📚 Core Concepts of KS3 CIE Science | KS3 CIE 科学核心知识点梳理
KS3 Science under the Cambridge International Examinations (CIE) syllabus builds a vital foundation for IGCSE and beyond. This comprehensive review covers the core knowledge across biology, chemistry and physics, equipping students with a clear, structured overview of key topics. From cells to forces, atoms to energy waves, understanding these fundamentals is essential for scientific literacy and exam success.
剑桥国际考试（CIE）KS3科学课程为IGCSE及后续学习打下重要基础。本文全面梳理了生物、化学和物理三个学科的核心知识，为学生提供清晰、结构化的关键主题概览。从细胞到力，从原子到能量波，掌握这些基础知识对培养科学素养和考试成功至关重要。
1. Cells and Organisation | 细胞与组织
All living organisms are made of cells. Animal cells contain a nucleus, cytoplasm, cell membrane and mitochondria. Plant cells have all these plus a cell wall, a large permanent vacuole and chloroplasts. The nucleus controls the cell, cytoplasm hosts chemical reactions, the membrane controls entry and exit, mitochondria release energy via respiration, and chloroplasts absorb light for photosynthesis.
所有生物体都由细胞构成。动物细胞包含细胞核、细胞质、细胞膜和线粒体。植物细胞除了上述结构，还有细胞壁、一个大液泡和叶绿体。细胞核控制细胞活动，细胞质是化学反应场所，细胞膜控制物质进出，线粒体通过呼吸作用释放能量，叶绿体则吸收光能进行光合作用。
Cells are organised into tissues, organs and systems. For example, muscle cells form muscle tissue, which makes up the heart (an organ), part of the circulatory system. Specialised cells are adapted to their functions: red blood cells have no nucleus to carry more oxygen, while root hair cells increase surface area for water absorption.
细胞组织形成组织、器官和系统。例如，肌肉细胞构成肌肉组织，进而组成心脏（器官），心脏是循环系统的一部分。特化细胞适应其功能：红细胞无核以便携带更多氧气，根毛细胞增大表面积以利于吸收水分。
| Feature | Animal Cell | Plant Cell |
|---|---|---|
| Nucleus | Yes | Yes |
| Cytoplasm | Yes | Yes |
| Cell membrane | Yes | Yes |
| Mitochondria | Yes | Yes |
| Cell wall | No | Yes |
| Large vacuole | No | Yes |
| Chloroplasts | No | Yes |
2. Nutrition and Digestion | 营养与消化
A balanced diet provides carbohydrates, proteins, lipids, vitamins, minerals, water and fibre. Carbohydrates and lipids supply energy, proteins aid growth and repair, while vitamins and minerals support body functions. Fibre prevents constipation and water maintains hydration and chemical reactions.
均衡饮食提供碳水化合物、蛋白质、脂类、维生素、矿物质、水和纤维素。碳水化合物和脂类提供能量，蛋白质促进生长与修复，维生素和矿物质支持身体机能。纤维素预防便秘，水维持水分和化学反应。
Digestion breaks down large insoluble molecules into small soluble ones. In the mouth, mechanical digestion by teeth and salivary amylase starts starch breakdown. The stomach produces protease and hydrochloric acid; the small intestine finishes digestion and absorbs nutrients via villi. The large intestine absorbs water.
消化将大分子不溶性物质分解为小分子可溶性物质。口腔中，牙齿的机械消化和唾液淀粉酶开始分解淀粉。胃产生蛋白酶和盐酸；小肠完成消化并通过绒毛吸收营养。大肠吸收水分。
3. Respiration and Photosynthesis | 呼吸作用与光合作用
Respiration is the release of energy from glucose inside cells. It is not the same as breathing. Aerobic respiration requires oxygen and produces carbon dioxide, water and a large amount of energy. The word equation is: glucose + oxygen → carbon dioxide + water (+ energy). The balanced chemical equation is:
呼吸作用是细胞内葡萄糖释放能量的过程，与呼吸气体交换不同。有氧呼吸需要氧气，产生二氧化碳、水和大量能量。文字表达式为：葡萄糖 + 氧气 → 二氧化碳 + 水（+能量）。配平化学方程式为：
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy)
Photosynthesis is the process by which plants make glucose using light. It occurs in chloroplasts and requires carbon dioxide, water and light. The word equation: carbon dioxide + water → glucose + oxygen. The balanced symbol equation:
光合作用是植物利用光制造葡萄糖的过程，发生在叶绿体中，需要二氧化碳、水和光。文字表达式：二氧化碳 + 水 → 葡萄糖 + 氧气。配平符号方程式：
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Respiration provides energy for metabolism, muscle contraction and maintaining body temperature. Photosynthesis produces oxygen and glucose, which is used in respiration or stored as starch.
呼吸作用为代谢、肌肉收缩和维持体温提供能量。光合作用产生氧气和葡萄糖，葡萄糖用于呼吸作用或以淀粉形式储存。
4. States of Matter and Particle Theory | 物质状态与粒子理论
Matter exists as solid, liquid or gas. The particle model explains properties: solids have fixed shape and volume with particles tightly packed in a regular pattern; liquids have fixed volume but take the shape of the container, with particles close but able to flow; gases have no fixed shape or volume, and particles are far apart and move rapidly.
物质以固态、液态或气态存在。粒子模型解释物质性质：固体有固定形状和体积，粒子紧密排列成规则结构；液体有固定体积但呈容器形状，粒子紧密但可流动；气体无固定形状和体积，粒子间距大且快速运动。
Changes of state are physical changes. Melting, boiling, condensing and freezing occur at specific temperatures. During these changes, energy is transferred but temperature remains constant. Diffusion is the movement of particles from a high concentration to a low concentration, which is fastest in gases.
状态变化是物理变化。熔化、沸腾、凝结和凝固在特定温度下发生。变化过程中能量转移但温度保持不变。扩散是粒子从高浓度区域向低浓度区域运动的过程，在气体中最快。
5. Atoms, Elements, and Compounds | 原子、元素与化合物
All substances are made of atoms. An element is a pure substance that contains only one type of atom. The Periodic Table arranges elements by atomic number. Compounds contain two or more elements chemically bonded in fixed proportions. For example, water (H₂O) is a compound of hydrogen and oxygen; its properties differ from its constituent elements.
所有物质由原子构成。元素是仅含一种原子的纯净物。元素周期表按原子序数排列元素。化合物由两种或多种元素按固定比例通过化学键结合而成。例如，水（H₂O）是氢和氧的化合物，其性质与组成元素不同。
Atoms have a central nucleus containing protons and neutrons, surrounded by electrons in shells. The atomic number equals the number of protons, and the mass number is the sum of protons and neutrons. Chemical reactions involve the rearrangement of atoms; no atoms are created or destroyed.
原子有一个包含质子和中子的中央原子核，电子在核外分层排布。原子序数等于质子数，质量数为质子数与中子数之和。化学反应涉及原子重新排列，原子不会凭空产生或消失。
6. Chemical Reactions and Equations | 化学反应与方程式
A chemical reaction produces new substances. Signs include colour change, temperature change, gas production or formation of a precipitate. Word equations show reactants and products: methane + oxygen → carbon dioxide + water. Symbol equations balance using subscript and coefficients. The combustion of methane:
化学反应产生新物质。迹象包括颜色变化、温度变化、气体生成或形成沉淀。文字方程式表示反应物和生成物：甲烷 + 氧气 → 二氧化碳 + 水。符号方程式用下标和系数配平。甲烷燃烧：
CH₄ + 2O₂ → CO₂ + 2H₂O
Types of reaction include combustion (burning in oxygen), thermal decomposition (breaking down by heat), and oxidation. The reactivity series ranks metals by their tendency to react. Conservation of mass means total mass of reactants equals total mass of products in a closed system.
反应类型包括燃烧（在氧气中燃烧）、热分解（受热分解）和氧化。金属活动性顺序根据反应倾向将金属排序。质量守恒定律意味着在封闭体系中，反应物的总质量等于生成物的总质量。
7. Acids and Alkalis | 酸与碱
Acids have a pH less than 7, produce hydrogen ions (H⁺) in water and taste sour. Common acids include hydrochloric acid, sulfuric acid and citric acid. Alkalis are soluble bases with a pH greater than 7, produce hydroxide ions (OH⁻) and feel soapy. The pH scale from 0 to 14 measures acidity or alkalinity; indicators like litmus change colour.
酸的pH小于7，在水中产生氢离子（H⁺），尝起来有酸味。常见酸包括盐酸、硫酸和柠檬酸。碱是可溶性碱，pH大于7，产生氢氧根离子（OH⁻），有滑腻感。pH标度从0到14衡量酸碱性；指示剂如石蕊试纸会变色。
Neutralisation is the reaction between an acid and an alkali, producing a salt and water. The general equation: acid + alkali → salt + water. Example: hydrochloric acid + sodium hydroxide → sodium chloride + water.
中和反应是酸与碱的反应，生成盐和水。通用方程式：酸 + 碱 → 盐 + 水。例如：盐酸 + 氢氧化钠 → 氯化钠 + 水。
HCl + NaOH → NaCl + H₂O
8. Forces and Motion | 力与运动
A force is a push or pull, measured in newtons (N). Forces can change an object’s speed, direction or shape. Contact forces include friction and tension; non-contact forces include gravity, magnetism and electrostatic force. Forces are represented by arrows; balanced forces result in no change in motion, unbalanced forces cause acceleration.
力是推或拉，单位为牛顿（N）。力可以改变物体的速度、方向或形状。接触力包括摩擦力和张力；非接触力包括重力、磁力和静电力。力用箭头表示；平衡力不会改变运动状态，非平衡力导致加速。
Speed is the distance travelled per unit time: speed = distance ÷ time. The average speed of an object can be calculated from a distance–time graph; a steeper gradient indicates higher speed. Acceleration is the change in velocity per unit time.
速度是单位时间内通过的距离：速度 = 距离 ÷ 时间。物体的平均速度可从距离–时间图计算；坡度越陡表示速度越快。加速度是单位时间内速度的变化量。
A resultant force relates to mass and acceleration by Newton’s second law: force = mass × acceleration. Weight is the force due to gravity: weight = mass × gravitational field strength (g = 10 N/kg on Earth).
合力与质量和加速度的关系遵循牛顿第二定律：力 = 质量 × 加速度。重量是重力产生的力：重量 = 质量 × 重力场强度（地球上g = 10 N/kg）。
9. Energy Transfers and Resources | 能量传递与资源
Energy is the capacity to do work and is measured in joules (J). There are many stores: kinetic, thermal, chemical, gravitational potential, elastic potential and nuclear. Energy can be transferred between stores via heating, doing work (mechanical), electrical currents, sound and light. Energy is never created or destroyed, only transferred or transformed.
能量是做功的能力，单位为焦耳（J）。能量有多种储存形式：动能、热能、化学能、重力势能、弹性势能和核能。能量可通过加热、做功（机械）、电流、声和光在储存之间传递。能量不会凭空产生或消失，只会转移或转化。
Renewable energy resources include solar, wind, hydroelectric, tidal, wave and geothermal. Non-renewable resources include fossil fuels (coal, oil, natural gas) and nuclear fuel. Renewable resources can reduce greenhouse gas emissions but may depend on weather conditions.
可再生能源包括太阳能、风能、水能、潮汐能、波浪能和地热能。不可再生资源包括化石燃料（煤、石油、天然气）和核燃料。可再生能源可减少温室气体排放，但可能受天气条件影响。
10. Waves (Sound and Light) | 波（声波与光波）
Waves transfer energy without transferring matter. Transverse waves oscillate perpendicular to energy transfer (e.g., light, water ripples). Longitudinal waves oscillate parallel to energy transfer (e.g., sound). Key wave properties include wavelength, frequency, amplitude and wave speed.
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（如光、水波）。纵波的振动方向与能量传递方向平行（如声波）。波的关键属性包括波长、频率、振幅和波速。
Sound is produced by vibrations and travels fastest in solids, then liquids, slowest in gases. The speed of sound in air is about 340 m/s. Humans hear frequencies from 20 Hz to 20 000 Hz. Light travels at 300 000 km/s in a vacuum. Reflection follows the law: angle of incidence equals angle of reflection. Refraction occurs when light changes speed entering a different medium, bending towards or away from the normal.
声音由振动产生，在固体中传播最快，液体次之，气体中最慢。空气中的声速约为340 m/s。人类能听到20 Hz至20 000 Hz的频率。光在真空中传播速度为300 000 km/s。反射遵循定律：入射角等于反射角。当光进入不同介质速度改变时发生折射，光线向法线或远离法线偏折。
11. Electricity and Magnetism | 电与磁
An electric current is a flow of charge, usually electrons, measured in amperes (A). A complete circuit is needed for current to flow. Voltage (potential difference) is the energy per unit charge, measured in volts (V). Resistance opposes current and is measured in ohms (Ω). Ohm’s Law links them: V = IR.
电流是电荷（通常是电子）的流动，单位为安培（A）。电流流动需要完整回路。电压（电势差）是单位电荷的能量，单位为伏特（V）。电阻阻碍电流，单位为欧姆（Ω）。欧姆定律将它们联系起来：V = IR。
Series circuits have one path; current is the same everywhere, voltage is shared. Parallel circuits have multiple paths; current splits and voltage is equal across branches. Magnets have north and south poles; like poles repel, unlike poles attract. An electromagnet is made by passing current through a coil around an iron core, and can be switched on and off.
串联电路只有一条通路；各处电流相同，电压分配。并联电路有多条通路；电流分流，各支路电压相等。磁铁有南北极；同极相斥，异极相吸。电磁铁通过电流通过绕在铁芯上的线圈制成，可以通断控制。
12. Earth and Space | 地球与太空
The Earth is a rocky planet with a layered structure: crust, mantle, outer core and inner core. The Earth’s rotation causes day and night; its orbit around the Sun takes 365.25 days and causes seasons. The Moon orbits Earth, reflecting sunlight and showing phases.
地球是一颗岩石行星，具有分层结构：地壳、地幔、外核和内核。地球自转产生昼夜；绕太阳公转一周需365.25天，形成四季。月球绕地球运行，反射太阳光并呈现月相。
Our Solar System consists of the Sun, eight planets, dwarf planets, moons, asteroids and comets. The Sun is a star that produces energy through nuclear fusion. Gravity keeps objects in orbit. The order of planets from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
我们的太阳系由太阳、八大行星、矮行星、卫星、小行星和彗星组成。太阳是一颗通过核聚变产生能量的恒星。引力使天体保持轨道运行。行星距太阳由近及远的顺序：水星、金星、地球、火星、木星、土星、天王星、海王星。
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