📚 Cambridge Lower Secondary Science Workbook 9 Key Concepts | 剑桥初中科学练习册9核心概念
Cambridge Lower Secondary Science Workbook 9 is designed to help learners aged 13–14 consolidate their understanding of essential scientific concepts across biology, chemistry, physics and earth science. This article compiles the most important topics and exam-style knowledge points found throughout the workbook, providing a clear bilingual revision guide. By working through each section, you will strengthen your ability to explain scientific ideas, interpret data and apply principles to new situations.
《剑桥初中科学练习册9》旨在帮助13至14岁的学生巩固生物学、化学、物理学和地球科学中的核心科学概念。本文汇集了整本练习册中最重要的主题和考试型知识点，提供了一份清晰的双语复习指南。通过学习每个部分，你将增强解释科学观点、分析数据以及将原理应用于新情境的能力。
1. Cell Structure and Function | 细胞结构与功能
All living organisms are composed of cells. Animal cells typically contain a cell membrane, cytoplasm and a nucleus. Plant cells have the same basic parts but also possess a rigid cell wall, a large central vacuole and often chloroplasts.
所有生物都由细胞构成。动物细胞通常含有细胞膜、细胞质和细胞核。植物细胞具有相同的基本部分，但也有坚硬的细胞壁、一个中央大液泡，通常还有叶绿体。
The nucleus controls the cell’s activities and stores genetic information in the form of DNA. Mitochondria, found in both plant and animal cells, are where aerobic respiration occurs to release energy.
细胞核控制细胞的活动，并以DNA的形式储存遗传信息。线粒体存在于植物和动物细胞中，是有氧呼吸释放能量的场所。
| Organelle (细胞器) | Function (功能) |
|---|---|
| Cell membrane (细胞膜) | Controls what enters and leaves the cell. / 控制物质进出细胞。 |
| Cytoplasm (细胞质) | Jelly-like substance where chemical reactions happen. / 胶状物质，是化学反应发生的地方。 |
| Nucleus (细胞核) | Contains genetic material and directs cell activities. / 含有遗传物质，指导细胞活动。 |
| Mitochondria (线粒体) | Release energy through respiration. / 通过呼吸作用释放能量。 |
| Chloroplasts (叶绿体) | Absorb light energy for photosynthesis (plant cells only). / 吸收光能进行光合作用（仅植物细胞）。 |
| Cell wall (细胞壁) | Provides support and shape (plant cells only). / 提供支撑和形状（仅植物细胞）。 |
2. Movement of Substances: Diffusion and Osmosis | 物质运输：扩散与渗透
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. It is a passive process that does not require energy.
扩散是粒子从高浓度区域向低浓度区域的净移动，沿着浓度梯度进行。这是一个被动过程，不需要能量。
Osmosis is a special type of diffusion involving water molecules moving through a partially permeable membrane. Water moves from a dilute solution (high water potential) to a more concentrated solution (low water potential).
渗透是一种特殊的扩散，涉及水分子通过半透膜的移动。水从稀溶液（高水势）向更浓的溶液（低水势）移动。
In plant cells, water entering by osmosis makes the cell turgid and supports the plant. If too much water leaves, the cell becomes flaccid and the plant wilts. Animal cells can burst if they gain too much water because they lack a cell wall.
在植物细胞中，通过渗透进入的水使细胞变得膨压饱满，支撑植物。如果失去太多水分，细胞变得松软，植物萎蔫。动物细胞如果吸收过多水分会胀破，因为它们没有细胞壁。
3. Photosynthesis | 光合作用
Photosynthesis is the process by which green plants make their own food using light energy. The leaf is the main organ for photosynthesis, and chloroplasts containing chlorophyll capture light energy.
光合作用是绿色植物利用光能制造自身食物的过程。叶片是进行光合作用的主要器官，含有叶绿素的叶绿体捕获光能。
The word equation for photosynthesis is:
光合作用的文字方程式为：
carbon dioxide + water → glucose + oxygen
The balanced chemical equation is:
配平的化学方程式为：
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Light energy is absorbed by chlorophyll, and the reaction requires carbon dioxide from the air and water from the soil. Glucose is used for respiration or stored as starch.
光能被叶绿素吸收，反应需要空气中的二氧化碳和土壤中的水。葡萄糖用于呼吸作用或转化为淀粉储存。
4. Human Digestive System and Enzymes | 人体消化系统与酶
Digestion breaks down large, insoluble food molecules into small, soluble molecules that can be absorbed into the bloodstream. The digestive system includes the mouth, oesophagus, stomach, small intestine, large intestine and accessory organs such as the liver and pancreas.
消化将大而不溶的食物分子分解成可以吸收进入血液的小而可溶的分子。消化系统包括口腔、食道、胃、小肠、大肠以及肝脏和胰脏等附属器官。
Enzymes are biological catalysts that speed up digestion without being used up. Amylase breaks down starch into simple sugars, protease breaks down proteins into amino acids, and lipase breaks down fats into fatty acids and glycerol.
酶是生物催化剂，可以加速消化而不被消耗。淀粉酶将淀粉分解为单糖，蛋白酶将蛋白质分解为氨基酸，脂肪酶将脂肪分解为脂肪酸和甘油。
Bile, produced by the liver, emulsifies fats into smaller droplets, increasing the surface area for lipase to work more effectively. Food is absorbed mainly in the small intestine through the villi.
肝脏产生的胆汁将脂肪乳化形成更小的液滴，增大表面积以便脂肪酶更有效地发挥作用。食物主要通过小肠中的绒毛被吸收。
5. Elements, Compounds and Mixtures | 元素、化合物和混合物
An element is a pure substance made up of only one type of atom. The Periodic Table lists all known elements, each represented by a chemical symbol. A compound contains two or more different elements chemically bonded in fixed proportions.
元素是仅由一种原子组成的纯物质。元素周期表列出了所有已知元素，每种元素用一个化学符号表示。化合物包含两种或更多不同元素，以固定比例经化学键结合。
A mixture consists of two or more substances not chemically joined, so each component retains its own properties. Mixtures can be separated by physical methods such as filtration, evaporation, distillation and chromatography.
混合物由两种或更多未经化学结合的物质组成，因此每种成分保持自身性质。混合物可以通过过滤、蒸发、蒸馏和色谱法等物理方法分离。
Examples: oxygen (O₂) is an element, water (H₂O) is a compound, and air is a mixture of gases mainly nitrogen and oxygen. Understanding these categories helps predict how substances behave.
例子：氧气（O₂）是一种元素，水（H₂O）是一种化合物，空气是主要由氮气和氧气组成的气体混合物。理解这些类别有助于预测物质的行为。
6. The Reactivity Series and Displacement Reactions | 金属活动性顺序与置换反应
The reactivity series ranks metals by how vigorously they react. A common order from most reactive to least reactive is: potassium, sodium, calcium, magnesium, aluminium, zinc, iron, lead, copper, silver, gold.
金属活动性顺序根据金属反应的剧烈程度进行排序。常见的由最活泼到最不活泼的顺序为：钾、钠、钙、镁、铝、锌、铁、铅、铜、银、金。
More reactive metals can displace less reactive metals from their compounds. For example, when zinc is added to copper sulfate solution, zinc displaces copper:
较活泼的金属可以将较不活泼的金属从其化合物中置换出来。例如，将锌加入硫酸铜溶液中，锌会置换出铜：
Zn + CuSO₄ → ZnSO₄ + Cu
Observations include the blue solution fading and a reddish-brown solid (copper) forming. Displacement reactions are useful for extracting metals from ores and in batteries.
观察到的现象包括蓝色溶液褪色，以及形成红棕色固体（铜）。置换反应用于从矿石中提取金属和在电池中。
The reactivity of a metal also relates to its reaction with water or acids. Potassium reacts violently with water, while magnesium reacts slowly with cold water but vigorously with steam.
金属的活动性也与其与水或酸的反应有关。钾与水剧烈反应，而镁与冷水反应缓慢，但与水蒸气反应剧烈。
7. Acids, Alkalis and Neutralisation | 酸、碱与中和
Acids are substances that release hydrogen ions (H⁺) in water and have a pH less than 7. Common laboratory acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃).
酸是在水中释放出氢离子（H⁺）且pH小于7的物质。常见的实验室酸包括盐酸（HCl）、硫酸（H₂SO₄）和硝酸（HNO₃）。
Alkalis are soluble bases that release hydroxide ions (OH⁻) and have a pH greater than 7. Examples are sodium hydroxide (NaOH) and potassium hydroxide (KOH).
碱是可溶性的碱，释放出氢氧根离子（OH⁻），pH大于7。例子有氢氧化钠（NaOH）和氢氧化钾（KOH）。
Neutralisation occurs when an acid reacts with an alkali to form a salt and water. The ionic equation for the neutralisation reaction is:
当酸与碱反应生成盐和水时，即发生中和反应。中和反应的离子方程式为：
H⁺ + OH⁻ → H₂O
Indicators like litmus or universal indicator show the pH. A change in colour during titration indicates the point of neutralisation.
指示剂如石蕊或通用指示剂显示pH。滴定过程中颜色的变化指示中和点。
8. Forces and Motion | 力与运动
A force is a push or a pull that can change an object’s speed, direction or shape. Forces are measured in newtons (N). Contact forces include friction and tension, while non-contact forces include gravity, magnetic and electrostatic forces.
力是推或拉，可以改变物体的速度、方向或形状。力的单位是牛顿（N）。接触力包括摩擦力和张力，非接触力包括重力、磁力和静电力。
When forces are balanced, an object remains at rest or moves at constant speed. Unbalanced forces cause an object to accelerate in the direction of the resultant force.
当力平衡时，物体保持静止或匀速运动。不平衡的力使物体在合力的方向上加速。
Speed can be calculated using the formula: speed = distance / time. Velocity includes the direction of motion. On a distance-time graph, a straight sloping line indicates constant speed.
速度可以用公式计算：速度 = 距离 / 时间。速率包含了运动方向。在距离—时间图中，一条倾斜直线表示匀速运动。
v = s / t
9. Energy Types and Energy Transfers | 能量类型与能量转移
Energy exists in various forms: kinetic, thermal, light, sound, electrical, chemical, elastic and gravitational potential energy. The law of conservation of energy states that energy cannot be created or destroyed, only transferred or transformed.
能量以多种形式存在：动能、热（内）能、光能、声能、电能、化学能、弹性势能和重力势能。能量守恒定律指出，能量不能被创造或销毁，只能被转移或转化。
In energy transfers, useful energy output is always less than the input because some energy is dissipated as thermal energy. Efficiency is calculated as: (useful output energy / total input energy) × 100%.
在能量转移中，有用的能量输出总是小于能量输入，因为部分能量以热能形式散失。效率的计算公式为：（有用输出能量 / 总输入能量）× 100%。
Conduction, convection and radiation are methods of heat transfer. Conduction occurs mainly in solids, convection in liquids and gases, and radiation via infrared waves that can travel through a vacuum.
传导、对流和辐射是热量传递的方式。传导主要发生在固体中，对流在液体和气体中，辐射通过红外波可以在真空中传播。
10. Electric Circuits: Current, Voltage and Resistance | 电路：电流、电压和电阻
An electric circuit needs a complete loop for current to flow. Current (I) is the rate of flow of charge, measured in amperes (A). Voltage (V) is the energy transferred per unit charge, measured in volts (V). Resistance (R) measures how much a component resists current flow, measured in ohms (Ω).
电路需要完整的闭合回路才能使电流流动。电流（I）是电荷流动的速率，单位为安培（A）。电压（V）是每单位电荷转移的能量，单位为伏特（V）。电阻（R）衡量元器件对电流的阻碍程度，单位为欧姆（Ω）。
Ohm’s law relates these quantities:
欧姆定律联系了这些量：
V = I × R
Series circuits have only one path for current, so current is the same everywhere. In parallel circuits, the current splits across branches, but the voltage across each branch is equal to the supply voltage.
串联电路只有一条电流路径，因此各处电流相同。在并联电路中，电流在支路中分流，但每条支路两端的电压等于电源电压。
Resistance affects how bright lamps glow or how fast motors turn. Adding resistors in series increases total resistance, while adding them in parallel decreases total resistance.
电阻影响灯泡的亮度或电机的转速。串联添加电阻会增加总电阻，并联添加电阻则会降低总电阻。
11. Sound and Light Waves | 声波与光波
Waves transfer energy without transferring matter. Sound waves are longitudinal waves that require a medium to travel; they travel fastest in solids and not at all in a vacuum.
波传递能量而不传递物质。声波是纵波，需要介质才能传播；它在固体中传播最快，在真空中不能传播。
The speed of sound can be calculated using the wave equation:
声速可以使用波动方程计算：
v = f × λ
where v is speed (m/s), f is frequency (Hz) and λ is wavelength (m).
其中v为速度（m/s），f为频率（Hz），λ为波长（m）。
Light waves are transverse electromagnetic waves that do not need a medium. Reflection obeys the law: angle of incidence equals angle of reflection. Refraction occurs when light passes through different media, changing speed and bending. White light can be split by a prism into a spectrum of colours.
光波是横波，属于电磁波，不需要介质。反射遵循定律：入射角等于反射角。当光穿过不同介质时会发生折射，速度改变并弯折。白光可以通过棱镜分解为色散光谱。
12. The Solar System and Gravity | 太阳系与重力
Our Solar System consists of the Sun, eight planets, their moons, dwarf planets, asteroids and comets. The planets in order from the Sun are 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、矮行星、小行星和彗星组成。按距离太阳由近及远的顺序，行星依次为水星、金星、地球、火星、木星、土星、天王星和海王星。
Gravity is a force of attraction between masses. The weight of an object is the gravitational force pulling it towards the centre of a planet and is calculated by:
重力是有质量物体之间的吸引力。物体的重量是将其拉向行星中心的引力，计算公式为：
W = m × g
On Earth the gravitational field strength g is approximately 10 N/kg. The Moon’s gravity is about 1/6 of Earth’s, so you would weigh less there, while your mass remains constant.
在地球上，重力场强度g约为10 N/kg。月球的引力大约是地球的1/6，所以你在那里称重会更轻，但你的质量保持不变。
The Earth’s seasons are caused by its tilted axis as it orbits the Sun. A lunar month is the time taken for the Moon to orbit Earth, and lunar phases occur due to the changing relative positions of the Earth, Moon and Sun.
地球的四季是由于其自转轴倾斜并绕太阳公转所致。一个朔望月是月球绕地球一周的时间，月相变化源于地球、月球和太阳相对位置的改变。
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