📚 Mastering Experimental Design for Edexcel IGCSE Science | 掌握Edexcel IGCSE科学实验设计
In IGCSE Science (Biology, Chemistry and Physics), experimental design is a core skill. Many exam marks are awarded for planning, recognising variables and evaluating evidence. This revision guide will show you how to build strong experiments and answer practical questions confidently.
在IGCSE科学（生物、化学和物理）中，实验设计是一项核心技能。许多考试分数来自制定计划、识别变量和评估证据。本复习指南将帮助你构建可靠的实验，并自信地回答实验类题目。
1. Practical vs Theoretical Work | 实验技能与理论知识
IGCSE Science exams test both your scientific knowledge and your practical skills. You must be able to recall facts and also understand how to design and evaluate experiments.
IGCSE科学考试同时考察你的科学知识和实验技能。你不仅要能回忆事实，还要理解如何设计和评价实验。
The practical component is not just about using apparatus. It also includes asking questions, collecting data, drawing conclusions and communicating your results clearly.
实验部分不仅仅是使用仪器，还包括提出问题、收集数据、得出结论并清晰地交流你的结果。
2. The Aim of an Investigation | 明确调查目的
Every experiment starts with a clear question or aim. For example, “How does temperature affect the rate of an enzyme-controlled reaction?” The aim tells you what you are going to change and what you are going to measure.
每个实验都以一个清晰的问题或目标开始。例如“温度如何影响酶促反应速率？”。实验目的告诉你将要改变什么，以及将要测量什么。
In an exam question, you might be asked to state the aim. You can use the phrasing: “To investigate the effect of [independent variable] on [dependent variable].”
在考试中，你可能会被要求写出实验目的。你可以这样表述：“研究[自变量]对[因变量]的影响。”
3. Variables: Independent, Dependent and Control | 变量：自变量、因变量和控制变量
Variables are the factors that can change in an experiment. The independent variable is the one that you deliberately change. The dependent variable is the one that you measure. Control variables are the ones that you keep constant to ensure a fair test.
变量是实验中可以改变的因素。自变量是你有意改变的量，因变量是你测量的量，控制变量是你保持恒定的量，以保证实验公平。
Here is an example for a temperature experiment on enzyme activity:
下面是一个关于温度对酶活性影响的实验例子：
| Type of variable | Meaning | Example |
| Independent | The factor you change | Temperature |
| Dependent | The factor you measure | Rate of reaction |
| Control | Factors kept constant | pH, enzyme concentration, substrate volume |
Always identify all three types of variables before you start planning. A common exam mistake is to confuse dependent and control variables.
在开始制定计划前，一定要识别出这三种变量。一个常见的考试错误是混淆因变量和控制变量。
4. Formulating a Hypothesis | 提出假设
A hypothesis is an educated prediction that links the independent variable to the dependent variable. It should be testable and based on scientific reasoning.
假设是基于科学推理的有根据的预测，它将自变量与因变量联系起来。假设应可检验，并且有科学依据。
For example: “As temperature increases, the rate of enzyme activity will increase until it reaches the optimum temperature, because higher kinetic energy leads to more frequent collisions between enzyme and substrate.”
例如：“随着温度升高，酶活性速率会增大，直到达到最适温度，因为更高的动能导致酶与底物之间的碰撞更频繁。”
Use the structure “If… then… because…” to write a clear hypothesis. This helps you show the cause-effect relationship in your answer.
使用“如果……那么……因为……”的结构来写出清晰的假设。这有助于你在答案中展示因果关系。
5. Planning the Experimental Steps | 设计实验步骤
A good plan must be logical, repeatable and safe. It should list the apparatus, the range of values for the independent variable, and the number of repeat readings.
一个好的实验计划必须逻辑清晰、可重复且安全。它应列出仪器、自变量的取值范围和重复读数的次数。
For a temperature-dependence experiment, you might plan to use a water bath set to 20 °C, 30 °C, 40 °C, 50 °C and 60 °C. You would add the same volume of enzyme solution to the same volume of substrate and time the reaction.
对于温度依赖性实验，你可以计划使用水浴分别设定在20 °C、30 °C、40 °C、50 °C和60 °C。将相同体积的酶溶液加入相同体积的底物中，并计时反应。
Mention how you will ensure safety, for example wearing goggles and using tongs when handling hot apparatus.
说明如何确保安全，例如佩戴护目镜，接触高温仪器时使用钳子。
6. Making it a Fair Test | 控制变量与公平测试
To keep the experiment fair, all control variables must be kept constant. If you are testing temperature, you must keep the light intensity, pH, enzyme concentration and substrate volume the same in every run.
为了保证实验公平，所有控制变量都必须是恒定的。如果测试温度，则每次都要保持光照强度、pH、酶浓度和底物体积相同。
Use a water bath to set the temperature precisely. Check the temperature with a thermometer before starting each trial.
使用水浴精确设定温度。每次实验前用温度计检查温度。
When you change only one variable at a time, you can be confident that any difference in the results is caused by that variable.
每次只改变一个变量，你才能确信结果中的差异是由该变量引起的。
7. Selecting Instruments and Measurements | 选择合适的仪器和测量
Choose an instrument that is precise enough for what you are measuring. For measuring volume, use a measuring cylinder or a burette. For temperature, use a thermometer or a datalogger.
选择足够精密的仪器来测量相应量。测量体积用量筒或滴定管；测量温度用温度计或数据记录器。
The resolution of the instrument is the smallest change it can measure. A thermometer marked in 0.5 °C steps has a higher resolution than one marked in 1 °C steps.
仪器的分辨率是它能测量的最小变化。标度为0.5 °C的温度计比标度为1 °C的温度计分辨率更高。
Always record the correct unit with each reading. For example, write “20.0 cm³” instead of “20” to show the precision of your measurement.
每次读数都要记录正确的单位。例如，写“20.0 cm³”而不是“20”，以示测量的精确性。
8. Repeating and Taking Averages | 重复实验并求平均值
Repeat each experiment at least twice, ideally three times, to reduce the effect of random errors and to spot anomalous results.
每个实验至少重复两次，理想情况下重复三次，以减少偶然误差的影响并发现异常结果。
Calculate the mean of the repeats, but ignore any anomalous point before averaging. Do not include a known outlier in your mean.
计算重复读数的平均值，但要在计算前忽略任何异常点。不要将已知的离群值包含在平均值中。
mean = (x₁ + x₂ + … + xₙ) ÷ n
平均值 =（x₁ + x₂ + … + xₙ）÷ n
For example, if three readings are 12 s, 14 s and 13 s, the mean is (12 + 14 + 13) ÷ 3 = 13 s.
例如，如果三次读数分别为12 s、14 s和13 s，则平均值是（12 + 14 + 13）÷ 3 = 13 s。
9. Recording Data in Tables | 用表格记录数据
A results table should include the independent variable, the dependent variable, repeat readings and the calculated mean. Put the units in the column heading, not in every cell.
结果表格应包括自变量、因变量、重复读数和计算出的平均值。在表头中标注单位，而不是在每个单元格中写单位。
Here is an example table for enzyme reaction rate at different temperatures:
下面是一个不同温度下酶反应速率的示例表格：
| Temperature (°C) | Trial 1 (s) | Trial 2 (s) | T
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