📚 Case Study Practice in Year 7 SQA Science | 七年级SQA科学案例分析实战演练
Case studies are an essential part of Year 7 SQA Science. They help you apply knowledge, interpret data and think like a real scientist. In this article, you will work through eight practical scenarios, each covering different topics from the curriculum. Read each case carefully, identify variables, analyse results and draw conclusions. By the end, you will feel confident tackling any case study in your assessments.
案例研究是七年级SQA科学的重要组成部分。它能帮助你运用知识、解读数据，并像真正的科学家一样思考。本文将带领你完成八个实践情景，每个情景都涵盖课程中的不同主题。请仔细阅读每个案例，识别变量，分析结果并得出结论。最后，你将能自信应对评估中的任何案例分析题目。
1. What Is a Case Study in Science? | 什么是科学案例分析？
A case study presents a real or simulated situation where you apply scientific inquiry skills. You might be asked to plan an investigation, interpret a graph or evaluate an experiment. These tasks build your understanding of how science works and how to communicate findings clearly.
案例研究提供了一个真实或模拟的情境，让你运用科学探究技能。你可能需要规划一项调查、解读图表或评估一个实验。这些任务能帮助你理解科学的工作原理，并学会清晰地传达发现。
Case studies often follow the scientific method: asking a question, forming a hypothesis, identifying variables, collecting data and drawing conclusions. Recognising these steps is the first key to success.
案例分析通常遵循科学方法：提出问题、形成假设、识别变量、收集数据并得出结论。识别这些步骤是成功的第一步。
2. Key Skills for Case Study Analysis | 案例分析的关键技能
To excel in case study questions, you need to practise several core skills. These include identifying independent and dependent variables, recognising control variables and distinguishing between observations and inferences.
要在案例分析题中表现出色，你需要练习几项核心技能，包括识别自变量和因变量、确认控制变量，以及区分观察与推断。
You must also be able to represent data in tables and graphs, describe trends and patterns, and use scientific language to explain results. Finally, evaluating reliability and suggesting improvements are critical higher-order skills.
你还必须能够用表格和图表呈现数据，描述趋势和规律，并使用科学语言解释结果。最后，评估可靠性并提出改进建议是至关重要的高阶技能。
Always keep the question ‘Why?’ in mind. Why did the scientist choose that method? Why did the result change? Asking ‘why’ will lead you to deeper understanding.
要时刻把“为什么”放在心上。为什么科学家选择了那种方法？为什么结果会变化？问“为什么”将引导你获得更深入的理解。
3. Case 1: Dissolving Sugar in Water | 案例一：糖在水中的溶解
A student wanted to find out how water temperature affects the time it takes for one sugar cube to dissolve. She used a thermometer and a stopwatch, placed one sugar cube into 200 ml of water at different temperatures, and stirred once gently. She recorded the time it took for the cube to disappear completely.
一名学生想探究水温如何影响一块方糖溶解所需的时间。她使用温度计和秒表，将一块方糖放入不同温度的200毫升水中，轻轻搅拌一次，并记录方糖完全消失所用的时间。
| Temperature (°C) | Time to dissolve (s) |
|---|---|
| 20 | 90 |
| 40 | 45 |
| 60 | 25 |
| 80 | 12 |
The independent variable is temperature, because it is the factor the student deliberately changed. The dependent variable is time to dissolve, which is what she measured. Controlled variables include the volume of water, type of sugar cube and stirring method.
自变量是温度，因为这是学生刻意改变的因素。因变量是溶解时间，是她测量的量。控制变量包括水的体积、方糖的种类和搅拌方式。
The data show that as temperature increases, dissolving time decreases. Particles move faster in hotter water, so sugar molecules spread out more quickly. A valid conclusion is: ‘The higher the water temperature, the shorter the time needed to dissolve a sugar cube.’
数据显示，随着温度升高，溶解时间缩短。在较热的水中，粒子运动更快，因此糖分子扩散得更快。有效的结论是：“水温越高，溶解一块方糖所需的时间越短。”
4. Case 2: Plant Growth and Light | 案例二：植物生长与光照
A gardener planted three identical bean seedlings in the same type of soil and gave them the same amount of water. One plant was placed in full sunlight, another in partial shade, and the third in a dark cupboard. After two weeks, the heights were measured.
一位园丁将三株相同的豆苗种在同一种土壤中，并浇灌等量的水。一株放在充足阳光下，一株放在半阴处，第三株放在黑暗的橱柜里。两周后测量了高度。
| Light condition | Height after 2 weeks (cm) |
|---|---|
| Full sunlight | 15 |
| Partial shade | 9 |
| Dark cupboard | 3 |
The independent variable is the amount of light. The dependent variable is plant height. Control variables include soil type, water volume and plant type.
自变量是光照量。因变量是植株高度。控制变量包括土壤类型、浇水量和植物种类。
The seedling in full sunlight grew the most because light is needed for photosynthesis, the process that makes food for the plant. Limited light means less food, so growth is slower. A possible conclusion: ‘Light is essential for healthy plant growth; less light results in shorter plants.’
全光照下的幼苗长得最高，因为光是为植物制造食物的光合作用所必需的。光照有限意味着食物减少，因此生长较慢。可能的结论是：“光照对植物健康生长至关重要；光照越少，植株越矮。”
5. Case 3: Friction on Different Surfaces | 案例三：不同表面的摩擦力
A class measured the force needed to pull a wooden block across different surfaces using a spring balance. They pulled the block at a steady speed and recorded the force in newtons (N). They tested sandpaper, carpet, a wooden table and a smooth plastic sheet.
全班同学使用弹簧秤测量在不同表面上匀速拉动一个木块所需的力，并以牛顿（N）为单位记录。他们测试了砂纸、地毯、木桌和光滑的塑料板。
| Surface | Force needed (N) |
|---|---|
| Sandpaper | 4.5 |
| Carpet | 3.8 |
| Wooden table | 2.1 |
| Smooth plastic | 1.2 |
The independent variable is the surface type. The dependent variable is the force required to pull the block. Controls include the same block, same spring balance and pulling at a constant speed.
自变量是表面类型。因变量是拉动木块所需的力。控制变量包括相同的木块、相同的弹簧秤以及匀速拉动。
Sandpaper required the largest force because its rough texture produces greater friction. Smooth plastic produced the least friction because there are fewer bumps to resist motion. The conclusion can be: ‘Rough surfaces generate more friction, so more force is needed to move an object across them.’
砂纸所需的力最大，因为其粗糙的质地产生了更大的摩擦力。光滑塑料产生的摩擦力最小，因为阻碍运动的凸起更少。结论可以是：“粗糙的表面产生更大的摩擦力，因此需要更大的力才能在其上移动物体。”
6. Case 4: Chemical Change – Baking Soda and Vinegar | 案例四：化学变化 – 小苏打与醋
A scientist mixed 5 g of baking soda with 50 ml of vinegar in an open beaker. Bubbles formed immediately. The total mass before mixing was 105 g, but after the reaction the mass was only 103 g. The class discussed whether mass was lost.
一位科学家在敞口烧杯中混合了5克小苏打和50毫升醋，气泡立即形成。混合前总质量为105克，但反应后质量仅为103克。同学们讨论了质量是否减少了。
. Carbon dioxide gas escapes into the air, so the mass appears to decrease. The independent variable is the type of container (open vs closed). If repeated in a sealed bag, the total mass would remain constant.
反应式为：NaHCO₃(s) + CH₃COOH(aq) → CH₃COONa(aq) + H₂O(l) + CO₂(g)。二氧化碳气体逸散到空气中，因此质量看起来减少了。自变量是容器类型（开放与封闭）。如果在密封袋中重复实验，总质量将保持不变。
This case demonstrates the conservation of mass. No atoms are destroyed, but the gas escapes. An evaluation point: using a closed system improves reliability. Conclusion: ‘Mass is conserved during a chemical reaction; any loss indicates a gas has escaped.’
这个案例证明了质量守恒定律。没有原子被消灭，但气体逃逸了。评估要点是：使用封闭系统可以提高可靠性。结论：“化学反应中质量是守恒的；任何质量损失都表明有气体逸出。”
7. Case 5: Simple Circuits and Bulb Brightness | 案例五：简单电路与灯泡亮度
A group built a circuit with one bulb, some wires and a switch. They measured the brightness of the bulb (using a light sensor) when they connected 1, 2 or 3 batteries in series. They kept the same bulb and wires throughout.
一个小组搭建了一个包含一个灯泡、几根导线和一个开关的电路。他们测量了当串联1节、2节或3节电池时灯泡的亮度（使用光传感器）。整个过程中他们使用了相同的灯泡和导线。
| Number of batteries | Brightness (lux) |
|---|---|
| 1 | 200 |
| 2 | 450 |
| 3 | 680 |
The independent variable is the number of batteries. The dependent variable is bulb brightness. Controls include the bulb, wires and light sensor distance.
自变量是电池的数量。因变量是灯泡亮度。控制变量包括灯泡、导线和光传感器的距离。
As the voltage increased (more batteries), the current flowing through the bulb increased, making the bulb shine brighter. A clear trend: brightness rises with battery number. Conclusion: ‘Adding more batteries in series increases the brightness of the bulb because a higher voltage pushes more current through the circuit.’
随着电压升高（更多电池），流过灯泡的电流增大，灯泡变亮。明显趋势：亮度随电池数量增加而上升。结论：“串联更多电池会增大灯泡亮度，因为更高的电压会驱动更强的电流通过电路。”
8. Case 6: Neutralising an Acid with Indigestion Tablet | 案例六：用抗酸药片中和胃酸
Indigestion tablets contain bases that neutralise stomach acid. A student crushed one tablet, added it to 25 ml of dilute hydrochloric acid (pH 2) and measured the pH every 30 seconds. The pH gradually rose to 7 after two minutes.
抗酸药片含有能中和胃酸的碱。一名学生将一片药片压碎，加入25毫升稀盐酸（pH值为2）中，并每30秒测量一次pH值。两分钟后pH值逐渐升至7。
The independent variable here is time (or you could argue the type of tablet if comparing brands). The dependent variable is the pH. Controlled variables include volume of acid, mass of tablet and temperature.
这里的自变量是时间（如果比较品牌，也可以说是药片的种类）。因变量是pH值。控制变量包括酸的体积、药片质量和温度。
s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g). The pH rises as acid is consumed. Conclusion: ‘Antacid tablets effectively neutralise acid over time, bringing pH toward neutral.’
中和作用的发生是由于碱（通常是碳酸钙）与酸反应，生成盐、水和二氧化碳：CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)。随着酸被消耗，pH值上升。结论：“抗酸药片可以随时间有效中和酸，使pH值趋于中性。”
9. Case 7: Food Chains in a Garden Ecosystem | 案例七：花园生态系统中的食物链
seen eating ladybirds. She sketched a food chain: rose → greenfly → ladybird → blackbird.
一位园丁观察到一株玫瑰丛的叶片上有许多蚜虫。她还注意到同一株灌木上有瓢虫。随后，一只黑鸟被看到在吃瓢虫。她画了一条食物链：玫瑰 → 蚜虫 → 瓢虫 → 黑鸟。
The producer is the rose bush, which makes its own food by photosynthesis. The primary consumer is the greenfly, which eats the plant. The secondary consumer is the ladybird, and the tertiary consumer is the blackbird. If the ladybirds were removed, the greenfly population would increase rapidly.
生产者是玫瑰丛，它通过光合作用制造自己的食物。初级消费者是蚜虫，它以植物为食。次级消费者是瓢虫，三级消费者是黑鸟。如果瓢虫被移除，蚜虫数量将迅速增加。
This case shows feeding relationships and energy transfer. The arrows represent the direction of energy flow. Case study questions might ask you to predict the effect of changing one population. Conclusion: ‘Organisms in a food chain depend on each other; removing one link can disrupt the whole community.’
这个案例展示了摄食关系和能量传递。箭头代表能量流动的方向。案例问题可能会要求你预测改变某一生物种群的效果。结论：“食物链中的生物相互依赖；移除某一环节可能会扰乱整个群落。”
10. Case 8: States of Matter – Melting Ice | 案例八：物质的状态 – 冰的熔化
A pupil placed 50 g of ice cubes in a beaker at room temperature (22 °C) and recorded the mass and state every 5 minutes. After 15 minutes, all ice had melted, leaving water at 0 °C. The mass remained 50 g throughout.
一名学生在室温（22 °C）下将50克冰块放入烧杯中，每5分钟记录质量和状态。15分钟后，所有冰都融化了，剩下0 °C的水。整个过程质量始终为50克。
The independent variable is time. The dependent variables are state and temperature. The mass is a controlled observation – it did not change because melting is a physical change, not a chemical one. The particles gain energy, break free from fixed positions and become liquid.
自变量是时间。因变量是状态和温度。质量是一个受控观测值 – 它没有改变，因为熔化是一种物理变化，不是化学变化。粒子获得能量，从固定位置挣脱并变成液体。
This case reinforces that mass is conserved during changes of state. Conclusion: ‘When a solid melts, its particles gain energy, but the total mass stays the same because no new substance is formed.’
这个案例强化了状态变化中质量守恒的概念。结论：“固体熔化时，其粒子获得能量，但总质量保持不变，因为没有形成新物质。”
11. How to Write a Conclusion from Data | 如何根据数据得出结论
A strong conclusion states the relationship between the independent and dependent variables and refers to the data. For example: ‘The experiment shows that as the temperature increases, the time taken for the sugar to dissolve decreases. This is supported by the results: at 20 °C it took 90 s, but at 80 °C only 12 s.’
有力的结论会陈述自变量与因变量之间的关系，并引用数据。例如：“实验表明，随着温度升高，糖溶解所需的时间减少。结果支持这一观点：在20 °C时用了90秒，而在80 °C时仅用了12秒。”
Avoid vague statements like ‘it worked’ or ‘it was good’. Instead, be specific and link back to the scientific concept. If the data show an anomaly, mention it and suggest a possible reason, such as a measurement error.
避免使用“它有效”或“它很好”等模糊表述。要具体化，并联系科学概念。如果数据出现异常，要提及异常并给出可能的原因，例如测量误差。
12. Common Mistakes to Avoid | 常见错误及避免方法
One frequent error is confusing independent and dependent variables. Remember: independent variable is what you change; dependent variable is what you measure. Another mistake is failing to list control variables or not explaining why they matter.
一个常见错误是混淆自变量和因变量。记住：自变量是你改变的量；因变量是你测量的量。另一个错误是没有列出控制变量或没有解释它们为何重要。
Students often forget to include units when presenting data or to label graph axes properly. When evaluating, they might say ‘do it more carefully’ without stating a specific improvement, such as ‘use a digital thermometer to get more precise readings’. Always be precise.
学生在展示数据时常常忘记写单位，或未正确标记图表坐标轴。在评估时，他们可能会说“做得更细心些”，却没有提出具体的改进措施，例如“使用数字温度计以获取更精确的读数”。要始终力求精确。
Finally, rushing through the readings without repeating trials can reduce reliability. Always consider if repeating the experiment and calculating an average would strengthen the evidence.
最后，匆忙进行读数而不进行重复实验会降低
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