📚 Case Study Practical Exercises | 案例分析实战演练
Welcome to your practical case study challenge! In Year 7 Cambridge Science, you are not only learning facts about biology, chemistry and physics, but also how to think and work like a scientist. Case studies help you apply the scientific method to real situations – from designing fair tests to analysing data and drawing evidence-based conclusions. This article will guide you through several hands-on case studies, complete with step-by-step exercises, so you can master the key skills of scientific enquiry.
欢迎来到你的实践案例分析挑战！在七年级剑桥科学中，你不仅要学习生物学、化学和物理学的事实知识，还要学会像科学家一样思考和工作。案例分析帮助你运用科学方法解决真实情境中的问题——从设计公平测试到分析数据，再到得出基于证据的结论。本文将带你完成几个动手案例分析，并配有分步练习，助你掌握科学探究的关键技能。
1. Understanding Scientific Case Studies | 理解科学案例分析
A scientific case study is a detailed investigation into a question or problem using the scientific method. Instead of simply remembering information, you follow the steps of enquiry: asking a question, making a hypothesis, planning a fair test, collecting data, presenting results, analysing patterns and writing a conclusion. Case studies let you practise these skills in a realistic context, just like a scientist in a laboratory.
科学案例分析是使用科学方法对某个问题或疑问进行的详细探究。你不再只是记住信息，而是要遵循探究的步骤：提出问题、作出假设、设计公平测试、收集数据、呈现结果、分析规律并撰写结论。案例分析让你在真实情境中练习这些技能，就像实验室里的科学家一样。
2. Variables and Fair Testing | 变量与公平测试
Before we dive into the case studies, it is essential to understand the three types of variables. The independent variable is the one you deliberately change (e.g. amount of water). The dependent variable is what you measure or observe (e.g. number of seeds germinated). Control variables are all the other factors you must keep the same to make the test fair (e.g. light, temperature, type of seed).
在我们深入案例研究之前，理解三类变量至关重要。独立变量是你有意改变的那个（例如水量）。因变量是你测量或观察的内容（例如发芽的种子数量）。控制变量是其他所有你必须保持不变以确保测试公平的因素（例如光照、温度、种子类型）。
If you do not control variables properly, you cannot be sure that the independent variable caused any change in the dependent variable. A fair test is the heart of every reliable investigation.
如果你没有恰当控制变量，你就无法确定是因变量导致了因变量的任何变化。公平测试是每一项可靠调查的核心。
3. Case Study 1: Effect of Water on Seed Germination | 案例1：水分对种子发芽的影响
In this case study, a Year 7 student asked: ‘How does the amount of water affect how many cress seeds germinate in one week?’ The hypothesis was that more water would lead to more seeds germinating, up to a point. Let’s work through the investigation together.
在这个案例研究中，一位七年级学生问道：“水量如何影响水芹种子在一周内的发芽数量？” 假设是：在一定范围内，水越多，发芽的种子越多。让我们一起完成这项调查。
The student chose to use 5 Petri dishes, each lined with a circle of filter paper. In each dish, 10 cress seeds were spaced evenly on the paper. The independent variable was the volume of water added to each dish: 0 mL, 5 mL, 10 mL, 15 mL and 20 mL. All dishes were placed on the same windowsill at room temperature, receiving the same amount of natural light. The control variables included the number of seeds, type of seed, size of dish, type of paper and position in the room.
该学生选择使用5个培养皿，每个培养皿内垫一张圆形滤纸。每个培养皿中，10粒水芹种子均匀放置在纸上。独立变量是加入每个培养皿的水量：0毫升、5毫升、10毫升、15毫升和20毫升。所有培养皿都放在同一个窗台上，室温相同，接收相同量的自然光。控制变量包括种子数量、种子种类、培养皿大小、纸张种类以及在房间中的位置。
4. Case Study 1: Designing the Experiment | 设计实验
A well-designed experiment includes a clear method so that another person could repeat it exactly. Here is the method planned for the germination investigation:
一个精心设计的实验包含清晰的方法，以便他人能准确复现。以下是为此发芽探究计划的方法：
1. Label five Petri dishes A, B, C, D and E.
2. Place one filter paper in each dish.
3. Place 10 cress seeds on each paper, spacing them apart.
4. Use a measuring cylinder to add water: 0 mL to A, 5 mL to B, 10 mL to C, 15 mL to D and 20 mL to E.
5. Put the lids on the dishes and place them on a tray by the window.
6. Observe the dishes each day for 7 days, counting the number of seeds that have germinated (visible radicle at least 2 mm long).
7. Record results in a table.
1. 给五个培养皿贴上标签 A、B、C、D 和 E。
2. 在每个培养皿中放一张滤纸。
3. 在每张纸上放 10 粒水芹种子，保持种子间距。
4. 用量筒加入水：A 加 0 毫升，B 加 5 毫升，C 加 10 毫升，D 加 15 毫升，E 加 20 毫升。
5. 盖上皿盖，将它们放在窗边的托盘上。
6. 每天观察培养皿，持续 7 天，数出已经发芽的种子数（可见胚根长度至少 2 毫米）。
7. 将结果记录在表格中。
Notice that the method specifies exact quantities and equipment, making it reproducible.
请注意，该方法标明了确切的数量和设备，使其具有可复现性。
5. Case Study 1: Collecting and Recording Data | 收集和记录数据
The student observed the dishes daily but here we present the final count after 7 days. The dependent variable was the number of germinated seeds out of 10. The raw data are shown below.
该学生每天观察培养皿，但这里我们展示第 7 天后的最终计数。因变量是 10 粒中发芽的种子数量。原始数据如下所示。
| Dish | Water added (mL) | Seeds germinated (out of 10) |
|---|---|---|
| A | 0 | 0 |
| B | 5 | 3 |
| C | 10 | 7 |
| D | 15 | 9 |
| E | 20 | 5 |
A results table must have clear headings with units where needed. It should also include the independent variable in the first column and the dependent variable in the right-hand column.
结果表格必须有清晰的标题，在需要时附上单位。还应该将独立变量放在第一列，因变量放在右侧列。
When you record data, always use the same level of precision – for example, counting in whole numbers. Note that dish E with 20 mL had fewer germinated seeds than dish D, perhaps because too much water prevented the seeds from getting enough air.
当你记录数据时，始终使用相同的精度——例如，以整数计数。注意，加有 20 毫升水的培养皿 E 发芽种子数比培养皿 D 少，可能是因为水太多使种子无法获得足够的空气。
6. Case Study 1: Creating a Bar Chart | 创建条形图
Since the independent variable (water volume) is a category, a bar chart is the correct choice for displaying the results. Follow these steps:
由于独立变量（水量）是一个分类，因此柱状图是展示结果的正确选择。请遵循以下步骤：
– Draw a horizontal x-axis labelled ‘Water added (mL)’ and a vertical y-axis labelled ‘Number of seeds germinated’.
– Choose a scale for the y-axis that goes up to at least 10, marking every 1 or 2.
– Draw bars of equal width, one for each water volume, with heights matching the number of germinated seeds.
– Leave spaces between the bars and add a title, e.g. ‘The effect of water on cress seed germination’.
– 画一条水平 x 轴，标注为“加入水量（毫升）”，一条垂直 y 轴，标注为“发芽种子数”。
– 为 y 轴选择一个至少到 10 的刻度，每 1 或 2 标记一次。
– 画出等宽的条柱，每个水量一个条柱，高度与发芽种子数匹配。
– 条柱之间留出间距，并添加标题，例如“水分对水芹种子发芽的影响”。
A well-drawn bar chart instantly shows the pattern: germination increases from 0 mL to 15 mL, then drops at 20 mL.
一张画得好的柱状图能立即显示出规律：发芽数量从 0 毫升到 15 毫升增加，然后在 20 毫升时下降。
7. Case Study 1: Analysis and Conclusion | 分析与结论
To analyse, describe the trend seen in the data. For example: ‘As the amount of water increased from 0 mL to 15 mL, the number of germinated seeds also increased. However, at 20 mL the germination fell to 5.’ This is a trend, not just a reading of numbers.
分析时，描述数据中看到的趋势。例如：“随着水量从 0 毫升增加到 15 毫升，发芽种子数也增加了。然而，在 20 毫升时，发芽数下降到 5。” 这是一种趋势，而不仅仅是读出数字。
The conclusion should state whether the hypothesis was supported. The hypothesis predicted more water leads to more germination, up to a point. The results support this: water is needed for germination, but too much can be harmful. Connect the conclusion to scientific ideas: seeds need water to activate enzymes and soften the seed coat, but excessive water can reduce oxygen availability.
结论应说明假设是否得到支持。假设预测在一定范围内，更多的水会导致更多的发芽。结果支持这一点：发芽需要水，但过多可能有害。将结论与科学概念联系起来：种子需要水来激活酶并软化种皮，但过量的水会减少氧气的可用性。
Always use data as evidence: ‘The seeds with 15 mL water had the highest germination (9 out of 10), whereas the seeds with no water did not germinate at all.’
始终用数据作为证据：“加 15 毫升水的种子发芽率最高（10 粒中 9 粒），而没有水的种子根本没有发芽。”
8. Case Study 2: Temperature and Sugar Dissolving | 案例2：温度与糖的溶解
Our second case study involves a chemistry-based investigation: ‘How does the temperature of water affect the time taken for a sugar cube to dissolve completely?’ A student predicted that a higher temperature would lead to a shorter dissolving time. Let’s examine the investigation and help evaluate it.
我们的第二个案例研究涉及一项基于化学的探究：“水温如何影响一块方糖完全溶解所需的时间？”一位学生预测，温度越高，溶解时间越短。我们来研究这项探究并帮助评估它。
The student used five beakers, each with 200 mL of water at different temperatures: 20 °C, 30 °C, 40 °C, 50 °C and 60 °C. A water bath was used to keep each temperature constant. A sugar cube of mass 5 g was dropped into each beaker and the mixture was stirred gently with a glass rod at a steady rate. The time from adding the cube until no solid sugar was visible was recorded in seconds. The independent variable was water temperature; the dependent variable was time to dissolve. Control variables included the volume of water, mass of sugar, stirring speed and beaker size.
该学生使用了五个烧杯，每个装有 200 毫升水，水温不同：20 °C、30 °C、40 °C、50 °C 和 60 °C。使用水浴保持每个温度恒定。一块质量为 5 克的方糖被放入每个烧杯，并用玻璃棒以稳定的速度轻轻搅拌。记录从放入糖块到看不到固体糖的时间（秒）。独立变量是水温；因变量是溶解时间。控制变量包括水的体积、糖的质量、搅拌速度和烧杯大小。
9. Case Study 2: Method and Fair Test | 方法与公平测试
Here is a summary of the method used. Read it and think about whether it is a fair test:
以下是所用方法的摘要。阅读并思考它是否是一个公平的测试：
1. Label beakers 20, 30, 40, 50 and 60.
2. Measure 200 mL of tap water into each using a measuring cylinder.
3. Place each beaker in a water bath set to the labelled temperature; wait 5 minutes for the water to reach the same temperature.
4. Use a digital thermometer to check the water temperature in the beaker.
5. Have a stopwatch ready. Add one 5 g sugar cube, start the watch and begin stirring gently at about one stir per second.
6. Stop the watch when the sugar is completely dissolved.
7. Record the time in a table.
8. Repeat the whole experiment twice more for each temperature to improve reliability.
1. 给烧杯贴上 20、30、40、50 和 60 的标签。
2. 用量筒量取 200 毫升自来水倒入每个烧杯。
3. 将每个烧杯放入设定到标签温度的水浴中；等待 5 分钟让水达到相同温度。
4. 用数字温度计检查烧杯内的水温。
5. 准备好秒表。加入一块 5 克方糖，启动秒表，并以大约每秒钟一圈的速度轻轻搅拌。
6. 当糖完全溶解时停止秒表。
7. 将时间记录在表格中。
8. 对每个温度重复整个实验两次，以提高可靠性。
Repeating readings allows you to calculate a mean time and spot any anomalous results. This investigation includes several strong control measures, such as the water bath and consistent stirring, making it a fair test.
重复读数可以计算平均时间并发现任何异常结果。该探究包含几项强有力的控制措施，如水浴和一致的搅拌，使其成为一个公平的测试。
10. Case Study 2: Data Table and Line Graph | 数据表与折线图
The results after calculating the mean of three trials are presented in the table below. In your own work, always show the raw data for each repeat and the mean.
经过计算三次试验的平均值后的结果展示在下表中。在你自己的工作中，始终展示每次重复的原始数据和平均值。
| Temperature (°C) | Mean dissolving time (s) |
|---|---|
| 20 | 120 |
| 30 | 80 |
| 40 | 45 |
| 50 | 25 |
| 60 | 15 |
Because temperature is a continuous variable, a line graph is the best way to show the relationship. Plot temperature on the x-axis (horizontal) and time on the y-axis (vertical). Draw a smooth line of best fit (not joining dot to dot with a ruler). Make sure axes are labelled with units and the graph has a clear title, such as ‘Graph to show how temperature affects the time taken for sugar to dissolve’.
因为温度是一个连续变量，所以折线图是展示这种关系的最佳方式。将温度绘在 x 轴（横向），时间绘在 y 轴（纵向）。画一条平滑的最佳拟合线（不要用尺子连接点）。确保坐标轴标有单位，并且图表有清晰的标题，例如“显示温度如何影响糖溶解所需时间的图表”。
The graph will show a downward-sloping curve: as temperature increases, dissolving time decreases. This is an inverse relationship.
图表将显示一条向下倾斜的曲线：随着温度升高，溶解时间减少。这是一种反向关系。
11. Case Study 2: Interpreting Results and Conclusion | 结果解读与结论
Interpreting data means explaining why the trend occurs. At higher temperatures, water particles move faster and have more energy. This means they collide with sugar particles more frequently and with greater force, pulling sugar molecules into solution more quickly. This scientific reasoning links the evidence to the particle model of matter.
解释数据意味着说明为什么会出现这种趋势。在较高温度下，水粒子运动更快，能量更大。这意味着它们与糖粒子的碰撞更频繁、更有力，能更快地将糖分子拉入溶液中。这一科学推理将证据与物质的粒子模型联系起来。
The conclusion can be written as: ‘The higher the temperature of water, the less time it takes for a sugar cube to dissolve. This supports the hypothesis and can be explained by the increased kinetic energy of water particles at higher temperatures.’ Always mention whether the data are reliable: ‘The results are considered reliable because each trial was repeated and the means were close to the raw times.’
结论可以这样写：“水温越高，方糖溶解所需时间越短。这支持了假设，并可由较高温度下水粒子动能增加来解释。” 务必提及数据是否可靠：“结果被认为是可靠的，因为每项试验都进行了重复，且平均值接近原始时间。”
If there were any unusual points, you should identify them as outliers and suggest a reason, such as a mistake in timing or unequal sugar cube size.
如果有任何异常点，你应该将其标识为离群值，并给出理由，例如计时错误或糖块大小不等。
12. Evaluating Investigations and Common Pitfalls | 评估探究与常见陷阱
Evaluation is about reflecting on the method – what worked well and what could be improved. Common pitfalls in case study exercises include not identifying all control variables, using unlabelled axes on graphs, forgetting units in tables, and writing conclusions that do not refer to specific data.
评估是关于反思方法——哪些做得好，哪些可以改进。案例分析练习中常见的陷阱包括：没有识别出所有控制变量、图表坐标轴未标注、表格中遗漏单位，以及撰写结论时未引用具体数据。
For the germination case study, a student might suggest improvements such as using more seeds per dish to increase reliability, repeating the experiment, or measuring the length of the radicle for more precise data. For the dissolving investigation, using a magnetic stirrer instead of hand stirring would control stirring speed more precisely.
对于发芽案例研究，学生可能会建议改进，例如每个培养皿使用更多种子以提高可靠性、重复实验，或测量胚根长度以获得更精确的数据。对于溶解探究，使用磁力搅拌器代替手动搅拌可以更精确地控制搅拌速度。
Always ask yourself: Was the test truly fair? Could the measurements be made more accurate? Is there another variable that might have affected the results? Practise writing evaluations by listing two strengths and two areas for improvement for any investigation you study.
总是问自己：测试真的公平吗？测量能否更准确？是否有其他变量可能影响了结果？通过为你学习的任何探究列出两个优点和两个改进领域来练习撰写评估。
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