IGCSE CIE Biology: Experimental Techniques Guide | IGCSE CIE 生物：实验操作指南

📚 IGCSE CIE Biology: Experimental Techniques Guide | IGCSE CIE 生物：实验操作指南

Mastering experimental skills is essential for success in the IGCSE CIE Biology course. This guide covers key practical techniques, from planning investigations and using apparatus to collecting reliable data and evaluating results. Each section pairs an explanation in English with its Chinese translation, following the core syllabus requirements for the practical assessment, Paper 5 or Paper 6.

掌握实验技能是学好 IGCSE CIE 生物的关键。本指南涵盖实验设计、仪器使用、数据收集与结果评估等关键实验技术，每个部分都提供了英文和中文对照说明，紧扣课程大纲对实验考试（试卷5或试卷6）的核心要求。

1. Planning an Investigation | 设计实验

Every investigation begins with a clear aim and a testable hypothesis. The hypothesis should state the expected relationship between the independent variable (the one you change) and the dependent variable (the one you measure), based on scientific reasoning.

任何实验都从一个明确的目的和可检验的假设开始。假设应基于科学原理，陈述自变量（你改变的变量）与因变量（你测量的变量）之间的预期关系。

You must identify all control variables and explain how you will keep them constant. For example, in an enzyme experiment, temperature and pH must be controlled using a water bath or buffer solutions. A valid method must be fully described, including how you will ensure reproducibility and accuracy, such as by repeating measurements and calculating a mean.

你必须确定所有的控制变量并说明如何保持它们不变。例如，在酶实验中，必须使用水浴或缓冲液来控制温度和 pH。有效的实验方法必须完整描述，包括如何确保重复性和准确性，比如通过重复测量并计算平均值。

Planning also involves selecting appropriate apparatus with suitable ranges and resolutions. A table of results should be designed before starting, with clear headings and units.

实验设计还需要选择合适的仪器，并注意其量程和分辨率。在开始实验前应设计好结果记录表，表格要有清晰的表头和单位。

2. Variables and Controls | 变量与对照组

The independent variable is deliberately changed by the investigator, such as the concentration of a sugar solution in an osmosis experiment. The dependent variable is measured quantitatively, like the length or mass of potato cylinders. All other variables must be controlled to ensure a fair test.

自变量由实验者有意改变，例如在渗透实验中改变蔗糖溶液的浓度。因变量需定量测量，如马铃薯条的长度或质量。所有其他变量都必须控制，以保证实验的公平性。

A control experiment serves as a baseline for comparison. In food tests, a control tube containing water instead of the sample ensures any colour change is due to the substance tested. In enzyme rate experiments, a denatured enzyme or boiled sample is used to confirm the reaction is enzyme-specific.

对照实验用作比较的基准。在食物测试中，用水代替待测样品的对照管可以确保颜色变化是由所测物质引起的。在酶反应速率实验中，使用变性的酶或煮沸的样品可确认反应是酶特异性的。

Controlling variables may involve using a thermostatically controlled water bath for temperature, a pH meter or buffer for pH, and identical volumes, concentrations, and incubation times. Without proper controls, conclusions become unreliable.

控制变量可能涉及使用恒温水浴控制温度，使用 pH 计或缓冲液控制 pH，以及保持相同的体积、浓度和反应时间。没有适当的对照，结论就不可靠。

3. Measuring and Recording Data | 测量与记录数据

Accurate measurements require reading instruments correctly. For liquids, measure from the bottom of the meniscus in a graduated cylinder or pipette. Use a stopwatch to time reactions and a thermometer for temperature, ensuring the bulb is completely immersed. Record readings to the nearest half of the smallest scale division for analogue instruments, or use all digits shown on digital displays.

准确测量需要正确读取仪器。测量液体时，要从量筒或移液管的凹液面底部读数。使用秒表计时，用温度计测量温度，并确保感温泡完全浸没。对于模拟仪器，读数记录到最小刻度的一半；对于数字显示仪表，保留所有显示的位数。

Design a results table before collecting data. The first column typically lists the independent variable values, and further columns hold the dependent variable readings for each repeat. Include a column for the calculated mean. Headings must state the quantity and its unit, e.g., ‘Temperature (°C)’ or ‘Mass of potato (g)’.

在收集数据前应设计好结果表。第一列通常列出自变量数值，后续列填入各重复组的因变量读数，并包含平均值计算列。表头必须注明量和单位，如“Temperature (°C)”或“Mass of potato (g)”。

Record raw data immediately in ink, never in pencil. If a mistake is made, strike through with a single line and write the correction clearly. Do not erase or use correction fluid.

立即用墨水笔记录原始数据，不要用铅笔。如果写错，用单线划掉并清晰地改正。不要擦除或使用修正液。

4. Use of Laboratory Equipment | 实验设备的使用

Common apparatus include beakers for rough volumes, conical flasks for mixing (reducing splashing), measuring cylinders for accurate volumes, and volumetric pipettes for precise delivery of a fixed volume. A burette is used in titration-style experiments but is less common in core biology tests.

常用设备有：适合粗略量取体积的烧杯、用于混合（减少飞溅）的锥形瓶、准确量取体积的量筒，以及精确移取固定体积的刻度移液管。滴定管在滴定式实验中使用，但在核心生物实验中较少见。

For heating, a water bath is preferred to a Bunsen burner when controlling temperature is critical, as it provides even heating and prevents overheating. When using a Bunsen burner, always use a tripod and gauze, and heat chemicals in a test tube held with a test tube holder, pointing the open end away from people.

加热时，当温度控制重要时，优选水浴而非本生灯，因为水浴加热均匀，能防止过热。使用本生灯时，务必使用三脚架和石棉网，并将试管放入试管夹中加热，管口勿朝向他人。

Microscopes require careful handling. Carry by the arm and base, use only lens paper for cleaning, and focus by moving the objective lens away from the slide to avoid cracking coverslips. Always start with the lowest power objective.

显微镜需小心操作。搬运时一手握住镜臂，一手托住底座；清洁镜头仅用擦镜纸；调焦时使物镜远离载玻片，以免压碎盖玻片。始终从低倍物镜开始观察。

5. Microscopy Skills | 显微镜使用技能

Preparing a temporary mount involves placing a thin specimen in a drop of water on a slide, adding a coverslip at an angle to avoid air bubbles, and optionally using a stain such as iodine solution to highlight structures. For cheek cells, methylene blue stains the nucleus clearly.

制作临时装片需将薄标本置于载玻片的一滴水中，倾斜盖上盖玻片以防气泡产生，并可选用碘液等染色剂来凸显结构。观察口腔细胞时，亚甲蓝能清晰染出细胞核。

To calculate magnification, use the formula:

Magnification = Image size ÷ Actual size

. When drawing from a microscope, use a sharp pencil, make clear continuous outlines, avoid shading, and label structures with straight ruled lines. Include a title and the total magnification.

计算放大倍数的公式：

Magnification = Image size ÷ Actual size

。镜下绘图时使用削尖的铅笔，画出清晰连续的轮廓，不要涂阴影，用直尺划线标注结构。注明标题和总放大倍数。

Estimating cell size involves using a stage micrometer and eyepiece graticule. The graticule must be calibrated for each objective lens because the scale changes with magnification. Measure the diameter of the field of view, then estimate the number of cells that fit across it.

估测细胞大小需使用镜台测微尺和目镜测微尺。目镜测微尺需要针对每个物镜进行校准，因为放大倍数改变会影响尺度。测量视野直径，然后估算能横跨视野的细胞数目。

6. Food Tests (Biochemical Tests) | 食物测试（生化测试）

Food tests identify the presence of biological molecules: starch, reducing sugars, proteins, and lipids. Each test uses a specific reagent and a characteristic positive result. For accuracy, always use a fresh sample and clean test tubes, and compare against a water control.

食物测试可检测生物分子的存在：淀粉、还原糖、蛋白质和脂质。每种测试使用特定试剂并产生典型的阳性结果。为保证准确性，应使用新鲜样品和清洁试管，并与水对照管相比较。

Substance | 物质	Reagent | 试剂	Positive result | 阳性结果
Starch | 淀粉	Iodine solution | 碘液	Blue-black | 蓝黑色
Reducing sugar | 还原糖	Benedict’s solution, heat | 本尼迪克特溶液，加热	Brick-red precipitate | 砖红色沉淀
Protein | 蛋白质	Biuret reagent (sodium hydroxide + copper sulfate) | 双缩脲试剂	Purple/violet | 紫色
Lipid | 脂质	Ethanol, then water (emulsion test) | 乙醇，再加水（乳化测试）	Cloudy white emulsion | 乳白色浑浊

For the Benedict’s test, use excess reagent and heat in a boiling water bath for about 5 minutes. A range of colours from green to orange to brick-red indicates increasing amounts of reducing sugar. The biuret test requires careful layering or mixing; sodium hydroxide is added first, then copper sulfate dropwise, and the mixture shaken gently.

本尼迪克特测试需使用过量试剂并在沸水浴中加热约5分钟。颜色从绿色到橙色再到砖红色，表明还原糖含量递增。双缩脲测试需注意先后顺序：先加入氢氧化钠溶液，再逐滴加入硫酸铜溶液，轻轻摇匀。

7. Enzyme Experiments | 酶实验

A common enzyme experiment investigates the effect of pH or temperature on the rate of an enzyme-controlled reaction, such as amylase breaking down starch. The endpoint is often determined by the time taken for the starch to disappear, tested by removing drops of the mixture at timed intervals and adding iodine solution on a spotting tile. The time when the iodine no longer turns blue-black indicates the starch has been fully digested.

常见的酶实验研究 pH 或温度对酶促反应速率的影响，例如淀粉酶分解淀粉。终点通常通过测定淀粉消失所需的时间来确定：每隔一段时间取样，滴加到白瓷板的碘液中。当碘液不再变为蓝黑色时，说明淀粉已被完全消化。

Key controls: maintain temperature using a water bath at the required setting, and let the enzyme and substrate equilibrate separately before mixing. Use buffer tablets or solutions to maintain pH. Record the time taken for each condition in a table, and calculate the rate as 1/time (s⁻¹). Plot a graph of rate against the independent variable.

关键控制：用水浴保持所需温度，并在混合前让酶与底物分别预热。用缓冲液维持 pH。在表中记录各条件下所需的时间，并以 1/时间（s⁻¹）计算速率。绘制速率对自变量的关系图。

When investigating temperature, be aware that high temperatures denature enzymes by breaking hydrogen and ionic bonds, changing the active site shape irreversibly. A rate graph will show an initial increase up to an optimum, then a sharp decline.

在研究温度时需注意，高温通过破坏氢键和离子键使酶变性，不可逆地改变活性位点形状。速率图会显示起初随温度升高而上升，达到最适温度后急剧下降。

8. Osmosis and Diffusion Experiments | 渗透与扩散实验

Osmosis is often demonstrated using potato cylinders immersed in different sugar or salt solutions. Measure the initial length or mass of each cylinder, then after a fixed time (e.g., 30 minutes), blot dry gently and re-measure. Calculate the percentage change to compare results fairly:

% change = (final − initial) / initial × 100

.

渗透作用常用马铃薯圆柱体浸泡在不同浓度的蔗糖或盐溶液中来演示。测量每根薯条的初始长度或质量，固定时间后（如30分钟），轻轻吸干表面水分并再次测量。计算变化百分比以便公平比较：

% change = (final − initial) / initial × 100

。

A positive percentage change indicates water has entered by osmosis (hypotonic solution); a negative change means water has left (hypertonic). At the point where the line of best fit crosses zero change, the solution is isotonic to the potato cells. This is a standard graph question.

变化百分比为正表示水通过渗透进入（低渗溶液）；为负表示水流出（高渗溶液）。最佳拟合线与零变化线交点处的溶液浓度与马铃薯细胞等渗。这是一个标准的作图考点。

Diffusion can be modelled using agar cubes containing an indicator (e.g., phenolphthalein) and an acid or alkali. The rate of colour change or the distance penetrated over time shows how surface area to volume ratio affects diffusion. Use cubes of different sizes, and record the time for complete decolourisation or measure the clear zone.

扩散作用可用含指示剂（如酚酞）的琼脂块和酸或碱来模拟。颜色变化速率或一段时间内的渗透距离可表明表面积与体积比对扩散的影响。使用不同大小的琼脂块，记录完全褪色所需的时间或测量透明区域的范围。

9. Photosynthesis Investigations | 光合作用实验

To show that light is essential for photosynthesis, a destarched plant is used. A leaf is partially covered with aluminium foil, and after several hours of light exposure, the leaf is tested for starch. The covered area should remain yellow-brown with iodine, while the exposed area turns blue-black.

为了证明光是光合作用必需的，使用事先暗处理的脱淀粉植物。用铝箔部分遮盖叶片，光照数小时后检测叶片内的淀粉。遮盖区域遇碘液应呈黄褐色，未遮盖区域则变成蓝黑色。

To investigate the effect of light intensity on the rate of photosynthesis, use pondweed (e.g., Elodea) in a beaker of water, placed at varying distances from a lamp. Count the number of oxygen bubbles produced per minute, or collect the gas in a capillary tube to measure volume. Control temperature with a heat shield (a glass tank of water) to prevent heat from the lamp affecting the results.

研究光强对光合速率的影响，可将水草（如伊乐藻）放在烧杯的水中，距光源不同距离处放置。计算每分钟产生的氧气泡数，或用毛细管收集气体测量体积。用水槽隔热屏控制温度，防止灯的热量影响结果。

A similar setup can test the effect of carbon dioxide concentration by adding sodium hydrogen carbonate (NaHCO₃) at different masses, which releases CO₂. Keep other conditions constant and measure the rate of photosynthesis. A graph of rate against distance (or 1/distance²) can be plotted.

类似装置可测试二氧化碳浓度的影响，加入不同质量的碳酸氢钠（NaHCO₃）释放 CO₂。保持其他条件不变，测量光合速率。可绘制速率对距离（或 1/距离²）的关系图。

10. Data Analysis and Graphing | 数据分析与作图

For most investigations, choose a line graph when both variables are continuous, or a bar chart when the independent variable is categorical. Plot the independent variable on the x-axis and the dependent on the y-axis. Use appropriate scales that allow the curve to cover more than half the grid. Mark points with small crosses (×) and draw a smooth curve or line of best fit—never join dot-to-dot.

大多数研究，当两个变量均为连续变量时选用折线图，当自变量为类别变量时选用条形图。将自变量绘制在 x 轴，因变量绘制在 y 轴。选择合适的刻度，使曲线占据网格的一半以上。用叉号（×）标记数据点，并绘制平滑曲线或最佳拟合线——绝对不要逐点连线。

From a graph, you may be asked to read a value using interpolation (within the data range) or extrapolation (beyond, with caution). Describe trends clearly: ‘as X increases, Y increases up to a point, then decreases’, and use data values to support your description.

根据图表，你可能需要利用内插法（在数据范围内）或外推法（超出数据范围，需谨慎）读取数值。清晰描述趋势：“随着 X 增加，Y 先增加到一个点后下降”，并使用具体数据值加以支持。

When calculating rates from a graph, draw a tangent at the specific time or concentration and calculate its gradient:

Gradient = change in y / change in x

. This gives the instantaneous rate.

从图表计算速率时，在特定时间或浓度处画切线，计算斜率：

Gradient = change in y / change in x

。这给出了瞬时速率。

11. Identifying Sources of Error | 识别误差来源

Systematic errors are consistent inaccuracies caused by faulty equipment or procedure, e.g., a thermometer reading 1°C too high. They affect accuracy but not precision. Random errors cause scatter in results—they can be reduced by repeating readings and calculating a mean.

系统误差由仪器故障或操作不当导致，且始终偏高或偏低，例如温度计始终偏高 1°C。它们影响准确度但不影响精确度。随机误差导致结果离散——可通过重复读取数据并计算平均值来减小。

Common practical errors include incomplete blotting of potato cylinders (giving inconsistent masses), contamination of reagents, not allowing sufficient equilibration time, parallax error when reading a meniscus, and timing inaccuracies. Always suggest an improvement for each limitation.

常见的操作误差包括：马铃薯条吸干不彻底（导致质量不一致）、试剂污染、未充分平衡时间、读取液面时产生视差，以及计时不准确。针对每个局限性，应提出改进建议。

In a conclusion, compare findings with expected biological theory. If results deviate, discuss reasons: ‘The temperature might have fluctuated because the water bath was not thermostatically controlled; using an insulated thermostated bath would improve control.’

在结论中，将发现与预期生物学理论作比较。如果结果偏离，说明原因：“温度可能因水浴无恒温控制而波动；使用隔热恒温水浴将改善控制。”

12. Safety and Ethical Considerations | 安全与伦理考量

Standard laboratory safety rules apply: wear safety goggles when heating or handling chemicals, tie back long hair, and never eat or drink in the lab. For experiments involving living organisms, such as yeast or small insects, treat them with respect and return them to their habitat unharmed. For human studies (e.g., breathing rate, reaction time), obtain informed consent and ensure no harm.

遵守标准实验室安全规则：加热或处理化学品时佩戴护目镜，束好长发，实验室内禁止饮食。涉及活体生物（如酵母或小昆虫）的实验，应尊重生命，实验后安全放回栖息地。人类研究（如呼吸频率、反应时间）需获得知情同意并确保无伤害。

When using microorganisms, follow aseptic techniques: flame the inoculating loop, work near a Bunsen burner to create an updraft, and seal Petri dishes with tape but do not fully seal to avoid anaerobic growth of pathogens. Incubate at a maximum of 25°C in schools to inhibit harmful pathogens.

使用微生物时，遵循无菌操作：灼烧接种环，在靠近本生灯处操作以形成上升气流，用胶带封住培养皿但不要完全密封，以防止病原体厌氧生长。学校培养温度不超过 25°C 以抑制有害病原体。

Ethical considerations also include minimising the number of animals or plants used, and choosing plant experiments or simulations when possible. Always follow the school’s policy and international guidelines for biological investigations.

伦理考量还包括尽量减少使用动植物数量，可能时选择植物实验或模拟实验。始终遵循学校规定和生物实验的国际指导方针。

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