📚 IGCSE Edexcel Science: Key Revision Guide | IGCSE Edexcel 科学：核心复习指南
The IGCSE Edexcel Science course covers biology, chemistry and physics, and rewards clear scientific knowledge, practical understanding and careful data handling. This revision guide condenses the most important ideas into manageable sections, with common pitfalls highlighted throughout. Use it alongside past papers and your own notes for best results.
IGCSE Edexcel 科学课程涵盖生物、化学和物理，重视清晰的科学知识、实验理解以及严谨的数据处理。本复习指南将最重要的概念浓缩成易于掌握的章节，并在全文中指出常见错误。请结合历年真题和你的笔记一起使用，效果最佳。
1. Biology: Cells and Organisation | 生物：细胞与组织结构
Everything in biology starts with cells. Plant and animal cells share essential features: a nucleus controls the cell, cytoplasm is where reactions happen, a cell membrane controls what enters and exits, and mitochondria release energy through respiration. Plant cells also have a rigid cell wall made of cellulose, chloroplasts for photosynthesis and a large permanent vacuole for support.
生物学的起点是细胞。动物细胞和植物细胞有共同的基本结构：细胞核控制细胞活动，细胞质是化学反应发生的场所，细胞膜控制物质进出，线粒体通过呼吸作用释放能量。植物细胞还拥有由纤维素构成的坚硬细胞壁、用于光合作用的叶绿体，以及起支持作用的大液泡。
Specialised cells are adapted for particular jobs. Red blood cells are biconcave discs to increase surface area and contain haemoglobin for oxygen transport. Root hair cells have long projections to absorb water and minerals from soil. Sperm cells have a flagellum for swimming and many mitochondria to provide energy.
特化细胞执行特定功能。红细胞呈双凹圆盘状以增大表面积，含有血红蛋白以运输氧气。根毛细胞有长突起，用于从土壤中吸收水分和矿物质。精子细胞拥有鞭毛用于游动，并有大量线粒体提供能量。
Biological organisation follows a clear hierarchy: cells form tissues, tissues form organs, and organs work together in organ systems. For example, muscle cells make up muscular tissue, which forms part of the stomach, and the stomach is part of the digestive system.
生物组织遵循清晰的层次：细胞形成组织，组织形成器官，器官协同工作构成器官系统。例如，肌肉细胞构成肌肉组织，肌肉组织组成胃的一部分，而胃是消化系统的一员。
2. Biology: Enzymes and Digestion | 生物：酶与消化
Enzymes are biological catalysts that speed up chemical reactions without being used up. They have an active site that fits a specific substrate, like a lock and key. Temperature and pH affect enzyme activity. At high temperatures, enzymes denature because the active site changes shape and can no longer bind the substrate.
酶是生物催化剂，能加快化学反应速率，但自身不被消耗。酶的活性位点与特定底物结合，就像锁和钥匙一样。温度和 pH 值会影响酶活性。温度过高时，酶会变性，因为活性位点形状改变，无法再与底物结合。
The digestive system breaks down large insoluble molecules into small soluble ones. Amylase breaks starch into sugars, protease breaks proteins into amino acids, and lipase breaks fats into fatty acids and glycerol. These products are absorbed into the bloodstream mainly in the small intestine.
消化系统将大的不溶性分子分解为小的可溶性分子。淀粉酶将淀粉分解为糖，蛋白酶将蛋白质分解为氨基酸，脂肪酶将脂肪分解为脂肪酸和甘油。这些产物主要在小肠中被吸收进入血液。
Enzyme experiments often involve temperature control and measuring product formation. In the starch-and-iodine test, iodine solution turns blue-black in the presence of starch; the faster the colour stays orange, the faster the enzyme has worked. Always repeat experiments to calculate a mean and identify anomalies.
酶实验通常需要控制温度并测量产物的生成。在淀粉和碘液测试中，碘液遇到淀粉会变蓝黑色；颜色保持橙色越快，说明酶作用越快。务必重复实验以计算平均值并识别异常数据。
3. Biology: Transport in Plants and Animals | 生物：动植物中的运输
Plants have two transport systems. Xylem carries water and minerals from roots to leaves, and phloem carries sugars from leaves to growing and storage areas. Transpiration is the loss of water vapour from leaves; it helps pull water up through the xylem in a continuous column.
植物有两套运输系统。木质部将水和矿物质从根部输送到叶片，韧皮部将糖从叶片输送到生长和储藏部位。蒸腾作用是叶片散失水蒸气的过程，它帮助水在木质部中形成连续水柱并被向上牵引。
Factors that increase transpiration include higher temperature, stronger wind, lower humidity and brighter light. To reduce water loss, plants may have small leaves, thick cuticles, sunken stomata or hair on leaf surfaces. Stomata open and close to control gas exchange and water loss.
促进蒸腾作用的因素包括温度升高、风力增强、湿度降低和光照增强。为减少水分散失，植物可能拥有小叶片、厚角质层、下陷气孔或叶片表面的绒毛。气孔通过开闭来控制气体交换和水分损失。
In animals, the circulatory system transports oxygen, nutrients, carbon dioxide and hormones. The heart pumps blood through arteries, capillaries and veins. Arteries carry blood away from the heart at high pressure, veins return blood with valves, and capillaries allow exchange of substances with tissues.
在动物中，循环系统运输氧气、营养物质、二氧化碳和激素。心脏将血液泵入动脉、毛细血管和静脉。动脉在高压下将血液带离心脏，静脉带有瓣膜并将血液送回心脏，毛细血管则允许物质与组织进行交换。
The components of blood are plasma, red blood cells, white blood cells and platelets. Plasma is the liquid that carries dissolved substances. White blood cells protect against infection, and platelets help blood to clot at wound sites.
血液的组成包括血浆、红细胞、白细胞和血小板。血浆是运输溶解物质的液体。白细胞抵御感染，血小板帮助伤口处血液凝固。
4. Chemistry: Atomic Structure and Bonding | 化学：原子结构与化学键
An atom is the smallest unit of an element. It contains 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.
原子是元素的最小单位，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。原子序数是质子数，质量数是质子数和中子数之和。
Atoms form bonds to achieve a stable outer electron arrangement. In ionic bonding, electrons are transferred from metals to non-metals, creating oppositely charged ions that attract each other. In covalent bonding, atoms share pairs of electrons. Metallic bonding involves delocalised electrons moving among positive ions.
原子通过形成化学键以获得稳定的外层电子排布。在离子键中，电子从金属转移到非金属，形成带相反电荷的离子并相互吸引。在共价键中，原子共享电子对。金属键涉及在正离子之间自由移动的离域电子。
Ionic compounds have high melting points and conduct electricity when molten or dissolved because ions are free to move. Covalent compounds often have low melting points and usually do not conduct electricity. Metals are malleable and conduct electricity because their delocalised electrons can move.
离子化合物熔点高，在熔融或溶解时能导电，因为离子可以自由移动。共价化合物通常熔点低，一般不能导电。金属具有延展性且能导电，因为离域电子可以移动。
Chemical equations must be balanced. For example, the reaction between hydrogen and oxygen to form water is:
2 H₂ + O₂ → 2 H₂O
Check that the number of atoms of each element is the same on both sides. Ionic equations show only the reacting particles; spectator ions are omitted.
化学方程式必须配平。例如，氢气和氧气生成水的反应为：
2 H₂ + O₂ → 2 H₂O
检查方程式两边每种元素的原子数是否相同。离子方程式只显示参与反应的粒子，旁观离子被省略。
5. Chemistry: Acids, Bases and Salts | 化学：酸、碱与盐
Acids release hydrogen ions (H⁺) in water, while bases are substances that neutralise acids. Bases that are soluble in water are called alkalis, and they release hydroxide ions (OH⁻). The pH scale runs from 0 to 14; pH 7 is neutral, below 7 is acidic and above 7 is alkaline.
酸在水中释放氢离子（H⁺），而碱是能中和酸的物质。可溶于水的碱称为碱液，它们释放氢氧根离子（OH⁻）。pH 值范围是 0 到 14；pH 为 7 表示中性，低于 7 为酸性，高于 7 为碱性。
The reaction between an acid and a base is called neutralisation:
H⁺ + OH⁻ → H₂O
For example, hydrochloric acid reacts with sodium hydroxide to produce sodium chloride and water: HCl + NaOH → NaCl + H₂O. Acid plus carbonate produces a salt, water and carbon dioxide.
酸与碱的反应称为中和反应：
H⁺ + OH⁻ → H₂O
例如，盐酸与氢氧化钠反应生成氯化钠和水：HCl + NaOH → NaCl + H₂O。酸与碳酸盐反应生成盐、水和二氧化碳。
To prepare a soluble salt, you can react an acid with an excess of insoluble solid, filter off the excess solid, and evaporate the filtrate. Antacid tablets contain bases such as magnesium hydroxide to neutralise excess stomach acid.
制备可溶性盐时，可以用过量不溶性固体与酸反应，过滤去除多余固体，再蒸发滤液。抗酸药片中含有氢氧化镁等碱，可中和过多的胃酸。
6. Chemistry: Electrolysis | 化学：电解
Electrolysis is the breakdown of an ionic compound (an electrolyte) when molten or dissolved in water, using an electric current. Positive ions move to the negative electrode (cathode) and are reduced, while negative ions move to the positive electrode (anode) and are oxidised.
电解是指离子化合物在熔融或溶于水时，通过电流将其分解的过程。正离子向阴极（负极）移动并被还原，而负离子向阳极（正极）移动并被氧化。
During the electrolysis of molten lead bromide, lead is produced at the cathode and bromine at the anode. In aqueous solutions, the ions of water compete with the solute ions. At the cathode, hydrogen is released unless the metal is below hydrogen in the reactivity series. At the anode, oxygen is released unless the solution contains halide ions.
在熔融溴化铅的电解中，阴极产生铅，阳极产生溴。在水溶液中，水产生的离子会与溶质离子竞争。在阴极，除非金属比氢活泼性低，否则会释放氢气。在阳极，除非溶液中含有卤离子，否则会释放氧气。
The amount of substance produced depends on the charge passed, which equals current multiplied by time:
charge (C) = current (A) × time (s)
Electroplating uses electrolysis to coat an object with a thin layer of metal, such as silver or copper, to improve appearance or reduce corrosion.
产生的物质质量取决于通过的电量，电量等于电流乘以时间：
电荷量（库仑）= 电流（安培）× 时间（秒）
电镀利用电解在物体表面镀上薄薄的金属层，如银或铜，以改善外观或减少腐蚀。
7. Physics: Forces and Motion | 物理：力与运动
Speed is the distance travelled per unit time. Average speed can be calculated using:
speed = distance ÷ time
Velocity is speed in a given direction. Acceleration is the change in velocity per unit time, with the equation: acceleration = change in velocity ÷ time. A distance-time graph shows speed through its gradient; a straight horizontal line means stationary.
速率是单位时间内通过的距离。平均速率可以用公式计算：
速率 = 距离 ÷ 时间
速度是带有方向的速率。加速度是单位时间内速度的变化量，公式为：加速度 = 速度变化量 ÷ 时间。位移-时间图中直线的斜率表示速率；水平的直线表示静止。
A resultant force changes an object’s motion. Newton’s first law says that if the resultant force is zero, a moving object keeps moving at constant velocity and a stationary object remains stationary. Newton’s second law gives:
force = mass × acceleration
合力改变物体的运动状态。牛顿第一定律指出，若合力为零，运动的物体保持匀速直线运动，静止的物体保持静止。牛顿第二定律给出：
力 = 质量 × 加速度
The weight of an object is the gravitational force on it, calculated as mass multiplied by gravitational field strength (g, approximately 9.8 N/kg). Friction and air resistance always oppose motion. Terminal velocity is reached when the driving force equals air resistance, so the acceleration becomes zero.
物体的重力是作用在其上的引力，计算公式为质量乘以重力场强度（g 约为 9.8 N/kg）。摩擦力和空气阻力总是阻碍运动。当驱动力等于空气阻力时，物体达到终端速度，此时加速度为零。
8. Physics: Energy and Electricity | 物理：能量与电学
Energy is measured in joules (J). A useful equation for kinetic energy is:
kinetic energy = ½ × mass × velocity²
Gravitational potential energy is calculated as: GPE = mass × g × height. Energy cannot be created or destroyed, only transferred from one store to another. In a closed system, total energy is conserved.
能量的单位是焦耳（J）。动能的计算公式为：
动能 = ½ × 质量 × 速度²
重力势能的计算公式为：GPE = 质量 × g × 高度。能量既不能凭空产生，也不能被消灭，只能从一种储存形式转移到另一种。在封闭系统中，总能量守恒。
Electric current is the flow of charge, measured in amperes. Potential difference (voltage) is the energy transferred per unit charge, measured in volts. Resistance, measured in ohms, opposes current. Ohm’s law states:
voltage = current × resistance
电流是电荷的流动，单位是安培。电势差（电压）是单位电荷所转移的能量，单位是伏特。电阻的单位是欧姆，它阻碍电流。欧姆定律表明：
电压 = 电流 × 电阻
In series circuits, the same current flows through each component and voltages add up. In parallel circuits, the voltage across each branch is the same and currents add where branches rejoin. Circuit diagrams must be drawn with standard symbols, and switch positions must be clearly labelled.
在串联电路中，每个元件中流过相同的电流，各电压相加。在并联电路中，每个支路两端电压相同，支路电流在汇合处相加。电路图必须使用标准符号绘制，并清晰标注开关位置。
9. Physics: Waves and Radioactivity | 物理：波与放射性
Waves transfer energy without transferring matter. All waves have frequency, wavelength, amplitude and speed. The wave equation is:
wave speed = frequency × wavelength
Transverse waves vibrate perpendicular to the direction of energy transfer; examples include light and waves on a string. Longitudinal waves vibrate parallel to the direction of energy transfer; sound is a longitudinal wave.
波传递能量但不传递物质。所有波都具有频率、波长、振幅和波速。波的方程为：
波速 = 频率 × 波长
横波的振动方向垂直于能量传递方向，例如光和绳上的波。纵波的振动方向平行于能量传递方向，声波是纵波。
Radioactivity involves the emission of ionising radiation from unstable nuclei. Alpha particles are helium nuclei (²He), beta particles are fast-moving electrons, and gamma rays are high-energy electromagnetic waves. Alpha is the most ionising but least penetrating; gamma is the most penetrating:
α (⁴₂He) → β (⁰₋₁e) → γ (electromagnetic)
放射性是原子核不稳定时发射电离辐射的过程。α 粒子是氦核（⁴₂He），β 粒子是高速电子，γ 射线是高能电磁波。α 电离能力最强但穿透力最弱；γ 穿透力最强。
Half-life is the time taken for half the radioactive nuclei to decay. It cannot be changed by temperature or pressure. Radioactive tracers, dating and radiotherapy all rely on predictable half-lives, but exposure to ionising radiation must be minimised.
半衰期是放射性核素半数衰变所需的时间，不受温度和压力影响。放射性示踪剂、年代测定和放射治疗都依赖可预测的半衰期，但应尽量减少电离辐射的暴露。
10. Experimental Skills and Data Analysis | 实验技能与数据分析
Scientific investigations require careful planning. You should identify the independent variable (the one you change), the dependent variable (the one you measure) and the control variables (those you keep constant). A valid experiment changes only one factor at a time.
科学探究需要仔细规划。你应该识别自变量（你要改变的变量）、因变量（你要测量的变量）和控制变量（你要保持不变的变量）。一个有效的实验每次只改变一个因素。
When reading measurements, record values to one decimal place if the scale allows, and always include units. Repeat measurements at least three times and calculate the mean, ignoring any anomalous results. Anomalies are mistakes or unusual readings that do not fit the pattern.
读取测量值时，如果刻度允许，应记录到一位小数，并始终带上单位。每组测量至少重复三次，计算平均值，并忽略异常结果。异常值是与规律不符的错误或特殊读数。
Graphs are essential for analysing data. Plot independent data on the x-axis and dependent data on the y-axis. Draw a line of best fit that reflects the trend, not necessarily through all points. If the relationship is a straight line through the origin, the variables are directly proportional.
作图对数据分析至关重要。自变量画在 x 轴上，因变量画在 y 轴上。绘制一条反映趋势的最佳拟合线，不一定要穿过所有点。如果关系是过原点的直线，则变量成正比。
Conclusions must link the evidence back to the hypothesis, not just describe the graph. Evaluate the method by discussing uncertainties, limitations and possible improvements, such as using sensors instead of human timing.
结论必须将证据与假设联系起来，而不仅仅是描述图像。评估方法时要讨论不确定度、局限性以及可能的改进，例如使用传感器代替人工计时。
11. Common Mistakes in IGCSE Science Exams | IGCSE 科学考试常见错误
One major mistake is confusing mass with weight. Mass is the amount of matter measured in kilograms; weight is a force measured in newtons. Another error is mixing up units, for example writing cm when the question expects m, or forgetting to convert minutes to seconds.
主要错误之一是混淆质量与重量。质量是物质的多少，单位是千克；重量是力，单位是牛顿。另一个错误是单位混淆，例如题目要求米却写成厘米，或者忘记将分钟转换为秒。
In biology, students often forget the word ‘active site’ when explaining how an enzyme works, or say genes are ‘in DNA’ instead of the chromosome. In chemistry, unbalanced equations lose marks; always check atoms on both sides. In physics, forgetting to square the velocity in kinetic energy is very common.
在生物中，学生解释酶的作用时常忘记提及”活性位点”，或者说基因”在 DNA 中”而不说在染色体上。在化学中，未配平的方程式会失分；一定要检查两边原子数。在物理中，动能计算忘记将速度平方是非常常见的错误。
Writing final answers to more than one decimal place can also be wrong if the data are less precise. Always match the precision of your final answer to the measurements given. Finally, do not use vague terms like ‘it goes down’; use scientific language such as ‘decreases’ or ‘reduces’, and refer to the variable by name.
如果数据精度不足，最终答案写成超过一位小数也可能出错。最终答案的精度要始终与所给测量值一致。最后，不要使用模糊的说法如”它下去了”，应该使用科学语言如”降低”或”减少”，并注明变量名称。
12. Exam Technique and Revision Strategy | 考试技巧与复习策略
Start by reading the question twice and highlighting command words: ‘State’ means give a short answer, ‘Describe’ means give a detailed account, and ‘Explain’ means give a reason with scientific evidence. Match the number of marks to the number of points; a 3-mark question usually needs three distinct statements.
先读两遍题目并圈出指令词：”State”表示给出简短答案，”Describe”表示详细叙述，”Explain”表示给出带有科学证据的原因。将分值与要点数量对应；3 分题通常需要三个独立的要点。
For calculations, show every step with the formula and substitution even if the final answer is wrong; you can still earn method marks. Write numbers with correct units and check significant figures. For practical-based questions, state why a step is done, not just what is done.
对于计算题，即使最终答案错误，也要写出公式和代入步骤，这样仍可得分。数字必须带正确单位并检查有效数字。对实验类问题，要写出某个步骤”为什么”这样做，而不仅仅是”做什么”。
Use the revision period actively. Create flashcards for definitions such as diffusion, osmosis, atomic number and half-life. Draw labelled diagrams from memory for the heart, plant cell, eye or circuit symbols. Practice past papers under timed conditions, then review every error and write the correct answer in your own words.
复习阶段要主动学习。制作定义闪卡，如扩散、渗透、原子序数和半衰期。凭记忆绘制带有标注的图，如心脏、植物细胞、眼睛或电路符号。在限时条件下练习真题，然后复习每个错误，并用你自己的话写出正确答案。
Finally, stay calm and manage time. A good pace is about one mark per minute. If a question is difficult, leave a clear gap and return to it later. Confidence comes from consistent practice and understanding, not from memorising model answers alone.
最后，保持冷静并合理管理时间。合理的节奏大约是每分钟做 1 分。如果某道题比较难，先留出清晰空位，之后回头再做。信心来自持续练习和真正理解，而不仅仅是记忆模板答案。
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