📚 IB WJEC Biology: Essential Lab Skills and Experimental Techniques | IB WJEC 生物：核心实验技能与操作指南
In IB and WJEC Biology, practical work is not just a requirement – it is the heartbeat of scientific understanding. Mastering core experimental techniques gives you the confidence to design robust investigations, collect reliable data, and critically evaluate your findings. This guide covers the most important laboratory procedures, from basic microscopy and biological drawing to enzyme kinetics, photosynthetic rate measurement, chromatography, and statistical testing, all aligned with IB internal assessment criteria and WJEC practical endorsement standards.
在 IB 和 WJEC 生物课程中，实验操作不仅是必修内容，更是科学理解的灵魂。掌握核心实验技能能让你自信地设计严谨的探究、收集可靠数据并批判性评价结果。本文涵盖最重要的实验室操作，从基础的显微镜使用、生物绘图，到酶动力学、光合速率测定、色谱分析和统计检验，全部紧扣 IB 内部评估标准与 WJEC 实践签核要求。
1. Microscope Setup and Calibration | 显微镜设置与校准
Begin by placing the compound light microscope on a stable bench. Rotate the nosepiece to the lowest-power objective (usually 4× or 10×) and ensure the condenser and diaphragm are adjusted for optimum illumination. Use the coarse focus knob to bring the stage close to the objective while looking from the side, then look through the eyepiece and focus away from the slide until the specimen becomes clear. Calibrate the eyepiece graticule using a stage micrometer: note that at ×40 magnification, 10 eyepiece units might correspond to 25 µm on the stage micrometer, so each eyepiece unit = 2.5 µm. Always record calibration factors when switching objectives.
先将复式光学显微镜放置在稳固的实验台上。旋转物镜转换器对准最低倍物镜（通常为 4× 或 10×），并调节聚光器和光阑以获得最佳照明。用粗准焦螺旋将载物台升高至接近物镜，眼睛从侧面观察，然后通过目镜观察，慢慢降低载物台直至样本清晰。利用镜台测微尺校准目镜测微尺：注意在 40 倍放大下，10 个目镜分度可能对应 25 µm 的镜台测微尺，因此每个目镜分度 = 2.5 µm。更换物镜时务必记录校准系数。
2. Biological Drawing and Annotation | 生物绘图与标注
Use a sharp HB or 2H pencil on plain white paper. Draw only what you observe – do not copy textbook diagrams. The drawing should be large, centred, and bounded by clear continuous lines; stippling or hatching is preferred over shading. Label structures with straight, non-crossing ruler lines, writing names horizontally to the right. Include a figure caption describing the specimen, section type, and magnification. For IB, annotations should explain features related to function; for WJEC, ensure scale bars are added where required and measured dimensions are recorded in µm.
使用削尖的 HB 或 2H 铅笔在纯白纸上绘图。只画你观察到的内容——不要抄课本图像。绘图要大幅、居中，用清晰连续的线条勾边；点描或排线优于阴影。用直尺画出互不交叉的标注线，标注文字水平写在右侧。图题需写明标本名称、切片类型和放大倍数。对 IB 而言，标注应解释结构与功能的关系；对 WJEC，需在需要时添加比例尺并用 µm 记录测量尺寸。
3. Controlling Variables and Fair Testing | 控制变量与公平实验
Identify the independent variable (the one you change), the dependent variable (the one you measure), and at least three controlled variables that must be kept constant to ensure a fair test. For example, when investigating the effect of temperature on catalase activity, control pH using a buffer, enzyme concentration, and substrate volume. In your write-up, explicitly state how each controlled variable was managed. Use a water bath or thermostatic chamber to maintain temperature within ±0.5 °C. Repeats at each level of the independent variable improve reliability, so plan for a minimum of five replicates per condition.
明确自变量（你改变的变量）、因变量（你测量的变量）以及至少三个必须保持恒定的控制变量以确保公平试验。例如，研究温度对过氧化氢酶活性的影响时，用缓冲液控制 pH，固定酶浓度和底物体积。在实验报告中清晰说明每个控制变量的具体管理方式。使用水浴或恒温箱将温度波动控制在 ±0.5 °C 以内。每个自变量水平下设置重复实验能提高可靠性，因此每个条件至少规划五个重复。
4. Measuring Enzyme Activity: Catalase and Peroxide | 酶活性测定：过氧化氢酶与过氧化氢
Cut uniform potato discs using a cork borer and scalpel, ensuring equal surface area. Submerge discs in a known concentration of hydrogen peroxide within a conical flask connected to a gas syringe or upturned measuring cylinder. Measure the volume of oxygen evolved every 30 seconds for 3 minutes. Alternatively, record the time taken for a filter paper disc soaked in catalase solution to rise from the bottom of a peroxide-filled beaker. Calculate initial rate of reaction (cm³ O₂ s⁻¹) from the steepest portion of the progress curve. For WJEC, you may also measure the decrease in absorbance of a coloured substrate using a colorimeter.
用打孔器和手术刀切取大小均匀的土豆圆片，确保表面积相等。将土豆片浸入已知浓度的过氧化氢溶液中，容器连接气体注射器或倒置量筒。每隔 30 秒记录释放的氧气体积，持续 3 分钟。或者记录浸过过氧化氢酶溶液的滤纸片在充满过氧化氢的烧杯中从杯底上浮所需的时间。从反应进程曲线最陡峭部分计算初始反应速率 (cm³ O₂ s⁻¹)。对于 WJEC 考试，你可能还需使用比色计测量有色底物吸光度的下降。
5. Photosynthesis Rate via Bubble Counting | 气泡计数法测定光合速率
Place a fresh Elodea sprig in a beaker of bicarbonate solution (providing CO₂) and expose it to a LED light source at a fixed distance. Count the number of oxygen bubbles released from the cut stem per minute. Adjust light intensity by varying the lamp distance (intensity ∝ 1/distance²) or by using neutral density filters. Maintain constant temperature by surrounding the beaker with a water jacket connected to a thermostatic circulator. Plot rate (bubbles min⁻¹) against light intensity; the graph shows an initial linear rise then a plateau where CO₂ or temperature becomes limiting. Include data on the wavelength of light by using coloured filters for a WJEC-required investigation of action spectrum.
将新鲜伊乐藻小枝置于含碳酸氢盐溶液（提供 CO₂）的烧杯中，用固定距离的 LED 光源照射。每分钟计算从切开茎端释放的氧气气泡数。通过改变灯距（光强 ∝ 1/距离²）或使用中性滤光片调节光强。烧杯外加水套连接恒温循环器以维持温度恒定。绘制速率（气泡数/分钟）与光强的关系图；曲线先直线上升后趋于平台，此时 CO₂ 或温度成为限制因子。用彩色滤光片获取不同波长下的数据，这通常是 WJEC 要求的吸收光谱探究。
6. Respirometer and Cellular Respiration | 呼吸计与细胞呼吸
Assemble a simple respirometer using a test tube with respiring organisms (germinating peas or larvae), a 1 ml graduated pipette horizontal to the bench, and a manometer fluid such as coloured water. Remove CO₂ by adding soda lime or KOH pellets in a mesh bag. Measure the movement of the fluid in the pipette every minute, reflecting oxygen uptake. Also set up a control tube containing inert glass beads of equal volume to correct for pressure and temperature fluctuations. Calculate the rate of oxygen consumption in mm³ min⁻¹. For WJEC, you can compare carbohydrate and lipid-based respiration rates using different seeds, linking findings to respiratory quotient values.
利用装有呼吸材料（萌发豌豆或幼虫）的试管、水平放置的 1 ml 刻度移液管和带色水的压力计液体装配简易呼吸计。用网袋装碱石灰或 KOH 颗粒去除 CO₂。每分钟记录移液管内液柱的移动距离，反映氧气消耗。同时设置含有等体积玻璃珠的对照管，以校正气压和温度波动。计算耗氧速率，单位 mm³ min⁻¹。在 WJEC 实验中，可选用不同种子比较碳水化合物类与脂质类的呼吸速率，并将结果与呼吸商数值关联。
7. DNA Extraction from Plant Tissue | 植物组织 DNA 提取
Grind fresh pea or spinach leaves in a chilled mortar with a pinch of sand and 10 ml of ice-cold extraction buffer (salt, detergent, EDTA). The detergent dissolves phospholipid membranes, salt neutralizes DNA’s negative charge, and EDTA chelates Mg²⁺ to inhibit nucleases. Filter the slurry through a cheesecloth into a clean beaker. Gently layer ice-cold ethanol or propan-2-ol down the side and watch for a white, spoolable precipitate at the interface – this is crude DNA. For further purification, treat with protease and wash with 70% ethanol. Quantify DNA yield using a UV spectrophotometer at 260 nm (A₂₆₀ of 1.0 ≈ 50 µg/ml dsDNA).
在预冷研钵中将新鲜豌豆或菠菜叶与少量石英砂和 10 ml 冰预冷的提取缓冲液（盐、去污剂、EDTA）一同研磨。去污剂溶解磷脂膜，盐中和 DNA 的负电荷，EDTA 螯合 Mg²⁺ 抑制核酸酶。将匀浆通过纱布过滤至干净烧杯中。沿壁轻轻加入冰乙醇或异丙醇，界面处可见白色可缠绕的沉淀——即粗提取的 DNA。进一步纯化可用蛋白酶处理并 70% 乙醇洗涤。使用紫外分光光度计在 260 nm 处定量 DNA 产量（A₂₆₀ = 1.0 约相当于 50 µg/ml 双链 DNA）。
8. Paper Chromatography of Photosynthetic Pigments | 光合色素的纸色谱分析
Extract pigments by grinding leaves in a mortar with acetone and a little sand. Spot a concentrated drop of the extract onto a pencil line 2 cm above the bottom of a chromatography paper. Suspend the paper in a chromatography tank containing petroleum ether–acetone solvent (9:1) ensuring the spot remains above the solvent level. Allow the solvent to ascend for 30–45 minutes until it nears the top. Mark the solvent front, dry the paper, and observe four separated bands: chlorophyll b (yellow-green), chlorophyll a (blue-green), xanthophylls (yellow), and carotenes (orange). Calculate Rf values: Rf = distance moved by pigment / distance moved by solvent front. Compare your values to published data for identification.
用丙酮和少量石英砂在研钵中研磨叶片提取色素。将浓缩提取液点在色谱纸条距底端 2 cm 的铅笔线上。将纸条悬挂在含石油醚-丙酮展开剂（9:1）的层析缸中，确保色点高于液面。展开 30–45 分钟至溶剂前沿接近顶端。标记前沿位置，干燥纸条，观察分离出的四条带：叶绿素 b (黄绿)、叶绿素 a (蓝绿)、叶黄素 (黄) 和胡萝卜素 (橙)。计算 Rf 值：Rf = 色素移动距离 / 溶剂前沿移动距离。将计算值与文献值比较以鉴定色素。
9. Osmosis and Water Potential Determination | 渗透作用与水势测定
Cut uniform cylinders from a potato using a cork borer, blot them gently, and weigh each to the nearest 0.01 g. Immerse cylinders in a series of sucrose solutions (0.0, 0.2, 0.4, 0.6, 0.8, 1.0 mol dm⁻³) for a standard time, typically 30 minutes. After incubation, reweigh to calculate percentage change in mass: (final mass – initial mass) / initial mass × 100%. Plot % change against sucrose concentration; the line of best fit intercepts the x-axis at the solute concentration where water potential is equal to that of the tissue – i.e., no net water movement. Convert to water potential (MPa) using the formula ψ = –iCRT, where i=1 for sucrose, C is concentration (mol dm⁻³), R=0.00831, and T is temperature in Kelvin.
用打孔器从马铃薯切取均匀圆柱条，轻轻吸干表面水分后称重至 0.01 g。将圆柱条浸入一系列蔗糖溶液（0.0、0.2、0.4、0.6、0.8、1.0 mol dm⁻³）中标准时间，通常 30 分钟。温育后重新称重，计算质量变化百分数：(终质量 – 初质量) / 初质量 × 100%。绘制质量变化百分数对蔗糖浓度的关系图；最佳拟合线与 x 轴的交点即为组织水势等于外界溶液水势时的浓度——此时无净水移动。利用公式 ψ = –iCRT 换算为水势 (MPa)，式中 i=1（蔗糖），C 为浓度 (mol dm⁻³)，R=0.00831，T 为开尔文温度。
10. Data Presentation and Descriptive Statistics | 数据呈现与描述性统计
Always present processed data in clearly labelled tables with units in headings. Produce graphs with the independent variable on the x-axis and dependent on the y-axis; draw line graphs for continuous data and bar charts for discrete categories, adding error bars representing ±1 standard deviation or standard error of the mean. Calculate mean, median, standard deviation (s = √[Σ(x – x̄)²/(n–1)]), and standard error (SE = s/√n). Use a calculator or spreadsheet to determine these values; for IB, you must explain why standard deviation is a better measure of spread than range, referring to its resistance to outliers.
处理后的数据务必用标注清晰的表格呈现，表头含单位。图形绘制时自变量置于 x 轴、因变量置于 y 轴；连续数据绘折线图，离散类别绘柱状图，并添加误差棒表示 ±1 标准差或均值标准误。计算平均数、中位数、标准差 (s = √[Σ(x – x̄)²/(n–1)]) 和标准误 (SE = s/√n)。使用计算器或电子表格求值；对于 IB，你必须解释标准差为何比极差更能反映离散程度，原因在于其对离群值的抗干扰性。
11. Statistical Tests: t‑test and Chi‑squared | 统计检验：t 检验与卡方检验
Use the Student’s t‑test to compare two independent sample means. Calculate t = (x̄₁ – x̄₂) / √[(s₁²/n₁) + (s₂²/n₂)] and compare with a critical value at n₁+n₂–2 degrees of freedom (usually p=0.05). If the calculated t exceeds the critical value, reject the null hypothesis, concluding a significant difference. For categorical frequency data, apply the chi‑squared test: χ² = Σ[(O – E)²/E], where O and E are observed and expected frequencies. A 2×2 Mendelian cross (9:3:3:1 ratio) expects three degrees of freedom; always state the null hypothesis and probability level. IB requires these tests for internal assessment when comparing treatments.
用学生 t 检验比较两个独立样本的均值。计算 t = (x̄₁ – x̄₂) / √[(s₁²/n₁) + (s₂²/n₂)]，并与自由度为 n₁+n₂–2 的临界值（通常 p=0.05）比较。若计算所得 t 值超出临界值，拒绝零假设，可得出存在显著差异的结论。对于频数分类数据，应用卡方检验：χ² = Σ[(O – E)²/E]，其中 O 和 E 分别为观察频数和期望频数。2×2 孟德尔杂交（9:3:3:1 比）对应三个自由度；检验时需完整陈述零假设与概率水平。IB 内部评估在处理间比较时要求进行上述检验。
12. Risk Assessment and Ethical Practice | 风险评估与伦理规范
Before any experiment, complete a thorough risk assessment identifying hazards (chemical, biological, physical) and control measures. Wear safety goggles, lab coat, and gloves when handling enzymes, stains, or organic solvents. Work in a fume cupboard when using volatile reagents like acetone. For living organisms, adhere to ethical guidelines: minimise harm, maintain suitable temperatures and oxygen levels, and return specimens to their original habitat where possible. In WJEC, the practical endorsement requires dated and signed records of risk assessment. In IB, the ethical and safety justification must be included in the internal assessment report for animal or human studies.
任何实验前均应完成详尽的风险评估，识别化学、生物、物理危害并列出控制措施。操作酶、染料或有机溶剂时须佩戴护目镜、实验服和手套。使用丙酮等挥发性试剂时应在通风橱内工作。对于活体生物，遵循伦理指南：将伤害降至最低，维持适宜温度和溶氧水平，并尽可能将生物放回原生栖息地。WJEC 的实践签核要求有日期和签名的风险评估记录。IB 涉及动物或人类研究时，内部评估报告须包含伦理与安全论证。
Published by TutorHao | Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导Cancel reply