📚 IGCSE Edexcel Science Revision Guide | IGCSE Edexcel 科学复习指南
This comprehensive revision guide is designed for students preparing for the Edexcel IGCSE Science examinations. It covers the essential topics across Biology, Chemistry, and Physics, focusing on the key concepts, common misconceptions, and exam techniques that will help you achieve your target grade. Whether you are studying for the Double Award or the separate Sciences, this guide breaks down complex ideas into clear, manageable sections with worked examples and practice questions.
本复习指南专为准备 Edexcel IGCSE 科学考试的学生设计。它涵盖了生物、化学和物理的核心主题，重点关注关键概念、常见误解和考试技巧，帮助你达成目标成绩。无论你是学习双奖证书还是独立科学科目，本指南都将复杂的概念分解为清晰、可管理的模块，并提供例题和练习题。
1. Cell Structure and Organisation | 细胞结构与组织
All living organisms are made of cells. In the Edexcel IGCSE syllabus, you must be able to compare animal and plant cells, identify the functions of organelles, and understand the differences between eukaryotic and prokaryotic cells.
所有生物体都由细胞组成。在 Edexcel IGCSE 课程中，你必须能够比较动物细胞和植物细胞，识别细胞器的功能，并理解真核细胞与原核细胞之间的差异。
- Animal cells contain a nucleus, cytoplasm, cell membrane, mitochondria, and ribosomes.
- 动物细胞包含细胞核、细胞质、细胞膜、线粒体和核糖体。
- Plant cells additionally have a cell wall, chloroplasts, and often a permanent vacuole.
- 植物细胞额外具有细胞壁、叶绿体，并通常含有永久性液泡。
- Bacteria are prokaryotic: they lack a true nucleus and membrane-bound organelles.
- 细菌是原核生物：它们缺乏真正的细胞核和膜结合的细胞器。
Plant cells only: cell wall (cellulose), chloroplasts, permanent vacuole.
植物细胞独有：细胞壁（纤维素）、叶绿体、永久性液泡。
se the formula: magnification = image size ÷ actual size. Ensure your units are consistent — convert millimetres to micrometres by multiplying by 1000.
计算放大倍数时，务必使用公式：放大倍数 = 图像大小 ÷ 实际大小。确保单位一致——将毫米转换为微米时乘以 1000。
2. Movement of Substances | 物质的运动
Diffusion, osmosis, and active transport are three processes that move substances across cell membranes. You need to understand their differences and be able to describe practical investigations.
扩散、渗透和主动运输是物质穿过细胞膜的三种过程。你需要理解它们的区别，并能描述实际调查研究。
- Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient, until equilibrium is reached. It is a passive process.
- 扩散是粒子从高浓度区域向低浓度区域沿浓度梯度的净运动，直到达到平衡。这是一个被动过程。
- Osmosis is the diffusion of water molecules across a partially permeable membrane from a dilute solution (high water potential) to a concentrated solution (low water potential).
- 渗透是水分子通过部分渗透性膜从稀溶液（高水势）向浓溶液（低水势）的扩散。
- Active transport moves substances against the concentration gradient. It requires energy from respiration and involves carrier proteins in the membrane.
- 主动运输逆浓度梯度移动物质。它需要呼吸作用提供的能量，并涉及膜中的载体蛋白。
A typical exam question asks: "Explain why wilting occurs when a plant is placed in a concentrated salt solution." Answer: Water leaves the plant cells by osmosis, the vacuole shrinks, the cytoplasm pulls away from the cell wall, and the cells become flaccid, so the plant loses turgor and wilts.
一个典型的考试问题：“解释为什么将植物放入浓盐溶液中会发生萎蔫。” 答案：水通过渗透离开植物细胞，液泡缩小，细胞质与细胞壁分离，细胞变得松弛，因此植物失去膨压而萎蔫。
3. Enzymes and Biological Reactions | 酶与生物反应
Enzymes are biological catalysts that speed up chemical reactions without being used up. They are proteins with a specific three-dimensional shape, including an active site that binds to a substrate.
酶是生物催化剂，能加速化学反应而自身不被消耗。它们是具有特定三维形状的蛋白质，包括与底物结合的活性位点。
- The "lock and key" model describes how the substrate fits exactly into the enzyme's active site.
- “锁钥模型”描述了底物如何恰好适合酶的活性位点。
- Higher temperature increases reaction rate until the optimum, then the enzyme denatures as the active site changes shape.
- 温度升高会增加反应速率直到最适温度，然后酶因活性位点形状改变而变性。
- Extreme pH values also denature enzymes. Most human enzymes work best at pH 7, but pepsin works at pH 2.
- 极端 pH 值也会使酶变性。大多数人体酶在 pH 7 时最佳，但胃蛋白酶在 pH 2 时起作用。
Practical investigation: test the effect of pH on the breakdown of starch by amylase. Use iodine solution to indicate when starch is no longer present.
实际调查：测试 pH 对淀粉酶分解淀粉的影响。使用碘溶液指示淀粉何时不再存在。
| pH | 1 | 4 | 7 | 10 |
| Time for starch to disappear (min) | >10 | 8 | 2 | >10 |
| Result | Very slow | Slow | Fast | Very slow |
The optimum pH for amylase is around 7.
淀粉酶的最适 pH 约为 7。
4. Plant Nutrition and Transport | 植物营养与运输
Photosynthesis is the process by which plants convert light energy into chemical energy. The word equation is:
光合作用是植物将光能转化为化学能的过程。其文字方程式为：
carbon dioxide + water → glucose + oxygen
二氧化碳 + 水 → 葡萄糖 + 氧气
Factors affecting photosynthesis include light intensity, carbon dioxide concentration, and temperature. The limiting factor is the one that is in shortest supply.
影响光合作用的因素包括光照强度、二氧化碳浓度和温度。限制因素是供应最不足的那个因素。
- Xylem transports water and mineral ions from roots to leaves; it consists of dead, hollow vessels with lignified walls.
- 木质部将水和矿物质离子从根部输送到叶片；它由具有木质化壁的死而中空的导管组成。
- Phloem transports sucrose and amino acids from source to sink (translocation); it contains living sieve tubes and companion cells.
- 韧皮部将蔗糖和氨基酸从源运输到库（转运）；它包含活的筛管和伴胞。
Leaf structure adaptations: large surface area, thin, chloroplasts near the upper surface, stomata for gas exchange, and a waxy cuticle to prevent water loss.
叶片结构适应性：大表面积、薄、叶绿体靠近上表面、气孔用于气体交换，以及防止水分流失的蜡质角质层。
5. Human Nutrition and Digestion | 人类营养与消化
Your diet must contain carbohydrates, proteins, lipids, vitamins, minerals, water, and dietary fibre. Each nutrient has a specific function.
你的饮食必须含有碳水化合物、蛋白质、脂质、维生素、矿物质、水和膳食纤维。每种营养素都有特定的功能。
| Nutrient | Function | Source |
| Carbohydrates | Provide energy | Rice, bread, potatoes |
| Proteins | Growth and repair | Meat, beans, eggs |
| Lipids | Insulation, energy storage | Butter, oil, nuts |
| Vitamin C | Healthy gums, skin | Citrus fruits |
| Iron | Haemoglobin formation | Red meat, spinach |
Digestion involves mechanical and chemical breakdown. Amylase breaks starch into maltose; protease breaks proteins into amino acids; lipase breaks lipids into fatty acids and glycerol. Bile, produced by the liver and stored in the gallbladder, emulsifies fats and neutralises stomach acid.
消化涉及机械分解和化学分解。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。肝脏产生并储存在胆囊中的胆汁能乳化脂肪并中和胃酸。
6. Atomic Structure and the Periodic Table | 原子结构与元素周期表
An atom consists of a nucleus containing protons and neutrons, surrounded by electrons in shells. The atomic number is the number of protons; the mass number is protons plus neutrons.
原子由包含质子和中子的原子核以及围绕核的电子壳层组成。原子序数是质子数；质量数是质子数加中子数。
For an atom: number of protons = number of electrons.
对于原子：质子数 = 电子数。
- Group 1 metals (alkali metals) react vigorously with water to form hydroxides and hydrogen gas.
- 第 1 族金属（碱金属）与水剧烈反应，生成氢氧化物和氢气。
- Group 7 elements (halogens) gain one electron to form -1 ions. Reactivity decreases down the group.
- 第 7 族元素（卤素）获得一个电子形成 -1 离子。反应活性向下递减。
- Group 0 elements (noble gases) have full outer shells — they are unreactive.
- 第 0 族元素（稀有气体）具有满外层电子壳层——它们不活泼。
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. Chlorine-35 and chlorine-37 are both isotopes of chlorine.
同位素是同一元素的原子，具有相同质子数但不同中子数。氯-35 和氯-37 都是氯的同位素。
7. Chemical Bonding and Structure | 化学键与结构
There are three main types of chemical bonding: ionic, covalent, and metallic. The type of bond determines the properties of the substance.
化学键主要有三种类型：离子键、共价键和金属键。键的类型决定了物质的性质。
- Ionic bonding occurs between a metal and a non-metal. Electrons are transferred to form oppositely charged ions. Example: sodium chloride (NaCl).
- 离子键发生在金属和非金属之间。电子转移形成带相反电荷的离子。例如：氯化钠（NaCl）。
- Covalent bonding occurs between non-metals. Electrons are shared to achieve a full outer shell. Example: methane (CH₄).
- 共价键发生在非金属之间。电子共享以实现满外层电子壳层。例如：甲烷（CH₄）。
- Metallic bonding involves a lattice of positive ions in a sea of delocalised electrons.
- 金属键涉及沉浸在离域电子海中的正离子晶格。
Ionic compounds have high melting points and conduct electricity when molten or dissolved. Covalent molecular substances have low melting points and do not conduct electricity. Giant covalent structures (diamond, graphite, silicon dioxide) have high melting points; diamond is hard, while graphite is soft and conducts electricity.
离子化合物具有高熔点，在熔融或溶解时导电。共价分子物质具有低熔点且不导电。巨型共价结构（金刚石、石墨、二氧化硅）具有高熔点；金刚石很硬，而石墨质软且导电。
8. Chemical Calculations and The Mole | 化学计算与摩尔
e is a unit for the amount of substance. One mole contains 6.02 × 10²³ particles (Avogadro' be able to calculate molar mass and use it to determine masses of reactants and products.
摩尔是物质的量的单位。一摩尔包含 6.02 × 10²³ 个粒子（阿伏伽德罗常数）。你需要能够计算摩尔质量，并利用它来确定反应物和产物的质量。
moles = mass (g) ÷ molar mass (g mol⁻¹)
摩尔数 = 质量（克）÷ 摩尔质量（克·摩尔⁻¹）
Concentration is often given in mol/dm³. The equation is:
浓度通常以摩尔/立方分米（mol/dm³）给出。公式为：
concentration (mol/dm³) = number of moles ÷ volume (dm³)
浓度（摩尔/立方分米）= 摩尔数 ÷ 体积（立方分米）
In a titration calculation, always balance the equation first, then convert known quantities to moles, use the mole ratio to find the unknown, and finally calculate the required value.
在滴定计算中，首先平衡方程式，然后将已知量转换为摩尔数，使用摩尔比求出未知量，最后计算所需值。
9. Electricity and Circuits | 电与电路
the energy transferred per coulomb of charge. Resistance opposes the flow of current. Ohm's law states that voltage = current × resistance.
电流是电荷的流动。电势差（电压）是每库仑电荷转移的能量。电阻阻碍电流流动。欧姆定律指出：电压 = 电流 × 电阻。
V = I × R
电压 = 电流 × 电阻
- In a series circuit, the same current flows through all components; voltages across components add up.
- 在串联电路中，所有组件通过相同的电流；各组件上的电压相加。
- In a parallel circuit, the voltage across each branch is the same; currents through branches add up.
- 在并联电路中，每个支路两端的电压相同；各支路电流相加。
LDR (light-dependent resistor) has a resistance that decreases as light intensity increases. Thermistor has a resistance that decreases as temperature increases. These are common in question contexts.
光敏电阻（LDR）的电阻随光照强度增加而减小。热敏电阻的电阻随温度升高而减小。这些常在问题情境中出现。
10. Forces and Motion | 力与运动
Speed, velocity, and acceleration are fundamental quantities. Velocity is speed in a given direction; acceleration is the rate of change of velocity.
速率、速度和加速度是基本量。速度是给定方向上的速率；加速度是速度的变化率。
acceleration = (final velocity - initial velocity) ÷ time
加速度 =（最终速度 - 初始速度）÷ 时间
Newton' ht is the force on an object due to gravity: weight = mass × gravitational field strength.
牛顿第二定律：力 = 质量 × 加速度。重力是物体在重力场中受到的力：重力 = 质量 × 重力场强度。
d system, the total momentum before a collision equals the total momentum after the collision.
动量 = 质量 × 速度。在封闭系统中，碰撞前总动量等于碰撞后总动量。
Be careful with distance-time graphs: a horizontal line means the object is stationary; a steeper gradient means a faster speed. On a velocity-time graph, the gradient is acceleration and the area under the graph is distance travelled.
注意位移-时间图像：水平线表示物体静止；梯度越陡表示速度越快。在速度-时间图像上，梯度是加速度，图像下的面积是行驶距离。
11. Energy Transfers and Transformations | 能量传递与转化
Energy is conserved — it cannot be created or destroyed, only transferred or transformed. Common energy stores include kinetic, gravitational potential, elastic potential, chemical, thermal, and nuclear.
能量是守恒的——它不能被创造或毁灭，只能被传递或转化。常见的能量储存包括动能、重力势能、弹性势能、化学能、热能和核能。
kinetic energy (J) = ½ × mass (kg) × velocity² (m²/s²)
动能（焦耳）= ½ × 质量（千克）× 速度²（米²/秒²）
tional potential energy (J) = mass (kg) × gravitational field strength (N/kg) × height (m)
重力势能（焦耳）= 质量（千克）× 重力场强度（牛顿/千克）× 高度（米）
. Efficiency = useful output energy ÷ total input energy, often expressed as a percentage.
桑基图表示能量传递：箭头的宽度与能量大小成正比。效率 = 有用输出能量 ÷ 总输入能量，通常以百分比表示。
12. Radioactivity and Particles | 放射性与粒子
Atoms of the same element can be unstable and emit radiation. There are three types of nuclear radiation: alpha (α), beta (β), and gamma (γ).
同一元素的原子可能不稳定，会发射辐射。核辐射有三种类型：α 射线、β 射线和 γ 射线。
- Alpha particles are helium nuclei (2 protons, 2 neutrons). They are highly ionising, stopped by paper, and have a short range.
- α 粒子是氦核（2 个质子，2 个中子）。它们电离能力强，能被纸阻挡，射程短。
- Beta particles are fast-moving electrons. They are moderately ionising, stopped by a few millimetres of aluminium.
- β 粒子是高速电子。它们电离能力中等，能被几毫米厚的铝阻挡。
- Gamma rays are electromagnetic waves. They are weakly ionising, stopped by thick lead or concrete.
- γ 射线是电磁波。它们电离能力弱，需要厚铅或混凝土阻挡。
During alpha decay, the mass number decreases by 4 and the atomic number decreases by 2. During beta decay, a neutron changes into a proton and an electron is emitted, so the mass number stays the same and the atomic number increases by 1.
在 α 衰变过程中，质量数减少 4，原子序数减少 2。在 β 衰变过程中，一个中子变成一个质子并发射一个电子，所以质量数不变，原子序数增加 1。
Half-life is the time taken for half of the radioactive nuclei in a sample to decay. It can be calculated from a decay graph by finding the time taken for the count rate to halve.
半衰期是样品中一半放射性核衰变所需的时间。可以通过衰变图找到计数率减半所需的时间来计算。
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