📚 Year 7 CAIE Science: Core Knowledge Overview | 核心知识点梳理
Year 7 CAIE Science follows the Cambridge Lower Secondary framework, introducing students to the essential disciplines of biology, chemistry, and physics. Throughout the year, learners develop scientific enquiry skills, learn to use laboratory equipment safely, and build a solid understanding of core concepts such as cells, particles, forces, energy, and electricity. This revision guide gathers the key knowledge you need in one place, linking ideas across topics and preparing you for Checkpoint progression tests.
七年级 CAIE 科学遵循剑桥初中课程框架，为学生们打开生物学、化学和物理学的大门。在这一年里，你需要培养科学探究能力，学会安全使用实验器材，并扎实掌握细胞、粒子、力、能量和电路等核心概念。这份梳理笔记将关键知识集中整理，帮助你串联各主题的脉络，为 Checkpoint 进阶测试做好准备。
1. The Scientific Method | 科学方法
Scientists follow a logical process to investigate questions about the natural world. The scientific method starts with making observations and asking a testable question. After gathering background information, you form a hypothesis—a suggested explanation that can be tested. You then design a fair test experiment, identifying independent, dependent, and controlled variables. The independent variable is the one you change, the dependent variable is what you measure, and controlled variables are kept the same. You record results, analyse them with graphs or calculations, and draw a conclusion that either supports or refutes the hypothesis. Finally, you evaluate the method and suggest improvements.
科学家通过一套逻辑步骤来探究自然世界的问题。科学方法始于观察并提出一个可测试的问题。收集背景信息后，你需要提出假设——一种可被检验的设想。接下来设计一个公平实验，明确自变量、因变量和控制变量。自变量是你改变的变量，因变量是测量的结果，而控制变量须保持不变。记录结果后，利用图表或计算分析数据，得出结论来支持或否定假设。最后还要评估实验方法并提出改进建议。
When presenting data, line graphs are used for continuous variables and bar charts for categorical data. Always label axes with quantity and unit, use sensible scales, and give the graph a clear title. A good conclusion states what you found, explains whether the evidence backs the hypothesis, and links findings to scientific knowledge. Reliability improves with repeated measurements and calculating a mean, while validity depends on controlling variables and measuring accurately.
展示数据时，连续变量用折线图，分类数据用条形图。坐标轴必须标注物理量和单位，选用合理的分度，并给图表明确的标题。好的结论会说明发现了什么、证据是否支持假设，并将结果与科学知识联系。多次测量取平均值可提高可靠性，而控制变量与准确测量则关乎有效性。
2. Laboratory Safety and Fundamental Equipment | 实验室安全与基本器材
Working safely in the laboratory is the most important habit in Year 7 Science. Always wear safety goggles when handling chemicals, heating substances, or doing activities that could cause splashes. Tie back long hair, tuck in loose clothing, and never eat or drink in the lab. Read hazard labels on chemicals—symbols such as a flame for flammable, a cross for irritant, and a skull for toxic help you recognise risks quickly. If you break glassware, report it to the teacher and use a dustpan and brush; never pick up broken glass with your bare hands.
在实验室安全操作是七年级科学最重要的习惯。接触化学品、加热物质或进行可能产生飞溅的实验时，务必佩戴护目镜。长发要扎紧，宽松衣物塞好，实验室内严禁饮食。学会阅读化学品上的危险标签，像易燃液体上的火焰标志、刺激物上的叉号标志、有毒物质上的骷髅标志都能帮你快速识别风险。玻璃器皿破碎要报告老师并用簸箕和刷子清理，绝不要用手直接捡。
You will encounter fundamental equipment early on: beakers for mixing and heating liquids, conical flasks for swirling without spilling, measuring cylinders for volume, test tubes for small-scale reactions, Bunsen burners for heating, and thermometers for temperature. The Bunsen burner has a safety flame (yellow, air hole closed) and a roaring blue flame (air hole open) used for strong heating. Learn to read the meniscus at eye level when measuring liquid volume—read the bottom of the curve for water. Microscopes are introduced to view cells: know the eyepiece lens, objective lenses, stage, coarse focus, and fine focus.
你会较早接触到基本器材：烧杯用于混合和加热液体，锥形瓶便于振荡不溅出，量筒量取体积，试管做小规模反应，本生灯加热，温度计测温度。本生灯有安全火焰（黄色，气孔关闭）和用于强热的蓝色内焰（气孔打开）。量取液体时视线与液面凹面最低处水平，即读取凹液面底部。显微镜用来观察细胞，需要认识目镜、物镜、载物台、粗准焦螺旋和细准焦螺旋。
3. Cells – Structure and Function | 细胞 – 结构与功能
All living things are made of cells. Plant and animal cells share several structures: a nucleus that controls the cell and contains genetic material, cytoplasm where chemical reactions occur, a cell membrane that selectively allows substances in and out, and mitochondria that release energy through respiration. Plant cells have three extra features: a rigid cell wall made of cellulose that maintains shape, a large permanent vacuole filled with cell sap that helps keep the cell turgid, and chloroplasts that contain chlorophyll for photosynthesis. Microscopes allow us to observe these structures, and you should be able to draw and label a typical plant and animal cell.
一切生物都由细胞构成。动植物细胞共有一些结构：控制细胞并含有遗传物质的细胞核，发生化学反应的细胞质，选择性允许物质进出的细胞膜，以及通过呼吸作用释放能量的线粒体。植物细胞还多出三种结构：由纤维素组成的坚固细胞壁能维持形状，充满细胞液的大液泡帮助维持细胞坚挺，含有叶绿素的叶绿体进行光合作用。使用显微镜可以观察到这些结构，你应该能绘制并标注典型的植物细胞和动物细胞图。
In Year 7 you also meet specialised cells, each adapted for a particular job. A root hair cell has a long, thin extension to increase surface area for absorbing water and minerals from the soil. A sperm cell has a tail (flagellum) to swim and many mitochondria for energy. A ciliated epithelial cell lines the airways and sweeps mucus with tiny hair-like cilia. A palisade mesophyll cell sits near the top of a leaf and is packed with chloroplasts. Understanding how structure relates to function is a unifying idea in biology.
七年级还会认识特化细胞，每一种都为特定功能而改变了结构。根毛细胞有细长的突起以增大表面积，便于从土壤吸水吸无机盐。精子有尾巴（鞭毛）可以游动，并含有大量线粒体提供能量。纤毛上皮细胞分布在呼吸道内壁，通过微小的纤毛摆动来扫走黏液。栅栏组织细胞位于叶片上表面附近，密布叶绿体。理解结构如何与功能相适应是生物学中的统贯思想。
4. Life Processes and Classification | 生命过程与分类
Living organisms carry out seven life processes, often remembered by the acronym MRS GREN: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition. Movement can involve internal transport or external action. Respiration is the release of energy from food—different from breathing. Sensitivity means detecting and responding to stimuli. Growth is a permanent increase in size. Reproduction allows organisms to produce offspring. Excretion removes metabolic waste, distinct from egestion of undigested food. Nutrition is taking in and using food materials.
生物体进行七种生命过程，常用的助记口诀是 MRS GREN：运动、呼吸、感应、生长、生殖、排泄和营养。运动可以是内部运输或外部动作；呼吸是从食物中释放能量，不同于日常说的呼吸；感应指探测并响应刺激；生长是体积的永久增大；生殖使生物产生后代；排泄移除代谢废物，与排出未消化的食物残渣不同；营养是摄取和利用养料。
Scientists classify organisms to make sense of biodiversity. The five kingdoms are Animals, Plants, Fungi, Protists, and Prokaryotes (bacteria). Within each kingdom, organisms are grouped further: phylum, class, order, family, genus, and species. A species is a group of organisms that can interbreed to produce fertile offspring. You use dichotomous keys to identify species by working through pairs of contrasting statements. Vertebrates are animals with backbones and fall into five classes: mammals, birds, reptiles, amphibians, and fish. Each class has defining features—for instance, mammals have hair and produce milk, birds have feathers and lay hard-shelled eggs.
科学家通过分类来理解生物多样性。五界系统包括动物界、植物界、真菌界、原生生物界和原核生物界（细菌）。每一界内又依次分为门、纲、目、科、属、种。物种是指能通过交配产生可育后代的一群生物。利用二分叉检索表，通过逐一对比两个相对特征可以识别物种。脊椎动物是有脊柱的动物，分为五大类：哺乳类、鸟类、爬行类、两栖类和鱼类。每类都有典型特征——例如哺乳动物有毛发并哺乳，鸟类有羽毛并产硬壳卵。
5. Particle Theory and States of Matter | 粒子理论与物质状态
The particle theory helps explain the behaviour of solids, liquids, and gases. All matter is made of tiny particles that move constantly; the energy of movement depends on temperature. In solids, particles are packed closely in a fixed, regular arrangement and can only vibrate. Liquids have particles that are close but can slide past each other, taking the shape of the container. In gases, particles are far apart, moving rapidly in all directions and filling the whole space. The model explains density, compressibility, and shape: solids have fixed shape and volume, liquids fixed volume but not shape, gases neither.
粒子理论能解释固体、液体和气体的行为。一切物质都由不断运动的微小粒子组成，粒子的运动能量取决于温度。固体中粒子紧密堆积成固定、规则的排列，仅能振动。液体粒子之间距离近但可以相互滑动，从而呈现容器的形状。气体粒子相距很远，高速随机运动，充满整个空间。这个模型解释了密度、可压缩性和形状：固体形状体积固定，液体体积固定但形状不固定，气体两者都不固定。
Changes of state are physical changes: melting (solid to liquid), freezing (liquid to solid), boiling/evaporation (liquid to gas), condensation (gas to liquid), and sublimation (solid directly to gas). During melting and boiling, energy is used to break bonds between particles without raising temperature, so the temperature stays constant at the melting point or boiling point. The water cycle illustrates these changes in nature: evaporation from oceans, condensation into clouds, and precipitation as rain. Diffusion is the net movement of particles from an area of higher concentration to one of lower concentration, fastest in gases and slower in liquids.
状态变化是物理变化：熔化（固→液）、凝固（液→固）、沸腾/蒸发（液→气）、凝结（气→液）和升华（固→气）。熔化和沸腾时，能量用于打破粒子间的结合而不升温，因此温度保持在熔点或沸点不变。水循环在自然界展示了这些变化：海洋蒸发、云层凝结、降水落下。扩散是粒子由高浓度区域向低浓度区域的净移动，气体中最快，液体中较慢。
6. Elements, Atoms, and the Periodic Table | 元素、原子与周期表
An element is a substance made of only one type of atom and cannot be broken down into simpler substances by chemical means. Each element is represented by a chemical symbol—for example, O for oxygen, C for carbon, Fe for iron, and Na for sodium (from the Latin natrium). The periodic table arranges all known elements in order of increasing atomic number. Vertical columns are called groups: Group 1 contains the reactive alkali metals, Group 7 the reactive halogens, and Group 0 (or 8) the unreactive noble gases. The horizontal rows are periods. Metals are on the left and centre; non-metals are on the right, with a zigzag line dividing them.
元素是仅由一种原子组成的物质，不能用化学方法再分解成更简单的物质。每种元素用一个化学符号表示，例如 O 代表氧，C 代表碳，Fe 代表铁，Na 代表钠（源自拉丁文 natrium）。周期表按原子序数递增顺序排列所有已知元素。纵列称为族：第 1 族是活泼的碱金属，第 7 族是活泼的卤素，第 0 族（或第 8 族）是非活泼的稀有气体。横排称为周期。金属位于左侧和中部，非金属位于右侧，中间有一条锯齿形分界线。
Atoms are made of three subatomic particles: protons (positive, in nucleus), neutrons (neutral, in nucleus), and electrons (negative, orbiting the nucleus in shells). In a neutral atom, the number of protons equals the number of electrons. The atomic number tells you the number of protons, and the mass number is the total of protons plus neutrons. The first electron shell holds up to 2 electrons, the second up to 8, and the third up to 8 in the simple model used at this stage. This arrangement helps explain reactivity—for instance, elements with a full outer shell, like noble gases, are stable and unreactive.
原子由三种亚原子粒子构成：质子（带正电，在原子核内）、中子（不带电，在核内）和电子（带负电，分层排布在核外）。中性原子里质子数等于电子数。原子序数等于质子数，质量数是质子数与中子数之和。在现阶段使用的简单模型中，第一电子层最多容纳 2 个电子，第二层最多 8 个，第三层最多 8 个。这种排布能解释活泼性——例如稀有气体拥有满外层电子，因此稳定不活泼。
7. Compounds, Mixtures and Separation Techniques | 化合物、混合物与分离技术
A compound is a substance formed when two or more elements chemically combine in fixed proportions. The properties of a compound are often completely different from those of its constituent elements. For example, sodium is a reactive metal and chlorine is a poisonous gas, but their compound sodium chloride is harmless table salt. Chemical formulas show the type and ratio of atoms: H₂O has two hydrogen atoms for every oxygen atom; CO₂ has one carbon and two oxygens. A mixture, on the other hand, contains different substances not chemically joined, each keeping its own properties. Air and sea water are common mixtures.
化合物是由两种或多种元素以固定比例通过化学结合形成的物质。化合物的性质往往与构成元素完全不同。例如，钠是活泼金属，氯是有毒气体，但它们的化合物氯化钠是无害的食盐。化学式表示原子的种类和个数比：H₂O 表示每个水分子有 2 个氢原子和 1 个氧原子；CO₂ 表示 1 个碳原子和 2 个氧原子。混合物则含有未发生化学结合的多种物质，各自保留原有性质。空气和海水都是常见混合物。
You can separate mixtures using physical techniques that exploit differences in physical properties. Filtration separates an insoluble solid from a liquid (e.g., sand from water). Evaporation removes a dissolved solid by boiling off the solvent, used to obtain salt from salt water. Simple distillation collects the solvent by boiling and condensing it, leaving impurities behind. Chromatography separates coloured substances based on differing solubilities. Knowing which technique to use depends on whether the solid is soluble and whether the liquid needs to be kept. A pure substance has a sharp, fixed melting and boiling point; a mixture often melts or boils over a range of temperatures.
可以利用物质物理性质的差异，通过物理方法分离混合物。过滤可以将不溶固体从液体中分离（如分离沙和水）。蒸发通过煮沸除去溶剂来得到溶解的固体，用于从盐水中获取食盐。简单蒸馏则使溶剂沸腾后冷凝收集，留下杂质。色谱法根据溶解度的不同分离有色物质。选择哪项技术取决于固体是否可溶以及是否需要保留液体。纯净物有固定、锐利的熔点和沸点；混合物则常在一段温度范围内熔融或沸腾。
8. Forces and Their Effects | 力及其效应
A force is a push or pull that can change an object’s speed, direction, or shape. Forces are measured in newtons (N) using a spring balance or force meter. When forces on an object are balanced, the object stays at rest or continues moving at a constant speed in a straight line. If forces are unbalanced, the object accelerates or decelerates. Friction is a contact force that opposes motion, often generating heat. Air resistance and water resistance are types of drag. Gravity is a non-contact force that pulls objects towards the centre of the Earth; it gives objects weight, which is calculated using weight = mass × gravitational field strength (w = m × g). On Earth, g ≈ 10 N/kg, so a 5 kg mass has a weight of 50 N.
力是能改变物体速度、方向或形态的推或拉。力的单位是牛顿 (N)，使用弹簧秤或测力计测量。当作用在同一物体上的力平衡时，物体会保持静止或沿直线匀速运动。若力不平衡，物体就会加速或减速。摩擦力是一种阻碍运动的接触力，通常会生热。空气阻力和水阻力都是拖曳力。重力是非接触力，将物体拉向地球中心，它使物体具有重量，计算公式为：重量 = 质量 × 重力场强度 (w = m × g)。在地球表面，g 约为 10 N/kg，因此 5 kg 的物体重 50 N。
Speed describes how fast an object moves; average speed is given by the equation:
average speed = distance ÷ time
Distance–time graphs provide a visual way to analyse motion. A horizontal line means the object is stationary; a straight sloping line shows constant speed; a steeper slope means a higher speed. The slope (gradient) equals speed. You should be able to calculate speed from a graph and describe the journey. Stretching a spring relates to Hooke’s Law: the extension is directly proportional to the force applied, as long as the elastic limit is not exceeded. An elastic material returns to its original shape when the force is removed.
速度描述物体运动的快慢；平均速度可由公式得出：平均速度 = 距离 ÷ 时间。距离–时间图提供了一种分析运动的直观方式。水平线表示物体静止；倾斜直线表示匀速；斜率越大速度越快。斜率（坡度）即为速度。你需要能从图中计算速度并描述运动过程。拉伸弹簧涉及胡克定律：只要不超过弹性限度，伸长量与施加的力成正比。弹性材料在撤去外力后能恢复原状。
9. Energy Transfers and Resources | 能量转移与能源资源
Energy is the ability to do work and is measured in joules (J) or kilojoules (kJ). The key principle is that energy can be transferred or stored but never created or destroyed—this is the law of conservation of energy. Common energy stores include chemical (in food and fuels), kinetic (movement), thermal (heat), gravitational potential (height), elastic potential (stretched or compressed), and nuclear. Energy transfers happen by forces doing work (mechanical transfer), heating (thermal transfer), or radiation (light and sound). For example, a battery-powered torch transfers energy from the chemical store in the battery to the electrical pathway, then to light and thermal stores.
能量是做功的本领，单位是焦耳 (J) 或千焦 (kJ)。最核心的原理是能量可以转移或储存，但绝不能凭空产生或消失——这称为能量守恒定律。常见的能量储存有化学能（食物和燃料中）、动能（运动）、热能（热量）、重力势能（高度）、弹性势能（拉伸或压缩）和核能。能量可以通过力做功（机械传递）、加热（热传递）或辐射（光和声）进行转移。例如，电池手电筒将电池中的化学能储存转移到电路径，再转化为光能和热能储存。
Energy resources are classified as renewable or non-renewable. Non-renewable resources include fossil fuels (coal, oil, natural gas) and nuclear fuels. They are finite and will eventually run out; burning fossil fuels also releases carbon dioxide that contributes to global warming. Renewable resources can be replenished: solar, wind, tidal, wave, hydroelectric, geothermal, and biomass. When generating electricity, a turbine usually spins a generator. In thermal power stations, fuel is burned to heat water into steam that drives the turbine. In solar cells, light is converted directly into electricity. Energy efficiency can be reduced by friction and heat loss; scientists and engineers try to minimise unwanted energy transfers.
能源资源分为可再生能源和不可再生能源。不可再生资源包括化石燃料（煤、石油、天然气）和核燃料。它们的储量有限，终将耗尽；燃烧化石燃料还会释放二氧化碳，加剧全球变暖。可再生能源可以自我补充，包括太阳能、风能、潮汐能、波浪能、水力、地热和生物质。发电时通常用涡轮机带动发电机。在火力发电站，燃料燃烧将水加热成蒸汽，蒸汽驱动涡轮机。太阳能电池则直接将光转化为电。摩擦和散热会降低能量效率；科学家和工程师致力于减少非期望的能量转移。
10. Electric Circuits and Current | 电路与电流
An electric circuit is a closed loop that provides a path for current to flow. For current to flow, the circuit must be complete and contain a source of voltage, such as a cell or battery. Current is the flow of electric charge—in metal wires, it is a flow of electrons. Current is measured in amperes (A) using an ammeter connected in series. Voltage (potential difference) is the ‘push’ that drives current around the circuit, measured in volts (V) with a voltmeter connected in parallel across a component. Conductors like copper allow current to pass easily, while insulators like plastic do not.
电路是一个闭合回路，为电流提供通路。要形成电流，电路必须完整，并包含电压源，如一节电池或电池组。电流是电荷的流动——在金属导线中就是电子的流动。电流用安培 (A) 为单位，用串联的电流表测量。电压（电势差）是推动电流流动的“推力”，单位为伏特 (V)，用并联在元件两端的电压表测量。导体如铜容易让电流通过，绝缘体如塑料则不能。
Circuit diagrams use standard symbols: a cell is shown as a long thin line (positive) and a short thick line (negative), a battery as multiple cells, a lamp (bulb) as a circle with a cross, a switch as a break in the line that can be closed, and a resistor as a rectangle. In a series circuit, components are connected one after another; if one lamp breaks, all go out. In a parallel circuit, each component has its own branch; if one lamp breaks, the others stay lit. Current is the same everywhere in a series circuit, while voltage is shared across components. In a parallel circuit, voltage is the same across each branch, and the total current is the sum of the branch currents. Understanding these rules helps you predict how adding cells or bulbs affects brightness.
电路图使用标准符号：电池用一长细线（正极）和一短粗线（负极）表示，电池组是多个电池，灯泡是圆圈内画叉，开关是线段中断可闭合，电阻器是矩形。串联电路中元件首尾相接，一个灯泡坏了全部熄灭。并联电路中每个元件有独立支路，若一个灯泡坏了其余仍亮。串联电路中各点电流相同，而电压被各个元件分担。并联电路中各支路两端电压相同，总电流等于各支路电流之和。掌握这些规则能帮你预测增减电池或灯泡对亮度的影响。
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