📚 Year 8 CAIE Science: Case Study Practice | 案例分析实战演练
Case studies are an excellent way to sharpen your scientific enquiry skills for the Year 8 CAIE Science curriculum. They challenge you to apply the scientific method to real‑world or simulated scenarios, just like a professional scientist would. By working through case studies, you practise identifying variables, designing fair tests, collecting and presenting data, and drawing evidence‑based conclusions. This article presents three complete case studies – on plant growth, dissolving, and series circuits – and guides you step by step through the core skills you need for success in your assessments.
案例分析是锻炼 CAIE 8 年级科学探究技能的绝佳方式。它要求你像真正的科学家一样，将科学方法应用到真实或模拟的情境中。通过分析案例，你可以练习识别变量、设计公平实验、收集和展示数据，并得出基于证据的结论。本文为你带来了三个完整的案例——植物生长、溶解和串联电路，并逐步指导你掌握评估中所需的核心技能。
1. What is a Scientific Case Study? | 什么是科学案例分析？
A scientific case study presents a detailed investigation of a particular problem or experiment. It often includes background information, a hypothesis, experimental data, and results that need to be analysed and explained. In CAIE Year 8 Science, case study questions test your ability to think like a scientist – they ask you to plan investigations, evaluate methods, and link findings to scientific ideas.
科学案例分析是对特定问题或实验的详细研究。它通常包括背景信息、假设、实验数据和需要分析与解释的结果。在 CAIE 8 年级科学中，案例分析题测试你像科学家一样思考的能力——它们要求你规划探究、评估方法并将发现与科学概念联系起来。
2. Case Study 1: Plant Growth and Light | 案例一：植物生长与光照
A student wanted to find out how light intensity affects the growth of bean seedlings. She placed three trays of seedlings in different light conditions: full sunlight, partial shade (covered with a thin cloth), and complete darkness (inside a cupboard). All trays received the same amount of water and were kept at the same room temperature. The heights of the seedlings were measured every two days for ten days.
一位学生想探究光照强度如何影响豆苗的生长。她把三盘幼苗分别放在不同的光照条件下：全日照、半遮阴（用薄布遮盖）和完全黑暗（放在橱柜里）。所有盘子浇等量的水，并保持相同的室温。每两天测量一次幼苗的高度，持续十天。
3. Identifying Variables | 识别变量
In any investigation, you must be able to identify the independent variable (the one you change), the dependent variable (the one you measure) and the control variables (the ones you keep the same). In this plant growth study, the independent variable is the light condition (full light, half shade, dark). The dependent variable is the height of the bean seedlings, usually measured in centimetres. Controlled variables include the type and amount of soil, volume of water given, size of the trays, and temperature.
在任何探究中，你都必须能够识别自变量（你改变的量）、因变量（你测量的量）和控制变量（保持不变的量）。在这个植物生长研究中，自变量是光照条件（全光照、半遮阴、黑暗）。因变量是豆苗的高度，通常以厘米为单位测量。控制变量包括土壤的类型和用量、浇水量、托盘大小和温度。
4. Designing a Fair Test | 设计公平测试
A fair test means changing only one factor at a time while keeping all other conditions identical. This allows you to be confident that any changes in the dependent variable are truly caused by the independent variable. The student ensured a fair test by using the same batch of bean seeds, identical plastic trays, and watering each tray with exactly 50 ml of tap water every morning. She also placed a thermometer in the room to confirm the temperature stayed constant at 22 °C.
公平测试意味着一次只改变一个因素，同时保持其他所有条件相同。这样你才能确信因变量的任何变化确实是由自变量引起的。学生通过使用同一批豆种、相同的塑料托盘，并每天早晨为每盘浇 50 毫升自来水，来确保公平测试。她还在房间内放置了温度计，以确认温度稳定在 22 °C。
5. Data Collection and Recording | 数据收集与记录
Accurate data collection is essential. The student recorded the height of three randomly chosen seedlings in each tray and calculated the mean height. Results were noted in a clearly labelled table. An example table is shown below.
准确的数据收集至关重要。学生测量了每盘中随机选取的三株幼苗的高度，并计算了平均高度。结果记录在一个标注清晰的表格中。下面是一个示例表格。
| Day | Full light (cm) | Half shade (cm) | Dark (cm) |
|---|---|---|---|
| 0 | 2.5 | 2.5 | 2.5 |
| 2 | 3.8 | 3.2 | 3.0 |
| 4 | 5.4 | 4.0 | 3.6 |
| 6 | 7.1 | 4.7 | 4.4 |
| 8 | 8.9 | 5.3 | 5.5 |
| 10 | 10.5 | 5.9 | 7.0 |
Table 1: Mean height of bean seedlings under different light conditions.
表 1: 不同光照条件下豆苗的平均高度。
6. Presenting Data: Graphs and Tables | 数据展示：图表与表格
Turning raw numbers into graphs helps you spot patterns quickly. The student plotted a line graph with 'Time (days)' on the x‑axis and 'Mean height (cm)' on the y‑axis. Three different coloured lines represented the three light conditions. The graph showed that seedlings in full light grew steadily and were tallest by day 10. The dark‑grown seedlings initially elongated but became thin, pale and unhealthy. You can also quantify the growth rate using the formula:
将原始数据转化为图表能帮助你快速发现规律。学生绘制了折线图，x 轴为 "时间（天）"，y 轴为 "平均高度（厘米）"。三种不同颜色的线代表三种光照条件。图表显示，全光照下的幼苗稳定生长，到第 10 天最高。黑暗环境中生长的幼苗最初徒长，但变得细长、苍白且不健康。你也可以用下面的公式量化生长速率：
Growth rate = (final height − initial height) ÷ number of days
roup: (10.5 − 2.5) ÷ 10 = 0.8 cm/day. This mathematical treatment strengthens conclusions.
全光照组： (10.5 − 2.5) ÷ 10 = 0.8 厘米/天。这样的数学处理能强化结论。
7. Interpreting Results | 结果解读
Interpreting results means explaining what the data tells us scientifically. In full sunlight, plants carried out photosynthesis efficiently, producing glucose for energy and growth, which led to strong green stems and leaves. The half‑shade plants grew more slowly because less light reached their leaves. Surprisingly, the dark‑grown seedlings were not the shortest; they grew tall, spindly and yellow because they were etiolating – using stored food reserves to search for light. Without light, they could not produce chlorophyll and eventually would die.
解读结果意味着从科学角度解释数据告诉我们的信息。在充足阳光下，植物高效地进行光合作用，产生葡萄糖用于能量和生长，因此茎叶强壮翠绿。半遮阴的植株生长较慢，因为叶片接收到的光较少。令人意外的是，黑暗环境中生长的幼苗并非最矮；它们长得又高又细又黄，这是因为发生了黄化现象——它们利用储存的养分拼命寻找光线。没有光，它们无法合成叶绿素，最终会死亡。
8. Drawing Conclusions | 得出结论
A valid conclusion states whether the results support the original hypothesis and is backed by data. The student concluded that light is essential for healthy plant growth. Adequate light increases growth rate and enables the production of chlorophyll. This is directly linked to the process of photosynthesis, summarised by the word equation:
有效的结论要说明结果是否支持最初的假设，并要有数据支撑。学生得出结论：光对植物的健康生长至关重要。充足的光照提高生长速率，并使植物能够合成叶绿素。这直接与光合作用过程相关，其文字方程式总结如下：
Carbon dioxide + water → glucose + oxygen
In symbols, using sunlight energy captured by chlorophyll:
用符号表示（利用叶绿素捕获的太阳能）：
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
The results clearly show that without light, photosynthesis cannot happen, and plants cannot thrive.
结果清楚地表明，没有光，光合作用无法进行，植物也就无法茁壮成长。
9. Case Study 2: Investigating Dissolving | 案例二：探究溶解
A second student investigated how temperature affects the time taken for table salt to dissolve. She added 5 g of salt to 100 cm³ of water at 10 °C, 20 °C, 30 °C, 40 °C and 50 °C, stirring each sample exactly 20 times with a glass rod. She recorded the time (in seconds) until no solid remained. Each trial was repeated twice more and a mean time was calculated. The table below shows the mean values.
第二位学生探究了温度如何影响食盐溶解所需的时间。她将 5 克盐加入 100 立方厘米水中，水温分别为 10 °C、20 °C、30 °C、40 °C 和 50 °C，每次用玻璃棒恰好搅拌 20 次。她记录下固体完全消失的时间（秒）。每个试验重复两次，然后计算平均时间。下表显示了这些平均值。
| Temperature (°C) | Mean dissolving time (s) |
|---|---|
| 10 | 85 |
| 20 | 52 |
| 30 | 31 |
| 40 | 18 |
| 50 | 10 |
The independent variable was temperature; the dependent variable was dissolving time. Control variables included mass of salt, volume of water, number of stirs, and using the same type of salt. The data show a clear trend: as temperature increases, dissolving time decreases. This is because warmer water particles move faster, collide more often and with greater energy, breaking apart the salt crystals more quickly.
自变量是温度；因变量是溶解时间。控制变量包括盐的质量、水的体积、搅拌次数和使用同一种盐。数据呈现出明显趋势：随着温度升高，溶解时间缩短。这是因为较热的水粒子运动更快，碰撞更频繁且能量更高，能更快地分开盐的晶体。
10. Evaluating Methods and Sources of Error | 评估方法与误差来源
No experiment is perfect. In the dissolving investigation, the main sources of error included difficulty in keeping the water temperature exactly constant during stirring, judging the exact moment all solid had dissolved, and variation in stirring speed. The student could have improved the method by using a water bath to maintain temperature, a stopwatch to time accurately, and a thermometer to check the water temperature before each trial. Calculating a mean from repeated readings also reduced random errors. A simple formula for percentage difference between highest and lowest trial can be used to assess precision:
没有实验是完美的。在溶解探究中，主要误差来源包括搅拌时难以保持水温完全恒定、判断固体全部溶解的精确时刻，以及搅拌速度的差异。学生可以通过使用水浴来维持温度、用秒表精确计时，以及在每次试验前用温度计检查水温，来改进方法。通过对重复读数计算平均值，也减少了随机误差。用以下简单公式可以计算最高与最低试验值之间的百分比差异，以评估精密度：
Percentage difference = (highest time − lowest time) ÷ mean time × 100%
11. Real-World Application: Case Study 3 – Series Circuits | 实际应用：案例三 – 串联电路
In a physics investigation, a student built a series circuit with a single cell, a switch, an ammeter and one bulb. She then added a second bulb in series and measured the current. She repeated the measurement with a third bulb. The aim was to find out how adding more bulbs changes the current in a series circuit. The results were recorded in a table.
在一次物理探究中，学生搭建了一个串联电路，包含一节电池、一个开关、一个电流表和一盏灯泡。然后她串联了第二盏灯泡并测量电流，接着又加上了第三盏灯泡。目的是探究在串联电路中增加灯泡如何改变电流。结果记录在表格中。
| Number of bulbs | Current (A) |
|---|---|
| 1 | 0.45 |
| 2 | 0.22 |
| 3 | 0.15 |
The independent variable was the number of bulbs (which changed the total resistance); the dependent variable was the current. Controlled variables included the cell voltage, the type of wire and bulbs, and the ammeter setting. The results show that as more bulbs are added in series, the current decreases. This is because each bulb adds resistance, and in a series circuit the total resistance is the sum of all individual resistances. Ohm’s law helps explain this mathematically:
自变量是灯泡数量（它改变了总电阻）；因变量是电流。控制变量包括电池电压、导线和灯泡类型以及电流表量程。结果表明，串联的灯泡越多，电流越小。这是因为每盏灯泡都增加了电阻，而在串联电路中，总电阻是所有单个电阻之和。欧姆定律有助于从数学上解释这一点：
V = I × R
tant at 1.5 V, the increased resistance caused the current to drop according to I = V ÷ R.
其中 V 是电压（伏特），I 是电流（安培），R 是总电阻（欧姆）。由于电池电压恒定为 1.5 伏，增加的电阻导致电流按照 I = V ÷ R 的关系下降。
12. Practice Tips for CAIE Science | CAIE 科学备考建议
To excel in case study questions, always read the scenario carefully. Underline the independent, dependent and controlled variables. Check whether the data in tables or graphs contain any anomalies, and suggest possible reasons. When drawing graphs, use a sharp pencil, label axes clearly with quantities and units, and draw a smooth line or curve of best fit. In conclusions, refer back to the hypothesis and support your answer with numerical evidence from the data. Finally, when evaluating, mention at least one source of error and one realistic improvement. Remember to always prioritise safety in any practical work.
要在案例分析题中取得优异成绩，务必仔细阅读情境。用下划线标出自变量、因变量和控制变量。检查表格或图表中的数据是否存在异常值，并推测可能的原因。绘图时，用尖铅笔，清晰标注坐标轴名称和单位，并画出平滑的最佳拟合线或曲线。在结论部分，要回扣假设，并用数据中的数字证据支撑你的答案。最后，在评估时，至少要提到一个误差来源和一个切实可行的改进方法。请记住，在任何实验操作中都要始终把安全放在第一位。
Published by TutorHao | Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图