📚 Year 7 Cambridge Science: Core Concepts Review | Year 7 Cambridge 科学：核心知识点梳理
Year 7 Cambridge Science sets the foundation for understanding the natural world through three main disciplines: Biology, Chemistry and Physics. This article brings together the essential topics you will encounter, from cells and body systems to atoms, forces and energy. Each section pairs clear explanations in English with Chinese translations to support bilingual learners and build strong scientific vocabulary.
七年级剑桥科学通过生物学、化学和物理学三大领域为你认识自然界打下基础。这篇文章汇集了你会遇到的核心主题，从细胞和人体系统到原子、力和能量。每个部分都将清晰的英文解释与中文翻译配对，帮助双语学习者建立扎实的科学词汇。
1. Cells – The Building Blocks of Life | 细胞——生命的基石
All living organisms are made of cells. A cell is the smallest unit of life that can carry out all life processes. The key parts of an animal cell include the cell membrane, cytoplasm and nucleus, while plant cells have extra structures such as a cell wall, chloroplasts and a large permanent vacuole.
所有生物都由细胞组成。细胞是能执行全部生命活动的最小单位。动物细胞的主要部分包括细胞膜、细胞质和细胞核，而植物细胞还有额外的结构，如细胞壁、叶绿体和一个大而永久的液泡。
The cell membrane controls what enters and leaves the cell. The nucleus contains genetic material and controls the cell’s activities. Cytoplasm is a jelly-like substance where most chemical reactions happen. Chloroplasts absorb light energy for photosynthesis, and the vacuole stores cell sap and helps keep the plant rigid.
细胞膜控制物质进出细胞。细胞核含有遗传物质并控制细胞的活动。细胞质是胶状物质，大多数化学反应在这里发生。叶绿体吸收光能进行光合作用，液泡储存细胞液并帮助植物保持挺直。
Microscopes allow us to observe cells. You should be able to calculate magnification using the formula: Magnification = size of image ÷ actual size of object. A simple animal cell drawing should label the membrane, cytoplasm and nucleus.
显微镜让我们可以观察细胞。你需要会用公式：放大倍数 = 图像大小 ÷ 物体的实际大小。一个简单的动物细胞图应标注细胞膜、细胞质和细胞核。
2. Plant Systems | 植物的系统
Plants are organized into tissues and organs. The main organs of a flowering plant are roots, stems, leaves and flowers. Each organ has a specific function. Roots anchor the plant and absorb water and minerals from the soil, while stems support the plant and transport substances.
植物由组织和器官构成。开花植物的主要器官是根、茎、叶和花。每个器官都有特定的功能。根固定植物并从土壤中吸收水分和矿物质，而茎支撑植物并运输物质。
Leaves are the primary site of photosynthesis, a process that converts light energy into chemical energy in the form of glucose. The equation for photosynthesis is: carbon dioxide + water → glucose + oxygen, with light energy and chlorophyll required. The leaf is adapted with a large surface area, stomata for gas exchange and veins containing xylem and phloem.
叶片是光合作用的主要场所，该过程将光能转化为化学能，以葡萄糖的形式储存。光合作用的方程式为：二氧化碳 + 水 → 葡萄糖 + 氧气，需要光能和叶绿素。叶片适应其功能，具有较大的表面积、用于气体交换的气孔以及含有木质部和韧皮部的叶脉。
Xylem transports water and dissolved minerals from the roots upwards, while phloem transports sugars produced in photosynthesis to all parts of the plant. Flowers are involved in reproduction; the male stamen produces pollen, and the female carpel contains the ovary where fertilisation occurs.
木质部将水和溶解的矿物质从根部向上运输，而韧皮部则将光合作用产生的糖类输送到植物全身。花参与生殖；雄蕊产生花粉，雌蕊内含有子房，受精过程在此发生。
3. The Human Body Systems | 人体系统
The human body consists of several organ systems that work together. The digestive system breaks down food into small, soluble molecules that can be absorbed into the blood. Key organs are the mouth, oesophagus, stomach, small intestine, large intestine, rectum and anus, along with accessory organs like the liver and pancreas.
人体由多个协同工作的器官系统组成。消化系统将食物分解成小的、可溶的分子，以便吸收进入血液。主要器官包括口腔、食道、胃、小肠、大肠、直肠和肛门，还有肝和胰腺等附属器官。
Enzymes in the digestive system speed up the breakdown of nutrients: carbohydrases break down carbohydrates into simple sugars, proteases break down proteins into amino acids, and lipases break down fats into fatty acids and glycerol. Absorption mainly occurs in the small intestine through villi, tiny finger-like projections that increase the surface area.
消化系统中的酶加速营养物质的分解：碳水化合物酶将碳水化合物分解为单糖，蛋白酶将蛋白质分解为氨基酸，脂肪酶将脂肪分解为脂肪酸和甘油。吸收主要发生在小肠，通过绒毛——细小的指状突起增加了表面积。
The circulatory system transports oxygen, nutrients and waste around the body. It includes the heart, blood vessels (arteries, veins and capillaries) and blood. The heart pumps blood; arteries carry oxygenated blood away from the heart, veins return deoxygenated blood, and capillaries allow exchange of substances with cells.
循环系统运输氧气、营养物质和废物到全身。它包括心脏、血管（动脉、静脉和毛细血管）和血液。心脏泵血；动脉将含氧血带离心脏，静脉将缺氧血送回心脏，而毛细血管则与细胞进行物质交换。
The respiratory system is responsible for gas exchange. Air enters through the nose or mouth, passes the trachea and bronchi, and reaches the lungs where oxygen diffuses into the blood and carbon dioxide diffuses out in the alveoli. Breathing involves the movement of the diaphragm and ribcage.
呼吸系统负责气体交换。空气通过鼻或口进入，经过气管和支气管，到达肺部，在肺泡中氧气扩散入血液，二氧化碳扩散出去。呼吸包括膈肌和肋骨的运动。
4. Particle Theory and States of Matter | 粒子理论与物质状态
All matter is made of tiny particles that are constantly moving. The particle theory explains the properties of solids, liquids and gases. In solids, particles are held closely together in a fixed, regular arrangement and only vibrate in place. In liquids, particles are close but can move past each other, taking the shape of the container. In gases, particles are far apart and move rapidly in all directions, filling any available space.
所有物质都由不断运动的微小粒子组成。粒子理论解释了固体、液体和气体的性质。在固体中，粒子紧密排列在固定的位置，只能就地振动。在液体中，粒子彼此靠近但能相互滑过，呈容器形状。气体中，粒子相距很远，迅速向各个方向运动，充满任何可用空间。
Changes of state, such as melting, freezing, boiling and condensing, can be explained by changes in particle energy and arrangement. When a solid is heated, particles gain energy and vibrate more, eventually breaking free from fixed positions to become a liquid. Further heating gives particles enough energy to overcome attractive forces completely, changing the liquid into a gas. These are physical changes because no new substance is formed.
物态变化，如熔化、凝固、沸腾和冷凝，可以通过粒子能量和排列的变化来解释。当固体受热时，粒子获得能量，振动加剧，最终从固定位置挣脱变成液体。进一步加热使粒子获得完全克服吸引力所需的能量，液体变成气体。这些是物理变化，因为没有新物质生成。
Diffusion provides evidence for particle movement. For example, a drop of ink spreads throughout a beaker of water because ink particles move randomly and mix with water particles. In gases, diffusion is even faster due to the large spaces between particles.
扩散现象为粒子运动提供了证据。例如，一滴墨水在水中扩散，因为墨水粒子随机运动并与水粒子混合。在气体中，由于粒子间距大，扩散速度更快。
5. Atoms, Elements and Compounds | 原子、元素和化合物
All materials are made of atoms. An element is a substance made of only one type of atom and cannot be broken down into simpler substances by chemical means. There are about 118 known elements, arranged in the Periodic Table. Examples include hydrogen (H), oxygen (O), carbon (C) and iron (Fe).
所有物质由原子组成。元素是由同一种原子组成的物质，不能通过化学方法分解成更简单的物质。已知大约有 118 种元素，排列在周期表中。例如氢 (H)、氧 (O)、碳 (C) 和铁 (Fe)。
A compound is formed when two or more different atoms chemically bond together. A compound has completely different properties from its constituent elements. For example, carbon dioxide (CO₂) is a gas made of carbon and oxygen, and water (H₂O) is a liquid formed from hydrogen and oxygen. Chemical formulas use symbols and subscript numbers to show the types and amounts of atoms.
当两种或多种不同原子以化学键结合时，形成化合物。化合物的性质与其组成元素截然不同。例如，二氧化碳 (CO₂) 是由碳和氧组成的气体，水 (H₂O) 是由氢和氧形成的液体。化学式使用符号和下标数字表示原子的种类和数量。
Mixtures contain two or more substances not chemically joined, and each substance keeps its own properties. Air is a mixture of nitrogen, oxygen, carbon dioxide and other gases. Mixtures can be separated by physical methods such as filtration, distillation and chromatography, depending on the properties of the components.
混合物含有两种或多种未化学结合的物质，每种物质保持自身性质。空气是氮气、氧气、二氧化碳和其他气体的混合物。混合物可以根据组分的性质，通过过滤、蒸馏和色谱等物理方法进行分离。
6. Acids and Alkalis | 酸与碱
Acids and alkalis are two groups of chemicals with characteristic properties. Common laboratory acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃). They taste sour (do not taste in the lab!), are corrosive and turn blue litmus paper red. Alkalis are soluble bases; common examples are sodium hydroxide (NaOH) and calcium hydroxide (Ca(OH)₂). Alkalis feel soapy and turn red litmus paper blue.
酸和碱是两组具有典型性质的化学物质。常见的实验室酸包括盐酸 (HCl)、硫酸 (H₂SO₄) 和硝酸 (HNO₃)。它们有酸味（不可在实验室品尝！），具有腐蚀性，可将蓝色石蕊试纸变红。碱是可溶性的碱；常见例子有氢氧化钠 (NaOH) 和氢氧化钙 (Ca(OH)₂)。碱手感滑腻，可将红色石蕊试纸变蓝。
The pH scale measures how acidic or alkaline a solution is, ranging from 0 (very acidic) to 14 (very alkaline). A neutral solution, like pure water, has a pH of 7. Indicators, such as universal indicator, show a range of colours to approximate pH. In neutralisation, an acid and an alkali react to form a salt and water: acid + alkali → salt + water.
pH 标度衡量溶液的酸碱性强弱，范围从 0（强酸性）到 14（强碱性）。中性溶液，如纯水，pH 值为 7。指示剂，如通用指示剂，会显示一系列颜色来估算 pH 值。在中和反应中，酸与碱反应生成盐和水：酸 + 碱 → 盐 + 水。
Everyday examples of neutralisation include treating indigestion with antacid tablets that contain a weak base, or spreading lime on acidic soil in agriculture. Handling acids and alkalis requires safety precautions, including wearing safety goggles and gloves, and knowing how to deal with spills.
日常生活中的中和例子包括用含有弱碱的抗酸片治疗消化不良，或在农业上将石灰撒在酸性土壤上。处理酸和碱需要安全预防措施，包括佩戴护目镜和手套，并知道如何处理溢出物。
7. Energy Forms and Transfers | 能量的形式与传递
Energy is the ability to do work. It exists in different forms: kinetic, thermal (heat), light, sound, electrical, chemical, elastic potential and gravitational potential. Energy can be transferred from one form to another, but it is never created or destroyed (the principle of conservation of energy).
能量是做功的能力。它以不同的形式存在：动能、热（内）能、光能、声能、电能、化学能、弹性势能和重力势能。能量可以从一种形式转化为另一种形式，但它永远不会被创造或消灭（能量守恒定律）。
An energy transfer diagram shows how energy changes in a device. For example, in a battery-powered lamp: chemical energy in the battery → electrical energy in the circuit → light energy + thermal energy from the bulb. Sankey diagrams can also represent energy flow, with arrow widths showing the amount of useful and wasted energy.
能量转化图显示设备中能量的变化。例如，在电池供电的灯泡中：电池中的化学能 → 电路中的电能 → 灯泡发出的光能 + 热能。桑基图也可以表示能量流，箭头宽度表示有用能量和浪费能量的数量。
Heat can be transferred by conduction, convection and radiation. Conduction occurs mainly in solids; metals are good conductors because they have free electrons. Convection happens in fluids (liquids and gases) when warmer, less dense regions rise and cooler, denser regions sink. Infrared radiation can travel through a vacuum and does not need particles.
热可以通过传导、对流和辐射传递。传导主要发生在固体中；金属因拥有自由电子而是良导体。对流发生在流体（液体和气体）中，当较热、较疏的部分上升，较冷、较密的部分下沉。红外辐射可以在真空中传播，不需要粒子。
8. Forces in Action | 力的作用
A force is a push or a pull that can change an object’s speed, direction or shape. Forces are measured in newtons (N). Forces acting in the same direction add together, while forces acting in opposite directions subtract. An object remains stationary or moves at a constant speed if the forces on it are balanced (net force = zero).
力是推或拉的作用，可以改变物体的速度、方向或形状。力的单位是牛顿 (N)。同方向的力相加，反方向的力相减。如果作用在物体上的力平衡（合力为零），物体保持静止或匀速运动。
Friction is a force that opposes motion between two surfaces in contact. It can be useful, like when it enables walking or braking, or wasteful, causing energy to be dissipated as heat. Air resistance and water resistance are types of friction that act on objects moving through fluids.
摩擦力是阻碍接触表面相对运动的力。它可能是有用的，例如使人能够行走或刹车，也可能是浪费的，导致能量以热的形式散失。空气阻力和水阻力是作用在流体中运动物体上的摩擦力。
Gravity is a force of attraction between masses. On Earth, the gravitational field strength g is about 10 N/kg. The weight of an object is a force and can be calculated using the formula: Weight (N) = mass (kg) × gravitational field strength (N/kg). Mass is the amount of matter in an object and does not change; weight changes with location.
引力是质量之间的吸引力。在地球上，引力场强度 g 约为 10 N/kg。物体的重量是一种力，可以用公式计算：重量 (N) = 质量 (kg) × 引力场强度 (N/kg)。质量是物体所含物质的多少，不发生变化；重量随位置改变。
Stretching a spring demonstrates Hooke’s Law: the extension of a spring is directly proportional to the applied force, provided the elastic limit is not exceeded. A force versus extension graph shows a straight line through the origin up to the limit of proportionality.
拉伸弹簧体现了胡克定律：只要不超过弹性限度，弹簧的伸长量与施加的力成正比。力-伸长量图是一条通过原点的直线，直到比例限度。
9. Electric Circuits | 电路
An electric circuit is a closed loop that allows current to flow from a power source, through components, and back to the source. Current (I) is the flow of electric charge and is measured in amperes (A) using an ammeter connected in series. For a current to flow, the circuit must be complete and contain a source of potential difference (voltage).
电路是一个闭合回路，允许电流从电源流出，通过元件，再回到电源。电流 (I) 是电荷的流动，用安培 (A) 为单位，由串联的电流表测量。要有电流流动，电路必须是完整的，并含有电势差（电压）源。
Voltage (V) is the energy transferred per unit charge and is measured in volts (V) using a voltmeter connected in parallel. The relationship between current, voltage and resistance is given by Ohm’s Law: V = I × R, where R is resistance in ohms (Ω). Conductors have low resistance; insulators have very high resistance.
电压 (V) 是每单位电荷传递的能量，单位为伏特 (V)，用并联的电压表测量。电流、电压和电阻之间的关系由欧姆定律给出：V = I × R，其中 R 是电阻，单位为欧姆 (Ω)。导体的电阻低；绝缘体的电阻非常高。
Components in a circuit can be connected in series or parallel. In a series circuit, there is only one path for current, so the current is the same everywhere, and the total voltage is shared. In a parallel circuit, each branch gets the full supply voltage, and the total current equals the sum of the branch currents. Circuit diagrams use standard symbols for cells, bulbs, switches, resistors and buzzers.
电路中的元件可以串联或并联连接。在串联电路中，电流只有一条通路，所以各处电流相等，总电压由各元件分担。在并联电路中，每个支路获得全部电源电压，总电流等于各支路电流之和。电路图使用标准符号表示电池、灯泡、开关、电阻和蜂鸣器。
10. Sound and Light Waves | 声音与光波
Sound is caused by vibrations and travels as a longitudinal wave through a medium such as air, water or a solid. Sound cannot travel through a vacuum because there are no particles to carry the vibrations. The speed of sound in air is approximately 340 m/s, much slower than light.
声音由振动引起，并以纵波的形式在空气、水或固体等介质中传播。声音不能在真空中传播，因为没有粒子来传递振动。声音在空气中的速度约为 340 m/s，比光慢得多。
The ear detects sound waves; the outer ear collects sound, the eardrum vibrates, and tiny bones in the middle ear transmit vibrations to the cochlea, where sound signals are sent to the brain. Loudness depends on the amplitude of the wave, and pitch depends on the frequency (number of vibrations per second, measured in hertz, Hz).
耳朵检测声波；外耳收集声音，鼓膜振动，中耳的小骨将振动传到耳蜗，在那里声音信号被传送到大脑。响度取决于波的振幅，音调取决于频率（每秒振动次数，单位为赫兹 Hz）。
Light travels in straight lines at a speed of about 300,000 km/s in a vacuum. We see objects because light reflects from them into our eyes. Reflection follows the law: the angle of incidence equals the angle of reflection, measured from the normal. Refraction is the bending of light as it passes from one transparent medium to another of different density, changing its speed.
光在真空中以大约 300,000 km/s 的速度沿直线传播。我们看到物体是因为光从它们反射进入我们的眼睛。反射遵循定律：入射角等于反射角，都从法线测量。折射是光从一种透明介质进入另一种密度不同的介质时，速度改变而导致的光线弯曲。
White light can be dispersed into a spectrum of colours (red, orange, yellow, green, blue, indigo, violet) by a prism, showing that it is made of a mixture of wavelengths. Colour filters and coloured objects appear coloured because they absorb some wavelengths and reflect or transmit others.
白光可通过棱镜色散成色谱（红、橙、黄、绿、蓝、靛、紫），表明它是由多种波长的光混合而成。滤色片和彩色物体呈现颜色，是因为它们吸收了某些波长的光而反射或透射其他波长。
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