📚 Scientific Investigation: Planning Steps for Experiments | 科学调查实验的规划步骤
In CIE A-Level Biology, the ability to plan a scientific investigation is a core practical skill, assessed in Paper 3 (AS) and Paper 5 (A-Level). A well-structured plan transforms a vague question into a reliable, valid, and safe experiment. This article presents the essential planning steps, from defining the aim to evaluating limitations, with the terminology and format examiners expect.
在 CIE A-Level 生物考试中，规划科学调查的能力是一项核心实验技能，分别在 Paper 3（AS）和 Paper 5（A-Level）中考查。一份结构清晰的规划能把模糊的问题转变成可靠、有效且安全的实验。本文将介绍从明确目的到评估局限性的关键规划步骤，采用考官期望的术语与表述格式。
1. Defining the Aim and Research Question | 明确目的与研究问题
Every investigation begins with a precise aim. The aim states what you intend to find out, often in the form “to investigate the effect of [independent variable] on [dependent variable]”. For example: “To investigate the effect of light intensity on the rate of photosynthesis in Elodea.” A good aim is specific, measurable, and feasible within the time and resources available.
每一项调查都始于精确的目的。目的说明你打算探究什么，通常以”探究 [自变量] 对 [因变量] 的影响”的形式表述。例如：”探究光照强度对伊乐藻光合作用速率的影响”。好的目的应当具体、可测量，并且在时间和资源允许的范围内可行。
The research question is the broader question your experiment answers. It helps you focus your planning and clarifies the biological context. For instance, understanding photosynthesis rates informs us about limiting factors in agriculture. You should also state any prior knowledge or theory that supports your prediction.
研究问题是实验所要回答的更宏观的问题。它帮助你集中规划思路，并明确生物学背景。例如，理解光合作用速率有助于我们认识农业中的限制因素。你还应说明支持你的预测的已有知识或理论。
2. Formulating a Hypothesis | 提出假设
A hypothesis is a testable statement predicting the relationship between variables. It must be based on biological knowledge and written in a way that can be supported or rejected by data. For example: “Increasing light intensity up to a saturation point will increase the rate of photosynthesis, after which it will plateau.”
假设是对变量之间关系的可检验预测陈述。它必须以生物学知识为基础，并且表述方式应能被数据支持或否定。例如：”在达到饱和点之前，增强光照强度会提高光合作用速率，之后速率趋于平稳。”
From the hypothesis, you should formulate a null hypothesis for statistical testing, such as “there is no significant difference between the rates of photosynthesis at different light intensities.” This allows you to use statistical tests (e.g., t-test or chi-squared test) to determine whether observed differences are due to chance.
从假设出发，你应提出用于统计检验的零假设，例如：”不同光照强度下的光合作用速率无显著差异。”这使你可以使用统计检验（如 t 检验或卡方检验）来判断观察到的差异是否由偶然因素引起。
3. Identifying Variables | 识别变量
Accurate identification of variables is the backbone of experimental design. The independent variable is the factor you deliberately change; the dependent variable is the factor you measure; controlled variables are factors you keep constant to ensure a fair test.
准确识别变量是实验设计的核心。自变量是你有意改变的因素；因变量是你测量的因素；控制变量是你保持恒定以确保公平测试的因素。
For a CIE investigation, you must state how you will measure the dependent variable and the units used. For example, measuring oxygen production in cm³ per minute using a gas syringe. You must also list at least three controlled variables and explain how each is controlled and why it matters, as shown in the table below.
对于 CIE 调查，你必须说明如何测量因变量及其使用单位。例如，使用气体注射器以 cm³/min 为单位测量氧气产生量。你还必须列出至少三个控制变量，并说明如何控制以及为何重要，如下表所示。
| Controlled variable | Method of control | Reason |
| Temperature | Use a water bath at 25 °C | Affects enzyme activity in photosynthesis |
| Light source distance | Fixed position, same lamp | Prevents variation in light intensity |
| Concentration of sodium hydrogencarbonate | Use same solution for all trials | Provides equal CO₂ availability |
4. Designing the Procedure | 设计实验流程
The procedure must be written as a clear, logical sequence of steps that another person could follow to obtain identical results. Each step should include the apparatus used, the quantity of material, and the timing of measurements. For repeated trials, state the number of replicates and explain why repeats improve reliability.
实验流程必须以清晰、合乎逻辑的步骤序列书写，使其他人能够按照步骤获得相同的结果。每一步都应包括所用仪器、材料用量以及测量时间。对于重复试验，说明重复次数并解释重复如何提高可靠性。
A key design decision is the range and interval of the independent variable. For example, if investigating temperature, you might choose 10 °C, 20 °C, 30 °C, 40 °C, and 50 °C. The range should cover the expected response, and the interval should be small enough to detect trends. You should also include a control experiment where the independent variable is set to zero or a baseline value.
关键的设计决策是自变量的范围与间隔。例如，若研究温度，你可能选择 10 °C、20 °C、30 °C、40 °C 和 50 °C。范围应覆盖预期的响应，间隔应足够小以察觉趋势。你还应设置对照实验，将自变量设为零或基线值。
Preliminary (trial) experiments are valuable during planning. They help you decide suitable concentrations, volumes, or time intervals, and can reveal problems such as reactions that occur too quickly or too slowly to measure. In the paper you can describe how a pilot study would guide your final procedure.
预备（预试）实验在规划阶段很有价值。它们帮助你确定合适的浓度、体积或时间间隔，并能揭示反应过快或过慢而难以测量等问题。在试卷中你可以描述预实验如何指导最终流程。
5. Selecting Apparatus and Materials | 选择仪器与材料
Choosing appropriate apparatus requires matching the precision and range of the measurement to the expected values. For volume measurements, a burette (to ±0.05 cm³) is more precise than a measuring cylinder (±0.5 cm³). For mass, a digital balance to ±0.01 g is typically required. You should state the precision of each instrument in your plan.
选择合适的仪器需要将测量的精度和量程与预期数值相匹配。对于体积测量，滴定管（±0.05 cm³）比量筒（±0.5 cm³）更精确。对于质量测量，通常需要精确到 ±0.01 g 的电子天平。在你的规划中应说明每种仪器的精度。
Materials must be specified with quantities. For example, “10 cm³ of 1.0 mol dm⁻³ glucose solution” or “5 g of agar containing 1% starch”. If enzymes are used, state the enzyme concentration, substrate concentration, buffer solution, and pH. This level of detail ensures reproducibility.
材料必须注明用量。例如，”10 cm³ 的 1.0 mol dm⁻³ 葡萄糖溶液”或”5 g 含 1% 淀粉的琼脂”。若使用酶，应说明酶浓度、底物浓度、缓冲溶液和 pH。这样的细节水平确保可重复性。
6. Risk Assessment | 风险评估
Risk assessment is a compulsory part of any CIE practical plan. You must identify hazards (potential sources of harm), evaluate the associated risks (likelihood and severity), and state precautions to minimise them. Common hazards in biology include corrosive chemicals, sharp objects, hot equipment, and biological materials.
风险评估是任何 CIE 实验规划中的必做部分。你必须识别危害（潜在伤害源），评估相关风险（发生的可能性和严重程度），并说明将其最小化的预防措施。生物学中常见的危害包括腐蚀性化学品、尖锐器具、高温设备和生物材料。
For example, if using a scalpel to cut potato cylinders, the hazard is the sharp blade, the risk is cutting skin, and the precaution is cutting onto a white tile, using a chopping action away from the body. If using concentrated hydrochloric acid, wear safety goggles, gloves, and handle it in a fume cupboard. Every chemical should be labelled with its hazard symbol where relevant.
例如，若使用解剖刀切马铃薯条，危害是锋利的刀片，风险是割伤皮肤，预防措施是在白色瓷砖上、远离身体的方向进行切割。若使用浓盐酸，应佩戴护目镜、手套，并在通风橱中操作。每种化学品都应酌情标注其危险符号。
7. Data Collection and Recording | 数据收集与记录
You must plan how data will be recorded. A results table should be drawn up before the experiment, with columns for the independent variable, dependent variable, and calculated values. Each column must have a heading with the quantity and unit in the correct format, for example, “Rate of photosynthesis / cm³ min⁻¹”.
你必须规划数据的记录方式。应在实验前绘制结果表格，包含自变量、因变量和计算值的列。每一列都应有包含物理量和单位的标题，格式正确，例如”光合作用速率 / cm³ min⁻¹”。
Repeated measurements are essential. For each value of the independent variable, you should take three repeats and calculate the mean. If one repeat is anomalous, you should record it but exclude it from the mean calculation. The number of repeats improves the reliability of the data and allows you to calculate standard deviation, a measure of spread.
重复测量至关重要。对于自变量的每个取值，应进行三次重复并计算平均值。若某个重复值异常，应记录但将其排除在平均值计算之外。重复次数提高数据的可靠性，并允许你计算标准差这一离散程度的度量。
8. Data Analysis and Presentation | 数据分析与呈现
After collection, data must be processed appropriately. Simple calculations include means, rates (e.g., mass change ÷ time), and percentages. You should choose the correct graph type: a line graph when the independent variable is continuous, and a bar chart when it is discrete or categorical. Graph axes should be labelled with quantity and unit, and points plotted accurately with a suitable scale.
收集数据后，必须进行适当处理。简单计算包括平均值、速率（如质量变化 ÷ 时间）和百分比。你应选择正确的图形类型：自变量为连续数据时用折线图，为离散或分类数据时用柱状图。坐标轴应标注物理量和单位，用合适的比例尺准确描点。
Statistical analysis may be required. The Student’s t-test compares two means; the chi-squared test compares observed and expected frequencies; Spearman’s rank correlation tests relationships between two variables. In your plan, state which test you would use and justify your choice, including the significance level (usually p < 0.05).
可能需要进行统计分析。学生 t 检验用于比较两个平均值；卡方检验用于比较观察频数与预期频数；斯皮尔曼等级相关检验用于检验两个变量之间的关系。在你的规划中，说明将使用哪种检验并论证你的选择，包括显著性水平（通常为 p < 0.05）。
t = (x̄₁ − x̄₂) ÷ √[(s₁²/n₁) + (s₂²/n₂)]
The formula above is the unpaired t-test equation, where x̄ is the sample mean, s² is the variance, and n is the sample size. You are not expected to calculate it by hand in the exam, but you should know when it is appropriate.
上式是独立样本 t 检验方程，其中 x̄ 是样本平均值，s² 是方差，n 是样本量。考试中不要求手工计算，但你应知道何时适用。
9. Evaluation and Limitations | 评估与局限性
Every experiment has limitations, and a good plan anticipates them. Sources of error can be systematic (e.g., an incorrectly calibrated balance, causing all readings to be too high) or random (e.g., timing inaccuracies on a stopwatch). You should identify the main sources of error in your procedure and suggest how to reduce them.
每个实验都有局限性，好的规划能预见这些局限。误差来源可以是系统性的（如天平校准不准确，导致所有读数偏高）或随机的（如秒表计时不精确）。你应识别流程中的主要误差来源并提出减少误差的方法。
Biological variation is an important limitation. Living material such as plant tissue or enzyme extracts varies between specimens. Using a large sample size and taking the mean of repeats reduces the impact of this variation. You should also consider whether the experiment measures what it claims to measure — that is, whether it has good validity.
生物变异是重要的局限性。植物组织或酶提取物等活体材料在不同样本之间存在差异。使用较大的样本量并对重复值取平均可减少这种变异的影响。你还应考虑实验是否测量了它声称要测量的对象——即是否具有良好的有效性。
10. Conclusion and Improvements | 结论与改进
Finally, a plan should indicate how conclusions will be drawn from the data. You should compare your results with the hypothesis: if the data support the hypothesis, the hypothesis is accepted; if not, it is rejected. You must explain the biological reasoning behind the conclusion, linking your findings to underlying concepts such as enzyme kinetics or membrane transport.
最后，规划应说明如何从数据得出结论。你应将结果与假设进行比较：若数据支持假设，则接受假设；若不支持，则拒绝假设。你必须解释结论背后的生物学推理，将发现与酶动力学或膜运输等潜在概念联系起来。
Suggesting improvements is a distinct skill. For each improvement, state the change, the reason for the change, and the expected effect. For example: “Using a thermostatically controlled water bath instead of a beaker of water at room temperature would maintain a constant temperature, reducing variability and increasing the validity of the comparison.” Improvements may involve apparatus, technique, sample size, or statistical analysis.
提出改进建议是一项独立的技能。对于每项改进，说明更改内容、更改原因和预期效果。例如：”使用恒温控制的水浴替代室温下的烧杯水，可维持恒定温度，减少变异性并提高比较的有效性。”改进可能涉及仪器、技术、样本量或统计分析。
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