IGCSE Edexcel Science Revision: Understanding Key Concepts | IGCSE Edexcel 科学复习：理解核心概念

📚 IGCSE Edexcel Science Revision: Understanding Key Concepts | IGCSE Edexcel 科学复习：理解核心概念

This revision guide brings together the essential ideas from Biology, Chemistry and Physics for the Edexcel IGCSE Science specification. It is designed to help you move from memorising facts to actually understanding the concepts, so that you can apply your knowledge to unfamiliar questions with confidence.

本复习指南整合了 Edexcel IGCSE 科学大纲中生物、化学和物理的核心思想。它帮助你从机械记忆转向真正理解概念，从而自信地将知识应用到陌生题目中。

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1. The Scientific Method and Variables | 科学方法与变量

Science is not just a collection of facts; it is a process of inquiry. In any experiment, you must identify the independent variable (what you change), the dependent variable (what you measure) and the control variables (what you keep the same). Without controlled variables, a fair test is impossible.

科学不仅仅是事实的集合，更是一个探究过程。在任何实验中，你必须明确自变量（你改变的量）、因变量（你测量的量）和控制变量（你保持不变的量）。没有控制变量，就无法进行公平测试。

For example, if you are investigating how temperature affects the rate of an enzyme-controlled reaction, the independent variable is temperature, the dependent variable is reaction rate, and the control variables include pH, enzyme concentration and substrate concentration.

例如，如果研究温度如何影响酶促反应速率，自变量是温度，因变量是反应速率，而控制变量包括 pH 值、酶浓度和底物浓度。

You should also be familiar with the terms precision and accuracy. Precision refers to how close repeated measurements are to each other; accuracy refers to how close a measurement is to the true value. Taking repeats and calculating the mean improves precision and reduces the effect of random errors.

你还应熟悉“精密度”和“准确度”这两个术语。精密度指重复测量结果之间的接近程度；准确度指测量值与真实值的接近程度。重复测量并计算平均值可以提高精密度，并减少随机误差的影响。

• Independent variable: the variable you deliberately change.

  自变量：你有意改变的变量。

• Dependent variable: the variable you measure.

  因变量：你测量的变量。

• Control variables: variables kept constant to ensure a fair test.

  控制变量：保持恒定以确保公平测试的变量。

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2. Biological Molecules | 生物分子

All living organisms are made of biological molecules. The main groups are carbohydrates, proteins, lipids and nucleic acids. Carbohydrates are made from simple sugars such as glucose. Starch and glycogen are polysaccharides used for energy storage, while cellulose is a structural carbohydrate in plant cell walls.

所有生物体都由生物分子构成。主要类别包括碳水化合物、蛋白质、脂质和核酸。碳水化合物由葡萄糖等单糖构成。淀粉和糖原是用于能量储存的多糖，而纤维素是植物细胞壁中的结构性碳水化合物。

Proteins are polymers made of amino acids. Each amino acid has an amino group and a carboxyl group. The sequence of amino acids determines the protein’s shape and function. Enzymes, antibodies and many hormones are proteins.

蛋白质是由氨基酸组成的聚合物。每个氨基酸都有一个氨基和一个羧基。氨基酸的序列决定了蛋白质的形状和功能。酶、抗体和许多激素都是蛋白质。

Lipids include fats and oils. They are made of glycerol and fatty acids. Lipids are insoluble in water but soluble in organic solvents. They provide long-term energy storage, insulation and protection of organs.

脂质包括脂肪和油。它们由甘油和脂肪酸组成。脂质不溶于水，但溶于有机溶剂。它们提供长期能量储存、保温作用和器官保护。

Food tests are a common exam topic. Use Benedict’s solution to test for reducing sugars, iodine solution to test for starch, Biuret reagent to test for protein and ethanol to test for lipids. Remember the colour changes precisely.

食物检测是一个常见的考试主题。用 Benedict 试剂检测还原糖，用碘液检测淀粉，用双缩脲试剂检测蛋白质，用乙醇检测脂质。请准确记住颜色变化。

Food group | 检测的食物	Test | 检测方法	Positive result | 阳性结果
Reducing sugar | 还原糖	Benedict’s solution + heat | Benedict 试剂＋加热	Brick-red precipitate | 砖红色沉淀
Starch | 淀粉	Iodine solution | 碘液	Blue-black colour | 蓝黑色
Protein | 蛋白质	Biuret reagent | 双缩脲试剂	Purple colour | 紫色
Lipid | 脂质	Ethanol then water | 乙醇后加水	White emulsion | 白色乳浊液

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3. Cell Structure and Function | 细胞结构与功能

Cells are the basic units of life. Animal cells contain a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells also contain a cell wall, chloroplasts and a permanent vacuole. The cell wall is made of cellulose and provides structural support.

细胞是生命的基本单位。动物细胞含有细胞核、细胞质、细胞膜、线粒体和核糖体。植物细胞还含有细胞壁、叶绿体和永久液泡。细胞壁由纤维素构成，提供结构支撑。

The nucleus contains chromosomes made of DNA and controls cell activities. Mitochondria are the sites of aerobic respiration, releasing energy in the form of ATP. Ribosomes are the sites of protein synthesis. Chloroplasts contain chlorophyll and carry out photosynthesis.

细胞核含有由 DNA 组成的染色体，控制细胞活动。线粒体是有氧呼吸的场所，以 ATP 的形式释放能量。核糖体是蛋白质合成的场所。叶绿体含有叶绿素，进行光合作用。

In the Edexcel IGCSE specification, you should compare animal and plant cells using a labelled diagram. You should also explain the function of specialised cells such as red blood cells, root hair cells and sperm cells, relating their structure to their role.

在 Edexcel IGCSE 大纲中，你应该用标注图比较动物细胞和植物细胞。你还应解释红细胞、根毛细胞和精子细胞等特化细胞的功能，将其结构与角色联系起来。

Diffusion is the net movement of particles from high to low concentration. Osmosis is the net movement of water molecules across a partially permeable membrane. Active transport moves particles from low to high concentration using energy from respiration.

扩散是粒子从高浓度到低浓度的净移动。渗透是水分子通过半透膜的净移动。主动运输利用呼吸产生的能量，将粒子从低浓度移动到高浓度。

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4. Enzymes and Metabolism | 酶与代谢

Enzymes are biological catalysts that speed up chemical reactions without being changed themselves. They are proteins with an active site that is specific to a particular substrate. The lock-and-key model describes how the substrate fits into the active site.

酶是生物催化剂，能加速化学反应，但自身不会被改变。它们是具有活性位点的蛋白质，活性位点对特定底物具有专一性。“锁钥模型”描述了底物如何与活性位点结合。

Temperature and pH affect enzyme activity. As temperature increases, the rate of reaction increases until the optimum temperature is reached. Above the optimum, the enzyme denatures and the active site changes shape, so the substrate can no longer bind.

温度和 pH 值影响酶活性。随着温度升高，反应速率增加，直到达到最适温度。超过最适温度后，酶变性，活性位点形状改变，底物无法再结合。

Enzymes can be intracellular, such as catalase inside cells, or extracellular, such as digestive enzymes released into the alimentary canal. Amylase breaks down starch into maltose, protease breaks down proteins into amino acids, and lipase breaks down lipids into fatty acids and glycerol.

酶可以是胞内酶，如细胞内的过氧化氢酶，也可以是胞外酶，如释放到消化道中的消化酶。淀粉酶将淀粉分解为麦芽糖，蛋白酶将蛋白质分解为氨基酸，脂肪酶将脂质分解为脂肪酸和甘油。

Rate of reaction ∝ 1 / time taken

In rate experiments, you can measure the time taken for a product to appear or a substrate to disappear. Use units carefully and present data clearly. The inverse of time gives a measure of the relative rate.

在速率实验中，你可以测量产物出现或底物消失所需的时间。注意单位并清晰呈现数据。时间的倒数可以表示相对速率。

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5. Atomic Structure and Bonding | 原子结构与化学键

Atoms are made of protons, neutrons and electrons. Protons are positively charged, neutrons are neutral and electrons are negatively charged. The atomic number is the number of protons, and the mass number is the sum of protons and neutrons.

原子由质子、中子和电子组成。质子带正电，中子不带电，电子带负电。原子序数等于质子数，质量数等于质子数与中子数之和。

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. They have the same chemical properties but different physical properties, such as mass. The notation for an isotope is written with the mass number at the top and the atomic number at the bottom.

同位素是同一元素中质子数相同但中子数不同的原子。它们具有相同的化学性质，但物理性质（如质量）不同。同位素符号写法是上面标质量数，下面标原子序数。

Ionic bonding occurs between metals and non-metals. Electrons are transferred from the metal atoms to the non-metal atoms, forming positive cations and negative anions. Ionic compounds have high melting points and conduct electricity when molten or dissolved in water.

离子键发生在金属和非金属之间。电子从金属原子转移到非金属原子，形成正阳离子和负阴离子。离子化合物熔点高，在熔融或溶于水时能导电。

Covalent bonding occurs between non-metal atoms. Electrons are shared between atoms. Covalent substances can be simple molecules, such as water (H₂O) and carbon dioxide (CO₂), or giant structures, such as diamond and graphite.

共价键发生在非金属原子之间。原子之间共享电子。共价物质可以是简单分子，如水（H₂O）和二氧化碳（CO₂），也可以是巨型结构，如金刚石和石墨。

Graphite contains layers of carbon atoms that can slide over each other, making it soft and useful as a lubricant. Diamond has a tetrahedral structure with strong covalent bonds in all directions, making it very hard. Graphene is a single layer of graphite with excellent electrical conductivity.

石墨含有可相互滑动的碳原子层，因此质地柔软，可用作润滑剂。金刚石具有四面体结构，各方向都有强共价键，因此非常坚硬。石墨烯是石墨的单层结构，具有优异的导电性。

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6. Chemical Reactions and Equations | 化学反应与方程式

Chemical equations describe reactants and products. In a balanced equation, the number of atoms of each element is the same on both sides. You must be able to write word equations and chemical equations, and balance them accurately.

化学方程式描述反应物和产物。在配平的方程式中，每种元素的原子数在两侧相等。你必须能够写出文字方程式和化学方程式，并准确配平。

The state symbols (s), (l), (g) and (aq) indicate solid, liquid, gas and aqueous solution. For example, the reaction between magnesium and hydrochloric acid can be written as:

状态符号 (s)、(l)、(g) 和 (aq) 分别表示固态、液态、气态和水溶液。例如，镁与盐酸的反应可以写作：

Mg (s) + 2HCl (aq) → MgCl₂ (aq) + H₂ (g)

Exothermic reactions release energy to the surroundings, causing the temperature to increase. Combustion, neutralisation and respiration are exothermic. Endothermic reactions absorb energy from the surroundings, causing the temperature to decrease. Photosynthesis and thermal decomposition are endothermic.

放热反应向环境释放能量，导致温度升高。燃烧、中和和呼吸作用都是放热反应。吸热反应从环境吸收能量，导致温度降低。光合作用和热分解是吸热反应。

In a displacement reaction, a more reactive element displaces a less reactive element from a compound. The reactivity series arranges metals in order of reactivity. Potassium is the most reactive of the common metals, while copper and gold are least reactive.

在置换反应中，较活泼的元素将较不活泼的元素从其化合物中置换出来。金属活动性顺序按反应活性排列金属。在常见金属中，钾的活动性最强，而铜和金的活动性最弱。

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7. Acids, Bases and Salts | 酸、碱与盐

Acids are substances that produce hydrogen ions (H⁺) in aqueous solution. Bases are substances that neutralise acids to form water. Alkalis are bases that dissolve in water to produce hydroxide ions (OH⁻).

酸是在水溶液中产生氢离子（H⁺）的物质。碱是能与酸中和生成水的物质。可溶性碱是溶于水后产生氢氧根离子（OH⁻）的碱。

The pH scale measures acidity and alkalinity. A pH of 7 is neutral, below 7 is acidic and above 7 is alkaline. Universal indicator can give a range of colours, while litmus paper only distinguishes between acid and alkali.

pH 标度测量酸性和碱性。pH 为 7 是中性，小于 7 是酸性，大于 7 是碱性。万用指示剂可以呈现多种颜色，而石蕊试纸只能区分酸和碱。

Acids react with metals to produce a salt and hydrogen gas. For example, zinc with hydrochloric acid produces zinc chloride and hydrogen. Acids react with carbonates to produce a salt, water and carbon dioxide.

酸与金属反应生成盐和氢气。例如，锌与盐酸反应生成氯化锌和氢气。酸与碳酸盐反应生成盐、水和二氧化碳。

Neutralisation is the reaction between an acid and a base. The general equation is:

中和反应是酸与碱之间的反应。通式如下：

Acid + Base → Salt + Water

To make a soluble salt, you can react an acid with an excess of an insoluble base, filter off the excess, then crystallise the filtrate. For example, copper oxide reacts with sulfuric acid to produce copper sulfate.

要制备可溶性盐，可以将酸与过量的不溶性碱反应，过滤除去过量碱，然后使滤液结晶。例如，氧化铜与硫酸反应生成硫酸铜。

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8. Motion and Forces | 运动与力

Speed is the distance travelled per unit time. Velocity is speed in a given direction. Acceleration is the rate of change of velocity. The equations of motion can be summarised by these relationships:

速率是单位时间内通过的距离。速度是沿给定方向的速率。加速度是速度的变化率。运动方程可以概括为以下关系：

distance = speed × time

acceleration = (final velocity − initial velocity) / time

Forces are pushes or pulls acting on objects. A force can change the shape, speed or direction of an object. Newton’s second law states that the resultant force equals mass multiplied by acceleration:

力是对物体的推或拉。力可以改变物体的形状、速度或方向。牛顿第二定律指出，合力等于质量乘以加速度：

F = m × a

Weight is the force of gravity acting on a mass. It is calculated by multiplying mass by gravitational field strength. On Earth, the gravitational field strength is approximately 9.8 N/kg.

重力是作用在质量上的引力。它等于质量乘以重力场强度。在地球上，重力场强度约为 9.8 N/kg。

Friction is a force that opposes relative motion. Air resistance is a type of fluid friction. A skydiver reaches terminal velocity when air resistance balances weight, so the resultant force is zero and the skydiver falls at a constant speed.

摩擦力是阻碍相对运动的力。空气阻力是一种流体摩擦。跳伞者达到终端速度时，空气阻力与重力平衡，合力为零，跳伞者以恒定速度下落。

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9. Energy Transfers and Electricity | 能量转化与电学

Energy can be stored in different forms, such as kinetic, gravitational potential, elastic potential, chemical, thermal and electrical. The principle of conservation of energy states that energy cannot be created or destroyed, only transferred from one form to another.

能量可以以不同形式储存，如动能、引力势能、弹性势能、化学能、热能和电能。能量守恒定律指出，能量不能被创造或消灭，只能从一种形式转化为另一种形式。

Gravitational potential energy is gained when an object is raised. Kinetic energy is the energy of movement. The equations are:

当物体被升高时，引力势能增加。动能是运动的能量。方程如下：

GPE = mass × gravitational field strength × height

KE = ½ × mass × velocity²

In an electric circuit, current is the flow of charge measured in amperes. Potential difference is the energy transferred per unit charge measured in volts. Resistance is the opposition to current and is measured in ohms.

在电路中，电流是电荷的流动，单位是安培。电势差是单位电荷转移的能量，单位是伏特。电阻是对电流的阻碍，单位是欧姆。

Ohm’s law states that the current through a resistor is directly proportional to the potential difference across it, provided that temperature remains constant. The relationship is:

欧姆定律指出，在温度保持恒定的条件下，通过电阻的电流与电阻两端的电势差成正比。关系式为：

V = I × R

In series circuits, the current is the same at every point and the potential differences add up. In parallel circuits, the potential difference is the same across each branch and the currents add up. You should be able to draw and interpret these circuits.

在串联电路中，电流处处相同，电势差相加。在并联电路中，各支路电势差相同，电流相加。你应该能够绘制和解读这些电路。

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10. Waves and the Electromagnetic Spectrum | 波与电磁波谱

Waves transfer energy and information without transferring matter. There are two types of waves: longitudinal and transverse. Sound waves are longitudinal, while electromagnetic waves are transverse.

波传递能量和信息，但不传递物质。波分为两类：纵波和横波。声波是纵波，电磁波是横波。

Wave speed is calculated using the equation:

波速使用以下方程计算：

speed = frequency × wavelength

The frequency of a wave is the number of complete waves passing a point per second, measured in hertz. The wavelength is the distance between two corresponding points on adjacent waves, such as from crest to crest.

波的频率是每秒通过某一点的完整波数，单位是赫兹。波长是相邻波上两个对应点之间的距离，例如从一个波峰到下一个波峰。

The electromagnetic spectrum is arranged in order of increasing frequency and decreasing wavelength. From lowest frequency to highest, the order is radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.

电磁波谱按频率递增和波长递减的顺序排列。从低频到高频依次是无线电波、微波、红外线、可见光、紫外线、X 射线和伽马射线。

Different regions of the electromagnetic spectrum have different uses and dangers. Radio waves are used for communication, microwaves for satellite communication and cooking, infrared for thermal imaging, visible light for sight, ultraviolet for sterilisation, X-rays for medical imaging and gamma rays for cancer treatment.

电磁波谱的不同区域有不同的用途和危害。无线电波用于通信，微波用于卫星通信和烹饪，红外线用于热成像，可见光用于视觉，紫外线用于杀菌，X 射线用于医学影像，伽马射线用于癌症治疗。

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11. Biological Cycles and Earth Processes | 生物循环与地球过程

The carbon cycle describes how carbon moves between the atmosphere, living organisms, oceans and rocks. Photosynthesis removes carbon dioxide from the air, while respiration, combustion and decomposition return carbon dioxide to the atmosphere.

碳循环描述了碳在大气、生物体、海洋和岩石之间的移动。光合作用从空气中吸收二氧化碳，而呼吸作用、燃烧和分解将二氧化碳返回大气。

The nitrogen cycle involves the transfer of nitrogen between the air, soil and organisms. Nitrogen fixation converts atmospheric nitrogen into ammonia, nitrification converts ammonia into nitrates, and denitrification converts nitrates back into nitrogen gas.

氮循环涉及氮在空气、土壤和生物体之间的转移。固氮作用将大气氮转化为氨，硝化作用将氨转化为硝酸盐，反硝化作用将硝酸盐转化为氮气。

In response to human activities, the greenhouse effect has intensified. Carbon dioxide and methane trap heat in the atmosphere, leading to global warming. Consequences include rising sea levels, changing weather patterns and habitat loss.

由于人类活动，温室效应加剧。二氧化碳和甲烷在大气中截留热量，导致全球变暖。后果包括海平面上升、天气模式改变和栖息地丧失。

You should be able to interpret diagrams of these cycles, identify the processes involved, and explain how human activities such as burning fossil fuels and deforestation affect them.

你应该能够解读这些循环的图示，识别所涉及的过程，并解释燃烧化石燃料和滥伐森林等人类活动如何影响这些循环。

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12. Exam Strategy and Command Words | 应试策略与指令词

Edexcel IGCSE Science questions often use specific command words that tell you exactly what to do. If you misread the command word, you cannot score full marks even if you write a correct statement.

Edexcel IGCSE 科学题目常使用特定的指令词，告诉你确切要做什么。如果误读指令词，即使写了正确的内容，也可能无法得满分。

• State: give a short factual answer without explanation.

  State（陈述）：给出简短的事实性答案，无需解释。

• Describe: give a detailed account of observations or trends.

  Describe（描述）：详细叙述观察结果或趋势。

• Explain: give reasons for why something happens, using scientific ideas.

  Explain（解释）：用科学原理解释某事发生的原因。

• Compare: give similarities and differences between two things.

  Compare（比较）：给出两事物的相似点和不同点。

• Calculate: show working and give your answer with units.

  Calculate（计算）：展示过程并给出带单位的答案。

• Suggest: use your knowledge in a new or unfamiliar context.

  Suggest（建议）：在新的或不熟悉的背景下运用你的知识。

For calculation questions, always write the equation first, substitute the numbers, and then calculate the final answer. Include units in every step. For six-mark extended response questions, plan your answer into clear paragraphs and use scientific terminology accurately.

对于计算题，务必先写出方程，再代入数字，最后计算答案。每一步都要带上单位。对于六分的扩展作答问题，将答案规划为清晰的段落，并准确使用科学术语。

Past papers are the most effective revision tool. After completing a paper, mark it honestly and identify the command words you misunderstood. Keep an error log and review it before the final examination.

历年真题是最有效的复习工具。完成一套试卷后，诚实地批改，并找出你误读的指令词。建立错题本，在最终考试前复习它。

Finally, read the question carefully. Many marks are lost because students answer a different question from the one asked. Underline key words, cross out wrong ideas in multiple-choice questions, and always check that your answer matches the number of marks available.

最后，请仔细审题。许多失分是因为学生回答了与题目不同的问题。在题目上圈出关键词，在多选选择题中排除错误选项，并始终检查你的答案是否与分值匹配。

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