📚 Key High-Frequency Topics in IGCSE CIE Science | IGCSE CIE 科学高频考点总结
This article brings together the most commonly examined concepts across IGCSE CIE Co-ordinated Sciences (or the individual Biology, Chemistry and Physics courses). By focusing on high-frequency topics, you can sharpen your revision and approach the exam with confidence. Each section presents key facts in bite-sized English–Chinese pairs to reinforce understanding and bilingual retention.
本文汇集了IGCSE CIE综合科学（或单独的生物、化学、物理课程）中最常考的概念。通过聚焦高频考点，你可以高效复习、从容应考。每个小节以精炼的英文-中文对照呈现关键事实，帮助加深理解并强化双语记忆。
1. Cell Structure and Function | 细胞结构与功能
Both animal and plant cells contain a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells additionally have a rigid cell wall, chloroplasts containing chlorophyll for photosynthesis, and a large permanent vacuole filled with cell sap.
动物细胞和植物细胞都含有细胞核、细胞质、细胞膜、线粒体和核糖体。植物细胞还有坚硬的细胞壁、含叶绿体（内有叶绿素，用于光合作用）以及一个充满细胞液的大液泡。
The cell membrane is partially permeable, controlling the movement of substances into and out of the cell. The nucleus contains DNA and controls cell activities. Mitochondria carry out aerobic respiration, releasing energy.
细胞膜具有选择通透性，控制物质进出细胞。细胞核含有DNA并控制细胞活动。线粒体进行有氧呼吸，释放能量。
Magnification and size calculations are frequently tested. The formula is: magnification = image size ÷ actual size. Always convert measurements to the same unit before calculating.
放大倍率和尺寸计算是常考点。公式为：放大倍率 = 图像大小 ÷ 实际大小。计算前必须将单位统一。
2. Biological Molecules and Enzymes | 生物分子与酶
Carbohydrates, proteins and lipids are the main biological molecules. Carbohydrates are made up of simple sugars such as glucose. Proteins are composed of long chains of amino acids. Lipids (fats and oils) consist of fatty acids and glycerol.
碳水化合物、蛋白质和脂质是主要的生物分子。碳水化合物由葡萄糖等简单糖类组成。蛋白质由氨基酸长链构成。脂质（脂肪和油）由脂肪酸和甘油组成。
Food tests are essential practical skills. Iodine solution turns blue-black with starch. Benedict’s solution turns brick-red when heated with reducing sugars. Biuret reagent turns purple with proteins. The ethanol emulsion test gives a cloudy white layer for lipids.
食物检验是必备的实验技能。碘液遇淀粉变蓝黑色。本尼迪克特试剂与还原糖加热后产生砖红色沉淀。双缩脲试剂遇蛋白质变紫色。乙醇乳化检验法用于脂质，出现浑浊的白色层。
Enzymes are biological catalysts that speed up reactions without being used up. They are proteins with an active site that is specific to the substrate. The lock-and-key hypothesis explains this specificity. Enzyme activity is affected by temperature and pH; denaturation at extreme conditions is irreversible.
酶是生物催化剂，能加速反应而自身不被消耗。酶是蛋白质，具有与底物专一结合的活性位点。“锁钥假说”解释了这种特异性。酶活性受温度和pH值影响；在极端条件下会变性且不可逆。
3. The Heart and Circulation | 心脏与循环
The heart is a double pump: the right side pumps deoxygenated blood to the lungs, while the left side pumps oxygenated blood to the rest of the body. The left ventricle has a thicker muscular wall because it needs to generate higher pressure.
心脏是一个双泵：右侧将缺氧血泵入肺部，左侧将富氧血泵至全身。左心室壁肌肉更厚，因为它需要产生更高的压力。
Blood flows through the heart in this sequence: vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta. Valves prevent backflow of blood.
血液流经心脏的顺序为：腔静脉 → 右心房 → 右心室 → 肺动脉 → 肺部 → 肺静脉 → 左心房 → 左心室 → 主动脉。瓣膜防止血液倒流。
Coronary heart disease is caused by the build-up of fatty plaques in the coronary arteries, reducing blood supply to the heart muscle. Risk factors include a high-fat diet, smoking, stress and lack of exercise.
冠心病是由冠状动脉内脂肪斑块堆积引起的，导致心肌供血减少。风险因素包括高脂饮食、吸烟、压力大和缺乏运动。
Arteries have thick, elastic walls to withstand high pressure. Veins have thinner walls and valves to prevent backflow. Capillaries are one cell thick to allow efficient diffusion of substances.
动脉壁厚而有弹性，可承受高压。静脉壁较薄且有瓣膜以防倒流。毛细血管壁仅一层细胞厚，利于物质高效扩散。
4. Plant Transport | 植物运输
Xylem vessels transport water and mineral ions from roots to leaves. They are dead, hollow cells arranged end-to-end with lignin-strengthened walls. The movement of water is driven by transpiration pull and root pressure.
木质部导管将水和无机盐离子从根部运到叶片。它们是死细胞，中空、端端相连，细胞壁有木质素加强。水分的运输主要靠蒸腾拉力和根压驱动。
Phloem tubes transport sucrose and amino acids from sources (e.g. leaves) to sinks (e.g. roots, developing fruits). This process is called translocation and requires energy from respiration.
韧皮部将蔗糖和氨基酸从“源”（如叶片）运输到“库”（如根部、发育的果实）。这一过程称为运输作用，需要呼吸作用提供能量。
Factors affecting the rate of transpiration include temperature, humidity, wind speed and light intensity. A potometer can be used to measure water uptake by a plant, which approximates transpiration rate.
影响蒸腾速率的因素包括温度、湿度、风速和光照强度。可以用蒸腾计测量植物的吸水量，从而近似得出蒸腾速率。
Stomata are pores mainly on the lower leaf surface, surrounded by guard cells. Guard cells control the opening and closing of stomata to balance gas exchange and water loss.
气孔主要分布在叶片下表皮，由保卫细胞围成。保卫细胞控制气孔的开闭，以平衡气体交换和水分流失。
5. Atomic Structure and Bonding | 原子结构与化学键
Atoms consist of a nucleus containing protons (positive) and neutrons (neutral), with electrons (negative) arranged in shells around the nucleus. The atomic number is the number of protons, and the mass number is the total of protons plus neutrons.
原子由原子核和核外电子组成，原子核内含质子（正电）和中子（不带电），电子（负电）分层排布。原子序数等于质子数，质量数是质子数加中子数。
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. They have identical chemical properties but different physical properties such as density.
同位素是同种元素中质子数相同而中子数不同的原子。它们化学性质相同，但物理性质（如密度）不同。
Ionic bonding occurs when atoms transfer electrons to form oppositely charged ions that attract each other. Giant ionic compounds such as sodium chloride have high melting points and conduct electricity when molten or dissolved.
离子键是原子通过电子转移形成带相反电荷的离子并相互吸引而形成的。氯化钠等具有离子型大分子结构的化合物熔点高，熔融态或溶于水时能导电。
Covalent bonding involves the sharing of electron pairs between atoms. Simple molecular substances (e.g. water, carbon dioxide) have low melting points, whereas giant covalent structures (e.g. diamond, silicon dioxide) have very high melting points.
共价键是原子间通过共用电子对形成的。简单分子物质（如水、二氧化碳）熔点低，而巨型共价结构（如金刚石、二氧化硅）熔点极高。
6. Chemical Calculations (Moles) | 化学计算（摩尔）
The mole is the unit for amount of substance. One mole contains 6.02 × 10²³ particles (Avogadro constant). The formula linking mass, moles and molar mass is:
摩尔是物质的量的单位。1摩尔含6.02 × 10²³个粒子（阿伏伽德罗常数）。质量、摩尔数、摩尔质量之间的关系式为：
number of moles = mass (g) ÷ molar mass (g/mol)
To calculate reacting masses, write a balanced equation, find the moles of the known substance, use the mole ratio to find moles of the unknown, and then convert to mass.
计算反应质量时，先写出配平的化学方程式，求出已知物质的摩尔数，利用摩尔比求出未知物质的摩尔数，再换算成质量。
Concentration of a solution can be expressed in mol/dm³. The equation is: number of moles = concentration (mol/dm³) × volume (dm³). Remember to convert cm³ to dm³ by dividing by 1000.
溶液浓度可用mol/dm³表示。关系式为：摩尔数 = 浓度 (mol/dm³) × 体积 (dm³)。注意将cm³换算成dm³需除以1000。
Percentage yield compares the actual yield to the theoretical yield. The formula is: percentage yield = (actual yield ÷ theoretical yield) × 100%. Yield is always less than 100% due to practical losses.
产率用于比较实际产量与理论产量。公式为：产率 = (实际产量 ÷ 理论产量) × 100%。由于实验损失，产率总是小于100%。
7. Acids, Bases and Salts | 酸、碱与盐
Acids are proton (H⁺) donors. Common acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃). Bases are proton acceptors, and alkalis are soluble bases that release OH⁻ ions in water.
酸是质子（H⁺）的供体。常见酸包括盐酸(HCl)、硫酸(H₂SO₄)和硝酸(HNO₃)。碱是质子受体，碱是指溶于水并能释放OH⁻离子的碱。
The pH scale ranges from 0 to 14: values below 7 are acidic, 7 is neutral, and above 7 are alkaline. Universal indicator or a pH probe can be used to measure pH.
pH值范围从0到14：低于7为酸性，7为中性，高于7为碱性。可用通用指示剂或pH探头测量pH值。
Neutralisation is the reaction between an acid and a base to produce a salt and water. For example: HCl + NaOH → NaCl + H₂O. The ionic equation for neutralisation involving strong acids and bases is: H⁺ + OH⁻ → H₂O.
中和是酸与碱反应生成盐和水的过程。例如：HCl + NaOH → NaCl + H₂O。强酸强碱中和反应的离子方程式为：H⁺ + OH⁻ → H₂O。
Salts can be prepared by various methods: titration for soluble salts where all reactants are soluble, and precipitation for insoluble salts (mixing two aqueous solutions to form a precipitate).
盐可以通过多种方法制备：可溶盐且反应物均可溶时采用滴定法；不溶性盐可用沉淀法（混合两种水溶液生成沉淀）。
8. Electrolysis | 电解
Electrolysis is the breakdown of an ionic compound, when molten or in aqueous solution, by the passage of electricity. The positive electrode (anode) attracts anions, and the negative electrode (cathode) attracts cations.
电解是在直流电作用下，使熔融态或水溶液中的离子化合物分解的过程。正极（阳极）吸引阴离子，负极（阴极）吸引阳离子。
In the electrolysis of molten lead(II) bromide, lead metal forms at the cathode and bromine gas forms at the anode. The half-equations are: at cathode, Pb²⁺ + 2e⁻ → Pb; at anode, 2Br⁻ → Br₂ + 2e⁻.
电解熔融溴化铅(II)时，阴极生成金属铅，阳极生成溴气。半反应式为：阴极，Pb²⁺ + 2e⁻ → Pb；阳极，2Br⁻ → Br₂ + 2e⁻。
When electrolysing aqueous solutions, the products depend on the relative reactivity of the ions. At the cathode, the less reactive cation (or hydrogen) is discharged. At the anode, a halide is discharged if present, otherwise oxygen from OH⁻ is released.
电解水溶液时，产物取决于离子的相对活泼性。在阴极，较不活泼的阳离子（或氢离子）被还原。在阳极，若有卤离子则优先放电，否则由OH⁻放电产生氧气。
Electrolysis is used in the extraction of aluminium from aluminium oxide (dissolved in molten cryolite) and in electroplating to coat one metal with a thin layer of another.
电解用于从氧化铝（溶于熔融冰晶石）中提取铝，也用于电镀，即在一种金属表面镀上另一种金属的薄层。
9. Organic Chemistry Basics | 有机化学基础
Crude oil is a mixture of hydrocarbons, mainly alkanes, which are separated by fractional distillation based on boiling points. The general formula for alkanes is CₙH₂ₙ₊₂.
原油是碳氢化合物（主要是烷烃）的混合物，通过分馏根据沸点不同进行分离。烷烃的通式为CₙH₂ₙ₊₂。
Cracking breaks long-chain alkanes into shorter, more useful alkanes and alkenes. Alkenes are unsaturated hydrocarbons with the general formula CₙH₂ₙ and contain a C=C double bond. They turn bromine water from orange to colourless.
裂化反应将长链烷烃断裂为更短、更有用的烷烃和烯烃。烯烃是不饱和烃，通式为CₙH₂ₙ，含有一个C=C双键。它们能使溴水由橙黄色变为无色。
Alcohols have the functional group –OH. Ethanol (C₂H₅OH) can be made by fermentation of glucose using yeast, or by hydration of ethene with steam and a catalyst. Carboxylic acids contain the –COOH group; ethanoic acid is the main acid in vinegar.
醇的官能团为–OH。乙醇(C₂H₅OH)可通过酵母发酵葡萄糖制得，或用乙烯与水蒸气在催化剂作用下加成制取。羧酸含–COOH基团，食醋中的主要酸是乙酸。
Esters are formed from an alcohol and a carboxylic acid, using concentrated sulfuric acid as a catalyst. They have fruity smells and are used as flavourings and solvents.
酯由醇与羧酸在浓硫酸催化下反应生成，具有水果香味，用作香料和溶剂。
10. Forces and Motion | 力与运动
Scalars have magnitude only (e.g. speed, distance, mass), while vectors have both magnitude and direction (e.g. velocity, displacement, force). The resultant force is the single force that has the same effect as all the forces acting on an object.
标量只有大小（如速率、路程、质量），矢量既有大小又有方向（如速度、位移、力）。合力是一个单独的力，其作用效果与作用在物体上的所有力完全相同。
Newton’s first law states that an object remains at rest or continues at constant velocity unless acted upon by a resultant force. Newton’s second law: resultant force = mass × acceleration (F = ma).
牛顿第一定律指出，物体在不受合力作用时将保持静止或匀速直线运动状态。牛顿第二定律：合力 = 质量 × 加速度 (F = ma)。
The acceleration of free fall, g, is approximately 9.8 m/s² on Earth. Weight is the gravitational force on an object: weight = mass × g. Mass is a scalar; weight is a vector.
地球表面自由落体加速度 g 约等于9.8 m/s²。重量是作用于物体的重力：重量 = 质量 × g。质量是标量，重量是矢量。
Stopping distance = thinking distance + braking distance. Thinking distance is affected by tiredness, alcohol and distractions. Braking distance increases with speed, worn tyres, wet/icy road conditions.
停车距离 = 反应距离 + 刹车距离。反应距离受疲劳、酒精和注意力分散影响。刹车距离随速度增加、轮胎磨损、路面湿滑/结冰而增大。
11. Energy, Work and Power | 能量、功与功率
Energy can be stored as kinetic, potential (gravitational, elastic), thermal, chemical, nuclear, etc. The principle of conservation of energy states that energy can be transferred or transformed but cannot be created or destroyed.
能量可以储存为动能、势能（重力势能、弹性势能）、热能、化学能、核能等。能量守恒定律指出，能量可以转移或转化，但不会凭空产生或消失。
Work is done when a force moves an object in the direction of the force: work done = force × distance moved in the direction of the force. Measured in joules (J).
力使物体沿力的方向移动时做功：功 = 力 × 沿力方向移动的距离。单位为焦耳(J)。
Kinetic energy = ½ × mass × speed². Gravitational potential energy = mass × g × height. Power is the rate of doing work: power = work done ÷ time taken, measured in watts (W).
动能 = ½ × 质量 × 速度²。重力势能 = 质量 × g × 高度。功率是做功的速率：功率 = 做功 ÷ 时间，单位为瓦特(W)。
Efficiency is the ratio of useful output energy (or power) to total input energy: efficiency = (useful output / total input) × 100%. Sankey diagrams illustrate energy transfers.
效率是有用输出能量（或功率）与总输入能量之比：效率 = (有用输出 / 总输入) × 100%。桑基图可直观表示能量传递过程。
12. Waves and Electricity | 波与电
Waves transfer energy without transferring matter. In transverse waves, particles vibrate perpendicular to the direction of energy transfer (e.g. light, water waves). In longitudinal waves, particles vibrate parallel to the direction (e.g. sound).
波传递能量而不传递物质。横波中质点的振动方向与能量传递方向垂直（如光波、水波）。纵波中质点的振动方向与能量传递方向平行（如声波）。
The wave equation is: wave speed = frequency × wavelength (v = fλ). Frequency is measured in hertz (Hz), wavelength in metres (m).
波动方程为：波速 = 频率 × 波长 (v = fλ)。频率单位是赫兹(Hz)，波长单位是米(m)。
In a series circuit, current is the same everywhere and the total resistance is the sum of individual resistances. In a parallel circuit, the voltage across each branch is the same and the total current is the sum of branch currents.
串联电路中，各处电流相等，总电阻等于各电阻之和。并联电路中，各支路两端电压相等，总电流等于各支路电流之和。
Ohm’s law: for a resistor at constant temperature, current is proportional to voltage: V = IR. The resistance of a thermistor decreases as temperature rises; for an LDR, resistance decreases as light intensity increases.
欧姆定律：对于温度恒定的电阻器，电流与电压成正比：V = IR。热敏电阻的阻值随温度升高而减小；光敏电阻的阻值随光照强度增加而减小。
Electrical power = current × voltage (P = IV), and also power = current² × resistance. Electrical energy transferred = power × time.
电功率 = 电流 × 电压 (P = IV)，也可表示为功率 = 电流² × 电阻。电能转移量 = 功率 × 时间。
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