📚 Year 8 CAIE Science: Key Concepts Review | Year 8 CAIE 科学：核心知识点梳理
Welcome to a comprehensive review of essential topics in the Year 8 CAIE Science curriculum. This guide covers the key concepts in Biology, Chemistry and Physics to help you consolidate your understanding and prepare effectively for assessments. Each section presents the core ideas, followed by a bilingual explanation to support learners studying in both English and Chinese.
欢迎阅读 Year 8 CAIE 科学核心知识点的全面梳理。本指南涵盖了生物、化学和物理中的关键概念，旨在帮助您巩固理解并为评估做好充分准备。每个部分首先介绍核心思想，接着提供中英双语解释，以支持双语学习。
1. Cells and Microscopy | 细胞与显微镜
All living organisms are made of cells, the basic unit of life. Plant and animal cells share structures such as a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells also have a rigid cell wall, a large permanent vacuole and chloroplasts for photosynthesis.
所有生物体都由细胞构成，细胞是生命的基本单位。植物和动物细胞都具有细胞核、细胞质、细胞膜、线粒体和核糖体等结构。植物细胞还拥有坚硬的细胞壁、一个大型中央液泡以及进行光合作用的叶绿体。
Specialised cells have adaptations to perform specific functions. For example, red blood cells lack a nucleus to carry more oxygen, nerve cells are long to transmit electrical signals, and root hair cells increase surface area for water uptake. Sperm cells have a tail to swim towards the egg.
特化细胞具有适应特定功能的特征。例如，红细胞没有细胞核以便运输更多氧气，神经细胞很长以传递电信号，根毛细胞通过增大表面积来吸收水分。精子细胞具有尾部，可以游向卵细胞。
ective lens magnification (e.g. ×4, ×10, ×40). To prepare a slide, a thin specimen is placed in water or stain on a glass slide and covered with a coverslip.
我们使用光学显微镜观察细胞。总放大倍数等于目镜放大倍数（通常为×10）乘以物镜放大倍数（如×4、×10、×40）。制作玻片标本时，需将薄样本放在载玻片上的水或染液中，并盖上盖玻片。
2. Nutrition and Digestion | 营养与消化
A balanced diet includes carbohydrates, proteins, lipids (fats), vitamins, minerals, dietary fibre and water. Carbohydrates supply energy, proteins are needed for growth and repair, and lipids provide energy storage and insulation. Vitamins and minerals are required in small amounts for health.
均衡饮食包括碳水化合物、蛋白质、脂类（脂肪）、维生素、矿物质、膳食纤维和水。碳水化合物提供能量，蛋白质用于生长和修复，脂类用于能量储存和隔热。维生素和矿物质需求量小，但对健康至关重要。
The digestive system breaks down large insoluble molecules into small soluble ones that can be absorbed into the blood. Mechanical digestion occurs through chewing and churning, while chemical digestion uses enzymes. Amylase in saliva breaks down starch into sugars; protease breaks down proteins into amino acids; lipase breaks down lipids into fatty acids and glycerol.
消化系统将大块不溶分子分解为可吸收进入血液的小分子可溶物质。机械消化通过咀嚼和搅拌实现，化学消化则依靠酶。唾液中的淀粉酶将淀粉分解为糖类；蛋白酶将蛋白质分解为氨基酸；脂肪酶将脂类分解为脂肪酸和甘油。
Food travels from the mouth down the oesophagus to the stomach, then to the small intestine where most absorption occurs. The large intestine absorbs water, and faeces are egested through the anus. The liver produces bile that helps emulsify fats, increasing the surface area for lipase action.
食物从口腔经食管进入胃，然后进入大部分吸收作用发生的小肠。大肠吸收水分，粪便通过肛门排出。肝脏产生胆汁，帮助乳化脂肪，增加脂肪酶作用的表面积。
3. Respiration and Gas Exchange | 呼吸与气体交换
Aerobic respiration is a chemical reaction that releases energy from glucose using oxygen. The word equation is:
glucose + oxygen → carbon dioxide + water (+ energy)
有氧呼吸是利用氧气从葡萄糖中释放能量的化学反应。文字方程式为：葡萄糖 + 氧气 → 二氧化碳 + 水（+ 能量）。
This process occurs continuously in the mitochondria of cells. The energy released is used for activities such as muscle contraction, maintaining body temperature and active transport.
该过程在细胞的线粒体中持续进行。释放的能量用于肌肉收缩、维持体温和主动运输等生命活动。
The respiratory system provides oxygen and removes carbon dioxide. Air enters through the nose or mouth, passes the trachea, bronchi and bronchioles, and reaches the alveoli in the lungs. Alveoli have thin walls, a large surface area and a rich blood supply to maximise gas exchange by diffusion.
呼吸系统提供氧气并排出二氧化碳。空气通过鼻或口进入，经过气管、支气管和细支气管，到达肺部的肺泡。肺泡壁薄、表面积大且血液供应丰富，以最大化通过扩散进行的气体交换。
Breathing involves inhalation (diaphragm contracts and flattens, ribcage moves up and out) and exhalation (diaphragm relaxes, ribcage moves down and in). Breathing rate increases during exercise to supply more oxygen and remove extra carbon dioxide.
呼吸包括吸气（膈肌收缩变平，肋骨上提外展）和呼气（膈肌放松，肋骨下移内收）。运动时呼吸频率加快，以提供更多氧气并排出额外二氧化碳。
4. Reproduction in Plants and Humans | 植物与人类的生殖
Flowering plants reproduce sexually. The male parts of a flower are the stamens, which include the anther (produces pollen) and filament. The female parts are the carpel, consisting of stigma, style and ovary (contains ovules). Pollination is the transfer of pollen from anther to stigma, which can be wind- or insect-pollinated.
开花植物进行有性繁殖。花的雄蕊由花药（产生花粉）和花丝组成。雌蕊群由柱头、花柱和子房（内含胚珠）组成。传粉是花粉从花药转移到柱头的过程，可以是风媒或虫媒传粉。
Fertilisation occurs when a pollen nucleus fuses with an ovule nucleus, forming a zygote that develops into a seed. The ovary develops into a fruit. Seed dispersal methods include wind, water, animals and explosion, helping reduce competition.
当花粉中的精核与胚珠中的卵核融合时完成受精，形成合子并发育为种子。子房发育成果实。种子传播方式包括风、水、动物和弹射，有助于减少竞争。
In humans, the male reproductive system produces sperm in the testes. The female system produces eggs (ova) in the ovaries. Fertilisation takes place in the oviduct (fallopian tube), and the fertilised egg implants in the uterus where it develops. The menstrual cycle prepares the uterus for possible pregnancy each month.
人类男性生殖系统在睾丸中产生精子。女性系统在卵巢中产生卵子。受精发生在输卵管中，受精卵植入子宫并在那里发育。月经周期每月为可能的怀孕做准备。
5. Particle Model and Changes of State | 粒子模型与状态变化
The particle model explains the properties of solids, liquids and gases. In solids, particles are closely packed in a regular pattern, vibrating in fixed positions. In liquids, particles are close but can move around each other. In gases, particles are far apart and move rapidly in all directions.
粒子模型解释了固体、液体和气体的性质。固体中，粒子紧密排列成规则图案，在固定位置振动。液体中，粒子彼此靠近但可以相互滑动。气体中，粒子相距很远，并在各个方向上快速运动。
Changes of state include melting (solid to liquid), freezing (liquid to solid), boiling/evaporation (liquid to gas), condensation (gas to liquid) and sublimation (solid directly to gas). These are physical changes because no new substances are made; the particles themselves do not change.
状态变化包括熔化（固体变液体）、凝固（液体变固体）、沸腾/蒸发（液体变气体）、冷凝（气体变液体）和升华（固体直接变气体）。这些都是物理变化，因为未生成新物质，粒子本身未改变。
Heating increases the kinetic energy of particles, causing them to overcome attractive forces. During a change of state, the temperature remains constant even though heating continues because energy is used to break bonds between particles rather than raise temperature.
加热后粒子动能增加，克服粒子间吸引力。状态变化过程中，即使持续加热，温度也保持不变，因为能量用于打破粒子间的键，而不是升高温度。
6. Atoms, Elements and Compounds | 原子、元素与化合物
All substances are made of atoms. An element contains only one type of atom and is listed on the Periodic Table. Each element has a unique chemical symbol, e.g. H for hydrogen, O for oxygen, Fe for iron. Elements can be metals, non-metals or metalloids.
所有物质都由原子构成。元素只含一种原子，被列入元素周期表。每种元素有唯一的化学符号，例如 H 表示氢，O 表示氧，Fe 表示铁。元素可以是金属、非金属或类金属。
A compound is a substance made of two or more different types of atom chemically bonded together in fixed proportions. Compounds have properties different from their elements. For example, water (H₂O) is a liquid, but hydrogen and oxygen are gases. A mixture contains different substances not chemically joined, so they can be separated by physical methods such as filtration, distillation or chromatography.
化合物是由两种或多种不同类型的原子以固定比例通过化学键结合而成的物质。化合物的性质与其组成元素不同。例如，水 (H₂O) 是液体，而氢和氧是气体。混合物含有未通过化学键结合的不同物质，因此可以通过过滤、蒸馏或色谱法等物理方法进行分离。
The Periodic Table arranges elements in order of increasing atomic number. Vertical columns are called groups; elements in the same group have similar chemical properties. Group 1 contains reactive alkali metals, Group 7 halogens, and Group 0 noble gases that are inert.
元素周期表按原子序数递增排列元素。纵列称为族；同一族元素化学性质相似。第 I 族是活泼的碱金属，第 VII 族是卤素，第 0 族是惰性的稀有气体。
7. Chemical Reactions | 化学反应
A chemical change produces new substances with different properties, unlike a physical change which only changes the form or state. Evidence of a chemical reaction includes colour change, temperature change, gas production (bubbles or fizzing), formation of a precipitate and light emission.
化学变化生成具有不同性质的新物质，而物理变化仅改变形态或状态。化学反应的证据包括颜色变化、温度变化、产生气体（气泡或嘶嘶声）、生成沉淀以及发光。
Chemical reactions can be represented by word equations showing reactants and products. For example:
magnesium + oxygen → magnesium oxide
化学反应可以用文字方程式表示，显示反应物和生成物。例如：镁 + 氧气 → 氧化镁。
Oxidation is the reaction of a substance with oxygen. Combustion (burning) is a rapid oxidation that releases heat and light. Rusting of iron requires both oxygen and water. Methods to prevent rusting include painting, oiling, galvanising or using sacrificial protection.
氧化是物质与氧气的反应。燃烧是释放热和光的快速氧化。铁生锈需要氧气和水相接触。防锈方法包括涂漆、涂油、镀锌或使用牺牲保护。
The Law of Conservation of Mass states that the total mass of reactants equals the total mass of products in a closed system, because atoms are rearranged but not created or destroyed.
质量守恒定律指出，在封闭系统中，反应物的总质量等于生成物的总质量，因为原子重新排列而没有产生或消失。
8. Acids and Alkalis | 酸与碱
Acids have a pH less than 7 and contain hydrogen ions. Common laboratory acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃). Alkalis are soluble bases with a pH greater than 7 and contain hydroxide ions (OH⁻). Examples are sodium hydroxide (NaOH) and potassium hydroxide (KOH).
酸的 pH 值小于 7，含有氢离子。常见实验室酸有盐酸 (HCl)、硫酸 (H₂SO₄) 和硝酸 (HNO₃)。碱是可溶性碱，pH 值大于 7，含有氢氧根离子 (OH⁻)。例子有氢氧化钠 (NaOH) 和氢氧化钾 (KOH)。
The pH scale ranges from 0 to 14: 7 is neutral (pure water). Indicators such as litmus, phenolphthalein and universal indicator show whether a solution is acidic or alkaline. Universal indicator gives a range of colours from red (strong acid) through green (neutral) to purple (strong alkali).
pH 值范围从 0 到 14：7 为中性（纯水）。指示剂如石蕊、酚酞和通用指示剂可显示溶液是酸性还是碱性。通用指示剂呈现从红（强酸）经绿（中性）到紫（强碱）的颜色范围。
Neutralisation is the reaction between an acid and an alkali (or base) to form a salt and water:
acid + alkali → salt + water
中和反应是酸与碱（或可以反应的碱）生成盐和水：酸 + 碱 → 盐 + 水。
This reaction has many applications, such as treating acidic soil with lime (calcium hydroxide), using antacid tablets for indigestion, and neutralising bee stings (acidic) with baking soda.
此反应应用广泛，例如用石灰（氢氧化钙）处理酸性土壤，使用抗酸药片缓解消化不良，以及用小苏打中和蜜蜂蜇伤（酸性）。
9. Forces and Motion | 力与运动
A force is a push or pull that can change an object's speed, direction or shape. Forces are measured in newtons (N). Contact forces include friction, tension and applied forces; non-contact forces include gravitational, magnetic and electrostatic forces.
力是能改变物体速度、方向或形状的推或拉。力的单位是牛顿 (N)。接触力包括摩擦力、张力和外加力；非接触力包括引力、磁力和静电力。
Force diagrams use arrows to represent the size and direction of forces. When forces on an object are balanced, the object remains at rest or moves at constant velocity. Unbalanced forces cause acceleration, deceleration or a change in direction.
力的示意图用箭头代表力的大小和方向。物体受力平衡时，保持静止或匀速直线运动。不平衡力会导致加速、减速或改变方向。
nce ÷ time. Average speed uses total distance over total time. Relative motion refers to how fast one object appears to move from the perspective of another object.
速率是单位时间内的路程，计算公式为 速率 = 距离 ÷ 时间。平均速率用总距离除以总时间。相对运动是指从另一物体观察时，一个物体似乎移动的快慢。
10. Energy Forms and Transfers | 能量形式与转移
Energy exists in many forms: kinetic (movement), thermal (heat), chemical (stored in bonds), gravitational potential (position in a field), elastic potential (stored in stretched materials), light, sound and electrical. Energy is measured in joules (J).
能量有多种形式：动能（运动）、热能（热量）、化学能（储存于化学键中）、重力势能（在场中的位置）、弹性势能（储存在拉伸材料中）、光能、声能和电能。能量的单位是焦耳 (J)。
Energy can be transferred from one store to another or from one object to another by forces, heating, electric currents and waves. The Law of Conservation of Energy states that energy cannot be created or destroyed, only transferred or transformed.
能量可以通过力、加热、电流和波从一个储存转移到另一个储存，或从一个物体转移到另一个物体。能量守恒定律指出，能量不能凭空产生或消失，只能转移或转换。
In an energy transfer diagram, we often show useful and wasted energy. For example, a light bulb transfers electrical energy into useful light energy and wasted thermal energy. Efficiency is the fraction of useful output energy compared to total input energy.
在能量转移图中，我们常标示出有用能量和浪费的能量。例如，灯泡将电能转化为有用的光能和浪费的热能。效率是有用输出能量与总输入能量的比值。
11. Electricity and Magnetism | 电与磁
An electric circuit requires a complete conducting loop for current to flow. Current (I) is the flow of charge, measured in amperes (A). Voltage or potential difference (V) is the energy supplied per unit charge, measured in volts (V). Resistance (R) opposes the flow of current, measured in ohms (Ω).
电路需要完整的导电回路才能使电流流动。电流 (I) 是电荷的流动，以安培 (A) 为单位。电压或电势差 (V) 是每单位电荷供应的能量，以伏特 (V) 为单位。电阻 (R) 阻碍电流，以欧姆 (Ω) 为单位。
In a series circuit, components are connected one after another. The current is the same everywhere, but the supply voltage is shared. In a parallel circuit, each branch receives the full supply voltage, and the current splits at junctions. Adding more resistors in series increases total resistance; adding parallel branches decreases it.
串联电路中，元件首尾相接连接。各处电流相等，但电源电压被分配。并联电路中，每个支路承受全部电源电压，电流在节点处分流。串联更多电阻会增加总电阻；增加并联支路则会减小总电阻。
Magnets have north (N) and south (S) poles; like poles repel, unlike poles attract. A magnetic field is the region around a magnet where a magnetic force can be felt. An electromagnet is made by sending an electric current through a coil of wire around an iron core; its magnetism can be switched on and off. Electromagnets are used in electric bells, relays and scrapyard cranes.
磁铁有北极 (N) 和南极 (S)；同极相斥，异极相吸。磁场是磁铁周围能感受到磁力的区域。电磁铁是将电流通过绕在铁芯上的线圈制成的；其磁性可以通断。电磁铁用于电铃、继电器和废料场起重机。
12. Light and Sound Waves | 光波与声波
Light travels in straight lines at a speed of about 300 000 km/s in a vacuum. When light strikes a smooth surface, it reflects obeying the law of reflection: the angle of incidence equals the angle of reflection. These angles are measured from the normal, a line perpendicular to the surface.
光在真空中以大约 300 000 km/s 的速度沿直线传播。当光照射到光滑表面时，它会遵循反射定律反射：入射角等于反射角。这些角是从法线（垂直于表面的线）量度的。
Refraction is the bending of light when it passes from one transparent medium to another of different density. Light bends towards the normal when entering a denser medium, and away from the normal when entering a less dense medium. White light can be dispersed by a prism into the colours of the spectrum (ROYGBIV).
折射是光从一种透明介质进入另一种密度不同的介质时发生的弯曲。光进入更密介质时向法线偏折，进入更疏介质时远离法线偏折。白光可被棱镜色散成光谱色（红橙黄绿蓝靛紫）。
gh a vacuum. The speed of sound in air is about 340 m/s. Pitch is determined by frequency (higher frequency = higher pitch), and loudness by amplitude.
声音由振动产生并以纵波形式传播。声音需要介质（固体、液体或气体）传播，不能在真空中传播。空气中的声速约为 340 m/s。音调由频率决定（频率越高，音调越高），响度由振幅决定。
The human ear detects sound waves: the outer ear directs sound to the eardrum, causing it to vibrate; these vibrations are transmitted through the ossicles to the cochlea, where they are converted into nerve signals sent to the brain.
人耳检测声波：外耳将声音导向鼓膜，使其振动；这些振动通过听小骨传递到耳蜗，在那里被转换为神经信号并发送至大脑。
Published by TutorHao | Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图