📚 Edexcel IGCSE Science (620): Core Principles in Biology, Chemistry & Physics | Edexcel IGCSE科学(620)：生物学、化学与物理学核心原理
The Edexcel IGCSE Science (620) qualification, typically studied as a Double Award course, integrates key concepts from Biology, Chemistry and Physics. This programme builds a solid foundation for A Level sciences and encourages scientific inquiry. Through a balanced mix of theoretical knowledge and practical investigations, students explore living organisms, chemical reactions, energy and the physical laws governing the universe. The following revision guide summarises the core topics, essential definitions and exam techniques you need to master.
Edexcel IGCSE 科学 (620) 通常作为双奖课程学习，融合了生物学、化学和物理学的核心概念。该课程为 A Level 科学科目奠定坚实基础，并鼓励科学探究。通过理论与实践研究的均衡结合，学生们探索生命体、化学反应、能量以及支配宇宙的物理定律。以下复习指南总结了需要掌握的核心主题、关键定义和考试技巧。
1. Cells and Cell Structure | 细胞与细胞结构
Cells are the fundamental units of life. All living organisms are composed of cells, which can be observed under a light microscope using stains such as methylene blue or iodine solution.
细胞是生命的基本单位。所有生物体都由细胞组成，可使用亚甲蓝或碘液等染色剂在光学显微镜下观察细胞。
A typical animal cell contains a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells share these organelles but also possess a rigid cell wall made of cellulose, a large permanent vacuole containing cell sap, and chloroplasts that carry out photosynthesis.
典型的动物细胞含有细胞核、细胞质、细胞膜、线粒体和核糖体。植物细胞同样具有这些细胞器，此外还有由纤维素构成的坚硬细胞壁、充满细胞液的大液泡以及进行光合作用的叶绿体。
Magnification can be calculated using the formula: magnification = image size ÷ actual size. Remember to convert units carefully when working with micrometres and millimetres.
放大倍数可通过公式计算：放大倍数 = 图像大小 ÷ 实际大小。在涉及微米和毫米时，切记仔细换算单位。
2. Biological Molecules and Enzymes | 生物分子与酶
Carbohydrates, proteins and lipids are the main biological molecules. Starch and glycogen are polysaccharides made of glucose units; proteins are composed of amino acids; lipids are formed from fatty acids and glycerol. A balanced diet includes these nutrients, along with vitamins, minerals, water and dietary fibre.
碳水化合物、蛋白质和脂质是主要的生物分子。淀粉和糖原是由葡萄糖单元组成的多糖；蛋白质由氨基酸构成；脂质由脂肪酸和甘油形成。均衡饮食包括这些营养素，以及维生素、矿物质、水和膳食纤维。
Food tests are a practical focus in IGCSE Science. The Benedict’s test identifies reducing sugars, iodine solution turns blue-black in the presence of starch, biuret reagent detects proteins and the ethanol emulsion test is used for lipids.
食物检验是 IGCSE 科学的实践重点。本尼迪克特试剂用于检测还原糖，碘液遇淀粉变蓝黑色，双缩脲试剂检测蛋白质，乙醇乳浊液测试用于鉴定脂质。
Enzymes are biological catalysts that speed up metabolic reactions. They are proteins with a specific active site that binds to substrates. Factors including temperature, pH and substrate concentration affect enzyme activity. Denaturation occurs when the active site loses its shape, often due to high temperature or extreme pH, stopping the reaction permanently.
酶是加速代谢反应的生物催化剂。它们是具有特定活性位点的蛋白质，能与底物结合。温度、pH 和底物浓度等因素影响酶活性。当活性位点因高温或极端 pH 而失去形状时，酶发生变性，反应永久停止。
3. Ecology and the Environment | 生态与环境
An ecosystem consists of a community of living organisms interacting with each other and their abiotic environment. Food chains and food webs represent the feeding relationships, with energy transferred from producers to primary consumers and further up the trophic levels.
生态系统由生物群落及其非生物环境相互作用组成。食物链和食物网展示了捕食关系，能量从生产者传递至初级消费者，进而沿营养级向上转移。
Pyramids of number, biomass and energy illustrate the structure of ecosystems. Typically, only about 10% of the energy is transferred from one trophic level to the next; the rest is lost through movement, heat and undigested material.
数量、生物量和能量金字塔体现了生态系统的结构。通常仅有约10%的能量从一个营养级传递至下一级，其余通过运动、热和未消化物质散失。
Human activities such as deforestation and the burning of fossil fuels increase atmospheric carbon dioxide, enhancing the greenhouse effect. The carbon cycle and nitrogen cycle are essential biogeochemical processes that you should be able to interpret using diagrams and explanations of decomposition, combustion and nitrogen fixation.
森林砍伐和化石燃料燃烧等人类活动增加了大气中的二氧化碳，加剧了温室效应。碳循环和氮循环是关键的生物地球化学过程，你需要能够通过图表和对分解、燃烧及固氮的解释来阐述它们。
4. Atomic Structure and the Periodic Table | 原子结构与元素周期表
Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons arranged in shells. The atomic number equals the number of protons, and the mass number is the total of protons and neutrons. Isotopes are atoms of the same element with different numbers of neutrons.
原子由包含质子和中子的原子核以及分层排布的电子组成。原子序数等于质子数，质量数为质子数与中子数之和。同位素是同一元素中中子数不同的原子。
Electron configuration for the first 20 elements follows the 2.8.8 pattern. Elements in the same group of the periodic table have the same number of outer electrons and similar chemical properties. Group 1 contains the alkali metals, Group 7 the halogens and Group 0 the noble gases.
前20种元素的电子排布遵循2.8.8模式。周期表中同族元素具有相同的最外层电子数和相似的化学性质。第1族为碱金属，第7族为卤素，第0族为稀有气体。
Ions form when atoms gain or lose electrons to achieve a full outer shell. Metals tend to lose electrons and form positive cations, while non-metals gain electrons and become negative anions.
当原子得到或失去电子以达到满壳层时，便形成离子。金属倾向于失去电子形成阳离子，而非金属得到电子成为阴离子。
5. Chemical Bonding and Structures | 化学键与结构
Ionic bonding involves the electrostatic attraction between oppositely charged ions. Compounds such as NaCl and MgO form giant ionic lattices, which conduct electricity when molten or dissolved in water because the ions are free to move.
离子键涉及带相反电荷离子之间的静电吸引。氯化钠和氧化镁等化合物形成巨型离子晶格，在熔融或溶于水时可导电，因为离子能够自由移动。
Covalent bonding occurs when atoms share pairs of electrons. Simple molecular substances like H₂O, CO₂ and NH₃ have low melting and boiling points, whereas giant covalent structures such as diamond and silicon dioxide (SiO₂) are very hard and have high melting points.
共价键是原子共享电子对形成的。水、二氧化碳和氨等简单分子物质熔点、沸点较低，而金刚石和二氧化硅等巨型共价结构硬度大、熔点高。
Metallic bonding consists of positive metal ions surrounded by a ‘sea’ of delocalised electrons. This structure explains why metals are malleable, ductile, and good conductors of heat and electricity.
金属键由正金属离子和包围它们的“电子海”组成。这种结构解释了金属具有延展性、韧性和良好的导热、导电性的原因。
6. Rates of Reaction and Energetics | 反应速率与能量学
The rate of a chemical reaction can be followed by measuring the volume of gas produced, the change in mass or the time taken for a precipitate to form. Key factors affecting the rate include concentration, temperature, surface area of solids and the use of catalysts.
可通过测量生成气体体积、质量变化或沉淀形成所需时间来监测化学反应速率。影响速率的关键因素包括浓度、温度、固体表面积以及催化剂的使用。
According to collision theory, particles must collide with sufficient energy (activation energy) and correct orientation for a reaction to occur. Increasing temperature gives particles more kinetic energy, thus more frequent and energetic collisions.
根据碰撞理论，粒子必须以足够的能量（活化能）和正确的取向碰撞才能使反应发生。升高温度使粒子动能增加，从而碰撞更频繁、更有能量。
Energy changes in reactions are classified as exothermic (energy released to surroundings, ΔH negative) or endothermic (energy absorbed from surroundings, ΔH positive). Bond breaking is endothermic; bond making is exothermic. Simple calorimetry experiments measure temperature changes during neutralisation or combustion.
反应中的能量变化分为放热（能量释放到周围环境，ΔH为负）和吸热（从周围环境吸收能量，ΔH为正）。断键需吸热；成键则放热。简单的量热实验用于测量中和或燃烧过程中的温度变化。
7. Motion, Forces and Energy | 运动、力与能量
Speed is the distance travelled per unit time. The gradient of a distance-time graph represents speed, while the gradient of a velocity-time graph gives acceleration. Key equations include: speed = distance ÷ time, acceleration = (final velocity – initial velocity) ÷ time, and final velocity² = initial velocity² + 2 × acceleration × distance.
速度是单位时间内移动的距离。距离-时间图的斜率表示速度，速度-时间图的斜率表示加速度。关键公式包括：速度 = 距离 ÷ 时间，加速度 = (末速度 – 初速度) ÷ 时间，以及末速度² = 初速度² + 2 × 加速度 × 距离。
Forces cause objects to accelerate, decelerate or change shape. Newton’s second law states: resultant force = mass × acceleration (F = m × a). Weight is the force due to gravity, calculated by weight = mass × gravitational field strength (g). Friction and air resistance oppose motion.
力使物体加速、减速或改变形状。牛顿第二定律指出：合力 = 质量 × 加速度 (F = m × a)。重量是重力产生的力，计算方式为重量 = 质量 × 重力场强度 (g)。摩擦力和空气阻力阻碍运动。
Energy can exist in kinetic, gravitational potential, thermal, chemical and other forms, and is conserved. Work done is equal to force × distance moved in the direction of the force. Efficiency is the ratio of useful energy output to total energy input, often expressed as a percentage.
能量可以动能、重力势能、热能、化学能等形式存在，并且是守恒的。所做的功等于力与沿力方向移动距离的乘积。效率是有用能量产出与总能量投入之比，通常以百分比表示。
8. Waves and the Electromagnetic Spectrum | 波与电磁波谱
Waves transfer energy without transferring matter. Transverse waves, such as light and water ripples, have oscillations perpendicular to the direction of energy transfer. Longitudinal waves, such as sound, have oscillations parallel to the energy transfer.
波传递能量而不传递物质。横波（如光和水波）的振动方向与能量传播方向垂直。纵波（如声音）的振动方向与能量传播方向平行。
The wave equation links speed, frequency and wavelength: wave speed = frequency × wavelength (v = f λ). Reflection, refraction and diffraction are key wave behaviours. Refraction occurs when a wave changes speed as it enters a different medium, causing a change in direction unless it enters along the normal.
波速方程将波速、频率和波长联系起来：波速 = 频率 × 波长 (v = f λ)。反射、折射和衍射是波的关键行为。当波进入不同介质速度改变时发生折射，除非沿法线射入，否则方向会改变。
The electromagnetic spectrum arranges waves by frequency and wavelength, from radio waves, microwaves, infrared, visible light, ultraviolet, X-rays to gamma rays. All travel at 3 × 10⁸ m/s in a vacuum. Each region has distinct uses: radio waves for communication, X-rays for medical imaging and microwaves for cooking.
电磁波谱按频率和波长排列，从无线电波、微波、红外线、可见光、紫外线、X射线到伽马射线。所有电磁波在真空中以 3 × 10⁸ m/s 传播。每种波都有独特的用途：无线电波用于通信，X射线用于医学成像，微波用于烹饪。
9. Electricity and Circuits | 电与电路
Current is the rate of flow of charge, measured in amperes. Voltage (potential difference) is the energy transferred per unit charge. Resistance, measured in ohms, is the opposition to current flow. Ohm’s law is expressed as voltage = current × resistance (V = I × R).
电流是电荷流动的速率，单位为安培。电压（电势差）是单位电荷转移的能量。电阻是电流流动的阻碍，单位是欧姆。欧姆定律表示为：电压 = 电流 × 电阻 (V = I × R)。
In series circuits, the current is the same throughout and the total resistance is the sum of individual resistances. In parallel circuits, the voltage across each branch is the same, while the total current splits at junctions. Lamps and diodes are common circuit components; a fixed resistor obeys Ohm’s law, while a filament lamp’s resistance increases with temperature.
在串联电路中，各处电流相同，总电阻为各电阻之和。在并联电路中，各支路两端电压相等，总电流在节点处分配。灯泡和二极管是常见电路元件；固定电阻器遵循欧姆定律，而灯丝的电阻随温度升高而增大。
Mains electricity uses alternating current (AC), while batteries supply direct current (DC). Electrical power is calculated using Power = voltage × current, and energy transferred is Power × time. Safety devices such as fuses and circuit breakers prevent overheating.
市电使用交流电 (AC)，而电池提供直流电 (DC)。电功率计算公式为：功率 = 电压 × 电流，能量传递 = 功率 × 时间。保险丝和断路器等安全装置可防止过热。
10. Practical Skills and Exam Strategy | 实验技能与考试策略
IGCSE Science papers assess your ability to plan investigations, record data, plot graphs and draw conclusions. You should be able to identify variables: independent (the one you change), dependent (the one you measure) and control variables (kept constant).
IGCSE 科学试卷考察你规划探究、记录数据、绘制图表和得出结论的能力。你应该能识别变量：自变量（你改变的）、因变量（你测量的）和控制变量（保持不变的）。
When drawing graphs, use sharp pencil, label axes with quantity and unit, and choose a sensible scale. For a straight line of best fit, draw through the middle of the plotted points. Use the gradient to make further calculations if required.
绘制图表时，使用尖细的铅笔，用数量和单位标记坐标轴，并选择合理的比例。对于最佳拟合直线，应穿过绘制点的中间。如需，利用斜率进行进一步计算。
Time management is crucial: allocate approximately one minute per mark. Read the command words carefully; ‘describe’ requires what happens, while ‘explain’ asks why it happens using scientific principles. Always show your working in calculations, as method marks are awarded even if the final answer is incorrect.
时间管理至关重要：大致按每分钟一分的比例分配时间。仔细阅读指令词；“描述”要求说明发生了什么，而“解释”则要运用科学原理解释为什么发生。计算时务必展示步骤，因为即使最终答案错误，方法分也可获得。
Revise actively by completing past papers under timed conditions, then reviewing mark schemes to understand common pitfalls. Make concise revision cards for definitions, formulae and key experiments across all three sciences.
通过限时完成历年真题进行主动复习，然后对照评分标准了解常见失分点。制作简明的复习卡，涵盖三科的定义、公式和关键实验。
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