📚 Cambridge Lower Secondary Science 9: Core Revision Guide | 剑桥初中科学9年级核心复习指南
This revision guide covers the key topics in the Cambridge Lower Secondary Science 9 Learner's Book. It is designed to help you consolidate your understanding of biology, chemistry, physics and Earth science, while building the scientific enquiry skills needed for progression to IGCSE level.
本复习指南涵盖剑桥初中科学9年级学习者用书中的核心主题。它旨在帮助你巩固对生物、化学、物理和地球科学的理解，同时培养进入 IGCSE 阶段所需的科学探究技能。
1. Cells and Organisation | 细胞与组织结构
All living organisms are made of cells. Plant cells have a cellulose cell wall, a large permanent vacuole and chloroplasts, which animal cells do not have. Both plant and animal cells contain a nucleus, cytoplasm, cell membrane and mitochondria.
所有生物体都由细胞构成。植物细胞有纤维素细胞壁、一个大的中央液泡和叶绿体，而动物细胞没有这些结构。植物细胞和动物细胞都含有细胞核、细胞质、细胞膜和线粒体。
Cells are organised into tissues, then organs, then organ systems. For example, muscle cells form muscle tissue, which forms the heart, which is part of the circulatory system.
细胞组织成组织，再构成器官，然后形成器官系统。例如，肌肉细胞构成肌肉组织，肌肉组织构成心脏，心脏是循环系统的一部分。
- Specialised cells include red blood cells, root hair cells, ciliated cells and sperm cells.
- 特化细胞包括红细胞、根毛细胞、纤毛细胞和精细胞。
2. Particles and Atomic Structure | 微粒与原子结构
The particle model explains the properties of solids, liquids and gases. In solids, particles vibrate in fixed positions; in liquids, particles move past each other; in gases, particles move rapidly in all directions.
微粒模型解释了固体、液体和气体的性质。在固体中，微粒在固定位置振动；在液体中，微粒相互滑动；在气体中，微粒向各个方向快速运动。
All substances are made of atoms. An atom consists of protons and neutrons in the nucleus, with electrons arranged in shells around the nucleus. Atoms of different elements contain different numbers of protons.
所有物质都由原子构成。原子由原子核中的质子和中子以及核外分层排列的电子组成。不同元素的原子含有不同数目的质子。
atomic number = number of protons
原子序数 = 质子数
3. Chemical Reactions and Equations | 化学反应与方程式
A chemical change produces new substances and is usually difficult to reverse. Signs of a chemical reaction include colour change, gas production, temperature change and the formation of a precipitate.
化学变化会产生新物质，通常难以逆转。化学反应的迹象包括颜色变化、气体产生、温度变化以及沉淀生成。
Word equations show the reactants and products of a reaction. A simple example is the reaction between magnesium and oxygen to form magnesium oxide. The total mass of reactants equals the total mass of products because atoms are rearranged, not created or destroyed.
文字方程式表示反应物和生成物。一个简单的例子是镁与氧气反应生成氧化镁。反应物的总质量等于生成物的总质量，因为原子只是重新排列，没有被创造或消灭。
magnesium + oxygen → magnesium oxide
镁 + 氧气 → 氧化镁
4. Acids, Bases and the pH Scale | 酸、碱与 pH 值
Acids have a pH below 7 and bases have a pH above 7. A neutral solution such as pure water has a pH of exactly 7. Universal indicator changes colour across the pH range and can be used to estimate the pH of a solution.
酸的 pH 值低于 7，碱的 pH 值高于 7。纯水等中性溶液的 pH 值恰好为 7。通用指示剂在 pH 范围内会改变颜色，可用于估计溶液的 pH 值。
When an acid reacts with a base, neutralisation occurs, producing a salt and water. This type of reaction is important in everyday contexts such as treating acidic soil with lime and taking antacids for stomach upset.
当酸与碱反应时会发生中和反应，生成盐和水。这类反应在日常生活中很重要，例如用石灰处理酸性土壤以及服用抗酸药缓解胃部不适。
acid + base → salt + water
酸 + 碱 → 盐 + 水
5. Forces and Motion | 力与运动
A force is a push or a pull. When forces on an object are balanced, the object remains at rest or continues moving at constant speed. Unbalanced forces cause acceleration, deceleration or a change in direction.
力是推或拉的作用。当物体受到的力平衡时，物体会保持静止或继续以恒定速度运动。不平衡的力会导致加速、减速或方向改变。
Speed can be calculated using the equation below. In the equation, distance is measured in metres and time in seconds, so speed has the unit metres per second (m/s).
速度可以用下面的公式计算。在该公式中，距离以米为单位，时间以秒为单位，因此速度的单位是米每秒（m/s）。
speed = distance ÷ time
速度 = 距离 ÷ 时间
Friction and air resistance oppose motion. They can be reduced by streamlining, lubrication or using smoother surfaces, which helps vehicles move more efficiently.
摩擦力和空气阻力会阻碍运动。可以通过流线型设计、润滑或使用更光滑的表面来减小它们，从而帮助车辆更高效地移动。
6. Energy Transfers and Resources | 能量转移与资源
Energy can exist in different forms, including kinetic, chemical, thermal, gravitational potential, elastic potential, sound, light and electrical energy. Energy is conserved: it cannot be created or destroyed, only transferred or stored.
能量可以以不同形式存在，包括动能、化学能、热能、重力势能、弹性势能、声能、光能和电能。能量守恒：它不能被创造或消灭，只能被转移或储存。
Energy transfer diagrams show how energy moves from one store to another. For example, a battery-powered torch transfers chemical energy to electrical energy and then to light and thermal energy.
能量转移图显示能量如何从一个能量库转移到另一个能量库。例如，电池供电的手电筒将化学能转化为电能，然后转化为光能和热能。
- Renewable resources include solar, wind, hydroelectric, geothermal and biomass energy.
- 可再生能源包括太阳能、风能、水能、地热能和生物质能。
- Non-renewable resources include coal, oil and natural gas, which release carbon dioxide when burned.
- 不可再生能源包括煤、石油和天然气，它们在燃烧时会释放二氧化碳。
7. Electricity and Magnetism | 电与磁
In a series circuit, components are connected one after another in a single loop. If one component breaks, the whole circuit stops working. In a parallel circuit, components are connected in separate branches, so each branch can work independently.
在串联电路中，元件一个接一个地连接在单一回路中。如果一个元件损坏，整个电路都会停止工作。在并联电路中，元件连接在独立的支路中，因此每条支路可以独立工作。
Current is the flow of electric charge, voltage is the push that drives the current, and resistance opposes the flow. Conductors such as copper allow current to pass easily, while insulators such as plastic do not.
电流是电荷的流动，电压是推动电流的驱动力，电阻则阻碍电流。铜等导体容易让电流通过，而塑料等绝缘体则不能。
An electromagnet is made by wrapping a coil of wire around an iron core and passing a current through the wire. Electromagnets are used in relays, loudspeakers and electric bells because their magnetism can be switched on and off.
电磁铁由缠绕在铁芯上的线圈制成，并在线圈中通入电流。电磁铁用于继电器、扬声器和电铃中，因为它们的磁性可以随时接通和断开。
8. Plant Biology: Photosynthesis and Transport | 植物生物学：光合作用与运输
Photosynthesis is the process by which green plants make glucose from carbon dioxide and water, using light energy absorbed by chlorophyll. Oxygen is released as a by-product. The process takes place mainly in the leaves.
光合作用是绿色植物利用叶绿素吸收的光能，将二氧化碳和水转化为葡萄糖的过程。氧气作为副产品被释放出来。该过程主要发生在叶片中。
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Xylem tissue transports water and mineral ions from the roots upward, while phloem tissue transports sugars and other nutrients from the leaves to the rest of the plant. These transport systems are essential for growth and survival.
木质部组织将水和无机盐离子从根部向上运输，而韧皮部组织将糖和其他营养物质从叶片运输到植物的其他部位。这些运输系统对植物的生长和生存至关重要。
Factors that affect the rate of photosynthesis include light intensity, carbon dioxide concentration and temperature. If one of these factors is in short supply, it limits the rate of the process.
影响光合作用速率的因素包括光照强度、二氧化碳浓度和温度。如果其中一个因素供应不足，它就会限制光合作用的速率。
9. Earth, Atmosphere and Ecosystems | 地球、大气与生态系统
Rocks are constantly changed by the rock cycle. Igneous rocks form from cooling magma or lava, sedimentary rocks form from compacted layers of sediment, and metamorphic rocks form when existing rocks are changed by heat and pressure.
岩石在岩石循环中不断发生变化。火成岩由岩浆或熔岩冷却形成，沉积岩由沉积物压实成层形成，变质岩则是由原有岩石在高温和高压下发生变化而形成。
The atmosphere is a mixture of gases, mainly nitrogen (about 78%) and oxygen (about 21%), with small amounts of carbon dioxide, argon and water vapour. The carbon cycle moves carbon between the atmosphere, living organisms, oceans and rocks.
大气是多种气体的混合物，主要是氮气（约 78%）和氧气（约 21%），还含有少量二氧化碳、氩气和水蒸气。碳循环使碳在大气、生物体、海洋和岩石之间循环移动。
In an ecosystem, food chains show the transfer of energy from producers to consumers. Producers such as plants make their own food, while consumers feed on other organisms. At each level in a food chain, some energy is lost as heat, so food chains usually have only a few steps.
在生态系统中，食物链显示能量从生产者到消费者的传递。植物等生产者自己制造食物，而消费者以其他生物为食。在食物链的每一级中，部分能量以热能形式散失，因此食物链通常只有几个环节。
10. Practical Skills and Scientific Enquiry | 实验技能与科学探究
Good scientific enquiry involves planning fair tests, making careful observations, recording data accurately and drawing conclusions from evidence. A fair test changes only one independent variable while all other variables are controlled.
良好的科学探究包括设计公平实验、细心观察、准确记录数据以及从证据中得出结论。公平实验只改变一个自变量，而所有其他变量都保持不变。
Safety is always the first priority in the laboratory. You should wear eye protection, tie back long hair, and follow your teacher's instructions when handling chemicals, heating substances or using electrical equipment.
安全始终是实验室中的第一要务。你应该佩戴护目镜、扎起长发，并在处理化学品、加热物质或使用电气设备时遵循老师的指导。
- Common apparatus includes beakers, measuring cylinders, test tubes, Bunsen burners, thermometers and stopwatches.
- 常用仪器包括烧杯、量筒、试管、本生灯、温度计和秒表。
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