合作用速率探究
An underwater plant, Elodea, was placed in a beaker of water. A lamp was moved to different distances, and the number of oxygen bubbles released per minute was counted. The data are recorded below.
将一株水生植物黑藻（Elodea）放在装有水的烧杯中。将一盏灯移动到不同的距离，并计算每分钟释放的氧气气泡数。数据记录如下。
| Distance from lamp (cm) | Bubbles per minute |
|---|---|
| 10 | 42 |
| 20 | 28 |
| 30 | 16 |
| 40 | 7 |
Question: Describe the trend shown by the data and explain the relationship between light intensity and photosynthesis rate.
问题：描述数据呈现的趋势，并解释光照强度与光合作用速率之间的关系。
The data show that as the distance from the lamp increases, the number of bubbles per minute decreases. This means the rate of photosynthesis drops when the plant receives less light.
数据表明，随着与灯的距离增大，每分钟的气泡数减少。这意味着当植物接受的光照减少时，光合作用速率下降。
Light provides the energy needed for photosynthesis. The word equation is:
carbon dioxide + water → glucose + oxygen (in the presence of light and chlorophyll). More intense light supplies more energy, allowing the reaction to proceed faster and produce more oxygen gas, which we see as bubbles.
光为光合作用提供能量。文字方程式为：
二氧化碳 + 水 → 葡萄糖 + 氧气（在光和叶绿素作用下）。更强的光照提供更多能量，使反应进行得更快，产生更多氧气，也就是我们观察到的气泡。
However, after a certain point, even if light intensity increases further, the rate may level off because other factors, such as carbon dioxide concentration or temperature, become limiting. In this experiment, the plant had sufficient CO₂ and warm water, so light was the main factor.
然而，到达某一点后，即使光照强度继续增加，速率也可能趋于平稳，因为其他因素，如二氧化碳浓度或温度，会变为限制因素。本实验中，植物有足够的 CO₂ 和温暖的水，因此光照是主要因素。
Conclusion: Closer lamp → higher light intensity → faster photosynthesis → more oxygen bubbles. This is a classic example of how a controlled variable influences a biological process.
结论：灯越近 → 光照强度越高 → 光合作用越快 → 氧气气泡越多。这是一个受控变量如何影响生物过程的经典案例。
6. Case Study 4: Food Web Disruption | 案例4：食物网破坏
A pond ecosystem contains the following organisms: algae, water fleas, small fish, perch and herons. The arrows in a food web represent energy flow. Due to pollution, the population of water fleas suddenly declined.
一个池塘生态系统包含以下生物：藻类、水蚤、小鱼、鲈鱼和苍鹭。食物网中的箭头表示能量流动。由于污染，水蚤的数量突然下降。
| Organism | Feeds on | Eaten by |
|---|---|---|
| Algae | Sunlight (photosynthesis) | Water fleas |
| Water fleas | Algae | Small fish |
| Small fish | Water fleas | Perch |
| Perch | Small fish | Herons |
| Herons | Perch | – |
Question: Predict and explain what is likely to happen to the populations of algae, small fish and perch in the short term.
问题：预测并解释短期内藻类、小鱼和鲈鱼种群数量可能发生的变化。
Because water fleas eat algae, fewer water fleas means less grazing pressure on algae. Therefore, the algae population will increase.
由于水蚤以藻类为食，水蚤数量减少意味着对藻类的牧食压力减小。因此，藻类数量会增加。
Small fish feed on water fleas. With fewer water fleas available, small fish will have less food. Their population is likely to decrease due to starvation.
小鱼以水蚤为食。随着水蚤数量减少，小鱼的食物变少。它们的种群数量可能因饥饿而减少。
Perch eat small fish. A decrease in the small fish population will reduce the food supply for perch, so the perch population may also decline.
鲈鱼以小鱼为食。小鱼数量减少将削减鲈鱼的食物来源，因此鲈鱼的数量也可能下降。
Herons, being top predators, will be affected last – they may find fewer perch and eventually move elsewhere. This case demonstrates the knock-on effects in a food web when one species is disturbed.
作为顶级捕食者的苍鹭最后才会受到影响——它们可能发现鲈鱼减少，最终迁往别处。这一案例展示了当一个物种受到干扰时食物网中的连锁反应。
7. Case Study 5: Friction and Motion | 案例5：摩擦力与运动
A student released a toy car from the top of a ramp covered with different surfaces. The distance the car travelled on the flat floor after leaving the ramp was measured.
一名学生从覆盖不同表面的斜坡顶端释放一辆玩具车。测量了小车离开斜坡后在平坦地面上行驶的距离。
| Ramp surface | Distance travelled (cm) |
|---|---|
| Smooth plastic | 145 |
| Carpet | 62 |
| Sandpaper | 38 |
Question: Explain why the car moved further on smooth plastic than on sandpaper, using the concept of friction.
问题：运用摩擦力的概念，解释为何小车在光滑塑料上行驶的距离比在砂纸上远。
Friction is a force that opposes motion. The rougher the surface, the greater the friction. Smooth plastic offers very little friction, so less of the car’s kinetic energy is converted into heat, allowing it to travel further.
摩擦力是阻碍运动的力。表面越粗糙，摩擦力越大。光滑塑料几乎不产生摩擦力，因此小车的动能转化为热能的很少，使它行驶得更远。
Sandpaper is very rough, so it creates a large friction force. This quickly slows the car down, converting much of its kinetic energy into heat, resulting in a short stopping distance.
砂纸非常粗糙，因此产生很大的摩擦力。这很快使小车减速，将大量动能转化为热，导致停车距离很短。
Carpet lies in between – it is rougher than plastic but smoother than sandpaper, so the distance is intermediate. This shows that the type of surface directly affects the amount of friction and hence the motion of objects.
地毯介于两者之间——它比塑料粗糙但比砂纸光滑，因此行驶距离居中。这表明表面类型直接影响摩擦力大小，进而影响物体的运动。
8. Case Study 6: Changing State – Melting Ice | 案例6：状态
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