📚 Mastering Cambridge Lower Secondary Science Stage 7: Core Concepts and Study Guide | 掌握剑桥初中科学第7阶段：核心概念与学习指南
Cambridge Lower Secondary Science Learner's Book 7 (ISBN 9781108742856) introduces learners aged 11-13 to the fundamental ideas of biology, chemistry, physics and Earth science. This article summarises the core content and practical skills covered in the book, helping students build a solid foundation before moving to IGCSE or O Level courses.
《剑桥初中科学学生用书第7册》（ISBN 9781108742856）面向11-13岁学习者，介绍生物、化学、物理和地球科学的基本概念。本文总结该书涵盖的核心内容和实验技能，帮助学生在进入IGCSE或O Level课程前打下扎实基础。
1. The Cell: Building Block of Life | 细胞：生命的基本单位
All living organisms are made of cells. A cell is the smallest unit that can carry out the seven life processes: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition. Animal cells contain a cell membrane, cytoplasm and a nucleus, while plant cells also have a cell wall, chloroplasts and a permanent vacuole. Chloroplasts absorb light energy for photosynthesis, and the cell wall gives the plant cell a fixed shape.
所有生物都由细胞组成。细胞是能够进行七种生命过程的最小单位：运动、呼吸、感应、生长、生殖、排泄和营养。动物细胞含有细胞膜、细胞质和细胞核，而植物细胞还有细胞壁、叶绿体和永久液泡。叶绿体吸收光能进行光合作用，细胞壁使植物细胞保持固定形状。
| Structure / 结构 | Animal cell / 动物细胞 | Plant cell / 植物细胞 |
|---|---|---|
| Cell membrane / 细胞膜 | Present / 有 | Present / 有 |
| Cytoplasm / 细胞质 | Present / 有 | Present / 有 |
| Nucleus / 细胞核 | Present / 有 | Present / 有 |
| Cell wall / 细胞壁 | Absent / 无 | Present / 有 |
| Chloroplasts / 叶绿体 | Absent / 无 | Present / 有 |
| Permanent vacuole / 永久液泡 | Absent / 无 | Present / 有 |
When observing cells under a light microscope, you should start with the lowest power objective lens, focus using the coarse adjustment knob first, then use the fine adjustment knob for a sharp image. Stains such as iodine solution are often used to make cell structures easier to see.
在光学显微镜下观察细胞时，应先用低倍物镜，先用粗准焦螺旋调焦，再用细准焦螺旋使图像清晰。常使用碘液等染色剂使细胞结构更容易观察。
2. Microorganisms and Disease | 微生物与疾病
Microorganisms, also called microbes, include bacteria, viruses and fungi. Many microorganisms are useful, for example bacteria help to break down dead organisms and fungi are used to make bread and antibiotics. However, some microorganisms cause diseases such as food poisoning, influenza and athlete's foot. Diseases can spread through air, water, food, contact or insect bites.
微生物包括细菌、病毒和真菌。许多微生物是有益的，例如细菌帮助分解死去的生物，真菌用于制作面包和抗生素。然而，一些微生物会导致食物中毒、流感和脚癣等疾病。疾病可以通过空气、水、食物、接触或昆虫叮咬传播。
- Bacteria / 细菌 - single-celled organisms that reproduce quickly in warm, moist conditions. / 在温暖潮湿条件下快速繁殖的单细胞生物。
- Viruses / 病毒 - much smaller than bacteria; they reproduce inside living cells and cause diseases such as the common cold. / 比细菌小得多；它们在活细胞内繁殖，引起普通感冒等疾病。
- Fungi / 真菌 - include yeasts and moulds; some cause skin infections, while others are useful in food production. / 包括酵母菌和霉菌；有些引起皮肤感染，有些在食品生产中有用。
Good hygiene, clean water, vaccination and proper food storage help prevent the spread of disease. Washing hands with soap removes many microbes and is one of the simplest ways to stay healthy.
良好的卫生习惯、清洁饮水、疫苗接种和适当储存食物有助于防止疾病传播。用肥皂洗手可以去除许多微生物，是保持健康最简单的方法之一。
3. States of Matter and the Particle Model | 物质状态与粒子模型
Matter exists in three main states: solid, liquid and gas. The particle model explains the properties of each state. In a solid, particles are tightly packed in a regular arrangement and can only vibrate in fixed positions. In a liquid, particles are close together but can move past each other, so liquids flow and take the shape of their container. In a gas, particles are far apart and move quickly in all directions, so gases spread out to fill any space.
物质主要以三种状态存在：固态、液态和气态。粒子模型解释了每种状态的性质。在固体中，粒子紧密地有规则排列，只能在固定位置振动。在液体中，粒子彼此靠近但可以互相滑动，因此液体可以流动并呈现容器的形状。在气体中，粒子相距很远并快速向各个方向运动，因此气体会扩散并充满任何空间。
Changes of state are physical changes because no new substance is formed. Melting, freezing, evaporation, condensation and sublimation can all be explained by changes in particle movement and arrangement. For example, heating a liquid gives particles more kinetic energy, so they escape from the surface as a gas during evaporation.
物态变化是物理变化，因为没有新物质生成。熔化、凝固、蒸发、凝结和升华都可以用粒子运动和排列的变化来解释。例如，加热液体使粒子获得更多动能，从而在蒸发过程中从液体表面逸出成为气体。
Density = mass ÷ volume
The density of a substance depends on how closely its particles are packed. Solids are usually denser than liquids and gases because their particles are packed most tightly.
物质的密度取决于其粒子排列的紧密程度。固体通常比液体和气体密度大，因为其粒子排列最紧密。
4. Atoms, Elements and Compounds | 原子、元素与化合物
All matter is made of atoms. An element is a substance that contains only one type of atom, such as oxygen, iron and gold. A compound is a substance made of two or more different elements chemically joined together, such as water and carbon dioxide. The periodic table lists all known elements in order of increasing atomic number.
所有物质都由原子组成。元素是只含有一种原子的物质，例如氧、铁和金。化合物是由两种或多种不同元素通过化学方式结合而成的物质，例如水和二氧化碳。元素周期表按原子序数递增的顺序排列所有已知元素。
Chemical formulae show the elements present in a compound. For example, H₂O represents water, which has two hydrogen atoms and one oxygen atom in each molecule. CO₂ represents carbon dioxide, and NaCl represents sodium chloride. A mixture contains different substances that are not chemically joined, so they can be separated by physical methods such as filtration or distillation.
化学式表示化合物中存在的元素。例如 H₂O 表示水，每个分子含有两个氢原子和一个氧原子。CO₂ 表示二氧化碳，NaCl 表示氯化钠。混合物含有不同物质，它们没有化学结合，因此可以通过过滤或蒸馏等物理方法进行分离。
Common examples of compounds covered in Stage 7 include water, carbon dioxide, methane (CH₄), sodium chloride and calcium carbonate. Learning to write word equations for simple reactions is an important early skill.
第7阶段涉及的常见化合物包括水、二氧化碳、甲烷（CH₄）、氯化钠和碳酸钙。学会书写简单反应的文字方程式是一项重要的早期技能。
5. Forces and Motion | 力与运动
resistance, tension and magnetic force. Weight is the force of gravity acting on an object's mass and is calculated using weight = mass × gravitational field strength.
力是推或拉，可以改变物体的速度、方向或形状。力用弹簧秤或测力计以牛顿（N）为单位测量。常见的力包括重力、摩擦力、空气阻力、张力和磁力。重量是作用在物体质量上的重力，计算公式为重量 = 质量 × 重力场强度。
Weight = mass × gravitational field strength (W = m × g)
On Earth, gravitational field strength is about 10 N/kg, so a 5 kg object has a weight of about 50 N. Balanced forces do not change an object's motion, while unbalanced forces cause acceleration, deceleration or a change of direction.
在地球上，重力场强度约为 10 N/kg，因此 5 千克物体的重量约为 50 牛。平衡力不会改变物体的运动状态，而非平衡力会导致加速、减速或改变运动方向。
Speed describes how fast an object is moving. It is calculated by dividing distance travelled by time taken. The standard unit of speed is metres per second (m/s).
速度描述物体运动的快慢。它等于运动的距离除以所用的时间。速度的标准单位是米每秒（m/s）。
Speed = distance ÷ time
6. Energy Transfers and Resources | 能量传递与能源
Energy is the ability to do work and is measured in joules (J). It exists in many forms, including kinetic energy, potential energy, thermal energy, chemical energy, electrical energy, light energy and sound energy. Energy can be stored or transferred from one object to another, but it is never created or destroyed. This is called the law of conservation of energy.
能量是做功的能力，以焦耳（J）为单位。能量以多种形式存在，包括动能、势能、热能、化学能、电能、光能和声能。能量可以储存或从一个物体传递到另一个物体，但永远不会被创造或毁灭。这被称为能量守恒定律。
- Kinetic energy / 动能 - energy of moving objects / 运动物体的能量
- Potential energy / 势能 - stored energy due to position or height / 由于位置或高度而储存的能量
- Thermal energy / 热能 - energy related to temperature / 与温度有关的能量
- Chemical energy / 化学能 - stored in fuels, food and batteries / 储存在燃料、食物和电池中
Energy resources are divided into renewable and non-renewable sources. Renewable resources include solar, wind, hydroelectric, geothermal and biomass energy. Non-renewable resources include coal, oil, natural gas and nuclear fuel. Burning fossil fuels releases carbon dioxide and other pollutants, so using renewable resources helps reduce environmental damage.
能源分为可再生能源和不可再生能源。可再生能源包括太阳能、风能、水能、地热能和生物质能。不可再生能源包括煤、石油、天然气和核燃料。燃烧化石燃料会释放二氧化碳和其他污染物，因此使用可再生能源有助于减少对环境的破坏。
7. Sound and Light | 声音与光
Sound is produced by vibrating objects and travels as a longitudinal wave. It cannot travel through a vacuum because it needs a medium, such as air, water or a solid, to carry the vibrations. Sound travels fastest in solids, then liquids, and slowest in gases. The loudness of a sound depends on amplitude, while pitch depends on frequency.
声音由振动物体产生，并以纵波形式传播。声音不能在真空中传播，因为它需要空气、水或固体等介质来传递振动。声音在固体中传播最快，其次是液体，在气体中最慢。声音的响度取决于振幅，音调取决于频率。
Light travels in straight lines and can travel through a vacuum. It travels much faster than sound, which is why you see lightning before you hear thunder. Light can be reflected by mirrors and refracted when it passes from one transparent medium to another, such as from air to glass. White light is made up of a spectrum of colours: red, orange, yellow, green, blue, indigo and violet.
光沿直线传播，可以在真空中传播。光的传播速度比声音快得多，所以你会先看到闪电后听到雷声。光可以被镜子反射，也可以从一种透明介质进入另一种透明介质（例如从空气到玻璃）时发生折射。白光由红、橙、黄、绿、蓝、靛、紫七种颜色组成。
A ray diagram uses a straight line with an arrow to show the direction of light travel. The angle of incidence equals the angle of reflection when light reflects from a flat mirror.
光线图用带箭头的直线表示光的传播方向。当光从平面镜反射时，入射角等于反射角。
8. Electrical Circuits | 电路
An electrical circuit is a complete path through which electric current can flow. Current is the flow of electric charge and is measured in amperes (A). Voltage, measured in volts (V), is the energy supplied to each unit of charge. A circuit must be closed for current to flow; a switch can open or close the circuit.
电路是电流可以流过的完整路径。电流是电荷的流动，以安培（A）为单位。电压以伏特（V）为单位，是提供给每单位电荷的能量。电路必须是闭合的才能有电流通过；开关可以断开或闭合电路。
Circuit diagrams use standard symbols for components such as cells, batteries, bulbs, switches, resistors and ammeters. In a series circuit, components are connected one after another, so the current is the same everywhere. In a parallel circuit, components are connected in separate branches, so the current splits and each component receives the full circuit voltage.
电路图使用标准符号表示电池、灯泡、开关、电阻和电流表等元件。在串联电路中，元件一个接一个连接，所以各处电流相同。在并联电路中，元件连接在不同的支路中，电流会分流，每个支路获得完整的电路电压。
Voltage = current × resistance (V = I × R)
Adding more cells to a series circuit increases the current, while adding more bulbs decreases the current because total resistance increases. Conductors such as copper allow current to flow easily, while insulators such as plastic do not.
在串联电路中增加电池会增大电流，增加灯泡会增大总电阻而使电流减小。铜等导体允许电流容易通过，而塑料等绝缘体不允许电流通过。
9. Earth and the Solar System | 地球与太阳系
The Earth is made up of three main layers: the crust, the mantle and the core. The crust is the thin outer layer, the mantle is semi-liquid rock below the crust, and the core is the hottest layer made mostly of iron and nickel. The rock cycle describes how igneous, sedimentary and metamorphic rocks are formed and changed over time.
地球由三个主要层组成：地壳、地幔和地核。地壳是薄的外层，地幔是地壳下方半液态的岩石，地核是最热的一层，主要由铁和镍组成。岩石循环描述了火成岩、沉积岩和变质岩如何形成并随时间变化。
The solar system consists of the Sun, eight planets and many smaller bodies such as moons, asteroids and comets. The planets in order from the Sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Earth's rotation on its axis causes day and night, while its orbit around the Sun causes the seasons.
太阳系由太阳、八大行星以及卫星、小行星和彗星等较小天体组成。行星按距太阳由近到远的顺序为水星、金星、地球、火星、木星、土星、天王星和海王星。地球绕地轴自转产生昼夜，绕太阳公转产生季节。
- Mercury / 水星 - closest planet to the Sun / 离太阳最近的行星
- Venus / 金星 - hottest planet because of thick atmosphere / 因厚大气层而最热的行星
- Earth / 地球 - the only known planet with liquid water and life / 已知唯一有液态水和生命的行星
- Mars / 火星 - called the red planet because of iron oxide dust / 因氧化铁尘埃而被称为红色星球
The Moon orbits the Earth roughly every 28 days, and the same side of the Moon always faces Earth. Solar eclipses occur when the Moon passes between the Sun and Earth, blocking sunlight.
月球大约每28天绕地球运行一圈，同一面始终朝向地球。当月球经过太阳和地球之间并挡住阳光时，就会发生日食。
10. Acids, Alkalis and Neutralisation | 酸、碱与中和
Acids and alkalis are types of chemical substances with different properties. Acids have a sour taste and turn blue litmus paper red. Alkalis feel soapy and turn red litmus paper blue. The pH scale measures how acidic or alkaline a solution is, ranging from 0 to 14. Values below 7 are acidic, 7 is neutral, and values above 7 are alkaline.
酸和碱是性质不同的化学物质。酸有酸味，使蓝色石蕊试纸变红。碱有滑腻感，使红色石蕊试纸变蓝。pH标度测量溶液的酸碱度，范围从0到14。pH值小于7为酸性，等于7为中性，大于7为碱性。
Indicators such as litmus, universal indicator and phenolphthalein change colour in acids and alkalis. Universal indicator gives a range of colours from red in strong acids to purple in strong alkalis. Neutralisation is the reaction between an acid and a base or alkali to form a salt and water.
石蕊、通用指示剂和酚酞等指示剂在酸和碱中会
Published by TutorHao | Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图