📚 IB Science: High-Frequency Revision Points Summary | IB 科学：高频考点总结
In the IB Diploma Programme, the Group 4 sciences – including Biology, Chemistry, and Physics – share a common core of assessment skills and recurring concepts. Mastering these high-frequency points not only boosts your performance on written papers but also strengthens your Internal Assessment. This article distils the most examined ideas across IB sciences, giving you a bilingual, dual-language revision guide that clarifies key terminology, experimental know-how, and analytical techniques.
在 IB 文凭课程中，第四学科组的科学（包括生物、化学和物理）拥有共同的评估技能核心和反复出现的概念。掌握这些高频考点不仅能提升笔试成绩，还能强化内部评估。本文提炼了 IB 科学中考查最多的内容，以中英双语的形式提供复习指南，厘清关键术语、实验技巧和分析方法。
1. Scientific Method and Experimental Design | 科学方法与实验设计
The scientific method is the backbone of all IB sciences. You must be able to formulate a focused research question, propose a testable hypothesis, and design a fair experiment in which variables are managed systematically.
科学方法是所有 IB 科学的基础。你必须能够提出明确的研究问题、可检验的假设，并设计一个公平实验，在其中系统地控制变量。
- Start with an observation and ask a question that can be investigated empirically.
- 从观察出发，提出一个可经实证探究的问题。
- Write a hypothesis as a predictive statement, e.g., ‘If the concentration of salt increases, then the rate of osmosis will increase.’
- 将假设表述为预测性陈述，例如：“如果盐浓度增加，那么渗透速率将增加。”
- Ensure the experiment includes a control group or controlled variables set to a baseline.
- 确保实验包含对照组或将控制变量设置为基线。
Always justify the choices of apparatus, range of measurements, and number of repeats. A well-designed experiment is replicable and minimizes bias.
始终要说明仪器选择、测量范围以及重复次数的理由。设计良好的实验应具有可重复性并尽量减少偏差。
2. Independent, Dependent and Controlled Variables | 自变量、因变量与控制变量
Correctly identifying and manipulating variables is one of the most common mark-earning skills. The independent variable (IV) is the factor you change deliberately; the dependent variable (DV) is what you measure as the outcome; controlled variables are kept constant to ensure a fair test.
正确识别和操作变量是最常见的得分技能之一。自变量是你有意改变的因素；因变量是你测量的结果；控制变量保持不变以确保公平测试。
| Variable Type | Example (Biology) | Example (Chemistry) | Example (Physics) |
|---|---|---|---|
| IV | Temperature of water bath | Concentration of HCl | Length of pendulum |
| DV | Rate of enzyme activity | Volume of CO₂ produced | Period of oscillation |
| Controlled | pH, substrate concentration | Mass of limestone, temperature | Amplitude, mass of bob |
When writing an IA, explicitly list all controlled variables and describe how each is kept constant. Use a table to show the range and increments for the independent variable.
在写内部评估时，要明确列出所有控制变量并说明如何保持恒定。用表格展示自变量的范围和递增值。
3. Measurements and Units | 测量与单位
IB examiners expect precise use of SI units, derived units, and conversion factors. You need to be fluent with prefixes from pico (p) to tera (T) and familiar with non-SI units accepted in the syllabus, such as °Celsius, litre (L), and atmosphere (atm).
IB 考官要求精确使用国际单位制单位、导出单位及换算因子。你需要熟练运用从皮(p)到太(T)的词头，并熟悉课程允许的非国际制单位，例如摄氏度、升(L)和大气压(atm)。
- Mass: kilogram (kg)
- 质量：千克(kg)
- Length: metre (m)
- 长度：米(m)
- Time: second (s)
- 时间：秒(s)
- Amount of substance: mole (mol)
- 物质的量：摩尔(mol)
- Temperature: kelvin (K) or °C
- 温度：开尔文(K)或°C
Use scientific notation, such as 3.0 × 10⁸ m s⁻¹ for the speed of light, to keep numerical values manageable. Always write units with a space after the number: 25.0 cm³ not 25.0cm³.
用科学记数法表示数值，如光速记为 3.0 × 10⁸ m s⁻¹，使数字易于处理。始终在数字和单位之间留一个空格：25.0 cm³ 而非 25.0cm³。
4. Errors and Uncertainties | 误差与不确定性
Distinguishing between random and systematic errors is a classic examination topic. Random errors affect precision and can be reduced by repeated measurements; systematic errors affect accuracy and are often caused by faulty apparatus or poor calibration.
区分随机误差和系统误差是经典考点。随机误差影响精密度，可通过多次测量降低；系统误差影响准确度，常由仪器故障或校准不良引起。
Uncertainty of a single reading from an analogue instrument is typically ± half the smallest division; for a digital instrument, it is ± the smallest digit unless stated otherwise. When combining measurements, propagate uncertainties correctly using the simple rules (add absolute uncertainties for sums, add percentage uncertainties for products).
模拟仪器单次读数的绝对不确定度通常为 ± 最小分度值的一半；数字仪器为 ± 最小位数，除非另有说明。当组合测量值时，要按简单规则正确传递不确定性（和差运算加绝对不确定度，积商运算加百分不确定度）。
Percentage uncertainty = (Absolute uncertainty / Measured value) × 100%
百分不确定度 = (绝对不确定度 / 测量值) × 100%
Always record uncertainties to one significant figure and match the last decimal place of the measurement with the uncertainty.
记录不确定度时保留一位有效数字，并使测量的最后一位小数与不确定度对齐。
5. Data Processing and Graphing | 数据处理与图表绘制
Graphing skills are assessed in every IB science paper. Draw a sharp, large graph (at least half a page in your exam booklet) with accurately scaled axes, labelled with quantity and unit separated by a solidus (e.g., Time / s). Plot data points as small crosses or encircled dots, and draw a line of best fit – not a dot-to-dot connection.
图表技能在每一份 IB 科学试卷中都会考查。绘制清晰且较大的图形（至少占答题纸半页），坐标轴比例适当，标签用斜线分隔量和单位（如 Time / s）。数据点用小十字或加圈点标记，并绘制最佳拟合线——不要逐点连线。
If the trend is linear, use a transparent ruler to draw a straight line that passes through as many error bars as possible. For curves, draw a smooth, freehand line. For linear relationships, calculate the gradient using two widely separated points on the line of best fit, not data points.
如果趋势为线性，用透明直尺画一条穿过尽可能多误差棒的直线。曲线则手绘平滑曲线。对于线性关系，用最佳拟合线上两个相距较远的点计算斜率，切勿使用原始数据点。
- Gradient = Δy / Δx (slope)
- 斜率 = Δy / Δx
- y-intercept = value where line crosses y-axis
- y 截距 = 直线与 y 轴交点的值
6. Significant Figures and Scientific Notation | 有效数字与科学记数法
Know the rules for significant figures: all non-zero digits are significant; zeros between non-zero digits are significant; leading zeros are never significant; trailing zeros are significant only if the number contains a decimal point. Calculations must reflect the precision of the least precise measurement.
掌握有效数字规则：所有非零数字均为有效数字；非零数字之间的零为有效；前导零永不为有效；末尾零仅当数字包含小数点时才有效。计算结果的精度必须反映最不精确测量值的精度。
For multiplication and division, the answer should have the same number of significant figures as the measurement with the fewest significant figures. For addition and subtraction, the answer should have the same number of decimal places as the measurement with the fewest decimal places.
乘除运算的结果有效数字位数应与有效数字最少的测量值相同。加减运算的结果小数位数应与小数位数最少的测量值相同。
Always express very large or very small numbers in scientific notation: e.g., 6.02 × 10²³ or 1.6 × 10⁻¹⁹.
始终用科学记数法表示极大或极小的数字：如 6.02 × 10²³ 或 1.6 × 10⁻¹⁹。
7. Laboratory Safety and Ethics | 实验室安全与伦理
Safety is a recurring theme in practical work. You must be able to identify hazards, assess risks, and propose relevant precautions. For instance, when using concentrated acids, wear gloves and goggles; when heating flammable liquids, use a water bath; for circuits, keep voltages below 12 V and check for damaged insulation.
安全是实验工作中反复出现的主题。你必须能够识别危险、评估风险并提出相关预防措施。例如，使用浓酸时戴手套和护目镜；加热易燃液体时用水浴；对于电路，保持电压低于 12 V 并检查绝缘是否破损。
In Biology, ethical treatment of living organisms (including plants, invertebrates, or yeast) must be considered. Replace organisms with simulations where possible; minimise stress or harm; no experiments involving human tissue or bodily fluids without explicit permission and safety protocols.
在生物学科中，必须考虑对生物体（包括植物、无脊椎动物或酵母）的伦理待遇。尽可能用模拟替代生物体；尽量减少压力和伤害；未经明确许可和安全规程，不得进行涉及人体组织或体液的实验。
Environmental considerations also appear: dispose of chemicals properly, reduce waste, and avoid release into ecosystems.
环境方面的考问也会出现：妥善处理化学药品，减少废物，避免释放到生态系统中。
8. Data Analysis and Evaluation of Conclusions | 数据分析与结论评估
After plotting a graph, IB questions often ask whether the data supports the hypothesis. Do not say ‘proves’; instead use phrases like ‘supports the hypothesis’ or ‘is consistent with the prediction’. Discuss the spread of data points, the presence of outliers, and the reliability indicated by error bars or R² values.
绘图之后，IB 问题常会问数据是否支持假设。不要使用“证明”一词；而要用“支持假设”或“与预测一致”等表述。讨论数据点的离散程度、异常值的存在以及误差棒或 R² 值显示的可靠性。
Always refer to the scientific context. For example, if measuring acceleration due to gravity, compare your value with the accepted 9.81 m s⁻² and calculate the percentage error. Comment on possible systematic errors that could have caused a consistent deviation.
始终结合科学情境。例如，若测量重力加速度，将你的值与公认的 9.81 m s⁻² 进行比较，并计算百分误差。评论可能导致一致性偏差的系统误差。
Percentage error = |(Experimental value – Accepted value) / Accepted value| × 100%
百分误差 = |(实验值 – 公认值) / 公认值| × 100%
Propose realistic improvements that address the most significant source of error, not a generic ‘use more precise instruments’.
提出解决最主要误差源的实际改进措施，而不是空泛地说“使用更精密的仪器”。
9. Scientific Communication and IA Writing | 科学交流与内部评估写作
The IA mark scheme rewards clear, structured, and concise communication. Use the third person passive voice (e.g., ‘The temperature was recorded every 30 seconds’) except in the personal engagement section, where first-person may be allowed. Organise your report using the required sections: Introduction, Methodology, Data, Analysis, Evaluation.
内部评估的评分方案奖励清晰、结构分明且简洁的表达。除个人投入部分可用第一人称外，一律使用第三人称被动语态（如“温度每隔 30 秒记录一次”）。按要求的章节组织报告：引言、方法、数据、分析、评估。
Label tables with a title above (‘Table 1: Raw data for…’), and number figures below (‘Figure 1: Graph of…’). Ensure all abbreviations are defined the first time they are used, and include units in column headers of tables.
表格标题置于上方（“表 1：…的原始数据”），图注编号置于下方（“图 1：…的图形”）。确保所有缩写首次出现时给出定义，表格表头包含单位。
10. Cross-Cutting Concepts and Models | 跨学科概念与模型
Many IB questions test your understanding of unifying ideas: energy conservation, equilibrium, systems, form and function, and the use of models. For example, in Chemistry, the ideal gas model is a simplification that ignores intermolecular forces; in Physics, treating a body as a point mass simplifies calculations but introduces limitations.
许多 IB 题目考查对统一性概念的理解：能量守恒、平衡、系统、形式与功能以及模型的使用。例如，在化学中，理想气体模型是忽略分子间作用力的简化处理；在物理中，将物体视为质点可简化计算，但带来局限性。
Be ready to evaluate the strengths and weaknesses of models. Discuss assumptions, the range of validity, and what happens when the model breaks down. In Biology, the fluid mosaic model of the cell membrane is a foundational concept that links structure to function.
准备好评价模型的优缺点。讨论假设、有效性范围以及模型失效时的情况。在生物中，细胞膜的流动镶嵌模型是将结构与功能联系起来的基本概念。
Connections across topics are frequently assessed, so revise how concepts like diffusion appear in both biological transport and chemical kinetics, or how wave theory applies to both sound and light.
跨主题的联系经常被考查，因此要复习扩散等概念如何同时出现在生物运输和化学动力学中，或波动理论如何同时适用于声和光。
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