📚 Cambridge Lower Secondary Science 7: Core Ideas and Exam Skills | 剑桥初中科学7：核心概念与应试技巧
This revision guide summarises the essential content of the Cambridge Lower Secondary Science 7 Learner's Book Second Edition. It covers key ideas from biology, chemistry, physics and scientific enquiry, with paired English and Chinese explanations to help you check understanding before tests or Checkpoint assessments.
本复习指南总结了《剑桥初中科学7学习者用书第二版》的核心内容。它涵盖生物、化学、物理和科学探究的关键概念，并配有中英文对照讲解，帮助你在测验或 Checkpoint 评估前检查理解。
1. Cells and Microscopy | 细胞与显微镜
All living organisms are made of cells. A cell is the smallest unit that can carry out the life processes such as movement, respiration, sensitivity, growth, reproduction, excretion and nutrition.
所有生物体都由细胞构成。细胞是能够进行生命活动的最小单位，如运动、呼吸、感应、生长、繁殖、排泄和营养。
nification. For example, a 10× eyepiece and a 40× objective give 400× total magnification.
光学显微镜使用透镜放大微小物体。总放大倍数等于目镜放大倍数乘以物镜放大倍数。例如，10× 目镜和 40× 物镜的总放大倍数为 400×。
When drawing cells, always use a sharp pencil, draw clear lines without shading, label the parts, and write the magnification underneath.
画细胞图时，始终使用削尖的铅笔，线条清晰不涂阴影，标注各部位，并在图下方写出放大倍数。
2. Plant and Animal Cells | 植物细胞与动物细胞
Animal cells contain a cell membrane, cytoplasm and nucleus. Plant cells have these three parts and also a cell wall, chloroplasts and a large permanent vacuole.
动物细胞含有细胞膜、细胞质和细胞核。植物细胞除了这三种结构外，还有细胞壁、叶绿体和大型永久液泡。
The nucleus controls the cell's activities and contains genetic material. The cell membrane controls which substances enter and leave the cell. Cytoplasm is the jelly-like site of chemical reactions.
细胞核控制细胞活动并含有遗传物质。细胞膜控制物质进出细胞。细胞质是发生化学反应的胶状场所。
| Feature | Animal cell | Plant cell |
|---|---|---|
| Cell wall | Absent | Present |
| Chloroplasts | Absent | Present |
| Vacuole | Small or none | Large permanent |
Remember that chloroplasts absorb light energy for photosynthesis, so they are found mainly in green parts of the plant such as leaves.
请记住，叶绿体吸收光能进行光合作用，因此主要存在于植物的绿色部分，如叶片中。
3. Particle Theory and States of Matter | 粒子理论与物质状态
Matter is made of tiny particles. The arrangement and movement of these particles explain the properties of solids, liquids and gases.
物质由微小粒子组成。这些粒子的排列方式和运动可以解释固体、液体和气体的性质。
In solids, particles are packed closely in a regular pattern and only vibrate in fixed positions. In liquids, particles are close but can slide past one another, so liquids can flow and take the shape of a container.
在固体中，粒子紧密排列成规则图案，只能在固定位置振动。在液体中，粒子彼此靠近但可以相互滑动，因此液体能够流动并呈现容器的形状。
In gases, particles are far apart and move quickly in all directions. This explains why gases can be compressed and spread out to fill any container.
在气体中，粒子相距很远并快速向各个方向运动。这解释了为什么气体可以被压缩并扩散以充满任何容器。
When a solid melts, the particles gain energy and start to slide past each other; the melting point is the temperature at which a solid becomes a liquid.
当固体熔化时，粒子获得能量并开始相互滑动；熔点是固体变为液体的温度。
4. Forces: Balanced, Unbalanced and Friction | 力：平衡力、非平衡力与摩擦力
A force is a push or a pull measured in newtons (N). Forces can change the speed, direction or shape of an object.
力是推或拉，单位为牛顿 (N)。力可以改变物体的速度、方向或形状。
When forces on an object are balanced, the object will remain at rest or continue moving at a steady speed in a straight line. When forces are unbalanced, the object will accelerate, decelerate or change direction.
当物体受到的力平衡时，物体将保持静止或沿直线匀速运动。当力不平衡时，物体将加速、减速或改变方向。
Friction is a force that opposes motion between two surfaces. It can be reduced by lubrication, using wheels or smoothing surfaces.
摩擦力是阻碍两个表面之间相对运动的
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