📚 IB & Edexcel Biology: Laboratory Practical Guide | IB & Edexcel 生物：实验操作指南
Biology is an experimental science, and mastering practical skills is essential for success in both IB and Edexcel Biology. Whether you are designing an investigation for your Internal Assessment (IA) or completing a core practical, a solid understanding of experimental techniques, data analysis, and evaluation will boost your confidence and exam performance. This guide covers key practical competencies, from controlling variables to assessing errors, helping you meet the assessment objectives of both specifications.
生物学是一门实验科学，掌握实验技能对于在 IB 和 Edexcel 生物课程中取得成功至关重要。无论你是在为内部评估（IA）设计探究实验，还是完成核心实践活动，扎实掌握实验技术、数据分析和评估方法，都能提升你的信心和考试成绩。本指南涵盖了从变量控制到误差分析的关键实验能力，帮助你达到两大课程体系的评估目标。
The guide is written so that a student following either syllabus can use it directly. Every section pairs the English terminology used in mark schemes with the Chinese explanation that makes the logic clear, so you can move from understanding to writing structured answers without losing marks on technical language.
本指南的编写方式让学习任一课程体系的学生都能直接使用。每一节都把评分标准中使用的英文术语与便于理解的中文解释配对呈现，让你从理解走向结构化答题时，不会因为技术性表达而失分。
1. Understanding Variables in Experiments | 理解实验变量
In any experiment, identifying the independent variable (the one you change), the dependent variable (the one you measure), and controlled variables (factors kept constant) is the first step. For example, when investigating the effect of temperature on enzyme activity, temperature is the independent variable, and the rate of reaction (measured as product formed per unit time) is the dependent variable. Other factors such as pH, substrate concentration, and enzyme concentration must be carefully controlled.
在任何实验中，首先要识别自变量（你改变的变量）、因变量（你测量的变量）和控制变量（保持不变的因素）。例如，在研究温度对酶活性影响的实验中，温度是自变量，反应速率（以单位时间内产物的生成量来测量）是因变量。pH、底物浓度和酶浓度等其他因素必须仔细控制。
A well-planned experiment should only have one independent variable, so to ensure that any observed effect can reasonably be attributed to that single factor. If two factors change at the same time, you cannot tell which one caused the result, and the investigation loses validity.
一个规划良好的实验只应有一个自变量，这样观察到的效应才能合理地归因于这一单一因素。如果两个因素同时变化，你就无法判断是哪一个造成了结果，实验便失去了有效性。
| Variable type | 变量类型 | Meaning | 含义 | Enzyme example | 酶实验示例 |
| Independent | 自变量 | The factor you deliberately change | 你有意改变的因素 | Temperature: 10, 20, 30, 40, 50 °C |
| Dependent | 因变量 | The factor you measure | 你测量的因素 | Time for colour change, or volume of gas produced |
| Controlled | 控制变量 | Factors kept constant | 保持恒定的因素 | pH, substrate concentration, enzyme volume, same batch of enzyme |
There are also two special categories you must be able to name. A confounding variable is an uncontrolled factor that varies with the independent variable; a control group is a treatment where the independent variable is absent or replaced by a known standard, such as distilled water instead of enzyme solution.
还有两类特殊变量你必须能够准确命名。混杂变量是随自变量一同变化的未受控因素；对照组则是自变量被去除、或替换为已知标准的处理组，例如用蒸馏水代替酶溶液。
2. Writing a Testable Hypothesis and Research Question | 提出可检验的假设与研究问题
A research question must be focused, measurable and biologically meaningful. A weak question asks whether temperature "affects" an enzyme; a strong one asks how the rate of an enzyme-catalysed reaction changes as temperature increases from 10 °C to 60 °C, measured as the volume of gas produced per minute.
研究问题必须聚焦、可测量并且具有生物学意义。一个薄弱的问题会问温度是否"影响"酶；一个强的问题则会问：当温度从 10 °C 升高到 60 °C 时，酶促反应速率如何变化，并以每分钟产生的气体体积来测量。
A hypothesis is a predicted, testable statement that links the independent and dependent variables and is justified by biological theory. For the enzyme example, the hypothesis is that the rate increases up to an optimum temperature and then falls sharply, because above the optimum the tertiary structure of the active site is denatured by the breaking of hydrogen and ionic bonds.
假设是一个可检验的预测性陈述，它把自变量与因变量联系起来，并由生物学理论支撑。以酶为例，假设为：反应速率随温度升高而增大，达到最适温度后急剧下降，因为超过最适温度后，维持活性位点三级结构的氢键与离子键断裂，酶发生变性。
Edexcel practicals and statistics questions normally require a null hypothesis. The null hypothesis states that there is no significant difference or no correlation between the variables, and any apparent pattern is due to chance. The alternative hypothesis states that a real difference or relationship exists.
Edexcel 的实验与统计题目通常要求写出零假设。零假设认为变量之间不存在显著差异或相关，任何表面上的规律都是偶然造成的。备择假设则认为存在真实的差异或关系。
Useful sentence frames for writing hypotheses include: if the independent variable increases, then the dependent variable will increase or decrease, because the biological reason is that ... This structure guarantees that both variables and a causal mechanism appear in your answer.
撰写假设时有用的句型包括：如果自变量增大，那么因变量将会增大或减小，因为其生物学原因是……这种结构能确保你的答案中同时出现两个变量和因果机制。
3. Designing a Method: Controls and Standardisation | 设计方法：对照与标准化
A good method is written as a numbered list of steps in the imperative, giving quantities, units and equipment. Read it back and ask whether another student could repeat the investigation exactly and obtain comparable results. This repeatability is what examiners call reliability of method.
好的方法应以命令式、编号步骤的形式书写，并给出量、单位与仪器。写完后请回读一遍，问自己另一位同学是否能完全重复该实验并得到可比结果。这种可重复性就是考官所说的"方法的可靠性"。
Standardisation means keeping every controlled variable at a fixed, stated value. In an enzyme experiment this includes using the same volume of buffer, the same volume and concentration of substrate, the same end point, and the same batch of enzyme, all equilibrated in a water bath for the same acclimatisation time.
标准化意味着把每一个控制变量都固定在明确说明的数值上。在酶实验中，这包括使用相同体积的缓冲液、相同体积与浓度的底物、相同的终点判断标准、同一批次的酶，并且全部在同一水浴中平衡相同的适应时间。
Controls fall into several types. A negative control contains everything except the factor being tested and should show no effect. A positive control contains a known substance that must produce a response, proving that the test system works. A blank is used to zero a colorimeter or spectrophotometer. In IB IA, you must also consider ethical and safety controls: risk assessments, disposal of biological waste, and consent for any human subjects.
对照可分为几种类型。阴性对照包含除被测因素之外的一切条件，应当不产生效应。阳性对照包含已知必须产生反应的物质，用以证明检测体系正常工作。空白液用于给比色计或分光光度计调零。在 IB 的 IA 中，你还必须考虑伦理与安全方面的控制：风险评估、生物废弃物的处理，以及涉及人类受试者时的知情同意。
- Repeat each treatment at least five times to allow the mean and standard deviation to be calculated. | 每个处理至少重复五次，以便计算平均值和标准差。
- Randomise the order of treatments to reduce systematic drift such as apparatus warming up. | 随机化处理顺序，以减少仪器升温等系统性漂移。
- Carry out a pilot study to check the range of the independent variable and the timings. | 进行预实验，检查自变量的取值范围与时间安排。
- Choose a sample size large enough to be representative of the population. | 选择足够大的样本量，使其能代表总体。
4. Measurement, Units and Uncertainty | 测量、单位与不确定度
All measurements must be recorded with the correct SI unit and a sensible number of decimal places. Biology uses a wide range of scales, and converting between them is a common source of lost marks in both IB and Edexcel papers.
所有测量都必须以正确的国际单位（SI）和合理的有效数字位数记录。生物学涉及的尺度范围很广，单位换算在 IB 与 Edexcel 的试卷中都是常见的失分点。
1 m = 10³ mm = 10⁶ µm = 10⁹ nm
1 m = 10³ mm = 10⁶ µm = 10⁹ nm
Every instrument has an inherent uncertainty, usually taken as half of the smallest scale division for a simple measuring device. This uncertainty must be quoted with the reading, and it should be propagated when you perform calculations.
每种仪器都有固有的不确定度。对于简单的测量器具，通常取最小分度值的一半。该不确定度必须与读数一同标注，并在进行计算时予以传递。
| Instrument | 仪器 | Typical uncertainty | 典型不确定度 |
| Metre ruler | 米尺 | ± 0.5 mm |
| Thermometer | 温度计 | ± 0.5 °C |
| Top-pan balance | 电子天平 | ± 0.01 g |
| Measuring cylinder (10 cm³) | 量筒（10 cm³） | ± 0.1 cm³ |
| Gas syringe | 气体注射器 | ± 0.5 cm³ |
Precision describes how closely repeated measurements agree with one another, while accuracy describes how close a measurement is to the true value. Precise but inaccurate data usually indicates a systematic error, such as a colorimeter that has not been zeroed or a thermometer reading consistently 1 °C high.
精密度描述重复测量之间的一致程度，而准确度描述测量值与真实值的接近程度。精密度高但不准确的数据通常说明存在系统误差，例如比色计未调零，或温度计读数始终偏高 1 °C。
Percentage uncertainty is calculated as the uncertainty divided by the measured value, multiplied by 100. When a value is obtained by multiplying or dividing measurements, add the percentage uncertainties; when adding or subtracting, add the absolute uncertainties.
百分比不确定度等于不确定度除以测量值，再乘以 100%。当数值由乘除运算得到时，应将各百分比不确定度相加；当进行加减运算时，应将绝对不确定度相加。
5. Core Practical Techniques: Microscopy and Magnification | 核心实验技术：显微镜与放大倍数
Light microscopy remains the foundation of cell biology practical work in both specifications. You must be able to prepare a temporary mount, stain cells where appropriate, focus at low power first, and calculate magnification and actual size correctly.
光学显微镜在两套课程体系的细胞生物学实验中都是基础。你必须能够制作临时装片、必要时对细胞染色、先在低倍镜下对焦，并正确计算放大倍数与实际尺寸。
Magnification = Image size ÷ Actual size
放大倍数 = 图像尺寸 ÷ 实际尺寸
ication. Always convert both lengths into the same unit before dividing, and answer in the unit requested by the question.
对这个三角关系进行变形，可以得到考试中需要的另外两种形式：图像尺寸 = 放大倍数 × 实际尺寸；实际尺寸 = 图像尺寸 ÷ 放大倍数。相除之前务必把两个长度换算成同一单位，并按照题目要求的单位作答。
To measure cells under the microscope, you must calibrate an eyepiece graticule against a stage micrometer. Record the number of graticule divisions that correspond to a known length on the stage micrometer, then calculate the value of one division. This calibration stays valid only for the same objective lens and the same microscope, so always recalibrate if the lens changes.
在显微镜下测量细胞，需要用台微尺校准目镜测微尺。记录与台微尺上已知长度相对应的目镜刻度数，然后计算每一格代表的长度。该校准值只对同一物镜和同一台显微镜有效，因此更换物镜后必须重新校准。
Haemocytometers allow cell counting for cell suspensions. Count cells in the ruled squares, multiply by the dilution factor and by 10⁴ to give cells per cm³, and always use the mean of several squares to reduce counting error.
血细胞计数板可用于细胞悬液的计数。统计计数区内的细胞数，乘以稀释倍数与 10⁴，即可得到每 cm³ 的细胞数；务必取多个计数区的平均值以降低计数误差。
6. Core Practical Techniques: Enzymes and Rate of Reaction | 核心实验技术：酶与反应速率
Enzyme practicals appear in every syllabus, and the skill being assessed is usually the reliable measurement of a changing quantity over time. Common approaches include timing a colour change, measuring gas volume with a gas syringe, measuring the decrease in mass of a substrate, and using a colorimeter or spectrophotometer to follow absorbance or transmission.
酶实验出现在所有课程体系中，而所考查的技能通常是随时间变化可靠地测量某个量。常见的思路包括：计时颜色变化、用气体注射器测量气体体积、测量底物质量的减少，以及用比色计或分光光度计跟踪吸光度或透光率。
Rate = 1 ÷ time taken for the end point
Rate = Δmass of substrate ÷ Δtime
The initial rate is the most reliable measure because substrate concentration and other conditions change least at the start of the reaction. If you plot a progress curve, the initial rate is the gradient of the tangent drawn at time zero.
初速率是最可靠的测量指标，因为反应开始时底物浓度等条件变化最小。若绘制进程曲线，初速率就是 t = 0 处所作切线的斜率。
The temperature coefficient Q₁₀ shows how much the rate changes for a 10 °C rise, and is a useful quantitative extension for high-scoring answers.
温度系数 Q₁₀ 表示温度升高 10 °C 时速率变化的倍数，是获得高分答案时有用的定量拓展内容。
Q₁₀ = (R₂ ÷ R₁) raised to the power 10 ÷ (T₂ − T₁)
Q₁₀ = (R₂ ÷ R₁) 的 10 ÷ (T₂ − T₁) 次方
Key practical points: use a buffer to fix pH, equilibrate all solutions in a water bath before mixing, use the same volume of enzyme and substrate each time, judge the end point against a white tile or black cross in a consistent way, and record the temperature of the water bath rather than assuming it matches the dial setting.
关键操作要点：用缓冲液固定 pH；混合前将所有溶液在水浴中预平衡；每次使用相同体积的酶与底物；在白色瓷板或黑十字背景下以一致标准判断终点；记录水浴的实际温度，而不要假定它与旋钮刻度一致。
7. Core Practical Techniques: Osmosis, Diffusion and Water Potential | 核心实验技术：渗透、扩散与水势
The classic osmosis practical uses potato or beetroot cylinders in a series of sucrose solutions. Measure the initial mass or length, leave the tissue in the solution for a fixed time, blot dry, reweigh, and express the change as a percentage so that cylinders of different starting size can be compared fairly.
经典的渗透实验是把马铃薯或甜菜根圆柱条放入一系列蔗糖溶液中。测量初始质量或长度，将组织在溶液中静置固定时间后吸干称重，并把变化表示为百分比，这样不同初始大小的圆柱条才能公平比较。
Percentage change in mass = (final mass − initial mass) ÷ initial mass × 100
质量变化百分比 = (最终质量 − 初始质量) ÷ 初始质量 × 100
Plotting percentage change against sucrose concentration gives a curve that crosses the zero line. The concentration at which there is no change in mass is isotonic with the cell contents, and its water potential can be read from a calibration table. In beetroot experiments, the same principle is used with a colorimeter: higher concentrations of pigment released indicate greater membrane damage.
以质量变化百分比对蔗糖浓度作图，所得曲线会穿过零线。质量不变时的溶液浓度与细胞内容物等渗，其水势可从校准表中读出。在甜菜根实验中，同样原理用比色计来实现：释放的色素越多，说明膜损伤越大。
Water potential is the tendency of water to move, and it is always negative in cells. The components are the solute potential and the pressure potential.
水势是水移动的趋势，在细胞中始终为负值。其组成部分为溶质势与压力势。
Ψ = Ψₛ + Ψₚ
Ψ = Ψₛ + Ψₚ
For a turgid plant cell, Ψₚ is positive and can nearly balance a very negative Ψₛ. In an animal cell there is no cell wall, so Ψₚ is zero and the cell will burst in a hypotonic solution. Plasmolysis in plant cells occurs when so much water leaves that the protoplast pulls away from the cell wall.
对于膨压饱满的植物细胞，Ψₚ 为正值，几乎可以抵消非常负的 Ψₛ。动物细胞没有细胞壁，Ψₚ 为零，因此在低渗溶液中会涨破。植物细胞发生质壁分离，是因为大量水分外流使原生质体与细胞壁分离。
8. Core Practical Techniques: Respiration, Photosynthesis and Chromatography | 核心实验技术：呼吸、光合作用与色谱
Respirometers measure oxygen uptake by organisms such as germinating seeds or maggots. The carbon dioxide produced is absorbed by soda lime or potassium hydroxide, so the change in gas volume reflects oxygen consumption only. A control tube containing inert material corrects for changes in temperature and pressure.
呼吸仪用于测量萌发种子或幼虫等生物的耗氧量。产生的二氧化碳被钠石灰或氢氧化钾吸收，因此气体体积的变化只反映氧气的消耗。装有惰性材料的对照管用于校正温度与压力的变化。
Photosynthesis practicals often use pondweed and a photosynthometer to count oxygen bubbles or collect gas. Because light intensity falls with the square of the distance from the lamp, results are best plotted against 1 ÷ d² rather than against distance itself.
光合作用实验常用黑藻与光合测量仪来计气泡或收集气体。由于光照强度随与灯距离的平方下降，结果最好以 1 ÷ d² 而不是距离本身作图。
Paper chromatography separates photosynthetic pigments. The Rf value identifies a pigment only if the solvent and the paper type are stated, because Rf depends on both.
纸色谱用于分离光合色素。只有在说明溶剂与滤纸类型时，Rf 值才能用于鉴定色素，因为 Rf 取决于这两者。
Rf = distance moved by the pigment ÷ distance moved by the solvent front
Rf = 色素移动距离 ÷ 溶剂前沿移动距离
Edexcel also assesses aseptic technique and microbiology practicals: flaming the neck of the bottle, sterilising the spreader, working near a Bunsen flame, sealing and incubating plates upside down at a temperature no higher than 25 °C in schools to avoid growing human pathogens. In IAL, you should also be familiar with the principles of PCR and gel electrophoresis as separation and amplification techniques.
Edexcel 还考查无菌操作与微生物学实验技能：灼烧瓶口、对涂布器灭菌、在酒精灯火焰附近操作、封口后倒置培养，且在学校中培养温度不超过 25 °C 以避免培养出人体病原体。在 IAL 中，你还应熟悉 PCR 与凝胶电泳作为扩增与分离技术的基本原理。
9. Drawing Tables, Graphs and Processing Data | 数据表、图表绘制与数据处理
Tables must have ruled borders, clear headings, and units. The independent variable goes in the first column and the dependent variable in the second, with repeated readings in further columns so that a mean can be calculated. Use the same number of decimal places throughout a column, and put the units in the heading rather than repeating them in every cell.
表格必须有清晰的边框、明确的表头与单位。自变量放在第一列，因变量放在第二列，重复读数放在后续列中以便计算平均值。同一列中的有效数字位数应保持一致，单位写在表头中，而不要在每个单元格重复。
A well-presented results table normally contains: the treatment or interval, the raw readings, the mean, and the standard deviation. Showing raw data and processed data together is one of the clearest ways to demonstrate that your method was reliable.
规范的结果表通常包括：处理组或区间、原始读数、平均值以及标准差。把原始数据与处理后的数据同时呈现，是证明你的方法可靠的最清楚的方式之一。
When drawing graphs, choose a line graph when the independent variable is continuous and a bar chart when it is categoric. Label both axes with quantity and unit, use a sensible scale that fills the paper, plot points with a small cross or a dot within a circle, draw a single smooth line or curve of best fit, and never join the points dot to dot.
绘图时，若自变量为连续变量应选择折线图；若为分类变量则应选择柱状图。两轴都要标注量和单位；刻度要合理并充分利用纸面；数据点用细十字或带圈圆点表示；画出一条平滑的最佳拟合直线或曲线；绝不要把各点用直线逐点连接。
- r bars of ± one standard deviation or the calculated uncertainty where they are available. | 在可用时标出 ± 一个标准差或已计算的不确定度的误差棒。
- Describe the trend in words: at low values the relationship is approximately linear; above the optimum the graph falls steeply. | 用文字描述趋势：在低值区关系近似线性；超过最优点后曲线急剧下降。
- Quote values from the graph with their units when you describe the optimum. | 描述最优点时，请从图上读出数值并带上单位。
10. Statistical Tests and Uncertainty | 统计检验与不确定度
Statistics allow you to decide whether a difference is real or simply due to chance. The three tests you are most likely to need are the chi-squared test for categorical data, the t-test for comparing two means, and a correlation coefficient for measuring the strength of a relationship between two continuous variables.
统计学帮助判断差异是真实存在的，还是仅仅由偶然造成。你最可能需要用到的三种检验是：用于分类数据的卡方检验、用于比较两个平均值的 t 检验，以及用于衡量两个连续变量关系强度的相关系数。
χ² = Σ (O − E)²
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