📚 Year 7 Science Case Study Drills: Plant Growth Investigation | 植物生长探究案例分析实战演练
Case studies are a core part of CAIE Year 7 Science. They require you to interpret data, identify variables, draw conclusions and evaluate experiments – just like a real scientist. This article takes you step by step through a plant growth investigation, so you can master the skills needed to tackle any case study confidently.
案例分析是 CAIE 7 年级科学的核心组成部分。它要求你解读数据、识别变量、得出结论并评估实验，就像真正的科学家一样。本文将通过一个植物生长探究案例，逐步带你掌握应对各类案例分析所需的技能。
1. What Is a Case Study? | 什么是案例分析？
A science case study presents a short investigation or scenario, followed by questions. It might describe an experiment, give you a table of results or ask you to spot mistakes in the method. The aim is to test how well you can think scientifically, not just recall facts.
科学案例分析会先给出一个简短的探究或情景，再提出一些问题。它可能描述一个实验、给你一张结果表格，或者让你找出方法中的错误。目的是检验你能否像科学家一样思考，而不仅仅是回忆知识点。
2. Reading the Scenario | 阅读情景描述
Let us begin with a typical Year 7 case study. Read it carefully before we start to analyse it:
我们先来看一个典型的 7 年级案例。在开始分析之前，请仔细阅读：
Scenario: Sarah wanted to find out how different types of fertiliser affect the growth of bean plants. She filled four identical trays with the same type of soil and planted ten bean seeds in each. Tray A received no fertiliser. Tray B received organic fertiliser. Tray C received chemical fertiliser. Tray D received a mixture of organic and chemical fertiliser. All trays were placed on the same windowsill and given 50 ml of water every two days. After four weeks, Sarah measured the height of each plant and calculated the average height for each tray. Her results are shown in the table below.
情景：Sarah 想弄清楚不同类型的肥料对豆类植物生长的影响。她在四个相同的托盘中装入同种土壤，每个托盘种植十粒豆种。托盘 A 不施肥料，托盘 B 施有机肥，托盘 C 施化肥，托盘 D 施有机肥与化肥的混合肥料。所有托盘都放在同一个窗台上，每两天浇 50 ml 水。四周后，Sarah 测量了每株植物的高度，并计算出每个托盘的平均高度。结果见下表。
| Tray | Fertiliser type | Average plant height (cm) |
|---|---|---|
| A | None | 15 |
| B | Organic | 22 |
| C | Chemical | 30 |
| D | Mixture | 25 |
3. Identifying Variables | 识别变量
Every experiment has three kinds of variable. The independent variable is the factor you change on purpose. Here Sarah changed the type of fertiliser in each tray. The dependent variable is what you measure – in this case the average plant height. Control variables are all the factors you must keep the same to make the test fair. Sarah kept the amount of water, type of soil, number of seeds, light and container size the same.
每个实验都有三种变量。自变量是你故意改变的因素，这里 Sarah 改变了每个托盘的肥料类型。因变量是你测量的量，这里是植物的平均高度。控制变量是所有你必须保持不变的因素，以确保测试公平。Sarah 保持了水量、土壤类型、种子数量、光照和容器大小不变。
A common exam question asks, ‘Write down one control variable in this investigation.’ A good answer would be ‘the volume of water given each time’ or ‘the number of bean seeds per tray’. Avoid vague answers like ‘the water’ – always be specific.
考试中常见的提问是：“写出本探究中的一个控制变量。” 一个好的回答是“每次浇水的量”或“每个托盘的豆种数量”。避免像“水”这样含糊的回答——一定要具体。
4. Analysing the Results | 分析结果
Look at the table. Tray A plants, with no fertiliser, only grew to 15 cm on average. Tray B reached 22 cm, showing organic fertiliser helped. The tallest plants were in Tray C (chemical fertiliser) with 30 cm. Tray D with the mixture reached 25 cm. This suggests chemical fertiliser gave the strongest growth in this four‑week period, while the mixture was better than organic alone.
观察表格。没有施肥的托盘 A 植物平均只长到 15 cm。托盘 B 达到 22 cm，表明有机肥有帮助。最高的植物在托盘 C（化肥），为 30 cm。混合肥料的托盘 D 达到 25 cm。这表明在四周内化肥带来的生长最旺盛，而混合肥料比单施有机肥效果更好。
When you describe results, use numbers from the table. For example: ‘The average height increased from 15 cm (no fertiliser) to 30 cm (chemical fertiliser), a difference of 15 cm.’ This shows the examiner you can work with data.
当你描述结果时，要用表格中的数字。例如：“平均高度从 15 cm（无肥）增加到 30 cm（化肥），相差 15 cm。” 这能向考官展示你会处理数据。
5. Drawing Conclusions | 得出结论
Based on the evidence, we can say chemical fertiliser produced the tallest bean plants over four weeks, while no fertiliser gave the shortest. However, a conclusion must not go beyond the data. You cannot claim ‘chemical fertiliser is always best’ because the experiment only lasted four weeks and used only bean plants. A valid conclusion is: ‘In this investigation, chemical fertiliser resulted in the greatest average plant height.’
根据证据，我们可以说在四周内化肥使豆类植物长得最高，而不施肥的植物最矮。但结论不能超越数据范围。你不能宣称“化肥总是最好的”，因为这个实验只持续了四周，且只用了一种植物。一个有效的结论是：“在本探究中，化肥带来了最大的平均植株高度。”
Many marks are lost when students write conclusions that are too broad or ignore the data. Always start your conclusion with phrases like ‘The results show that…’ and mention specific numbers.
很多失分是因为学生写的结论太宽泛或忽略了数据。一定要用“结果表明……”这样的句式开头，并提及具体数字。
6. Evaluating the Experiment | 评估实验
Even well‑designed investigations have weaknesses. Sarah used ten seeds per tray, which is good because it gives a more reliable average. However, she did not repeat the whole experiment. Repeats would tell us if the pattern happens again. Another possible issue is that window light might not be perfectly even – some trays could have received slightly more sunlight. She also did not measure the initial height of seeds, though seeds start at zero. A further improvement would be to use a ruler with millimetre markings to increase precision.
即使是设计良好的探究也有不足之处。Sarah 每个托盘用了十粒种子，这很好，因为能得出更可靠的平均值。但是，她没有重复整个实验。重复能告诉我们该规律是否会再次出现。另一个可能的问题是窗台的光照可能不完全均匀——有些托盘可能接受了稍多的阳光。她也没有测量种子的初始高度，尽管种子从零开始。进一步的改进可以是使用有毫米刻度的尺子来提高精确度。
When evaluating, always suggest a realistic improvement. For example: ‘Place the trays in a controlled environment with artificial light to ensure all plants get exactly the same light intensity.’
评估时，总要提出切实可行的改进建议。例如：“将托盘放在受控环境中，使用人工光源，确保所有植物获得完全相同的光照强度。”
7. Practice Task: Your Turn | 练习任务：轮到你了
Now apply the same skills to a new scenario. Read it and try to answer the questions in your head before reading the guidance.
现在将同样的技能应用到一个新情景中。阅读情景，在查看指导前试着自己思考问题。
Scenario: James investigated how water temperature affects the time it takes for a sugar cube to dissolve. He placed 200 ml of water into each of three identical beakers. Beaker 1 had water at 10 °C, Beaker 2 at 25 °C and Beaker 3 at 50 °C. He dropped one sugar cube into each beaker and stirred once every 10 seconds. He recorded the time until no solid sugar was visible. His results: Beaker 1 – 180 s, Beaker 2 – 85 s, Beaker 3 – 35 s.
情景：James 探究水温对方糖溶解时间的影响。他在三个相同的烧杯中各倒入 200 ml 水。烧杯 1 水温 10 °C，烧杯 2 为 25 °C，烧杯 3 为 50 °C。他在每个烧杯中放入一块方糖，每 10 秒搅拌一次，记录直到看不见固态糖的时间。结果：烧杯 1 – 180 秒，烧杯 2 – 85 秒，烧杯 3 – 35 秒。
Identify the independent and dependent variables, describe the trend, write a conclusion and suggest one improvement.
识别自变量和因变量，描述趋势，写一个结论并提出一项改进。
Model thoughts: Independent variable = water temperature; dependent variable = dissolving time. Trend: as temperature rose, dissolving time decreased. Conclusion: ‘The higher the temperature, the faster the sugar cube dissolved in this investigation.’ Improvement: use a thermometer to check temperatures or stir at exactly the same speed using a magnetic stirrer.
答题思路：自变量 = 水温；因变量 = 溶解时间。趋势：温度升高，溶解时间缩短。结论：“在本探究中，温度越高，方糖溶解越快。” 改进：使用温度计核查温度，或使用磁力搅拌器以完全相同的速度搅拌。
8. Common Mistakes to Avoid | 常见错误避免
First, confusing the independent and dependent variables. Remember: the independent variable is the one you change, the dependent variable is the one you measure. Second, forgetting control variables. Always ask yourself, ‘What must I keep the same to make the test fair?’ Third, writing a conclusion that does not refer to the data. Use the numbers. Fourth, offering weak evaluations like ‘do the experiment more carefully’. Instead, specify how – control more variables, use more precise instruments or increase sample size.
第一，混淆自变量和因变量。记住：自变量是你改变的那个，因变量是你测量的那个。第二，忘记控制变量。总是问自己：“我必须保持什么不变才能确保测试公平？” 第三，写结论不提数据。要使用数字。第四，提出软弱的评估，如“更仔细地做实验”。相反，要具体说明怎么做——控制更多变量、使用更精密的仪器或增加样本量。
Finally, some students panic when they see a table they have never seen before. Relax – the science skills are always the same: read the headings, note the units and look for patterns.
最后，有些学生一看到从未见过的表格就慌张。放轻松——科学技能总是相同的：阅读表头，注意单位并寻找规律。
Published by TutorHao | Science Revision Series | aleveler.com
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