📚 Key Concepts in Cambridge Lower Secondary Science Stage 7 (Second Edition) | 剑桥初中科学7年级关键概念（第二版）
The Cambridge Lower Secondary Science Stage 7 Learner’s Book (Second Edition) builds a strong foundation in biology, chemistry, and physics by introducing core scientific ideas through enquiry and real-world contexts. This article distils the essential concepts from the course, helping learners and educators review living things, cells, particles, forces, energy, electricity, and the solar system in a clear, bilingual format.
剑桥初中科学7年级学习者用书（第二版）通过探究和真实情境引入核心科学概念，为生物、化学和物理打下坚实基础。本文萃取课程中的关键知识，以清晰的双语形式帮助学习者和教师回顾生物与分类、细胞、粒子、力与运动、能量、电学以及太阳系等重要主题。
1. Living Things and Classification | 生物与分类
All living organisms carry out seven life processes, often remembered by the acronym MRS GREN: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion and Nutrition. These processes define whether something is alive.
所有生物都执行七种生命过程，常用缩写 MRS GREN 记忆：运动、呼吸、感应、生长、繁殖、排泄和营养。这些过程决定了某物是否具有生命。
Scientists classify living things into five kingdoms: Animals, Plants, Fungi, Prokaryotes (bacteria), and Protoctists (unicellular organisms like amoeba and algae). Each kingdom has distinct features, such as the presence of a nucleus or cell wall.
科学家将生物分为五界：动物界、植物界、真菌界、原核生物界（细菌）和原生生物界（如变形虫和藻类等单细胞生物）。每一界都有明显的特征，例如是否存在细胞核或细胞壁。
Within the animal kingdom, vertebrates are further divided into five classes: mammals, birds, reptiles, amphibians and fish. They can be distinguished by body covering, method of reproduction and how they breathe.
在动物界中，脊椎动物又分为五个纲：哺乳动物、鸟类、爬行动物、两栖动物和鱼类。它们可以通过体表覆盖物、繁殖方式以及呼吸方式加以区分。
2. Cells – The Building Blocks of Life | 细胞——生命的基石
All living things are made of cells. A typical animal cell contains a cell membrane, cytoplasm, nucleus and mitochondria. The nucleus controls the cell’s activities and carries genetic information, while mitochondria release energy through respiration.
所有生物都由细胞构成。典型的动物细胞包含细胞膜、细胞质、细胞核和线粒体。细胞核控制细胞的活动并携带遗传信息，线粒体则通过呼吸作用释放能量。
Plant cells have three additional structures: a rigid cell wall made of cellulose, a large permanent vacuole that stores cell sap, and chloroplasts where photosynthesis takes place, converting light energy into chemical energy.
植物细胞还多出三种结构：由纤维素构成的坚固细胞壁、储存细胞液的大液泡以及进行光合作用的叶绿体，光合作用将光能转化为化学能。
To observe cells, we use a microscope. The total magnification is calculated by multiplying the eyepiece lens magnification by the objective lens magnification. For example, a x10 eyepiece and a x40 objective give a total magnification of x400.
我们使用显微镜观察细胞。总放大倍数是目镜放大倍数乘以物镜放大倍数。例如，10倍目镜和40倍物镜的总放大倍数为400倍。
total magnification = eyepiece magnification x objective magnification
3. Particles and States of Matter | 粒子与物质状态
Everything around us is made up of tiny particles. The particle model explains the properties of solids, liquids, and gases. In solids, particles are closely packed in a regular arrangement, vibrate in fixed positions, and have low energy.
我们周围的一切都由微小粒子构成。粒子模型解释了固体、液体和气体的性质。在固体中，粒子紧密排列成规则结构，在固定位置振动，能量较低。
In liquids, particles are still close together but can move past each other, taking the shape of the container. In gases, particles are far apart, move rapidly in all directions, and have high energy. This explains why gases can be compressed and fill any container.
在液体中，粒子仍然紧密，但可以相互滑动，呈容器的形状。气体粒子相距很远，在各个方向快速运动且能量高。这就解释了为什么气体可以被压缩并能充满任何容器。
The physical state can change when heat energy is added or removed. Melting (solid to liquid) and freezing (liquid to solid) occur at the melting point, while boiling (liquid to gas) and condensing (gas to liquid) occur at the boiling point.
物质在获得或失去热能时会发生状态改变。熔化（固体到液体）和凝固（液体到固体）发生在熔点时，沸腾（液体到气体）和冷凝（气体到液体）发生在沸点时。
solid → liquid (melting) liquid → gas (boiling)
4. Properties of Materials and Diffusion | 材料性质与扩散
Different materials have distinct properties that determine their uses. Key properties include hardness, strength, flexibility, electrical conductivity, thermal conductivity, and solubility. For example, metals are good conductors of heat and electricity, while plastics are insulators.
不同材料具有不同的性质，这些性质决定了其用途。关键性质包括硬度、强度、柔韧性、导电性、导热性和溶解度。例如，金属是热和电的优良导体，而塑料是绝缘体。
Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. It occurs in liquids and gases and does not require extra energy. You can observe diffusion when a coloured crystal dissolves in water or a smell spreads through a room.
扩散是粒子从高浓度区域向低浓度区域的运动。它发生在液体和气体中，不需要额外的能量。当有色晶体在水中溶解或气味在室内散开时，你就能观察到扩散现象。
Gas pressure is caused by gas particles colliding with the walls of their container. When the volume of a container decreases, particles are closer together and collide more often, increasing the pressure.
气体压力是由气体粒子撞击容器壁引起的。当容器的体积减小时，粒子更加靠近，碰撞更加频繁，压力随之升高。
5. Forces and Their Effects | 力及其作用效果
A force is a push or a pull that can change the speed, direction, or shape of an object. Forces are measured in newtons (N) using a forcemeter. Common forces include gravity, friction, air resistance, and upthrust.
力是能够改变物体速度、方向或形状的推或拉。力的单位是牛顿（N），用力计测量。常见的力包括重力、摩擦力、空气阻力和浮力。
Gravity is the force of attraction between any two masses. On Earth, the gravitational field strength is about 10 N/kg, meaning each kilogram of mass experiences a weight of 10 N. Weight is different from mass: mass is the amount of matter, measured in kg, while weight is a force.
重力是任何两个质量之间的吸引力。地球上的引力场强度约为 10 N/kg，意味着每千克质量受到 10 N 的重力。重量不同于质量：质量是物质的多少，以千克（kg）计量，而重量是一种力。
weight (N) = mass (kg) x gravitational field strength (N/kg)
Friction is a force that opposes motion between two surfaces in contact. It can be useful, such as allowing us to walk without slipping, or unwanted, when it causes wear and reduces efficiency. Lubricants reduce friction.
摩擦力是阻碍两接触表面相对运动的力。它可能是有用的，例如让我们能够走路而不滑倒；也可能是不利的，会造成磨损并降低效率。润滑剂可以减少摩擦。
6. Speed, Distance and Time | 速度、距离与时间
Speed describes how fast an object moves. The average speed of an object is calculated by dividing the total distance travelled by the time taken. The standard unit for speed is metres per second (m/s), though kilometres per hour (km/h) is also common.
速度描述物体运动的快慢。物体的平均速度用总路程除以所用时间计算。速度的标准单位是米/秒（m/s），千米/小时（km/h）也很常用。
speed = distance ÷ time
A distance–time graph shows how far an object has travelled over a period of time. A straight, sloping line indicates constant speed; the steeper the slope, the faster the object moves. A horizontal line means the object is stationary.
距离－时间图显示了物体在一段时间内移动的路程。一条倾斜的直线表示匀速运动；斜率越大，物体运动越快。水平线表示物体静止。
In a journey, there may be periods of acceleration, steady speed, and deceleration. Relative motion explains how the movement of one object appears different depending on the observer’s frame of reference.
在一次旅途中，可能会有加速、匀速和减速的阶段。相对运动解释了根据观察者参考系的不同，一个物体的运动看起来会有不同的情况。
7. Energy Forms and Transfers | 能量的形式与转化
Energy is the ability to do work and is measured in joules (J). It exists in many forms: kinetic (movement), thermal (heat), light, sound, electrical, chemical potential, elastic potential, and gravitational potential. Energy cannot be created or destroyed, only transferred or transformed.
能量是做功的能力，其单位是焦耳（J）。能量存在多种形式：动能、热能、光能、声能、电能、化学势能、弹性势能和重力势能。能量既不能被创造也不能被消灭，只能被转移或转化。
An energy transfer describes energy moving from one place to another, for example, heat energy transferred from a hot cup to the cooler air. Energy transformation is when energy changes from one form to another, such as a light bulb transforming electrical energy into light and heat.
能量转移是指能量从一个地方移动到另一个地方，例如热能从热杯子传递到较冷的空气中。能量转化则是能量从一种形式变为另一种形式，比如灯泡将电能转化为光和热。
In any energy conversion, some energy is always ‘lost’ as thermal energy to the surroundings, which can make the process less efficient. Sankey diagrams help visualise energy transfers and show how much energy is useful and how much is wasted.
在任何能量转换中，总有一部分能量以热能形式“散失”到周围环境，这会降低过程的效率。桑基图有助于可视化能量转移，显示有多少能量是有用的，有多少被浪费了。
8. Electrical Circuits | 电路
An electrical circuit needs a complete loop for current to flow. The key components include a cell or battery (power supply), wires, a switch, and a load such as a bulb or buzzer. Current is the flow of electric charge and is measured in amperes (A).
电路需要完整的回路才能使电流流动。关键元件包括电池（电源）、导线、开关以及灯泡或蜂鸣器等负载。电流是电荷的流动，单位是安培（A）。
Conductors, such as copper and aluminium, allow electricity to pass through easily because they have free electrons. Insulators, like plastic and rubber, prevent the flow of electricity, making them useful for safety coatings.
导体如铜和铝允许电流轻松通过，因为它们有自由电子。绝缘体如塑料和橡胶阻止电流通过，因此常用于安全包覆层。
Components can be connected in series or in parallel. In a series circuit, there is only one path for the current; if one component fails, the whole circuit stops. In a parallel circuit, there are multiple paths, so other components continue to work if one fails.
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；如果一个元件损坏，整个电路停止工作。在并联电路中，有多条通路，因此一个元件损坏时其他元件仍可工作。
Electrical hazards, such as overloaded sockets or damaged wires, can cause overheating and fires. Understanding circuit safety is essential when designing and using electrical devices.
电气危险，例如插座过载或导线损坏，可能导致过热和火灾。在设计和应用电器时，理解电路安全是至关重要的。
9. The Solar System and Beyond | 太阳系及更远
Our solar system consists of the Sun, eight planets, their moons, and smaller objects such as asteroids and comets. The order of the planets from the Sun is: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
我们的太阳系由太阳、八大行星及其卫星，以及小行星和彗星等较小的天体组成。行星距离太阳从近到远的顺序是：水星、金星、地球、火星、木星、土星、天王星和海王星。
The Sun is a star, a giant ball of hot gas that produces energy through nuclear fusion. Its immense gravity keeps all the planets in orbit. The Earth’s orbit is nearly circular, and it takes about 365.25 days to complete one revolution, causing the year.
太阳是一颗恒星，一个通过核聚变产生能量的炽热气体球。它巨大的引力使所有行星保持在轨道上运行。地球的轨道接近圆形，绕太阳一周约需 365.25 天，形成一年。
The Earth rotates on its axis once every 24 hours, creating day and night. The tilt of Earth’s axis and its orbit around the Sun give rise to the seasons. When the Northern Hemisphere tilts towards the Sun, it experiences summer, while the Southern Hemisphere has winter.
地球每 24 小时自转一周，产生昼夜交替。地轴的倾斜和绕日公转产生了四季。当北半球倾向太阳时，为夏季，而南半球则为冬季。
Beyond our solar system are billions of galaxies, each containing millions or billions of stars. Light from distant stars takes many years to reach us, so looking into space is like looking back in time.
在太阳系之外有数十亿个星系，每个星系包含数百万或数十亿颗恒星。来自遥远恒星的光需要许多年才能到达我们这里，因此眺望太空就像回顾过去。
10. Rocks and the Changing Earth | 岩石与变化中的地球
The Earth’s structure is divided into four main layers: the inner core, outer core, mantle, and crust. The crust is the thin, solid outermost layer where we live. Below the crust, the mantle is semi-solid and flows very slowly.
地球的结构主要分为四层：内核、外核、地幔和地壳。地壳是我们生活的薄且坚硬的最外层。地壳之下，地幔呈半固态且非常缓慢地流动。
Rocks are classified into three main groups: igneous, sedimentary, and metamorphic. Igneous rocks, like granite and basalt, form from cooled magma or lava. Sedimentary rocks, such as sandstone and limestone, are made from compressed layers of sediment. Metamorphic rocks, like marble and slate, are formed when existing rocks are changed by heat and pressure.
岩石分为三大类：火成岩、沉积岩和变质岩。火成岩如花岗岩和玄武岩，由冷却的岩浆或熔岩形成。沉积岩如砂岩和石灰岩，由沉积物经挤压层叠而成。变质岩如大理岩和板岩，则是在热和压力作用下由原有岩石变成的。
The rock cycle shows how rocks are continuously recycled over millions of years through processes like weathering, erosion, sedimentation, melting, and cooling. This dynamic system links all rock types together.
岩石循环显示了岩石如何在数百万年里通过风化、侵蚀、沉积、熔融和冷却等过程不断循环再造。这一动态系统将所有类型的岩石联结在一起。
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