Case Study Practical Exercises | 案例分析实战演练

📚 Case Study Practical Exercises | 案例分析实战演练

Case studies are a key part of the WJEC Year 9 science course. They test your ability to think like a scientist by asking you to plan investigations, handle data, spot patterns and evaluate experiments. In this article, we will work through a complete case study together, step by step, so you can build the skills you need to tackle any science scenario with confidence.

案例研究是WJEC九年级科学课程的关键部分。它通过要求你规划调查、处理数据、发现规律和评估实验，来测试你像科学家一样思考的能力。在这篇文章中，我们将一步步地共同完成一个完整的案例研究，帮你建立所需的技能，自信地应对任何科学场景。

1. Understanding the Case Study Scenario | 理解案例研究背景

A student wants to find out how different concentrations of liquid fertiliser affect the growth of mung bean seedlings. She prepares four groups of seedlings, giving each group a different fertiliser concentration: 0% (distilled water only), 5%, 10% and 15%. All other conditions, such as light, temperature and watering schedule, are kept the same. After 7 days, she measures the height of each seedling.

一名学生想探究不同浓度的液体肥料如何影响绿豆幼苗的生长。她准备了四组幼苗，每组给予不同的肥料浓度：0%（仅蒸馏水）、5%、10%和15%。所有其他条件，如光照、温度和浇水时间均保持一致。7天后，她测量了每株幼苗的高度。

Before diving into the method, always read the scenario carefully and underline the key information: the aim of the experiment, the independent variable (what is changed), the dependent variable (what is measured), and the controlled variables (what must stay the same). This forms the foundation of your analysis.

在深入方法之前，务必仔细阅读情景并标出关键信息：实验的目的、自变量（改变的因素）、因变量（测量的因素）和控制变量（必须保持一致的因素）。这构成了你分析的基础。

2. Identifying the Variables | 识别变量

Independent variable: the concentration of fertiliser (%). This is the factor the student deliberately changes.

自变量：肥料浓度（%）。这是学生故意改变的因素。

Dependent variable: the height of the seedlings (cm) after 7 days. This is what is measured; its value depends on the independent variable.

因变量：7天后幼苗的高度（cm）。这是测量的对象；其数值依赖于自变量。

Controlled variables: amount of light (e.g. by a window for 12 hours daily), temperature (kept at 22°C), volume of water given (20 ml each day), type and number of seeds per pot, and size of pots. These must be kept constant to ensure a fair test.

控制变量：光照量（例如每天靠窗12小时）、温度（保持22°C）、浇水量（每天20毫升）、每盆种子的类型和数量以及花盆的大小。这些必须保持不变，以确保公平测试。

3. Formulating a Hypothesis | 提出假设

A hypothesis is a testable statement that predicts the outcome. For example: ‘As fertiliser concentration increases from 0% to 10%, seedling height will increase, but at 15% growth will decrease because high salt levels in the fertiliser may cause water to move out of plant cells by osmosis.’ This uses scientific reasoning and is directional.

假设是一种可检验的陈述，预测结果。例如：“随着肥料浓度从0%增加到10%，幼苗高度会增加，但在15%时生长会下降，因为肥料中的高盐分可能导致水分通过渗透作用移出植物细胞。”这使用了科学推理并且具有方向性。

And in Chinese: 假设是一个可检验的预测性陈述。例如：“随着肥料浓度从0%增加到10%，幼苗高度会增加，但在15%时生长会下降，因为肥料中的高盐分可能导致水分通过渗透作用移出植物细胞。”要学会用科学知识来解释你的预测。

当你提出假设时，要用科学知识解释预测。不要只说“它会长得更高”，而要说明为什么。提及渗透作用或养分可得性，能展示你对概念的深刻理解。

4. Designing the Method | 设计实验方法

A clear step-by-step method must allow another scientist to repeat the investigation exactly. The student should write numbered steps, mentioning quantities, timings and safety precautions.

一个清晰的、分步骤的方法必须让另一位科学家能精确地重复该项调查。应编写编号步骤，提及数量、时间和安全预防措施。

Example steps:

示范步骤：

• Soak 40 mung bean seeds in water overnight. Plant 3 seeds in each of 12 small pots filled with the same type of compost. | 将40粒绿豆种子浸泡一夜。在12个装有同种堆肥的小盆中各播种3粒。

• Label four groups (0%, 5%, 10%, 15%), with three pots per group. Place all pots in the same sunny location. | 标记四组（0%、5%、10%、15%），每组三个盆。将所有盆放在同一阳光充足的位置。

• Every day, water the 0% group with 20 ml distilled water; water other groups with 20 ml of the corresponding fertiliser solution. | 每天，用20毫升蒸馏水浇灌0%组；用相应浓度的肥料溶液20毫升浇灌其他组。

• After 7 days, gently remove seedlings from the soil, measure the height from base to tip using a ruler, and record the measurements. | 7天后，轻轻从土中取出幼苗，用尺子测量从基部到顶梢的高度，并记录测量值。

• Wear gloves when handling fertiliser solutions and wash hands afterwards. | 处理肥料溶液时戴手套，事后洗手。

Always include a control group (0%) to see what happens without the treatment, and repeat measurements (3 trials) to improve reliability.

务必包含一个对照组（0%），以便了解未经处理的情况；并重复测量（3次试验），以提高可靠性。

5. Collecting and Recording Data | 收集与记录数据

Data must be recorded in a clear table with headings, units and averages where appropriate. Below is the data collected by the student. She calculated the mean height for each concentration.

数据必须记录在清晰的表格中，包含标题、单位，并在合适处计算平均值。以下是学生收集的数据。她计算了每个浓度下的平均高度。

Fertiliser concentration (%)	Trial 1 (cm)	Trial 2 (cm)	Trial 3 (cm)	Mean (cm)
0	4.2	3.8	4.0	4.0
5	6.5	7.0	6.8	6.8
10	5.6	5.4	5.8	5.6
15	3.0	2.5	2.9	2.8

The mean is calculated using the formula:

平均值使用以下公式计算：

Mean = (Trial 1 + Trial 2 + Trial 3) ÷ 3

Notice that within each group, the individual trial values are close together (small spread), which suggests good repeatability. An anomalous result would be one that does not fit the pattern—for instance, if a trial in the 10% group had given 8.2 cm, it would stand out and may be excluded if a reason (like a measurement error) could be identified. Always check for outliers before calculating a mean.

注意，每组内各次试验的数值很接近（离散度小），这表明重复性良好。异常结果是指不符合整体规律的数据——例如，如果10%浓度组中有一个试验结果为8.2 cm，它会很突出，如果能够查明原因（如测量错误），则可以将其排除。在计算平均值前，务必检查异常值。

6. Presenting Data in a Graph | 用图表呈现数据

A well-drawn graph makes trends easier to see. For continuous independent variables like concentration, a line graph is suitable; for discrete categories, a bar chart may be used. Here, a line graph with points plotted for each mean and joined with straight lines will help show how height changes with concentration. You could also plot bar charts with error ranges using the trial values.

画得好的图表能让趋势一目了然。对于浓度这类连续的自变量，适合用折线图；对于离散的类别，可使用条形图。在此，用各平均值描点并连成直线的折线图有助于展现高度随浓度如何变化。你也可以利用试验数值绘制带误差范围的条形图。

Key graph features:

图表的关键要素：

• Title: ‘Effect of Fertiliser Concentration on the Height of Mung Bean Seedlings’ | 标题：“肥料浓度对绿豆幼苗高度的影响”

• x-axis: Fertiliser concentration (%) with a clear scale | x轴：肥料浓度（%），刻度清晰

• y-axis: Mean seedling height (cm) starting from zero | y轴：幼苗平均高度（cm），从零开始

• Plot the four points: (0, 4.0), (5, 6.8), (10, 5.6), (15, 2.8) | 标出四个点：(0, 4.0)、(5, 6.8)、(10, 5.6)、(15, 2.8)

• Draw a smooth curve or straight line segments to show the trend. | 画平滑曲线或折线段以显示趋势。

Never forget to label axes with units and use a pencil and ruler for neatness.

绝不要忘记给坐标轴标注单位，并使用铅笔和直尺以保持整洁。

7. Analysing the Results | 分析结果

As fertiliser concentration increases from 0% to 5%, the mean height increases from 4.0 cm to 6.8 cm. This is a rise of 2.8 cm, suggesting that the seedlings benefit from the added nutrients.

随着肥料浓度从0%增加到5%，平均高度从4.0 cm上升到6.8 cm，升高了2.8 cm，表明幼苗从添加的养分中获益。

However, at 10% the mean height falls to 5.6 cm, and at 15% it drops further to 2.8 cm, which is lower than the control group. This shows that while a small amount of fertiliser promotes growth, higher concentrations inhibit it, likely because the high solute concentration in the soil makes it harder for roots to absorb water by osmosis—water can even be drawn out of the plant cells.

然而，浓度为10%时平均高度降至5.6 cm，15%时进一步降至2.8 cm，甚至低于对照组。这表明，少量肥料可促进生长，但高浓度会抑制生长，很可能是因为土壤中的高溶质浓度使根系难以通过渗透作用吸收水分——水分甚至可能从植物细胞中被抽出。

Describing the overall pattern: height increases then decreases, showing an optimum around 5% fertiliser concentration for these seedlings.

描述整体规律：高度先升后降，显示这些幼苗的最适肥料浓度约在5%。

8. Evaluating the Investigation | 评估调查

An evaluation considers the quality of the data and the method. Strengths: three trials were conducted, allowing a mean to be calculated and reducing the effect of random errors. The same compost type and pot size were used, keeping variables controlled.

评估需要考虑数据和方法的品质。优点：进行了三次试验，可以计算平均值并减少随机误差的影响；使用了相同的堆肥类型和花盆尺寸，控制了变量。

Weaknesses: measuring seedling height with a ruler might introduce parallax error if the eye is not level with the top of the seedling. Also, 7 days may not be enough time for full effects to show, and only one type of fertiliser was tested—the results might differ with other brands. The sample size (3 seedlings per group) is small; more replicates would make the data more reliable.

弱点：用尺子测量幼苗高度时，如果眼睛没有与幼苗顶端保持水平，可能引入视差误差。此外，7天可能不足以显现全部效应，而且仅测试了一种肥料——其他品牌的结果可能不同。样本量（每组3株幼苗）较小；增加重复将使数据更可靠。

9. Suggesting Improvements | 提出改进建议

To improve accuracy, use a clamp stand to hold the ruler vertically and measure to the nearest millimetre with an eye-level reading. You could also use a digital balance to control the exact mass of fertiliser used in each solution, ensuring more precise concentrations.

为提高准确性，可使用铁架台垂直固定尺子，在视线水平的情况下测量到最接近的毫米。还可以使用电子天平来控制每种溶液中肥料的确切质量，确保浓度更精确。

To increase reliability, grow at least 5 seedlings per concentration instead of 3, and repeat the entire experiment at different times of the year to check reproducibility. Extending the growing period to 14 days might reveal longer-term effects, such as plant death at high concentrations.

为增强可靠性，每组至少种植5株幼苗而非3株，并在一年中的不同时段重复整个实验，以检验可重复性。将生长期延长至14天可能揭示长期效应，例如高浓度下植株死亡。

10. Drawing Conclusions | 得出结论

The hypothesis is partially supported: fertiliser at 5% does increase growth compared to no fertiliser, but at 15% growth is severely reduced, matching the prediction that high salt levels cause osmotic stress. The optimal concentration under these conditions is around 5%.

该假设得到部分支持：与不施肥相比，5%的肥料确实促进了生长，但在15%浓度下生长严重减缓，这与高盐分引起渗透胁迫的预测相符。在这些条件下的最适浓度约为5%。

A conclusion must directly refer back to the data. For instance: ‘The results show that increasing fertiliser concentration up to 5% leads to an increase in seedling height, but concentrations above this cause a decrease, with the 15% group growing least. This suggests that low fertiliser levels supply essential nutrients, whereas high levels impose osmotic water loss.’ Avoid making claims not supported by the data.

结论必须直接引用数据。例如：“结果表明，肥料浓度增加到5%会导致幼苗高度增加，但超过此浓度会引起下降，其中15%组生长最差。这表明低浓度肥料提供必需养分，而高浓度造成渗透性失水。”不要作出数据不支持的主张。

11. Applying to Exam Questions | 应用到考试问题

WJEC case study questions often ask: ‘Identify one variable the student controlled and explain why it must be kept constant,’ or ‘Describe the relationship shown in the graph,’ or ‘Suggest one way to improve the investigation and explain your choice.’ Practice writing precise answers using scientific keywords.

WJEC案例研究题常会问：“指出学生控制的一个变量，并解释为何必须保持它不变”，或“描述图表所示的关联”，或“提出一种改进调查的方法并解释你的选择”。练习使用科学关键词写出精确的答案。

For example: ‘Why was it important to use the same volume of liquid for all groups?’ Answer: ‘To ensure that any differences in growth were due to fertiliser concentration, not to different amounts of water, making it a fair test.’

例如：“为何所有组使用等体积液体很重要？”答：“为了确保生长的任何差异是由于肥料浓度而非水量不同造成的，从而实现公平测试。”

Always link your answer to the principle of a fair test: only the independent variable should change; everything else stays the same. This is at the heart of scientific inquiry.

回答时始终联系公平测试原则：只有自变量应改变；其他一切保持不变。这是科学探究的核心。

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Published by TutorHao | Science Revision Series | aleveler.com

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