IB Biology Laboratory Practical Guide | IB 生物实验操作指南

📚 IB Biology Laboratory Practical Guide | IB 生物实验操作指南

The IB Biology course places a strong emphasis on practical skills and the internal assessment (IA). Mastering laboratory techniques, data handling, and error analysis is essential for success. This guide provides a comprehensive overview of key experimental skills, from designing a valid investigation to presenting results accurately. Follow these guidelines to enhance your practical work and achieve high marks in your IA.

IB 生物课程高度重视实验技能与内部评估（IA）。掌握实验技术、数据处理和误差分析是取得高分的关键。本指南全面介绍从设计有效研究到准确呈现结果的各项核心实验技能。遵循这些指南，提升你的实验操作，在IA中取得优异成绩。

1. Experimental Design | 实验设计

The foundation of any IB Biology investigation is a well-defined research question. It should be specific, measurable, and include the independent variable (IV) and dependent variable (DV). For example: ‘How does temperature (IV) affect the rate of catalase activity (DV) as measured by oxygen production?’. A clear hypothesis, based on prior knowledge, predicts the relationship.

任何IB生物探究的基础都是一个明确的研究问题。它必须具体、可测量，并包含自变量（IV）和因变量（DV）。例如：“温度（IV）如何影响过氧化氢酶活性速率（DV，通过氧气产量测量）？”基于先验知识的明确假说可以预测变量间的关系。

Replication and adequate sample size (at least five replicates per condition) are crucial for statistical validity. The procedure must be written in a stepwise, reproducible manner so that another student can follow it exactly. Consider the range and intervals of your independent variable to capture the relationship fully.

重复实验和足够的样本量（每个条件至少5个重复）对于统计有效性至关重要。实验步骤必须按顺序书写，具有可重复性，以便其他学生能准确重复。考虑自变量的范围和间隔，以全面捕捉变量关系。

2. Variables and Controls | 变量与对照

All variables other than the IV must be kept constant or controlled to ensure a fair test. These are called controlled variables (CVs). List all CVs and specify how each is controlled (e.g., pH buffer, room temperature, same batch of enzyme). Include a control group where the IV is set to zero or a standard condition to provide a baseline comparison.

除自变量外的所有变量必须保持恒定或受到控制，以确保公平测试。这些变量称为控制变量（CVs）。列出所有控制变量并说明控制方法（例如使用pH缓冲液、恒定室温、同一批次的酶）。设置对照组，令自变量为零或标准条件，以提供基线对照。

Avoid confounding variables that change along with the IV accidentally. If you are testing temperature, ensure other factors like light and humidity do not shift. In a well-controlled experiment, only the IV is purposefully altered.

避免与自变量一同意外变化的混杂变量。如果测试温度，确保光照和湿度等其他因素不发生偏移。在控制良好的实验中，仅故意改变自变量。

3. Data Collection and Recording | 数据收集与记录

Record raw data immediately in a pre-designed table. Each column should have a clear heading with units (e.g., Temperature / °C). Qualitative observations (colour change, bubbles) should also be noted. If using digital sensors, record the reading to the full precision of the instrument.

在预先设计的表格中立即记录原始数据。每列应有带单位的清晰标题（如温度 / °C）。定性观察（颜色变化、气泡）也应记录。若使用数字传感器，需按仪器全部精度记录读数。

Hand-drawn tables are acceptable for IA but must be neat, with ruled lines and correct headings. Never erase data; if a mistake is made, cross it out with a single line and initial it. Raw data must remain legible.

手绘表格在IA中可接受，但必须整洁，使用直尺画线并正确标注标题。切勿擦除数据；如有错误，单线划掉并签上姓名缩写。原始数据必须保持清晰可读。

4. Measurement Uncertainty and Error | 测量不确定度与误差

Every measurement has uncertainty. For analog instruments (ruler, thermometer), the uncertainty is usually ± half the smallest division. For digital instruments, it is ± the last significant digit. Always quote uncertainties with your measurements, e.g., 2.5 cm ± 0.05 cm.

任何测量都有不确定度。对于模拟仪器（直尺、温度计），不确定度通常为±最小刻度的一半。对于数字仪器，是±最后一个有效数字。始终在测量值旁标注不确定度，如2.5 cm ± 0.05 cm。

Distinguish between systematic errors (e.g., miscalibrated balance) that bias results, and random errors (e.g., temperature fluctuations) that affect precision. Discuss how you minimized or accounted for errors. Repeating measurements and using proper technique reduce random error.

区分系统误差（如校准错误的天平，导致结果偏差）和随机误差（如温度波动，影响精密度）。讨论如何最小化或计算误差。重复测量和使用正确技术可降低随机误差。

5. Data Presentation and Graphing | 数据呈现与绘图

Present processed data in a scatter plot or bar chart as appropriate. The independent variable goes on the x-axis, the dependent on the y-axis. Label axes with quantity and unit. Add error bars to represent standard deviation or uncertainty.

根据数据类型使用散点图或柱状图呈现处理后数据。自变量置于x轴，因变量置于y轴。标注轴名称和单位。添加误差棒表示标准差或不确定度。

Draw a line of best fit (curve or straight) through data points, not necessarily connecting all of them. If the error bars are small, you can draw a smooth curve; if overlapping, the difference may not be significant. Do not force the line through the origin unless physically justified.

通过数据点画出最佳拟合线（曲线或直线），无需连接所有点。若误差棒较小，可画平滑曲线；若误差棒重叠，可能差异不显著。除非有物理依据，否则不要强制通过原点。

6. Statistical Analysis (t-test and Standard Deviation) | 统计分析（t检验与标准差）

Calculate the mean (average) for each set of replicates. Then compute the standard deviation to assess variability. A small SD indicates consistent data. The standard deviation can be calculated as:

计算每组重复的均值。然后计算标准差评估变异性。标准差小表示数据一致性好。标准差公式如下：

s = √( Σ(x – x̄)² / (n – 1) )

Here, x̄ is the mean, n is the number of replicates. To compare two means, use an unpaired Student’s t-test. The formula for t is:

式中，x̄ 为均值，n 为重复次数。比较两个均值时，使用非配对 Student t 检验。t 值公式为：

t = (x̄₁ – x̄₂) / √( s₁²/n₁ + s₂²/n₂ )

Compare calculated |t| with critical t-value at 5% significance (p < 0.05) using appropriate degrees of freedom (df = n₁ + n₂ - 2). If |t| > critical value, reject the null hypothesis; the difference is statistically significant. Always state your conclusion clearly.

计算得到的 |t| 与 5% 显著性水平（p<0.05）的临界 t 值比较，自由度 df = n₁ + n₂ - 2。若 |t| > 临界值，拒绝零假设；差异具有统计显著性。务必清晰地陈述结论。

7. Microscopy and Biological Drawing | 显微镜使用与生物绘图

When using a light microscope, start with the lowest magnification objective and use the coarse focus to find the specimen. Switch to higher magnifications, using only fine focus. For biological drawings in your IA, draw clear, single lines without shading or coloring.

使用光学显微镜时，先用低倍物镜，用粗调焦找到标本。转换到高倍镜时，仅用细调焦。IA中的生物绘图要求用清晰单线，不可涂色或上色。

Include a scale bar, and label structures with straight ruling lines. Indicate magnification. A plan diagram shows tissue arrangement without individual cells. A high-power diagram should depict a few cells with their organelles visible, properly proportioned.

添加比例尺，并用直尺画线标注结构。标明放大倍数。平面图展示组织排列，不画单个细胞。高倍镜下草图应描绘少数细胞，显示可见细胞器，比例恰当。

8. Chromatography and Gel Electrophoresis | 色谱法与凝胶电泳

Paper chromatography separates photosynthetic pigments based on solubility. Calculate the retention factor (Rf) = distance travelled by pigment / distance travelled by solvent front. Always use pencil to mark the origin, not pen, as ink would run.

纸色谱法根据溶解性分离光合色素。计算比移值 Rf = 色素移动距离 / 溶剂前沿移动距离。务必用铅笔标记原点，勿用钢笔，因为墨水会扩散。

For gel electrophoresis (DNA analysis), DNA fragments migrate toward the positive electrode; smaller fragments move faster. Use a standard DNA ladder to estimate fragment size. Always wear gloves and handle gels with care. The agarose concentration affects separation range.

凝胶电泳（DNA分析）中，DNA片段向正极移动；小片段移动较快。使用标准 DNA 阶梯估测片段大小。始终戴手套并小心处理凝胶。琼脂糖浓度影响分离范围。

9. Spectrophotometry and Colorimetry | 分光光度法与比色法

A spectrophotometer measures absorbance (A) at specific wavelengths. For a colored solution, follow Beer-Lambert law (A ∝ concentration). Construct a standard curve by measuring known concentrations of the substance, then use the curve to determine unknown sample concentrations.

分光光度计测量特定波长下的吸光度。对于有色溶液，遵循比尔-朗伯定律（吸光度与浓度成正比）。通过测量已知浓度制作标准曲线，再利用曲线推算未知样品浓度。

Zero the instrument with a blank (solvent only) before measuring. This technique is common for enzyme kinetics (product formation) and pigment quantification. Use the same cuvette orientation and clean it carefully to avoid smudges.

测量前用空白液（仅溶剂）调零。此技术常用于酶动力学（产物形成）和色素定量。保持比色皿方向一致并仔细清洁，避免指印干扰。

10. Enzyme Activity Experiments | 酶活性实验

Typical enzyme experiments investigate how temperature, pH, or substrate concentration affect enzyme activity. Use fixed enzyme and substrate concentrations, varying only one factor. Measure the initial rate of reaction (e.g., volume of O₂ produced in the first 30 seconds) to avoid substrate depletion.

典型的酶实验探究温度、pH或底物浓度对酶活性的影响。固定酶和底物浓度，仅改变一个因素。测量反应初速率（如最初30秒产生O₂的体积），避免底物耗尽。

Repeat at each condition. Stop the reaction with acid or boiling if needed, or use continuous monitoring. Handle enzyme solutions carefully; they may denature. Use a water bath for stable temperature control, and pre-equilibrate all solutions.

每个条件均需重复。必要时加酸或煮沸终止反应，或使用连续监测。小心处理酶溶液，它们可能变性。使用水浴保持温度稳定，并预热所有溶液至目标温度。

11. Osmosis and Diffusion Practicals | 渗透与扩散实验

For osmosis in potato strips, measure change in mass or length after incubation in solutions of different sucrose concentrations. Calculate percentage change in mass: % change = (final mass – initial mass)/initial mass × 100%. Plot a graph and determine the isotonic point where % change = 0.

用土豆条进行渗透实验，测量在不同蔗糖浓度溶液中浸泡后质量或长度的变化。计算质量变化百分比：%变化 =( 最终质量 – 初始质量)/初始质量 × 100%。绘制图表并确定%变化为零的等渗点。

For diffusion, use agar cubes with pH indicator and measure diffusion rate based on distance travelled or time for a color change. Control temperature and stirring. Surface area to volume ratio is a crucial concept here.

对于扩散实验，使用含pH指示剂的琼脂块，根据扩散距离或颜色变化所需时间测量速率。控制温度和搅拌。表面积与体积之比是其中的关键概念。

12. Lab Safety and Ethical Considerations | 实验室安全与伦理考量

Always wear safety goggles, lab coat, and closed-toe shoes. Handle chemicals (acids, bases, stains) in a fume hood if necessary. Dispose of biological waste properly. Never eat or drink in the lab, and wash hands after any practical.

始终佩戴护目镜、实验服和不露趾的鞋子。必要时在通风橱中处理化学品（酸、碱、染色剂）。妥善处理生物废弃物。实验室内禁止饮食，实验后必须洗手。

When using living organisms (e.g., yeast, plants), follow ethical guidelines: minimize harm, avoid unnecessary stress, and return organisms to their environment if possible. For human subjects (e.g., heart rate experiments), obtain consent and ensure no risk. Your IA must respect safety and ethical principles.

使用活体生物（如酵母、植物）时，遵守伦理准则：最小化伤害、避免不必要压力、可能时放归环境。对于人类受试者（如心率实验），取得知情同意并确保无风险。你的IA必须符合安全与伦理原则。

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IB Biology Laboratory Practical Guide | IB 生物实验操作指南