📚 KS3 OCR Science: Core Knowledge Review | KS3 OCR 科学：核心知识点梳理
Welcome to this comprehensive KS3 OCR Science revision guide. Here you will find a structured overview of the key topics across biology, chemistry, and physics, aligned with the OCR Key Stage 3 curriculum. Each section pairs essential English explanations with their Chinese translations, helping you build a solid foundation and prepare confidently for tests.
欢迎来到这份全面的 KS3 OCR 科学复习指南。在这里，你将找到对生物、化学和物理核心主题的结构化梳理，与 OCR KS3 课程大纲紧密匹配。每一节都将核心英文讲解与其中文翻译配对呈现，帮助你打下扎实基础，自信备考。
1. Cells – The Building Blocks of Life | 细胞——生命的基本单位
All living organisms are made of cells. Animal cells typically contain a nucleus, cytoplasm, cell membrane, and mitochondria. The nucleus controls the cell and holds genetic material. Mitochondria are the sites of respiration, where energy is released.
所有生物体皆由细胞构成。动物细胞通常包含细胞核、细胞质、细胞膜和线粒体。细胞核控制细胞并承载遗传物质。线粒体是呼吸作用的场所，在此释放能量。
Plant cells have all the structures found in animal cells, plus three extra features: a rigid cell wall made of cellulose, chloroplasts that absorb light for photosynthesis, and a large permanent vacuole filled with cell sap.
植物细胞除了拥有动物细胞的所有结构，还有三个额外特征：由纤维素构成的坚硬细胞壁、吸收光能进行光合作用的叶绿体，以及一个充满细胞液的大液泡。
Specialised cells are adapted to perform specific functions. For example, red blood cells have no nucleus to carry more oxygen, sperm cells have a tail for swimming, and root hair cells have a large surface area to absorb water.
特化细胞适应执行特定功能。例如，红细胞没有细胞核以便携带更多氧气，精子具有用于游动的尾部，根毛细胞有较大的表面积以吸收水分。
2. From Cells to Systems | 从细胞到系统
Groups of similar cells work together to form tissues. Muscle tissue, for instance, contains cells that can contract. Different tissues are organised into organs, each with a specific job. The heart is an organ made of muscle, nerve, and connective tissues.
相似的细胞集合起来形成组织。例如，肌肉组织含有可收缩的细胞。不同的组织构成器官，每个器官有特定任务。心脏就是一个由肌肉组织、神经组织和结缔组织构成的器官。
Organs work together in organ systems. The digestive system includes the mouth, oesophagus, stomach, intestines, and liver; it breaks down food and absorbs nutrients. The respiratory system brings oxygen into the body and removes carbon dioxide.
器官协同工作构成器官系统。消化系统包括口腔、食道、胃、肠和肝脏，负责分解食物并吸收营养。呼吸系统将氧气带入体内，并排出二氧化碳。
The circulatory system transports blood, nutrients, gases, and wastes around the body. The heart pumps blood through arteries, veins, and capillaries. Organ systems are interdependent and keep the organism alive.
循环系统在全身运输血液、营养、气体和废物。心脏泵送血液流经动脉、静脉和毛细血管。各器官系统相互依存，维持生物体存活。
3. Human Reproduction and Adolescence | 人类生殖与青春期
Adolescence is the stage when a child's body matures into an adult's. Hormones trigger physical changes such as growth spurts, development of pubic hair, and voice deepening in males. In males, the testes start producing sperm cells; in females, the ovaries begin to release egg cells (ova).
青春期是儿童身体发育为成人的阶段。激素引发身体变化，如快速生长、阴毛发育和男性嗓音变低沉。男性睾丸开始产生精子细胞；女性卵巢开始释放卵细胞。
Fertilisation occurs when a sperm cell fuses with an egg cell to form a zygote. This normally takes place in the oviduct (fallopian tube). The zygote divides and becomes an embryo, which implants in the lining of the uterus.
当精子细胞与卵细胞融合形成受精卵时，受精便发生了。这通常发生在输卵管内。受精卵分裂并形成胚胎，胚胎植入子宫内膜。
The placenta allows nutrients and oxygen to pass from the mother's blood to the fetus while removing waste products. The amniotic fluid protects the developing baby from bumps. Birth occurs after about 40 weeks of pregnancy.
胎盘让营养物质和氧气从母体血液传递给胎儿，同时清除废物。羊水保护发育中的婴儿免受撞击。怀孕约 40 周后分娩。
4. Atoms, Elements, and Compounds | 原子、元素与化合物
All substances are made of tiny particles called atoms. An element contains only one type of atom. The Periodic Table lists all known elements, each with its own symbol. Examples include oxygen (O), iron (Fe), and gold (Au).
所有物质都由称为原子的微小粒子组成。元素只包含一种类型的原子。元素周期表列出所有已知元素，每种元素有其专属符号。例如氧 (O)、铁 (Fe) 和金 (Au)。
A compound forms when atoms of two or more different elements chemically bond together. The properties of a compound are often completely different from those of its constituent elements. Water (H₂O) is a compound made from hydrogen and oxygen.
当两种或多种不同元素的原子通过化学键结合，就形成化合物。化合物的性质通常与其组成元素的性质截然不同。水 (H₂O) 是由氢和氧组成的化合物。
Mixtures contain two or more substances that are not chemically joined. They can be separated by physical techniques: filtration separates an insoluble solid from a liquid; distillation separates a liquid from a mixture using boiling; chromatography separates dissolved substances.
混合物含有两种或多种未发生化学结合的物质。它们可以通过物理方法分离：过滤将不溶性固体从液体中分离；蒸馏利用沸腾从混合物中分离液体；色谱法可分离溶解的物质。
5. Chemical Reactions and Changes | 化学反应与变化
In a chemical reaction, new substances are always formed. Signs that a reaction has taken place include a colour change, a gas being produced (bubbles), a temperature change, or the formation of a precipitate (solid). Chemical reactions are different from physical changes, where no new substance is made.
在化学反应中，总是会生成新物质。发生反应的迹象包括颜色变化、产生气体（气泡）、温度变化或形成沉淀（固体）。化学反应不同于物理变化，物理变化中不会产生新物质。
carbon dioxide + water. The total mass stays the same during a reaction; this is the law of conservation of mass.
反应可用文字方程式表示：反应物 + 反应物 → 生成物。例如，甲烷 + 氧气 → 二氧化碳 + 水。反应过程中总质量保持不变；这就是质量守恒定律。
The pH scale runs from 0 (strong acid) to 14 (strong alkali), with 7 being neutral. Acids have a pH less than 7; alkalis have a pH greater than 7. Neutralisation is a reaction between an acid and an alkali that produces a salt and water.
pH 值范围从 0（强酸）到 14（强碱），7 为中性。酸的 pH 值小于 7；碱的 pH 值大于 7。中和反应是酸与碱之间的反应，生成盐和水。
6. Forces and Motion | 力与运动
A force is a push or a pull, measured in newtons (N). Forces can change the speed, direction, or shape of an object. Contact forces, such as friction and air resistance, act when objects touch. Non-contact forces include gravity, magnetic force, and electrostatic force.
力是推或拉，以牛顿 (N) 为单位。力可以改变物体的速度、方向或形状。接触力如摩擦力和空气阻力，发生在物体接触时。非接触力包括重力、磁力和静电力。
Friction opposes motion and can be useful (brakes) or a nuisance (engine wear). Gravity is the force that pulls objects towards the centre of the Earth. Weight is a measure of the gravitational force on an object and is calculated using:
摩擦力阻碍运动，既可能有用（如刹车），又可能带来麻烦（如发动机磨损）。重力是将物体拉向地球中心的力。重量是物体所受重力大小的量度，可由下式计算：
weight (N) = mass (kg) × gravitational field strength (N/kg)
重量 (N) = 质量 (kg) × 重力场强度 (N/kg)
Speed is how fast something is moving. Average speed can be found using:
速度表示物体运动的快慢。平均速度可由下式求出：
speed (m/s) = distance (m) ÷ time (s)
速度 (m/s) = 距离 (m) ÷ 时间 (s)
Balanced forces acting on an object result in a constant speed or no movement. Unbalanced forces cause acceleration (speeding up, slowing down, or changing direction).
作用在物体上的平衡力导致匀速运动或静止。非平衡力则引起加速（加快、减慢或改变方向）。
7. Energy Transfers and Stores | 能量转移与储存
Energy can be stored in various ways. The main energy stores include kinetic energy (movement), thermal energy (heat), chemical energy (in fuels and food), gravitational potential energy (stored in raised objects), and elastic potential energy (stored in stretched or compressed objects).
能量可以多种形式储存。主要的能量储存包括动能（运动能）、热能（热）、化学能（存在于燃料和食物中）、重力势能（储存于被举高的物体中）和弹性势能（储存于拉伸或压缩的物体中）。
Energy is transferred between stores through four pathways: heating (by conduction, convection, or radiation), waves (light and sound), electric current, and forces (mechanical work). Energy cannot be created or destroyed; it is always conserved.
能量通过四种途径在储存间转移：加热（传导、对流或辐射）、波（光和声）、电流和力（做功）。能量既不能创造也不能毁灭；它总是守恒的。
In an energy transfer, some energy often ends up in a store that is not useful (usually thermal energy). Efficiency compares useful output energy to total input energy:
在能量转移中，部分能量常常最终进入无用的储存（通常是热能）。效率将有用的输出能量与总输入能量进行比较：
efficiency = useful output energy transfer ÷ total input energy transfer
效率 = 有用输出能量转移 ÷ 总输入能量转移
Efficiency can be given as a decimal or a percentage. The more efficient a device, the less energy is wasted.
效率可用小数或百分比表示。设备效率越高，能量浪费越少。
8. Electricity and Circuits | 电与电路
Electric current is the flow of electric charge around a circuit. Current is measured in amperes (A) using an ammeter. For current to flow, the circuit must be complete, with no gaps, and there must be a source of potential difference (voltage).
电流是电荷在电路中的流动。电流以安培 (A) 为单位，用电流表测量。要让电流流动，电路必须完整、无断路，并且必须有电位差的来源（电压）。
Voltage (potential difference) measures the push that moves charge around a circuit, measured in volts (V) with a voltmeter. Components like bulbs and buzzers provide resistance, which opposes the flow of current and is measured in ohms (Ω).
电压（电位差）衡量推动电荷在电路中移动的“推动力”，以伏特 (V) 为单位，用电压表测量。灯泡和蜂鸣器等元件提供电阻，电阻阻碍电流流动，以欧姆 (Ω) 为单位。
In a series circuit, there is only one path for current. The current is the same everywhere, but the voltage is shared between components. In a parallel circuit, the current splits into different branches. The voltage across each branch is the same as the supply voltage.
在串联电路中，电流只有一条路径。各处电流相同，但电压在元件之间分配。在并联电路中，电流分成不同支路。各支路两端的电压与电源电压相同。
Circuit diagrams use standard symbols for components. A cell provides energy, a switch opens or closes a circuit, and a resistor limits current. Always draw wires as straight lines with a ruler.
电路图使用标准符号表示元件。电池提供能量，开关接通或断开电路，电阻限制电流。画导线时一定要用直尺画成直线。
9. Waves – Sound and Light | 波——声音与光
Sound is produced by vibrating objects. It travels as a longitudinal wave through a medium (solid, liquid, or gas), but cannot travel through a vacuum. The speed of sound in air is approximately 340 m/s.
声音由物体振动产生。它以纵波的形式通过介质（固体、液体或气体）传播，但不能在真空中传播。声音在空气中的速度约为 340 m/s。
Loudness is related to the amplitude of the wave; a larger amplitude means a louder sound. Pitch depends on frequency; a higher frequency gives a higher pitch. The human ear detects these waves and converts them into electrical signals for the brain.
响度与波的振幅有关；振幅越大，声音越响。音调取决于频率；频率越高，音调越高。人耳检测这些波并将其转换为电信号传递给大脑。
Light travels as a transverse wave. It does not need a medium and can travel through a vacuum at a speed of about 300,000 km/s. When light strikes a surface, it can be reflected, absorbed, or transmitted.
光以横波形式传播。它不需要介质，可在真空中以约 300,000 km/s 的速度传播。当光照射到表面时，可以被反射、吸收或透射。
The law of reflection states that the angle of incidence equals the angle of reflection. Both angles are measured from the normal – an imaginary line perpendicular to the surface. White light is made up of a spectrum of colours, which can be separated by refraction (dispersion).
反射定律指出，入射角等于反射角。两个角度都从法线（垂直于表面的假想线）量起。白光由一系列颜色的光组成，可通过折射（色散）将它们分开。
10. Earth and Space | 地球与太空
The solar system consists of the Sun (a star), eight planets, their moons, and smaller objects like asteroids and comets. Planets orbit the Sun in elliptical paths. The order from the Sun is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
太阳系由太阳（一颗恒星）、八大行星、它们的卫星以及小行星和彗星等更小的天体组成。行星以椭圆形轨道绕太阳运行。由内向外顺序为：水星、金星、地球、火星、木星、土星、天王星、海王星。
The Earth rotates on its axis once every 24 hours, causing day and night. It takes about 365¼ days to orbit the Sun, which gives us the year. The Earth's axis is tilted, and this tilt causes the seasons as different parts of the Earth receive more direct sunlight.
地球每 24 小时自转一周，导致昼夜交替。环绕太阳公转一周约需 365¼ 天，这构成了一年。地轴是倾斜的，这种倾斜使得地球不同区域接收到的直射阳光不同，从而形成四季。
The Moon is a natural satellite that orbits the Earth about every 28 days. It does not produce its own light; we see it because it reflects sunlight. The changing shapes of the Moon are called phases.
月球是一颗天然卫星，大约每 28 天绕地球一周。它本身不发光；我们看到它是因为它反射了太阳光。月球的形状变化称为月相。
Gravity is the force that keeps planets in orbit around the Sun and moons in orbit around planets. The Sun's enormous mass creates a strong gravitational pull that holds the whole solar system together.
引力是维持行星绕太阳公转、卫星绕行星公转的力。太阳巨大的质量产生了强大的引力，将整个太阳系维系在一起。
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