📚 KS3 Cambridge Science: Core Concepts Review | KS3 剑桥科学：核心知识点梳理
The KS3 Cambridge Science curriculum builds a strong foundation across biology, chemistry, physics and scientific enquiry. Students explore how living organisms function, how materials behave, how forces and energy shape the universe, and how to investigate the world scientifically. This article reviews the essential knowledge every learner should master.
KS3 剑桥科学课程为生物学、化学、物理学以及科学探究打下坚实基础。学生将探索生物体的运作方式、物质的性质、力与能量如何塑造宇宙，以及如何用科学的方法研究世界。本文梳理了每位学习者必须掌握的核心知识点。
1. Cells – The Building Blocks of Life | 细胞——生命的基石
All living organisms are made of cells. Animal cells have a cell membrane, cytoplasm and nucleus. Plant cells also possess a rigid cell wall, chloroplasts for photosynthesis and a large central vacuole filled with cell sap.
所有生物体都由细胞构成。动物细胞拥有细胞膜、细胞质和细胞核。植物细胞则还具有坚固的细胞壁、进行光合作用的叶绿体以及充满细胞液的大中央液泡。
Specialised cells are adapted for their roles. Red blood cells lack a nucleus to maximise oxygen carriage, root hair cells have an elongated shape to absorb water and minerals, and ciliated cells move mucus in airways.
特化细胞各具适应功能。红细胞没有细胞核以携带更多的氧气，根毛细胞呈长形以吸收水分和矿物质，纤毛细胞则在气道中推动黏液。
s. For instance, muscle cells form muscle tissue, which builds the heart, part of the circulatory system.
生命体的结构层次为：细胞 → 组织 → 器官 → 器官系统。例如，肌细胞构成肌肉组织，肌肉组织构成心脏，心脏属于循环系统。
2. Reproduction and Growth | 生殖与生长
Reproduction can be sexual or asexual. Sexual reproduction involves the fusion of male and female gametes, producing offspring with genetic variation. In humans, sperm fertilise an egg, leading to embryo development in the uterus.
生殖分为有性生殖和无性生殖。有性生殖涉及雌雄配子的融合，产生具有遗传变异的子代。在人体中，精子使卵子受精，胚胎在子宫内发育。
Asexual reproduction produces genetically identical clones. Examples include binary fission in bacteria, budding in yeast, and vegetative propagation in plants such as runners or tubers.
无性生殖产生基因完全相同的克隆。例子包括细菌的二分裂、酵母的出芽生殖，以及植物通过匍匐茎或块茎进行的营养繁殖。
In plants, pollination transfers pollen from anther to stigma, leading to fertilisation. Seeds develop inside fruits, aiding dispersal by wind, water or animals. Germination requires water, oxygen and warmth.
在植物中，传粉将花粉从花药传到柱头，随后发生受精。种子在果实内部发育，通过风、水或动物帮助传播。种子萌发需要水分、氧气和适宜的温度。
3. Ecosystems and Feeding Relationships | 生态系统与摄食关系
An ecosystem consists of a community of living organisms interacting with their abiotic environment. Producers (e.g. green plants) make their own food via photosynthesis: carbon dioxide + water → glucose + oxygen, using light energy captured by chlorophyll.
生态系统由生物群落与其非生物环境相互作用组成。生产者（如绿色植物）通过光合作用制造食物：二氧化碳 + 水 → 葡萄糖 + 氧气，利用叶绿素捕获的光能。
ws represent energy flow. Food webs are interconnected chains showing complex feeding links.
食物链显示能量传递：生产者 → 初级消费者 → 次级消费者 → 三级消费者。箭头表示能量流动。食物网是相互连接的食物链，展示复杂的摄食关系。
Changes in population size are influenced by predators, prey, competition and disease. A decline in a predator can cause prey numbers to rise, affecting vegetation. Bioaccumulation concentrates toxins up the food chain.
种群数量变化受捕食者、猎物、竞争和疾病影响。捕食者数量下降可能导致猎物数量增加，进而影响植被。生物积累使毒素沿食物链不断浓缩。
4. Variation and Inheritance | 变异与遗传
Variation exists within species: some traits are continuous (e.g. height) and some are discontinuous (e.g. blood group). Genetic information is carried on chromosomes inside the nucleus, made of DNA.
物种内存在变异：有些性状是连续的（如身高），有些是不连续的（如血型）。遗传信息由细胞核内染色体上的 DNA 携带。
Genes control characteristics. A dominant allele masks a recessive one. Genotype describes the alleles present, while phenotype is the observable trait. Punnett squares help predict inheritance patterns.
基因控制性状。显性等位基因会掩盖隐性等位基因。基因型描述存在的等位基因，表现型是可观察的性状。旁氏方格可用于预测遗传模式。
Selective breeding involves choosing parents with desired traits to produce offspring for agriculture or pets. Natural selection explains how species adapt over generations – individuals with advantageous traits survive and reproduce more.
选择性育种是指选择具有所需性状的亲本进行繁殖，用于农业或宠物。自然选择解释了物种如何在世代间适应——具有优势特征的个体更容易生存和繁殖。
5. Atoms, Elements and Compounds | 原子、元素与化合物
All matter is made of atoms. An element contains only one type of atom and is listed on the Periodic Table. Each element has a chemical symbol, e.g. O for oxygen, Fe for iron. Compounds form when elements chemically combine, e.g. H₂O (water), CO₂ (carbon dioxide).
所有物质均由原子组成。元素只含一种原子，列于元素周期表中。每种元素都有化学符号，如 O 代表氧，Fe 代表铁。当元素经化学结合时形成化合物，例如 H₂O（水）、CO₂（二氧化碳）。
The Periodic Table arranges elements by increasing atomic number. Groups are vertical columns with similar properties; periods are horizontal rows. Group 1 are alkali metals, Group 7 are halogens, Group 0 are noble gases.
元素周期表按原子序数递增排列。族是性质相近的纵列；周期是横排。第 1 族为碱金属，第 7 族为卤素，第 0 族为稀有气体。
Particle models explain states of matter: solids (fixed shape, particles vibrate in place), liquids (take shape of container, particles move past each other), gases (spread to fill container, particles move rapidly).
粒子模型可以解释物态：固体（形状固定，粒子在原地振动）、液体（随容器改变形状，粒子可相互滑过）、气体（扩散充满容器，粒子快速运动）。
6. Chemical Reactions and Equations | 化学反应与方程式
In a chemical reaction, reactants are transformed into products. Signs include colour change, temperature change, gas production or precipitate formation. Mass is conserved: total mass of reactants equals total mass of products.
在化学反应中，反应物转化为生成物。现象包括颜色变化、温度变化、产生气体或形成沉淀。质量守恒：反应物的总质量等于生成物的总质量。
Word equations show reactants and products: methane + oxygen → carbon dioxide + water. Symbol equations use formulae with balancing, e.g. CH₄ + 2O₂ → CO₂ + 2H₂O.
文字方程式表示反应物和生成物：甲烷 + 氧气 → 二氧化碳 + 水。符号方程式使用化学式并配平，例如 CH₄ + 2O₂ → CO₂ + 2H₂O。
own into simpler substances when heated), and neutralisation (acid + base → salt + water).
常见的反应类型包括燃烧（燃料 + 氧气 → 氧化物 + 能量）、热分解（一种化合物受热分解为更简单物质）和中和反应（酸 + 碱 → 盐 + 水）。
Acids release H⁺ ions in water; alkalis release OH⁻ ions. pH scale ranges from 0 (strongly acidic) to 14 (strongly alkaline), with 7 neutral. Indicators like litmus or universal indicator show pH.
酸在水中释放 H⁺ 离子；碱释放 OH⁻ 离子。pH 值范围从 0（强酸性）到 14（强碱性），7 为中性。像石蕊或通用指示剂可以显示 pH 值。
7. Forces and Motion | 力与运动
A force is a push or pull measured in newtons (N). Contact forces (e.g. friction, tension) require touching; non-contact forces (e.g. gravity, magnetic) act over a distance. Forces are vectors – they have both magnitude and direction.
力是推或拉，以牛顿（N）为单位。接触力（如摩擦力、张力）需要接触；非接触力（如重力、磁力）可隔空作用。力是矢量，既有大小又有方向。
Balanced forces produce no change in motion. Unbalanced forces cause acceleration, deceleration or change in direction. Friction opposes motion and can be useful (grip) or a problem (wear and heat).
平衡力不会改变运动状态。非平衡力导致加速、减速或方向改变。摩擦力阻碍运动，可能有利（抓地力）也可能造成麻烦（磨损与发热）。
Speed is distance travelled per unit time:
speed = distance ÷ time
A distance–time graph shows motion; a horizontal line means stationary, a steeper slope means faster speed.速度是单位时间内通过的距离：
速度 = 距离 ÷ 时间
距离–时间图表示运动；水平线表示静止，斜率越陡速度越快。Gravity gives weight: weight = mass × gravitational field strength = m × g). On Earth g ≈ 10 N/kg. Mass (kg) does not change with location; weight (N) does.
重力产生重量：重量 = 质量 × 重力场强度（W = m × g）。地球上 g ≈ 10 N/kg。质量（kg）不随地点改变；重量（N）却会变化。
8. Energy Transfers and Resources | 能量传递与能源
Energy cannot be created or destroyed, only transferred or converted. Common energy stores include kinetic, thermal, chemical, gravitational potential, elastic potential, and nuclear. Energy is measured in joules (J).
能量不能凭空创造或消失，只能转移或转化。常见的能量储存包括动能、热能、化学能、重力势能、弹性势能和核能。能量以焦耳（J）为单位。
Energy transfers occur by heating, waves, electric current or mechanical motion. The conservation principle means total energy in a closed system stays constant, but it often disperses as waste heat.
能量通过加热、波、电流或机械运动传递。能量守恒意味着封闭系统中的总能量保持不变，但常以废热的形式散失。
Renewable resources (solar, wind, tidal, hydroelectric, geothermal) replenish quickly and produce less pollution. Non-renewable resources (coal, oil, gas) are finite and release CO₂ when burned, contributing to climate change.
可再生能源（太阳能、风能、潮汐能、水力、地热）可快速补充且污染较少。不可再生能源（煤、石油、天然气）储量有限，燃烧时释放 CO₂，加剧气候变化。
Efficiency measures useful energy output compared to total input:
efficiency = (useful output energy ÷ total input energy) × 100%
Sankey diagrams visualise energy flows.效率衡量有效能量输出与总输入能量的比值：
效率 = （有效输出能量 ÷ 总输入能量）× 100%
桑基图可直观展示能量流动。9. Waves: Light and Sound | 波：光与声
Waves transfer energy without transferring matter. Transverse waves (e.g. light, water waves) vibrate perpendicular to travel direction. Longitudinal waves (e.g. sound) vibrate parallel, creating compressions and rarefactions.
波传递能量而不传递物质。横波（如光、水波）的振动方向与传播方向垂直。纵波（如声波）的振动方向平行于传播方向，形成压缩和稀疏区。
lection. Refraction occurs when light changes speed entering a different medium, bending the ray.
光沿直线传播，在真空中速度为 3 × 10⁸ m/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，光线弯曲。
White light can be dispersed by a prism into the spectrum of colours (ROYGBIV). Coloured filters transmit only their own colour and absorb others. Objects appear coloured by reflecting certain wavelengths.
白光可通过棱镜色散成光谱（红橙黄绿蓝靛紫）。彩色滤光片只透过自身颜色的光并吸收其他颜色。物体通过反射特定波长而显现颜色。
Sound is produced by vibrations and travels fastest in solids, slower in liquids and slowest in gases. The ear detects sound; loudness relates to amplitude, pitch to frequency. Human hearing range is roughly 20–20 000 Hz.
声音由振动产生，在固体中传播最快，液体次之，气体中最慢。耳能听到声音；响度与振幅有关，音调与频率有关。人耳听觉范围大约在 20–20 000 Hz。
10. Electricity and Magnetism | 电与磁
Electric current is the flow of charge, measured in amps (A). In a circuit, electrons flow from negative to positive. For current to flow, a complete loop and a potential difference (voltage, V) from a cell or power supply are needed.
电流是电荷的流动，单位为安培（A）。在电路中，电子从负极流向正极。电流流动需要完整的回路以及电池或电源提供的电势差（电压，V）。
Resistance (R, measured in ohms, Ω) opposes current. Ohm's Law links them:
V = I × R
Components like lamps, motors and resistors change circuit behaviour.电阻（R，单位为欧姆，Ω）阻碍电流。欧姆定律将它们联系起来：
V = I × R
灯、电动机和电阻器等元件改变电路行为。Series circuits have one path; current is the same everywhere. Parallel circuits have multiple branches; current splits, but voltage across each branch is the same. Fuses and circuit breakers protect against overload.
串联电路只有一条路径，各处电流相同。并联电路有多条支路，电流分流，但各支路电压相同。保险丝和断路器可防止过载。
Magnetism – like poles repel, unlike poles attract. Magnetic materials (iron, nickel, cobalt) can be magnetised. Electromagnets use a coil of wire around an iron core; their strength depends on current, number of turns and core material.
磁性：同性相斥，异性相吸。磁性材料（铁、镍、钴）可被磁化。电磁铁由缠绕在铁芯上的线圈构成；其强度取决于电流、线圈匝数和铁芯材料。
11. Earth and Space | 地球与太空
The Earth rotates on its axis, causing day and night. It orbits the Sun in about 365.25 days, causing seasons due to its tilted axis. The Moon orbits Earth, showing phases as reflected sunlight; eclipses occur when shadows align.
地球绕地轴自转，产生昼夜交替。它约在 365.25 天内绕太阳公转，地轴倾斜导致四季变化。月球绕地公转，因反射阳光而呈现月相；当阴影对齐时发生日食或月食。
The Solar System consists of the Sun, eight planets, moons, dwarf planets, asteroids and comets. Gravity keeps objects in orbit. The Sun, a medium-sized star, generates energy by nuclear fusion.
太阳系由太阳、八大行星、卫星、矮行星、小行星和彗星组成。引力使天体维持轨道。太阳是一颗中等大小的恒星，通过核聚变产生能量。
Rock cycle links igneous, sedimentary and metamorphic rocks through melting, cooling, weathering, erosion, compaction and heat/pressure. Fossils and rock layers provide evidence of Earth's history.
岩石循环通过熔融、冷却、风化、侵蚀、压实和热/压力将火成岩、沉积岩和变质岩联系起来。化石和岩层为地球历史提供证据。
The atmosphere has changed over time. Early gases included carbon dioxide and water vapour; photosynthesis by early organisms increased oxygen levels. Today’s air is about 78% nitrogen, 21% oxygen.
大气随时间演变。早期气体包括二氧化碳和水蒸气；早期生物的光合作用提升了氧气含量。当今空气约含 78% 氮气、21% 氧气。
12. Scientific Enquiry Skills | 科学探究技能
Working scientifically involves observing, hypothesising, planning fair tests, taking measurements, recording data, analysing patterns and drawing conclusions. Variables – independent (changed), dependent (measured) and controlled (kept constant) – ensure reliable results.
科学工作涉及观察、提出假设、设计公平实验、测量、记录数据、分析规律并得出结论。变量——自变量（改变的量）、因变量（测量的量）和控制变量（保持不变的量）确保结果可靠。
Repeat readings improve reliability; anomalies are identified and may be discarded. Graphs plot scatter points or lines; a line of best fit reveals trends. Units and correct scales must be used.
重复读数可提高可靠性；识别异常值后可将其剔除。图表描点或绘线；最佳拟合线揭示趋势。必须使用单位与合适的坐标刻度。
Safety symbols (e.g. corrosive, flammable, toxic) and lab rules must always be followed. Risk assessments identify hazards and precautions before experiments.
务必遵守安全标志（如腐蚀性、易燃、有毒）及实验室规则。实验前需评估风险，识别危险并采取预防措施。
Peer review and evaluating methods allow scientists to judge the validity of claims. Presenting findings clearly, using tables and charts, is a core skill at KS3 and beyond.
同行评审和方法评估让科学家能判断结论的有效性。清晰展示发现，使用表格和图表，是 KS3 及以后的核心技能。
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