📚 IGCSE OCR Science: End-of-Term Revision Guide | IGCSE OCR 科学：期末复习提纲
As the end of term approaches, consolidating your knowledge across Biology, Chemistry, and Physics is essential for IGCSE OCR Science success. This revision guide highlights the core topics, key equations, and practical skills you must master.
期末临近，巩固生物学、化学和物理学科的知识对 IGCSE OCR 科学考试至关重要。本复习提纲突出了你必须掌握的核心主题、关键方程和实验技能。
1. Biology: Cells and Organisation | 生物：细胞与组织
All living organisms are built from cells. Eukaryotic cells (plants and animals) contain membrane-bound organelles such as the nucleus, mitochondria, and ribosomes, while prokaryotic cells (bacteria) lack a nucleus and have free-floating DNA.
所有生物体都由细胞构成。真核细胞（植物和动物）含有核、线粒体和核糖体等膜包被的细胞器，而原核细胞（细菌）没有细胞核，DNA 游离在细胞质中。
You need to be able to label the main structures of an animal cell (nucleus, cytoplasm, cell membrane, mitochondria, ribosomes) and a plant cell (same plus cell wall, chloroplasts, permanent vacuole).
你需要给动物细胞（细胞核、细胞质、细胞膜、线粒体、核糖体）和植物细胞（同上，再加细胞壁、叶绿体、中央液泡）的主要结构标注名称。
Enzymes are biological catalysts that speed up reactions, and their activity is explained by the lock-and-key model. Each enzyme has an active site specific to its substrate; temperature and pH extremes denature the enzyme, changing the active site shape.
酶是生物催化剂，能加速反应，其活性可用锁钥模型解释。每种酶都有一个与底物特异性匹配的活性位点；高温和极端 pH 会使酶变性，活性位点形状改变。
Cells differentiate to become specialised – for example, red blood cells lose their nucleus to carry more haemoglobin, and root hair cells have a large surface area for absorbing water and minerals.
细胞分化后变得特化——例如，红细胞失去细胞核以携带更多血红蛋白，根毛细胞有较大的表面积以吸收水分和矿物质。
Organisation in multicellular organisms goes from cells → tissues → organs → organ systems. The digestive system is a classic example, where different organs work together to break down and absorb food.
多细胞生物的层次从细胞 → 组织 → 器官 → 器官系统。消化系统就是一个经典例子，不同器官协同工作以分解和吸收食物。
2. Biology: Transport and Health | 生物：运输与健康
The human circulatory system consists of the heart, blood vessels (arteries, veins, capillaries) and blood. The heart is a double pump – the right side pumps deoxygenated blood to the lungs, and the left side pumps oxygenated blood to the rest of the body.
人体循环系统由心脏、血管（动脉、静脉、毛细血管）和血液组成。心脏是一个双泵——右侧将缺氧血泵到肺部，左侧将含氧血泵到全身。
Arteries have thick, elastic walls to withstand high pressure; veins have valves to prevent backflow and thinner walls; capillaries are one cell thick to allow efficient diffusion of gases and nutrients.
动脉壁厚而有弹性，可承受高压；静脉具有瓣膜以防止回流，壁较薄；毛细血管仅一层细胞厚，可让气体和营养物质高效扩散。
Breathing involves the diaphragm and intercostal muscles. During inhalation, the diaphragm contracts and moves downwards, increasing thoracic volume and drawing air into the lungs, where gas exchange occurs in the alveoli by diffusion.
呼吸涉及膈肌和肋间肌。吸气时，膈肌收缩向下移动，增加胸腔容积，空气被吸入肺中，在肺泡处通过扩散进行气体交换。
Pathogens such as bacteria, viruses, fungi and protists cause communicable diseases. The body’s first line of defence includes the skin, mucus and white blood cells, which engulf pathogens or produce antibodies.
病原体如细菌、病毒、真菌和原生动物会引起传染病。人体的第一道防线包括皮肤、黏液和白细胞，后者可吞噬病原体或产生抗体。
Vaccination introduces a dead or weakened form of a pathogen, triggering an immune response and producing memory cells. Antibiotics kill bacteria but do not work on viruses; misuse has led to antibiotic resistance in bacteria like MRSA.
疫苗接种引入灭活或减毒的病原体，触发免疫应答并产生记忆细胞。抗生素能杀死细菌，但对病毒无效；滥用已导致细菌产生耐药性，如 MRSA。
3. Chemistry: Atoms, Bonding and Trends | 化学：原子、化学键与周期律
An atom consists of a central nucleus containing protons (positive charge) and neutrons (neutral), surrounded by electrons in energy levels. Atomic number = number of protons; mass number = protons + neutrons.
原子由包含质子（带正电）和中子（不带电）的原子核以及分层排布的电子组成。原子序数 = 质子数；质量数 = 质子数 + 中子数。
Ionic bonding occurs between metals and non-metals. Metals lose electrons to form positive cations, while non-metals gain electrons to form negative anions; the electrostatic attraction between oppositely charged ions holds the lattice together.
离子键出现在金属和非金属之间。金属失去电子形成阳离子，非金属得到电子形成阴离子；带相反电荷的离子之间的静电引力将离子晶体结合在一起。
Covalent bonding involves sharing pairs of electrons between non-metal atoms. Simple molecules such as H₂O and CO₂ have weak intermolecular forces, while giant covalent structures like diamond and SiO₂ are strong and have high melting points.
共价键涉及非金属原子间共用电子对。简单分子如 H₂O 和 CO₂ 分子间作用力较弱，而像金刚石和二氧化硅这样的巨型共价结构则很强、熔点很高。
In the Periodic Table, elements are arranged in order of increasing atomic number. Group 1 (alkali metals) are highly reactive and form 1⁺ ions; Group 7 (halogens) form 1⁻ ions and reactivity decreases down the group; Group 0 (noble gases) are inert due to full outer shells.
在元素周期表中，元素按原子序数递增排列。第 1 族（碱金属）非常活泼，形成 1⁺ 离子；第 7 族（卤素）形成 1⁻ 离子，活泼性从上到下减弱；第 0 族（稀有气体）由于最外层电子已满而惰性。
When writing ionic equations, you must show only the species that change. For example, the neutralisation: H⁺ + OH⁻ → H₂O. Make sure the equation is balanced in terms of atoms and charge.
书写离子方程式时，只需标出实际变化的微粒。例如中和反应：H⁺ + OH⁻ → H₂O。要确保方程式在原子数和电荷上均配平。
4. Chemistry: Reactions and Calculations | 化学：反应与计算
Key reaction types include neutralisation (acid + base → salt + water), combustion (fuel + O₂ → CO₂ + H₂O), displacement (more reactive metal displaces a less reactive one), and redox (reduction and oxidation happen simultaneously).
关键的反应类型包括中和（酸 + 碱 → 盐 + 水）、燃烧（燃料 + O₂ → CO₂ + H₂O）、置换（较活泼金属置换较不活泼金属）和氧化还原（氧化与还原同时发生）。
The mole concept is central to quantitative chemistry. One mole of a substance contains 6.02 × 10²³ particles, and the mass of one mole (molar mass) equals the relative formula mass in grams. Use the equation: moles = mass / Mᵣ.
摩尔概念是定量化学的核心。1 mol 物质含有 6.02 × 10²³ 个微粒，1 mol 的质量（摩尔质量）等于相对分子质量数值（克）。使用公式：物质的量 = 质量 / Mᵣ。
Concentration of solutions is measured in mol/dm³ or g/dm³. Titration and reacting mass calculations require you to convert between mass, moles and volume confidently.
溶液的浓度以 mol/dm³ 或 g/dm³ 计量。滴定和根据化学方程式计算时，需要你能在质量、物质的量和体积之间进行熟练换算。
Electrolysis uses electrical energy to split ionic compounds into their elements. At the cathode (negative electrode), cations gain electrons (reduction); at the anode (positive electrode), anions lose electrons (oxidation). For molten lead bromide, lead forms at the cathode and bromine gas at the anode.
电解利用电能将离子化合物分解为单质。在阴极（负电极），阳离子得电子（还原）；在阳极（正电极），阴离子失电子（氧化）。对于熔融溴化铅，铅在阴极生成，溴气在阳极生成。
Reactivity of metals determines the method of extraction. Metals above carbon in the reactivity series are extracted by electrolysis (e.g. aluminium), while those below can be extracted by reduction with carbon (e.g. iron).
金属的活泼性决定其提取方法。活动顺序中位于碳之上的金属通过电解提取（如铝），位于碳之下的可用碳还原（如铁）。
5. Chemistry: Energy and Rate | 化学：能量与速率
Exothermic reactions transfer energy to the surroundings, often causing a temperature rise (e.g. combustion, neutralisation). Endothermic reactions take in energy, cooling the surroundings (e.g. thermal decomposition).
放热反应向环境释放能量，常引起温度升高（如燃烧、中和）。吸热反应从环境吸收能量，使周围变冷（如热分解）。
Reaction profile diagrams show the energy changes. The activation energy is the minimum energy needed for a reaction to start; a catalyst provides an alternative pathway with a lower activation energy, increasing the rate without being used up.
反应剖面图显示能量变化。活化能是反应启动所需的最小能量；催化剂提供一条活化能更低的替代路径，加快反应速率而自身不被消耗。
Collision theory states that reacting particles must collide with sufficient energy (above activation energy) and the correct orientation. Increasing temperature gives particles more kinetic energy, so collisions are more frequent and more energetic.
碰撞理论认为，反应物粒子必须发生碰撞，并具有足够的能量（高于活化能）和正确的取向。升高温度使粒子动能增大，碰撞更频繁、更有力。
Rate can also be increased by higher concentration (more particles per unit volume), larger surface area (more exposed reactant), and the use of a catalyst. Measuring rate often involves monitoring gas volume or mass loss over time.
加快反应速率的方法还包括：增大浓度（单位体积粒子数增多）、增大表面积（暴露的反应物更多）和使用催化剂。测量速率常通过记录气体体积或质量随时间的变化来实现。
Reversible reactions reach dynamic equilibrium when the forward and reverse rates are equal. Changing temperature or pressure shifts the equilibrium position, as predicted by Le Chatelier’s Principle. In the Haber process for NH₃, high pressure favours the forward reaction because it reduces the number of gas molecules.
可逆反应在正向和逆向速率相等时达到动态平衡。改变温度或压强会移动平衡位置，这可用勒夏特列原理预测。在合成氨的哈伯法中，高压有利于正反应，因为产物气体分子数更少。
6. Physics: Motion and Forces | 物理：运动与力
Motion can be described using distance–time and velocity–time graphs. The gradient of a distance–time graph gives speed; the gradient of a velocity–time graph gives acceleration, and the area under the line represents displacement.
运动可用距离–时间图和速度–时间图描述。距离–时间图的斜率表示速率；速度–时间图的斜率表示加速度，线下面积表示位移。
The essential equations of uniformly accelerated motion are: v = u + at, s = ut + ½at², v² = u² + 2as. Remember that u is initial velocity, v final velocity, a acceleration, s displacement, t time.
匀加速运动的基本方程为：v = u + at、s = ut + ½at²、v² = u² + 2as。记住，u 代表初速度，v 末速度，a 加速度，s 位移，t 时间。
Newton’s First Law states an object remains at rest or in uniform motion unless acted upon by a resultant force. Second Law relates resultant force, mass and acceleration: F = ma. Third Law: for every action there is an equal and opposite reaction.
牛顿第一定律：物体将保持静止或匀速直线运动，除非受到非零合力。第二定律关联合力、质量和加速度：F = ma。第三定律：作用力与反作用力大小相等、方向相反。
Weight is the force due to gravity: W = mg, where g on Earth is 9.8 m/s² (often rounded to 10 N/kg). Mass is the amount of matter, measured in kg; weight is a force, measured in newtons.
重量是由于重力产生的力：W = mg，地球上 g 约为 9.8 m/s²（常取 10 N/kg）。质量是物质的多少，单位 kg；重量是力，单位 N。
Stopping distance of a vehicle equals thinking distance + braking distance. Factors like speed, mass, road conditions and driver alertness affect each component – this is frequently examined in context questions.
汽车的停止距离 = 反应距离 + 制动距离。车速、质量、路面状况和驾驶员警觉性等因素均会分别影响这两个部分，这是考试中常见的应用背景。
7. Physics: Energy and Electricity | 物理：能量与电
Energy is conserved: it cannot be created or destroyed, only transferred, stored or dissipated. Kinetic energy Eₖ = ½mv²; gravitational potential energy Eₚ = mgh. When energy is dissipated, it becomes less useful, often as thermal energy spreading to the surroundings.
能量守恒：能量不会凭空产生或消失，只会转化、储存或耗散。动能 Eₖ = ½mv²；重力势能 Eₚ = mgh。能量耗散后变为不再集中的热能等，通常扩散到环境中。
Work done equals energy transferred: W = Fd, where F is the force and d the distance moved in the direction of the force. Power is the rate of energy transfer: P = E / t or P = W / t.
做功等于能量转化：W = Fd，其中 F 是力，d 是在力的方向上移动的距离。功率是能量转化速率：P = E / t 或 P = W / t。
Efficiency is the ratio of useful output energy to total input energy, often expressed as a percentage: efficiency = (useful energy out / total energy in) × 100%. No device can be 100% efficient because some energy is always dissipated.
效率是输出有用能量与输入总能量之比，常以百分数表示：效率 = (有用能量输出 / 总能量输入) × 100%。没有设备能达到 100% 效率，因为总会有能量耗散。
Electric circuits require a complete loop for current to flow. Current (I, measured in amps) is the rate of flow of charge; voltage (V, volts) is the energy per unit charge; resistance (R, ohms) opposes current. The relationship is V = IR.
电路需要闭合回路才能有电流。电流（I，单位 A）是电荷流动的速率；电压（V，单位 V）是单位电荷的能量；电阻（R，单位 Ω）阻碍电流。三者关系为 V = IR。
In series circuits, current is the same everywhere, and voltage splits across components. In parallel circuits, voltage is the same across each branch, while current splits. Combining resistors in series gives R_total = R₁ + R₂; in parallel: 1/R_total = 1/R₁ + 1/R₂.
串联电路中，各处电流相等，电压在各元件间分配。并联电路中，各支路电压相等，电流分配到各支路。串联总电阻：R_total = R₁ + R₂；并联总电阻：1/R_total = 1/R₁ + 1/R₂。
8. Physics: Waves and Radiation | 物理：波与辐射
Waves transfer energy without transferring matter. Transverse waves (e.g. EM waves, water ripples) have oscillations perpendicular to the direction of travel; longitudinal waves (e.g. sound) have oscillations parallel to travel, creating compressions and rarefactions.
波传递能量而不传递物质。横波（如电磁波、水波）的振动方向与传播方向垂直；纵波（如声波）的振动方向与传播方向平行，形成疏部和密部。
The wave equation links speed (v), frequency (f) and wavelength (λ): v = fλ. Frequency is measured in hertz (Hz), wavelength in metres (m). Ensure you can read values from wave diagrams accurately.
波速方程联系波速 (v)、频率 (f) 和波长 (λ)：v = fλ。频率单位是赫兹 (Hz)，波长单位是米 (m)。要确保能从波形图中准确读取数值。
The electromagnetic spectrum runs from radio waves (longest λ, lowest f) to gamma rays (shortest λ, highest f). Visible light is a small part. Uses include: radio – broadcasting, microwaves – cooking, infrared – remote controls, UV – tanning and sterilisation, X-rays – medical imaging, gamma rays – cancer therapy.
电磁波谱从无线电波（λ 最长、f 最低）到伽马射线（λ 最短、f 最高）。可见光只占一小部分。应用包括：无线电通信、微波加热、红外遥控、紫外杀菌晒黑、X 光医学成像、伽马射线癌症治疗。
Radiation from unstable nuclei can be alpha (α: helium nuclei, stopped by paper, strongly ionising), beta (β: fast electrons, stopped by aluminium, moderately ionising) or gamma (γ: electromagnetic wave, stopped by lead or thick concrete, weakly ionising).
不稳定原子核发出的辐射包括 α（氦核，纸张可阻挡，电离能力强）、β（高速电子，铝片可阻挡，电离能力中等）和 γ（电磁波，铅或厚混凝土可阻挡，电离能力弱）。
Half-life is the time taken for half the nuclei in a sample to decay. It can be found from a decay curve and is used in radiocarbon dating and in determining safe storage times for waste. The activity decreases, but the half-life remains constant for a given isotope.
半衰期是指样品中半数原子核发生衰变所需的时间。可从衰变曲线中求得，用于放射性碳定年法和确定废物安全存放期。活度下降，但给定同位素的半衰期保持不变。
9. Practical Skills and Investigative Approaches | 实验技能与探究方法
For any investigation, identify the independent variable (what you change), dependent variable (what you measure) and control variables (what you keep constant). Planning a fair test is essential for reliable results.
任何探究都要识别自变量（你改变的量）、因变量（你测量的量）和控制变量（保持不变的量）。设计公平实验是获得可靠结果的基础。
Results should be recorded in clearly labelled tables with units. When drawing graphs, put the independent variable on the x-axis and dependent on the y-axis; draw a line or curve of best fit – do not simply join all the dots.
实验结果应记录在带单位、标题清晰的表格中。作图时，自变量放在 x 轴，因变量放在 y 轴；画出最佳拟合线或曲线——不要简单连接所有数据点。
Common required practicals include: using a microscope to observe cell structure, testing food samples for starch and reducing sugars, investigating the effect of pH or temperature on enzyme activity, measuring reaction rate by gas collection, constructing electrical circuits to test the relationship between V and I, and measuring the specific heat capacity of a material.
常见的必备实验包括：用显微镜观察细胞结构、检测食物中的淀粉和还原糖、探究 pH 或温度对酶活性的影响、通过收集气体测量反应速率、搭建电路验证 V- I 关系，以及测量材料的比热容。
When evaluating experiments, discuss repeatability, reproducibility, and possible sources of error. Suggest improvements such as using more precise instruments, controlling variables more carefully, or increasing the number of readings.
在评估实验时，要讨论可重复性、再现性以及可能的误差来源。可提出改进建议，如使用更精密的仪器、更严格地控制变量，或增加读数次数。
10. Model Answers and Past Paper Strategy | 标准答案与真题策略
OCR exam questions often include command words: ‘State’ requires a short, factual answer; ‘Describe’ asks for details of what happens; ‘Explain’ demands a scientific reason using ‘because’; ‘Calculate’ needs working and a final answer with units; ‘Evaluate’ involves giving balanced arguments and a conclusion.
OCR 考题中常包含指令词：“State” 要求简短事实性答案；“Describe” 要求描述发生的事情；“Explain” 要求用 because 给出科学原因；“Calculate” 需要演算过程和带单位的答案；“Evaluate” 要求权衡双方论据并得出结论。
When describing a graph, always quote data points and trends. For example, ‘As temperature rises from 20 °C to 40 °C, the rate of reaction increases from 2.5 to 6.0 cm³/min, then falls above 50 °C because the enzyme is denatured.’ Full-sentence answers with precise terminology score higher.
描述图表时，务必引用数据点和变化趋势。如：“温度从 20 °C 升至 40 °C，反应速率从 2.5 升至 6.0 cm³/min，超过 50 °C 后下降，因为酶已变性。” 用完整句子和专业术语作答能得更高分。
Manage your time in the exam: allocate roughly one minute per mark. Read the question carefully, underline key information, and check your answers for slip-ups, especially with units, significant figures, and balancing equations.
考试中要管理好时间：大致按每分钟作答 1 分来分配。仔细读题，勾画关键信息，检查答案，特别是单位、有效数字和方程式配平这些容易出错的地方。
Use past papers under timed conditions to build confidence. Review the mark schemes to understand exactly what examiners look for – often a point on a graph or a specific phrase in a written answer can be the difference between grades.
在限时条件下练习历年真题以增强信心。仔细研读评分标准，确切了解阅卷人看重什么——往往图中一个点或答案中的一个特定措辞就是等级提升的关键。
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