📚 IGCSE WJEC Science: End-of-Term Revision Guide | IGCSE WJEC 科学：期末复习提纲
This revision guide consolidates the most important concepts from the WJEC IGCSE Science syllabus, covering Biology, Chemistry and Physics. It is designed to help you focus your final revision, spot common exam errors, and build confidence in applying knowledge to unfamiliar contexts. Each section pairs key facts with clear explanations so you can review actively and effectively.
本复习提纲整合了 WJEC IGCSE 科学课程中最核心的概念，涵盖生物、化学和物理。旨在帮助你聚焦期末复习，发现常见考试易错点，并建立将知识应用于陌生情境的信心。每个部分都将关键事实与清晰解释配对，让你能够主动、高效地复习。
1. Biological Molecules and Enzymes | 生物分子与酶
Carbohydrates are made of simple sugars such as glucose and provide energy for cells. Starch is a large polymer of glucose used for energy storage in plants.
碳水化合物由葡萄糖等单糖组成，为细胞提供能量。淀粉是葡萄糖的多聚体，是植物储存能量的形式。
Proteins are built from amino acids and are essential for growth and repair. Enzymes are protein catalysts that speed up metabolic reactions without being used up.
蛋白质由氨基酸构成，对生长和修复至关重要。酶是蛋白质催化剂，能够加快代谢反应而自身不被消耗。
Each enzyme has an active site with a specific shape that fits only one substrate, described by the lock-and-key hypothesis. High temperatures denature enzymes by changing the shape of the active site permanently.
每种酶都有一个形状特定的活性部位，只能与一种底物结合，这可以用锁钥假说解释。高温会使酶变性，永久改变活性部位的形状。
Investigating enzyme activity often involves measuring how pH or temperature affects the rate of breakdown of starch by amylase. The rate increases up to an optimum and then decreases sharply.
研究酶活性通常涉及测量 pH 或温度如何影响淀粉酶分解淀粉的速率。速率会升高至最适点，然后急剧下降。
- Benedict's test: turns brick-red when reducing sugars are present.
本尼迪克特试验：有还原糖时呈砖红色。 - Iodine test: turns blue-black with starch.
碘液试验：遇淀粉变蓝黑色。 - Biuret test: turns purple for proteins.
双缩脲试验：遇到蛋白质变紫色。
2. Cells, Tissues and Transport | 细胞、组织与运输
All living things are composed of cells. Animal cells contain a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells also have a rigid cell wall, a large permanent vacuole and chloroplasts for photosynthesis.
所有生物都由细胞组成。动物细胞含有细胞核、细胞质、细胞膜、线粒体和核糖体。植物细胞还有坚硬的细胞壁、大型液泡和进行光合作用的叶绿体。
Specialised cells have adaptations that help them perform specific functions. For example, root hair cells have a large surface area to absorb water, and red blood cells have no nucleus to carry more haemoglobin.
特化细胞具有适应特定功能的特征。例如，根毛细胞有巨大表面积以吸收水分，红细胞没有细胞核以便携带更多血红蛋白。
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. Osmosis is the diffusion of water through a partially permeable membrane, moving from a dilute solution to a more concentrated one.
扩散是粒子从高浓度区域向低浓度区域的净移动。渗透是水通过半透膜的扩散，从稀溶液向浓溶液移动。
Active transport moves substances against the concentration gradient using energy from respiration. The sodium–potassium pump in nerve cells is a key example.
主动运输利用呼吸作用提供的能量，逆浓度梯度运输物质。神经细胞中的钠钾泵是一个典型例子。
In plants, xylem vessels carry water and dissolved minerals from roots to leaves. Phloem tubes transport sucrose and amino acids both up and down the plant.
植物中，木质部导管将水和溶解的矿物质从根部运送到叶片。韧皮部管将蔗糖和氨基酸在植物体内上下运输。
3. Genetics and Evolution | 遗传与进化
DNA is a double helix containing genes, which are sections of DNA that code for specific proteins. Each gene exists in alternative forms called alleles.
DNA 是双螺旋结构，包含基因——编码特定蛋白质的 DNA 片段。每个基因有不同形式，称为等位基因。
In sexual reproduction, gametes are produced by meiosis, which halves the chromosome number so that fertilisation restores the full set. Mitosis produces genetically identical cells for growth and repair.
有性生殖中，配子通过减数分裂产生，染色体数目减半，受精后恢复全套染色体。有丝分裂产生遗传相同的细胞，用于生长和修复。
Monohybrid inheritance can be predicted using Punnett squares. If a homozygous dominant parent (TT) is crossed with a homozygous recessive parent (tt), all offspring will be heterozygous (Tt) and show the dominant trait.
单基因遗传可以通过庞纳特方格预测。如果纯合显性亲本（TT）与纯合隐性亲本（tt）杂交，所有后代都是杂合子（Tt），表现显性性状。
Mutations are random changes in DNA sequence. Natural selection states that individuals with advantageous variants are more likely to survive, reproduce and pass on their genes. Over generations, this leads to evolution.
突变是 DNA 序列的随机改变。自然选择指出，具有有利变异的个体更可能存活、繁殖并传递其基因。经过多代，这导致进化。
Selective breeding involves choosing parents with desired traits to produce offspring with enhanced characteristics. Genetic engineering transfers genes from one organism to another to introduce new features, such as human insulin produced by bacteria.
选择性育种是指选择具有所需性状的亲本来繁殖具有增强特征的后代。基因工程将一个生物体的基因转移到另一个生物体，以引入新特性，例如让细菌产生人胰岛素。
4. Atomic Structure and the Periodic Table | 原子结构与元素周期表
Atoms consist of a central nucleus containing protons and neutrons, surrounded by electrons arranged in shells. The atomic number tells you the number of protons, and the mass number is the total of protons and neutrons.
原子由中央原子核（含质子和中子）以及分层排布的电子组成。原子序数表示质子数，质量数是质子与中子之和。
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. Relative atomic mass is an average that takes isotope abundances into account.
同位素是质子数相同但中子数不同的同种元素原子。相对原子质量是考虑了同位素丰度的平均值。
Elements are arranged in the Periodic Table in order of increasing atomic number. Groups run vertically; elements in the same group have the same number of outer electrons and therefore similar chemical properties.
元素在周期表中按原子序数递增排列。竖列称为族；同族元素具有相同的最外层电子数，因此化学性质相似。
Group 1 metals (alkali metals) are very reactive, soft, and become more reactive down the group. Group 7 elements (halogens) are diatomic non-metals that react vigorously with metals, and reactivity decreases down the group.
第 1 族金属（碱金属）非常活泼、质软，且越往下越活泼。第 7 族元素（卤素）是双原子非金属，与金属剧烈反应，活泼性越往下越弱。
Noble gases (Group 0) are monatomic gases with full outer electron shells, making them extremely unreactive. The period number indicates the number of occupied electron shells.
稀有气体（第 0 族）是具有满层外电子的单原子气体，极不活泼。周期数表示已占用的电子层数。
5. Bonding, Structure and Properties | 键合、结构与性质
Ionic bonding occurs between metals and non-metals, where electrons are transferred from the metal to the non-metal. The resulting oppositely charged ions are held together by strong electrostatic forces in a giant ionic lattice.
离子键形成于金属和非金属之间，电子从金属转移到非金属。产生的正负离子在巨型离子晶格中通过强静电引力结合。
Ionic compounds have high melting and boiling points and conduct electricity only when molten or dissolved because the ions are free to move.
离子化合物具有高熔点和沸点，只有熔融或溶于水时才能导电，因为此时离子可以自由移动。
Covalent bonding involves sharing pairs of electrons between non-metal atoms. Simple molecular substances, like water or carbon dioxide, have strong covalent bonds within molecules but weak intermolecular forces, resulting in low melting points.
共价键涉及非金属原子之间共享电子对。简单分子物质（如水或二氧化碳）内部分子有强共价键，但分子间作用力弱，因此熔沸点低。
Giant covalent structures, such as diamond (each carbon bonded to four others) and graphite (layers of carbon with delocalised electrons), have very high melting points. Graphite conducts electricity due to its delocalised electrons.
巨型共价结构，如金刚石（每个碳原子与另外四个碳原子键合）和石墨（碳层与离域电子），具有极高熔点。石墨因具有离域电子而能导电。
Metallic bonding is a lattice of positive metal ions surrounded by a 'sea' of delocalised electrons. This allows metals to conduct heat and electricity and to be malleable.
金属键是正金属离子被离域电子“海洋”包围的晶格。这使金属能够导热、导电，并具有延展性。
6. Chemical Reactions and Energetics | 化学反应与能量学
During a chemical reaction, atoms are rearranged and the total mass stays the same. Word equations and balanced symbol equations represent reactants turning into products.
化学反应中，原子重新排列，总质量保持不变。文字方程式和配平的符号方程式表示反应物转变为产物。
2Mg + O₂ → 2MgO
Acids release hydrogen ions (H⁺) in solution, while alkalis release hydroxide ions (OH⁻). The pH scale measures acidity; pH 7 is neutral. Neutralisation produces a salt and water.
酸在溶液中释放氢离子（H⁺），碱释放氢氧根离子（OH⁻）。pH 标度衡量酸碱性；pH 7 为中性。中和反应生成盐和水。
The rate of reaction can be increased by raising temperature, increasing concentration, using smaller solid pieces, or adding a catalyst. Catalysts lower the activation energy and are chemically unchanged at the end.
反应速率可以通过升高温度、增大浓度、使用更小固体颗粒或加入催化剂来提高。催化剂降低活化能，且反应前后化学性质不变。
Exothermic reactions transfer energy to the surroundings, causing a temperature rise. Endothermic reactions absorb energy from the surroundings. Bond breaking is endothermic; bond making is exothermic.
放热反应向环境传递能量，导致温度升高。吸热反应从环境吸收能量。断键吸热，成键放热。
Calculating overall energy change: total energy absorbed for bond breaking minus total energy released in bond making. A negative enthalpy change shows an exothermic reaction.
计算总能量变化：断键吸收的总能量减去成键释放的总能量。焓变为负值表示放热反应。
7. Forces and Motion | 力与运动
A force can change an object's shape, speed or direction. Newton's first law states that an object remains at rest or moves with constant velocity unless a resultant force acts on it.
力可以改变物体的形状、速度或方向。牛顿第一定律指出，除非受到合外力作用，物体将保持静止或匀速直线运动。
Resultant force is found by subtracting opposing forces. Acceleration is produced when a resultant force acts on a mass.
F = m × a
Velocity is speed in a given direction. Acceleration is a change in velocity per unit time and can involve a change in speed, direction or both.
速度是具有方向的速度。加速度是单位时间内速度的变化量，可能涉及速度大小的变化、方向变化或两者兼有。
On a distance–time graph, a straight line shows constant speed, and a steeper line means a faster speed. A curve indicates acceleration. On a velocity–time graph, the gradient gives acceleration and the area under the graph gives distance travelled.
在距离-时间图上，直线表示匀速，斜率越大速度越快；曲线表示加速度。在速度-时间图上，斜率给出加速度，图线下的面积表示行驶的距离。
Stopping distance is the sum of thinking distance and braking distance. It is affected by speed, driver's reaction time, road conditions and vehicle mass.
停车距离是反应距离与制动距离之和。它受车速、驾驶员反应时间、路面状况和车辆质量的影响。
Forces between objects often come in pairs: when object A exerts a force on object B, B exerts an equal and opposite force on A (Newton's third law).
物体之间的力通常成对出现：当物体 A 对 B 施加力时，B 对 A 施加大小相等方向相反的力（牛顿第三定律）。
8. Electricity and Circuits | 电学与电路
Electric current is the flow of charge; in metal wires it is the movement of delocalised electrons. Current is measured in amperes (A) using an ammeter connected in series.
电流是电荷的流动；在金属导线中是离域电子的移动。电流以安培（A）为单位，用串联的电流表测量。
Potential difference (voltage) is the energy transferred per unit charge between two points and is measured in volts (V) using a voltmeter in parallel.
电势差（电压）是两点间每单位电荷传递的能量，以伏特（V）为单位，用并联的电压表测量。
Resistance, measured in ohms (Ω), opposes the flow of current. Ohm's law relates these quantities.
V = I × R
In a series circuit, current is the same everywhere, and the total resistance is the sum of individual resistances. The supply voltage is shared between components.
在串联电路中，各处电流相等，总电阻是各电阻之和。电源电压在各元件间分配。
In a parallel circuit, the total current splits across branches, while each branch experiences the full supply voltage. The total resistance is lower than the smallest individual resistor.
在并联电路中，总电流在各支路分流，而各支路两端电压等于电源电压。总电阻小于最小的单个电阻。
= I² × R. The domestic kilowatt-hour (kWh) is a unit of energy used for electricity bills.
电功率（P）是能量传递的速率，可由 P = I × V 或 P = I² × R 计算。家用电度表使用的千瓦时（kWh）是能量单位。
9. Waves and the Electromagnetic Spectrum | 波与电磁波谱
Waves transfer energy without transferring matter. Transverse waves vibrate perpendicular to the direction of energy transfer, while longitudinal waves vibrate parallel to it.
波传递能量而不传递物质。横波的振动方向与能量传递方向垂直，纵波的振动方向与之平行。
The amplitude is the maximum displacement from the rest position. Wavelength is the distance between two consecutive crests, and frequency is the number of waves passing a point per second, measured in hertz (Hz).
振幅是偏离平衡位置的最大位移。波长是两个连续波峰之间的距离，频率是每秒通过某点的波数，单位为赫兹（Hz）。
The wave equation links speed, frequency and wavelength.
v = f × λ
wavelength to shortest, is: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.
电磁波谱是一组横波，在真空中均以光速（3.0 × 10⁸ m/s）传播。按波长从长到短排列为：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 have different uses and dangers. Microwaves can heat food, while X-rays are used for medical imaging but can cause cell damage. Gamma rays are the most penetrating and are used to sterilise equipment and treat cancer.
不同波段有不同的用途和危害。微波可加热食物；X 射线用于医学成像，但可能损伤细胞；伽马射线穿透力最强，用于灭菌和治疗癌症。
Sound waves are longitudinal and require a medium to travel. Their pitch is determined by frequency and loudness by amplitude. Reflection of sound can produce echoes.
声波是纵波，需要介质传播。音调由频率决定，响度由振幅决定。声波的反射可产生回声。
10. Energy Resources and Transfer | 能源与能量转移
Energy cannot be created or destroyed, only transferred between stores or dissipated. The main stores include kinetic, gravitational potential, elastic potential, thermal, chemical and nuclear energy.
能量不能被创造或消灭，只能在储存库之间转移或耗散。主要的能量储存包括动能、重力势能、弹性势能、热能、化学能和核能。
Work done is equal to the energy transferred when a force moves an object.
W = F × d
Renewable energy resources, such as solar, wind, tidal, wave, hydroelectric and geothermal, are replenished quickly. Non-renewable resources, like fossil fuels and nuclear fuel, will eventually run out.
可再生能源，如太阳能、风能、潮汐能、波浪能、水能和地热能，可快速再生。不可再生能源，如化石燃料和核燃料，终将耗尽。
In any energy transfer, some energy is always transferred to the thermal store of the surroundings, making the process less than 100% efficient. Efficiency is calculated as useful output energy divided by total input energy.
在任何能量转移中，总有部分能量转移到周围环境的热能中，使过程效率低于 100%。效率可用有用输出能量除以总输入能量计算。
Conduction, convection and radiation are three methods of thermal energy transfer. Conduction occurs mainly in solids, convection in liquids and gases, and radiation via infrared waves that can travel through a vacuum.
热传导、热对流和热辐射是热传递的三种方式。传导主要在固体中发生，对流在液体和气体中，辐射通过红外波进行，可在真空中传播。
Insulation reduces unwanted energy transfers. Examples include loft insulation, double glazing, cavity wall foam and shiny foil behind radiators.
保温隔热可减少不必要的能量转移。例子包括阁楼隔热、双层玻璃、中空墙泡沫和暖气片背后的反射箔。
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