📚 IGCSE AQA Science: High-Frequency Topics Summary | IGCSE AQA 科学：高频考点总结
This article compiles the most frequently examined topics in IGCSE AQA Science (Double Award or Separate Sciences), helping you focus revision on key concepts across Biology, Chemistry and Physics. Each section pairs an English explanation with a Chinese translation to reinforce understanding. Use this as a checklist and quick reference for your exams.
本文汇总了 IGCSE AQA 科学（双证书或单科）最高频的考点，帮助你把复习重点放在生物、化学和物理的核心概念上。每个部分都提供中英文对照讲解，以加深理解。请把它当作考前检查表和快速参考。
1. Cell Structure and Microscopy | 细胞结构与显微镜使用
All living organisms are made of cells. Animal and plant cells share common features such as a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells additionally have a cellulose cell wall, a large permanent vacuole and often chloroplasts for photosynthesis.
所有生物都由细胞构成。动物细胞和植物细胞共有细胞核、细胞质、细胞膜、线粒体和核糖体等结构。植物细胞还含有纤维素细胞壁、一个中央大液泡以及用于光合作用的叶绿体。
The magnification equation is magnification = image size ÷ actual size. You must be able to convert between millimetres (mm), micrometres (µm) and nanometres (nm). 1 mm = 1000 µm; 1 µm = 1000 nm.
放大倍数计算公式为 放大倍数 = 图像尺寸 ÷ 实际尺寸。你必须掌握毫米 (mm)、微米 (µm) 和纳米 (nm) 之间的换算：1 mm = 1000 µm; 1 µm = 1000 nm。
In microscopy practicals, you need to prepare a temporary mount of onion epidermis or cheek cells, add iodine solution or methylene blue as a stain, and draw labelled diagrams using clear lines and correct scale.
显微镜实验中，你需要制作洋葱表皮或口腔细胞的临时装片，用碘液或亚甲基蓝染色，并用清晰线条和正确比例画出标注示意图。
The nucleus contains DNA arranged as chromosomes. In human body cells there are 46 chromosomes, while gametes contain 23.
细胞核中含有以染色体形式存在的 DNA。人体细胞有 46 条染色体，而配子只有 23 条。
2. Transport in Cells | 细胞运输
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. It is a passive process that does not require energy. The rate of diffusion increases with a larger surface area, steeper concentration gradient, shorter diffusion distance and higher temperature.
扩散是粒子从高浓度区域向低浓度区域净移动的过程，顺浓度梯度进行。它是一种被动过程，不需要能量。扩散速率随着表面积增大、浓度梯度变大、扩散距离缩短和温度升高而加快。
Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution). Plant cells become turgid when placed in a hypotonic solution and plasmolysed in a hypertonic solution.
渗透是指水分子经部分透性膜从较高水势（稀溶液）的区域向较低水势（浓溶液）的区域净移动。植物细胞在低渗溶液中会变得硬挺，在高渗溶液中会发生质壁分离。
Active transport moves substances against a concentration gradient, from low to high concentration, using energy from respiration and carrier proteins in the membrane. Roots absorb mineral ions from dilute soil solutions by active transport.
主动运输利用呼吸作用提供的能量和膜上的载体蛋白，逆浓度梯度（从低浓度到高浓度）运输物质。植物根通过主动运输从稀薄的土壤溶液中吸收矿质离子。
3. Enzymes and Digestion | 酶与消化
Enzymes are biological catalysts made of protein. They speed up metabolic reactions by providing an alternative pathway with a lower activation energy. The lock-and-key model states that the substrate fits exactly into the enzyme’s active site.
酶是蛋白质构成的生物催化剂，通过提供较低活化能的替代途径来加速代谢反应。锁钥模型认为底物能精确地匹配酶的活性位点。
Each enzyme works best at an optimum temperature and pH. High temperatures or extreme pH denature the enzyme by breaking the bonds that hold its specific shape, causing the active site to change permanently so the substrate can no longer bind.
每种酶都有最适温度和最适 pH。高温或极端 pH 会破坏维持酶特定形状的化学键，导致活性位点永久改变，使底物无法结合，酶即失活。
Digestive enzymes include amylase (starch → maltose, produced in salivary glands and pancreas), protease (proteins → amino acids, produced in stomach, pancreas) and lipase (fats → fatty acids + glycerol, produced in pancreas). Bile, made in the liver and stored in the gall bladder, neutralises stomach acid and emulsifies fats to increase surface area for lipase action.
消化酶包括淀粉酶（淀粉 → 麦芽糖，由唾液腺和胰腺分泌）、蛋白酶（蛋白质 → 氨基酸，由胃和胰腺分泌）和脂肪酶（脂肪 → 脂肪酸 + 甘油，由胰腺分泌）。胆汁在肝脏生成、储存在胆囊，能中和胃酸并将脂肪乳化成小液滴，增大脂肪酶作用的表面积。
4. Photosynthesis and Plant Biology | 光合作用与植物生物学
The word equation for photosynthesis is: carbon dioxide + water → glucose + oxygen, taking place in chloroplasts with light energy absorbed by chlorophyll. The balanced symbol equation is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
光合作用的文字方程式为：二氧化碳 + 水 → 葡萄糖 + 氧气，该过程在叶绿体中进行，由叶绿素吸收光能。配平的化学方程式为：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。
Limiting factors for photosynthesis include light intensity, carbon dioxide concentration and temperature. At low light intensity the rate is limited by light; as light increases, a point is reached where another factor becomes limiting.
光合作用的限制因素包括光照强度、二氧化碳浓度和温度。低光照时速率受光照限制；当光照增强到一定程度后，另一个因素便成为限制因素。
Glucose produced in photosynthesis is used for respiration, stored as insoluble starch, converted to cellulose for cell walls or combined with nitrate ions to form amino acids and proteins.
光合作用产生的葡萄糖用于呼吸作用，以不溶性淀粉形式储存，转变为细胞壁所需的纤维素，或与硝酸根离子结合形成氨基酸和蛋白质。
5. Atomic Structure and Bonding | 原子结构与化学键
An atom consists of a nucleus containing protons and neutrons, surrounded by electrons in energy levels. The atomic number is the number of protons; the mass number is the total number of protons and neutrons. Isotopes are atoms of the same element with different numbers of neutrons.
原子由一个含质子和中子的原子核以及分层排布的核外电子构成。原子序数等于质子数；质量数为质子数与中子数之和。同位素是同种元素的原子，具有相同质子数但中子数不同。
Ionic bonding occurs between metals and non-metals. Metal atoms lose electrons to form positive ions, non-metal atoms gain electrons to form negative ions. Oppositely charged ions are held together by strong electrostatic forces in a giant ionic lattice structure.
离子键形成于金属与非金属之间。金属原子失去电子成为阳离子，非金属原子得到电子成为阴离子。阴阳离子通过强静电引力结合形成巨大的离子晶格。
Covalent bonding forms between non-metal atoms by sharing pairs of electrons. Simple molecular substances, such as H₂O, CO₂ and CH₄, have strong covalent bonds within the molecules but weak intermolecular forces, giving them low melting and boiling points. Giant covalent structures like diamond and silicon dioxide have very high melting points due to many strong covalent bonds.
共价键通过非金属原子间共享电子对形成。简单分子物质，如 H₂O、CO₂ 和 CH₄，分子内共价键很强，但分子间作用力弱，因此熔沸点低。像金刚石和二氧化硅这样的巨型共价结构则因大量强共价键而具有极高的熔点。
6. Quantitative Chemistry and Moles | 化学计量与摩尔
The relative atomic mass (Aᵣ) is the average mass of an atom compared to 1/12 the mass of carbon-12. The relative formula mass (Mᵣ) is the sum of Aᵣ values of all atoms in the formula. One mole of any substance contains 6.02 × 10²³ particles (Avogadro constant) and has a mass equal to its Mᵣ in grams.
相对原子质量 (Aᵣ) 是一个原子相对于碳-12 原子质量 1/12 的平均质量。相对式量 (Mᵣ) 是化学式中所有原子 Aᵣ 的总和。1 mol 任何物质含有 6.02 × 10²³ 个微粒（阿伏伽德罗常数），其质量以克为单位时等于其 Mᵣ。
The number of moles equation: moles = mass (g) ÷ Mᵣ. For solutions, moles = concentration (mol/dm³) × volume (dm³). Gas volume at room temperature and pressure: volume (dm³) = moles × 24.
摩尔数计算公式：摩尔数 = 质量 (g) ÷ Mᵣ。对于溶液，摩尔数 = 浓度 (mol/dm³) × 体积 (dm³)。常温常压下气体体积：体积 (dm³) = 摩尔数 × 24。
Reacting mass calculations require a balanced equation, converting given masses to moles, finding the mole ratio and converting back to mass. Percentage yield and atom economy are also tested: atom economy = (Mᵣ of desired product ÷ total Mᵣ of reactants) × 100%.
反应质量计算需要先配平方程式，将已知质量换算成摩尔数，利用摩尔比计算，再换回质量。百分产率和原子经济性也是常考内容：原子经济性 = (期望产物的 Mᵣ ÷ 反应物总 Mᵣ) × 100%。
7. Energy Changes and Rates of Reaction | 能量变化与反应速率
Exothermic reactions transfer heat energy to the surroundings, causing a temperature rise (e.g., combustion, neutralisation). Endothermic reactions absorb energy from the surroundings, causing a temperature drop (e.g., thermal decomposition). Reaction profiles show the relative energy of reactants and products, and the activation energy.
放热反应向周围环境释放热能，导致温度升高（如燃烧、中和反应）。吸热反应从环境中吸收能量，使温度降低（如热分解）。反应剖面图能够显示反应物和产物的相对能量以及活化能。
Required practical: use a polystyrene cup calorimeter to measure the temperature change when a solid dissolves or two solutions react, then calculate the energy transferred using q = m × c × ΔT, where c for water is 4.2 J/g°C.
必需实验：用聚苯乙烯杯量热计测量固体溶解或两种溶液反应时的温度变化，再用 q = m × c × ΔT 计算热量，其中水的比热容 c 为 4.2 J/g°C。
The rate of reaction can be measured by the volume of gas produced, change in mass or the time taken for a colour change or precipitate to appear. Factors affecting rate include concentration, temperature, surface area and the use of catalysts. Collision theory states that particles must collide with sufficient energy (activation energy) for a reaction to occur.
反应速率可通过测量气体产生体积、质量变化或出现颜色变化/沉淀所需的时间来确定。影响速率的因素有浓度、温度、表面积和催化剂的使用。碰撞理论认为粒子必须以不小于活化能的能量碰撞才能发生反应。
8. Forces and Motion | 力与运动
Scalar quantities have magnitude only (speed, distance, mass, energy, time). Vector quantities have both magnitude and direction (velocity, displacement, force, acceleration, momentum). Resultant force is the single force that has the same effect as all forces acting on an object.
标量只有大小（速率、路程、质量、能量、时间），矢量既有大小又有方向（速度、位移、力、加速度、动量）。合力是能够产生与所有作用力一样效果的一个单独力。
Equations of motion for uniform acceleration: v = u + at; v² = u² + 2as; s = ut + ½ at². Where u = initial velocity, v = final velocity, a = acceleration, t = time, s = displacement.
匀加速直线运动的公式：v = u + at；v² = u² + 2as；s = ut + ½ at²。其中 u 为初速度，v 为末速度，a 为加速度，t 为时间，s 为位移。
Newton’s First Law: an object remains at rest or in uniform motion unless acted on by a resultant force. Newton’s Second Law: F = m × a (force = mass × acceleration). Newton’s Third Law: when two objects interact, they exert equal and opposite forces on each other.
牛顿第一定律：若不受合力作用，物体将保持静止或匀速直线运动状态。牛顿第二定律：F = m × a（力 = 质量 × 加速度）。牛顿第三定律：两物体相互作用时，彼此施加大小相等、方向相反的力。
Stopping distance = thinking distance + braking distance. Factors affecting thinking distance include speed, reaction time (affected by alcohol, drugs, tiredness). Braking distance is affected by speed, mass of vehicle, condition of brakes, tyres and road surface.
停车距离 = 反应距离 + 制动距离。影响反应距离的因素包括车速和反应时间（受酒精、药物、疲劳影响）。制动距离受车速、车辆质量、刹车状况、轮胎及路面状况影响。
9. Electricity and Circuits | 电学与电路
Current (I) is the rate of flow of charge, measured in amperes (A). In a series circuit, the current is the same everywhere. In a parallel circuit, the current divides at the junctions. Potential difference (V) is the energy transferred per unit charge.
电流 (I) 是电荷流动的速率，单位为安培 (A)。串联电路中各处电流相等，并联电路中电流在节点处分流。电势差（电压 V）是单位电荷所转移的能量。
Ohm’s Law applies to ohmic conductors at constant temperature: V = I × R. Resistance increases with temperature in a filament lamp, causing a curved IV graph. A diode allows current to flow in one direction only.
欧姆定律适用于温度恒定的欧姆导体：V = I × R。白炽灯的电阻随温度升高而增大，因此其伏安特性曲线是弯曲的。二极管只允许电流单向导通。
Power and energy equations: P = V × I, P = I² × R, E = P × t = V × I × t. Mains electricity is AC, typically 230 V and frequency 50 Hz. The live wire is brown, neutral is blue, and earth wire is green/yellow.
功率和电能公式：P = V × I，P = I² × R，E = P × t = V × I × t。市电是交流电，通常为 230 V、频率 50 Hz。火线为棕色，零线为蓝色，地线为黄绿双色。
10. Waves and Electromagnetic Spectrum | 波与电磁波谱
Transverse waves have oscillations perpendicular to the direction of energy transfer (e.g., light, water ripples, all EM waves). Longitudinal waves have oscillations parallel to the direction of energy transfer (e.g., sound waves), consisting of compressions and rarefactions.
横波的振动方向与能量传递方向垂直（如光、水波、所有电磁波）。纵波的振动方向与能量传递方向平行（如声波），由压缩和稀疏区域构成。
The wave equation: wave speed (m/s) = frequency (Hz) × wavelength (m), or v = f × λ. Frequency is related to period: f = 1/T. All electromagnetic waves travel at the same speed in a vacuum, 3.0 × 10⁸ m/s.
波速公式：波速 (m/s) = 频率 (Hz) × 波长 (m)，或 v = f × λ。频率与周期的关系为 f = 1/T。所有电磁波在真空中传播速度相同，均为 3.0 × 10⁸ m/s。
The electromagnetic spectrum in order of increasing frequency and decreasing wavelength: radio waves, microwaves, infrared, visible light, ultraviolet, X‑rays, gamma rays. Uses and dangers vary: microwaves for communication and heating, infrared for thermal imaging, X‑rays for medical imaging, gamma rays for sterilisation and cancer treatment; UV, X‑rays and gamma rays are ionising and can damage DNA.
电磁波谱按频率递增、波长递减的顺序为：无线电波、微波、红外线、可见光、紫外线、X 射线、伽马射线。各自的应用与危害不同：微波用于通信和加热，红外线用于热成像，X 射线用于医学影像，伽马射线用于灭菌和癌症治疗；紫外线、X 射线和伽马射线具有电离能力，可能损伤 DNA。
11. Magnetism and Electromagnetism | 磁学与电磁学
Permanent magnets produce their own magnetic field; induced magnets become magnetic only when placed in a magnetic field. Like poles repel, unlike poles attract. Magnetic field lines point from north to south.
永磁体产生自己的磁场；感应磁体只有在放入磁场中时才具有磁性。同名磁极相互排斥，异名磁极相互吸引。磁感线方向由北极指向南极。
When a current flows through a wire, a magnetic field is generated around it. The direction can be found using the right-hand grip rule. An electromagnet consists of a coil of wire (solenoid) often with an iron core; its magnetic field strength increases with current, number of turns and presence of a soft iron core.
当电流流过导线时，会在导线周围产生磁场，方向可用右手螺旋定则判断。电磁铁由一个线圈（螺线管）和通常的铁芯组成；其磁场强度随电流大小、线圈匝数和软铁芯的有无而增强。
The motor effect: when a current-carrying conductor is placed in a magnetic field, it experiences a force. The direction of force is given by Fleming’s left-hand rule. The magnitude of the force depends on magnetic flux density, current and length of conductor: F = B × I × L.
电动机效应：通电导体在磁场中会受到力的作用，力的方向由弗莱明左手定则确定。力的大小取决于磁通量密度、电流大小和导体长度：F = B × I × L。
Electromagnetic induction: when a conductor cuts magnetic field lines, a potential difference is induced. If the circuit is complete, a current flows. This is the principle of generators and dynamos. Transformers change the size of an alternating voltage, based on the principle of mutual induction, and only work with AC.
电磁感应：当导体切割磁感线时，会产生感应电动势；若电路闭合，则产生感应电流。这是发电机和直流发电机的基本原理。变压器基于互感原理，用于改变交流电压的大小，且只能用于交流电。
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