📚 IGCSE WJEC Biology: Practical Skills Guide | IGCSE WJEC 生物：实验操作指南
Practical work sits at the heart of IGCSE WJEC Biology. Not only do you need to recall key investigations, but you must also demonstrate an understanding of how to design safe, reliable experiments, record observations accurately, and draw valid conclusions. This guide walks you through the essential practical skills and core required investigations, from mastering the microscope to testing a leaf for starch, helping you prepare for both the written examination and the practical assessment.
实验操作是 IGCSE WJEC 生物的核心。你不仅需要记住关键的探究实验，还必须展示如何设计安全、可靠的实验，准确记录观察结果，并得出有效结论。本指南将带你回顾基本的实验技能和核心必做实验，从掌握显微镜操作到检验叶片中的淀粉，帮助你为笔试和实践评估做好充分准备。
1. Using a Light Microscope | 使用光学显微镜
Always start with the lowest power objective lens, use the coarse focus knob to bring the stage close to the lens while looking from the side, and then look through the eyepiece, adjusting the coarse focus away from the slide until the image appears. Fine focus is then used to sharpen the image.
始终从最低倍物镜开始，从侧面观察时使用粗准焦螺旋将载物台移近镜头，然后通过目镜观察，转动粗准焦螺旋使物镜远离玻片，直至看到图像。最后用细准焦螺旋调焦使图像清晰。
The total magnification is calculated by multiplying the eyepiece magnification by the objective lens magnification. For example, a 10x eyepiece with a 40x objective gives a total magnification of 400x.
总放大倍数是目镜放大倍数乘以物镜放大倍数。例如，10 倍目镜配 40 倍物镜，总放大倍数为 400 倍。
When making measurements with a graticule, you must calibrate it using a stage micrometer for each objective lens. The size of a cell or organelle can then be calculated using the formula: actual size = image size ÷ magnification (after converting units).
使用目镜测微尺测量时，必须为每个物镜用镜台测微尺进行校准。然后可用公式计算细胞或细胞器的实际大小：实际大小 = 图像大小 ÷ 放大倍数（换算单位后）。
2. Making Biological Drawings | 绘制生物图
Biological drawings should be made with a sharp HB pencil, using clear, continuous outlines. Do not shade or colour; use stippling (small dots) to show darker regions. The drawing must be large enough to show detail, and all visible structures should be labelled with straight, horizontal label lines that do not cross.
生物图应用削尖的 HB 铅笔绘制，轮廓线清晰连续。不要涂阴影或上色，用点描法（小点）表示较暗区域。图应足够大以展示细节，所有可见结构都要用直的、水平的、不交叉的标注线标注。
Always include a title that states what the specimen is and the magnification used. For a plan diagram (low-power drawing), show only the outlines of tissues, not individual cells. For a high-power drawing, draw a few representative cells in detail and label organelles such as the nucleus, cell wall, chloroplasts, etc.
始终包含标题，说明所观察的标本以及使用的放大倍数。对于轮廓图（低倍绘图），只画出组织的轮廓，不要画单个细胞。对于高倍绘图，详细画出几个代表性细胞，并标注细胞核、细胞壁、叶绿体等细胞器。
3. Planning an Investigation and Variables | 计划调查与变量
Every experiment should have a clear independent variable (the one you change), a dependent variable (the one you measure), and controlled variables (those you keep the same to ensure a fair test). For example, when investigating the effect of temperature on enzyme activity, temperature is the independent variable, time taken for starch to disappear is the dependent variable, and pH, enzyme concentration, and starch concentration are controlled variables.
每个实验都应明确自变量（你改变的变量）、因变量（你测量的变量）和控制变量（你保持不变的变量，以确保公平测试）。例如，探究温度对酶活性的影响时，温度是自变量，淀粉消失所需的时间是因变量，而 pH、酶浓度和淀粉浓度是控制变量。
A well-planned method includes a step-by-step procedure that another person could follow, specifies the range and intervals of the independent variable, and describes repeats to improve reliability. Always identify potential hazards and state precautions, such as wearing safety goggles when heating or using enzymes that may irritate the skin.
一个周密的方法应包括他人可重复的分步操作程序，指明自变量的范围和间隔，并描述重复实验以提高可靠性。始终要识别潜在的危险并说明预防措施，如加热时佩戴护目镜，或使用可能刺激皮肤的酶时做好防护。
4. Food Tests – Identifying Nutrients | 食物测试 – 鉴定营养物质
Reducing sugars: Add Benedict’s solution to the food sample in a test tube and heat in a boiling water bath for 3–5 minutes. A positive result is a colour change from blue, through green and yellow, to a brick-red precipitate. This test is semi‑quantitative: the more reducing sugar present, the more red the precipitate.
还原糖：在试管中将本尼迪克特溶液加入食物样品，置于沸水浴中加热 3–5 分钟。阳性结果会从蓝色变为绿色、黄色，最后形成砖红色沉淀。该测试是半定量的：还原糖越多，沉淀越红。
Starch: Add a few drops of iodine solution (iodine in potassium iodide) to the food sample. A blue‑black colour indicates the presence of starch. Use this test to monitor the progress of amylase‑starch experiments.
淀粉：在食物样品上滴加几滴碘液（碘的碘化钾溶液）。蓝黑色表示存在淀粉。可用此测试监测淀粉酶-淀粉实验的进程。
Protein (biuret test): Add an equal volume of sodium hydroxide solution to the sample, then add a few drops of dilute copper(II) sulfate solution and shake. A purple or mauve colour indicates protein.
蛋白质（双缩脲测试）：向样品中加入等体积的氢氧化钠溶液，然后滴加几滴稀硫酸铜（II）溶液并摇匀。紫色或淡紫色表示存在蛋白质。
Lipids (emulsion test): Shake the food sample with absolute ethanol, then pour the liquid into a test tube containing cold water. A milky‑white emulsion indicates the presence of lipids.
脂质（乳浊液测试）：将食物样品与无水乙醇一起摇匀，然后将液体倒入盛有冷水的试管中。乳白色的乳浊液表示存在脂质。
5. Investigating Enzyme Activity – Effect of Temperature | 探究酶活性 – 温度的影响
The typical investigation uses amylase and starch solution. Place one test tube of starch solution and one test tube of amylase solution in a water bath at a fixed temperature for 5 minutes to equilibrate. Then mix them and, at regular intervals (e.g., every 30 seconds), remove a drop of the mixture using a glass rod and add it to a drop of iodine solution on a spotting tile. Record the time taken for the blue‑black colour to disappear (indicating all starch has been broken down).
典型的实验使用淀粉酶和淀粉溶液。将一支装淀粉溶液的试管和一支装淀粉酶溶液的试管放在设定温度的水浴中平衡 5 分钟。然后混合二者，每隔固定时间（如每 30 秒）用玻璃棒取出一滴混合物，加到白瓷板上的碘液中。记录蓝黑色消失所需的时间（表明淀粉已被完全分解）。
Repeat the procedure at a range of temperatures, e.g., 0°C (ice bath), 20°C, 30°C, 40°C, 50°C, 60°C. Plot a graph of temperature (x-axis) against rate of reaction (1/time, on the y-axis). The rate increases with temperature up to an optimum, then declines as the enzyme denatures.
在不同温度下重复该步骤，例如 0°C（冰浴）、20°C、30°C、40°C、50°C、60°C。绘制温度（x 轴）与反应速率（1/时间，y 轴）的关系图。速率随温度升高而增加，到达最适温度后，随着酶变性而下降。
Rate of reaction = 1 / time (s⁻¹)
反应速率 = 1 / 时间 (s⁻¹)
6. Investigating Enzyme Activity – Effect of pH | 探究酶活性 – pH 的影响
This experiment follows a similar method but uses buffer solutions at different pH values (e.g., pH 4, 7, 9) to provide the environment for the amylase‑starch reaction. The enzyme, starch and buffer are equilibrated at the chosen temperature (kept constant, such as 30°C). The time for starch disappearance is recorded for each pH.
该实验方法相似，但使用不同 pH 的缓冲液（如 pH 4、7、9）为淀粉酶-淀粉反应提供环境。酶、淀粉和缓冲液在选定的常数温度（如 30°C）下平衡，记录每个 pH 下淀粉消失所需的时间。
The optimum pH for amylase is usually around neutral (pH 7). Extreme pH values denature the enzyme by altering the shape of its active site, so the substrate no longer fits. A graph of pH against rate of reaction typically forms a bell-shaped curve.
淀粉酶的最适 pH 通常在中性附近（pH 7）。极端 pH 值会通过改变酶的活性部位形状使酶变性，底物无法再与之契合。pH 与反应速率的关系图通常呈钟形曲线。
7. Osmosis in Potato Strips | 土豆条的渗透作用
Cut potato into equal-sized chips, blot them dry, measure their initial mass (or length), and place them into a series of sucrose solutions of known concentrations (e.g., 0.0, 0.2, 0.4, 0.6, 0.8, 1.0 mol/dm³). After a set time (usually 30 minutes or until there is a measurable change), remove the chips, blot gently and record the final mass.
将土豆切成相同大小的条，吸干水分，测量其初始质量（或长度），然后放入一系列已知浓度的蔗糖溶液中（如 0.0、0.2、0.4、0.6、0.8、1.0 mol/dm³）。经过设定的时间后（通常 30 分钟或直到出现可测量的变化），取出薯条，轻轻吸干，记录最终质量。
Calculate the percentage change in mass for each chip using the formula:
% change = (final mass − initial mass) / initial mass × 100
计算每个薯条的质量变化百分比，公式：
% 变化 = (最终质量 − 初始质量) / 初始质量 × 100
Plot a graph of percentage change in mass against sucrose concentration. The point where the curve crosses the x‑axis (zero mass change) indicates the water potential of the potato tissue, i.e., the concentration at which there is no net movement of water.
绘制质量变化百分比与蔗糖浓度的关系图。曲线与 x 轴的交点（质量变化为零）表示土豆组织的水势，即该浓度下水分没有净移动。
8. Photosynthesis – Effect of Light Intensity | 光合作用 – 光照强度的影响
Use an aquatic plant such as Elodea (Canadian pondweed) placed in a beaker of water. Add a source of carbon dioxide by using water that contains dissolved sodium hydrogencarbonate (1%). Position a lamp at a measured distance from the plant and count the number of oxygen bubbles released per minute, or collect the gas in a capillary tube and measure the volume.
使用水生植物，如伊乐藻（加拿大水草），放在盛有水的烧杯中。通过使用溶有 1% 碳酸氢钠的水提供二氧化碳源。将灯放在与植物一定距离的位置，计算每分钟释放的氧气气泡数，或者用毛细管收集气体并测量体积。
Vary the light intensity by changing the distance of the lamp. Light intensity follows an inverse square law: light intensity ∝ 1/d² where d is the distance from the lamp. Plot the rate of photosynthesis (bubbles per minute) against light intensity (or 1/d²). The rate increases with light intensity until another factor, such as CO₂ or temperature, becomes limiting.
通过改变灯的距离来改变光照强度。光照强度遵循平方反比定律：光照强度 ∝ 1/d²，其中 d 是灯的距离。绘制光合作用速率（每分钟气泡数）与光照强度（或 1/d²）的关系图。速率随光照强度增加而上升，直至其他因素如 CO₂ 或温度成为限制因素。
9. Photosynthesis – Testing a Leaf for Starch | 光合作用 – 检验叶片中的淀粉
To show that photosynthesis produces starch in a green leaf, first place a leaf, which has been exposed to light for several hours, into boiling water to kill it and stop all metabolic reactions. Then transfer it to a tube of boiling ethanol (in a water bath, never over a direct flame) to remove chlorophyll. The leaf becomes pale and brittle.
为证明光合作用在绿叶中产生淀粉，首先将已经光照数小时的叶片放入沸水中杀死组织并停止所有代谢反应。然后将其转入沸腾的乙醇中（在水浴中加热，绝不可直接在火焰上加热）以脱去叶绿素。叶片变得苍白且脆。
Rinse the leaf in cold water to soften it, then spread it on a white tile and add a few drops of iodine solution. Areas of the leaf that were photosynthesising will stain blue‑black. A variegated leaf can be used to show that only the green areas (containing chlorophyll) produce starch.
在冷水中漂洗叶片使其软化，然后将其平铺在白色瓷砖上，滴加几滴碘液。进行光合作用的叶片区域将染成蓝黑色。可用斑叶进行实验，证明只有绿色区域（含有叶绿素）才能产生淀粉。
10. Respiration – Producing Carbon Dioxide | 呼吸作用 – 产生二氧化碳
Germinating seeds or small organisms (e.g., woodlice, maggots) are placed in a chamber with a delivery tube leading to a test tube of limewater or hydrogencarbonate indicator. A control setup containing dead, boiled seeds (washed with disinfectant) is used to show that any CO₂ is due to respiration of living things, not microbes on the surface.
将萌发的种子或小生物（如潮虫、蝇蛆）放在一个容器中，容器与一支盛有石灰水或碳酸氢盐指示剂的试管相连。对照装置使用经煮沸杀死并冲洗消毒的种子，以表明任何 CO₂ 都是生物体呼吸产生的，而非表面微生物所致。
Limewater turns from clear to milky when carbon dioxide is bubbled through it. Hydrogencarbonate indicator, which is red or orange at atmospheric CO₂, turns yellow in the presence of higher CO₂ levels, confirming that respiring organisms release carbon dioxide.
当二氧化碳通入石灰水时，石灰水由澄清变为浑浊。碳酸氢盐指示剂在大气 CO₂ 下为红色或橙色，在 CO₂ 含量升高时变为黄色，从而证实呼吸作用的生物释放二氧化碳。
The balanced equation for aerobic respiration summarises the overall process:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy)
有氧呼吸的总平衡方程式为：
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ 能量)
11. Diffusion in a Non‑Living System | 非生命系统中的扩散
Although not a living model, this investigation demonstrates the factors affecting diffusion. Use agar cubes stained with a pH indicator (such as phenolphthalein and dilute sodium hydroxide, making the cube pink) and place them in dilute hydrochloric acid. As the acid diffuses in, the pink colour disappears. Measure the time taken for the colour to clear completely.
尽管不是活体模型，该实验可以展示影响扩散的因素。使用含有 pH 指示剂的琼脂块（如酚酞和稀氢氧化钠，使琼脂块呈粉红色），将其放入稀盐酸中。酸扩散进入时，粉红色消失。测量颜色完全褪去所需的时间。
By varying the size of the agar cubes (e.g., 1 cm, 2 cm, 3 cm), you can calculate the surface area to volume ratio and show that smaller cubes (higher SA:V) lose colour faster. This principle explains why cells and organisms need to be small or have adaptations to increase surface area.
通过改变琼脂块的大小（如 1 cm、2 cm、3 cm），你可以计算表面积与体积之比，并证明较小的块（较高的比表面积）颜色消失得更快。这一原理解释了为什么细胞和生物体需要保持较小的体积，或者具备增大表面积的适应结构。
12. Heart Rate and Exercise | 心率与运动
Design a simple investigation to measure the effect of exercise on heart rate. Take the resting pulse at the wrist or neck for 15 seconds and multiply by four to obtain beats per minute (bpm). Perform a step exercise for a set time (e.g., 2 minutes), then immediately measure the pulse again at regular intervals during recovery until it returns to resting.
设计一个简单的实验来测量运动对心率的影响。在手腕或颈部测量安静时的脉搏 15 秒，乘以 4 得到每分钟心率（bpm）。进行设定时间的台阶运动（如 2 分钟），然后立即在恢复期间每隔固定时间测量脉搏，直至恢复到安静水平。
Plot a graph of time (x-axis) against heart rate (y-axis). The results show that heart rate increases to supply more oxygen and glucose to muscles and to remove carbon dioxide produced during increased respiration. Control variables include the type and duration of exercise, the person’s fitness level, and the environmental temperature.
绘制时间（x 轴）与心率（y 轴）的关系图。结果显示心率增加，以便为肌肉提供更多的氧气和葡萄糖，并清除呼吸作用增加所产生的二氧化碳。控制变量包括运动类型和时长、被测者的健康水平以及环境温度。
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