📚 IGCSE CIE Science: Last-Minute Revision Notes | IGCSE CIE 科学：考前冲刺笔记
These last-minute revision notes cover the highest-yield topics for IGCSE CIE Science (Co-ordinated Sciences 0654 or Combined Science 0653), bringing together essential concepts from Biology, Chemistry and Physics. Use them to sharpen your recall of key definitions, equations and experimental skills in the final hours before your exam.
这份考前冲刺笔记涵盖了 IGCSE CIE 科学（协调科学 0654 或综合科学 0653）中的高频考点，汇总了生物、化学和物理的核心概念。在考前的最后几小时，用它们来强化你对关键定义、公式和实验技能的记忆。
1. Cell Structure and Organisation | 细胞结构与组织层次
All living organisms are made of cells. The key organelles are: nucleus (contains DNA), cytoplasm (site of metabolic reactions), cell membrane (partially permeable barrier), mitochondria (aerobic respiration) and ribosomes (protein synthesis). Plant cells also have a cellulose cell wall, a large permanent vacuole and chloroplasts for photosynthesis.
所有生物体都由细胞构成。关键细胞器包括：细胞核（含 DNA）、细胞质（代谢反应场所）、细胞膜（选择透过性屏障）、线粒体（有氧呼吸）和核糖体（蛋白质合成）。植物细胞还有纤维素细胞壁、一个大液泡和用于光合作用的叶绿体。
In multicellular organisms, cells are organised into tissues, organs and organ systems. For example, the human respiratory system includes the trachea, bronchi and alveoli, where gas exchange happens by diffusion.
在多细胞生物中，细胞构成组织、器官和器官系统。例如，人的呼吸系统包括气管、支气管和肺泡，气体交换通过扩散在肺泡进行。
2. Movement of Substances | 物质的运输
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. Osmosis is the diffusion of water molecules through a partially permeable membrane from a dilute solution to a more concentrated one. Active transport moves molecules against the concentration gradient using energy from ATP.
扩散是指粒子从高浓度区域向低浓度区域沿浓度梯度的净运动。渗透是水分子通过选择透过性膜从稀溶液向较浓溶液的扩散。主动运输利用 ATP 提供的能量逆浓度梯度运输分子。
In plant roots, mineral ions are taken up by active transport. In the human small intestine, glucose is co-transported with sodium ions. Osmosis explains why animal cells burst in pure water while plant cells become turgid but are protected by their cell wall.
在植物根部，矿质离子通过主动运输被吸收。在人体小肠，葡萄糖与钠离子协同转运。渗透解释了为什么动物细胞在纯水中会胀破，而植物细胞会变得坚挺但因细胞壁保护不会破裂。
3. Enzymes | 酶
Enzymes are biological catalysts made of protein. They lower activation energy and are specific to their substrate due to the complementary shape of the active site. The lock-and-key model describes how the substrate fits into the active site to form an enzyme–substrate complex.
酶是由蛋白质构成的生物催化剂。它们降低活化能，并且由于活性位点形状互补而对底物具有特异性。锁钥模型描述了底物如何嵌入活性位点形成酶–底物复合物。
Enzyme activity is affected by temperature and pH. Each enzyme has an optimum; extreme conditions denature the enzyme, changing the shape of the active site permanently. Amylase breaks down starch into maltose; catalase breaks down hydrogen peroxide into water and oxygen. The rate can be measured by recording gas production or colour change.
酶活性受温度和 pH 影响。每种酶都有最适条件；极端条件会使酶变性，永久改变活性位点形状。淀粉酶将淀粉分解为麦芽糖；过氧化氢酶将过氧化氢分解为水和氧气。反应速率可通过记录产气量或颜色变化来测量。
4. Plant Nutrition and Photosynthesis | 植物营养与光合作用
Photosynthesis is the process by which plants produce glucose and oxygen from carbon dioxide and water, using light energy absorbed by chlorophyll. The balanced equation is:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
光合作用是植物利用叶绿素吸收光能，将二氧化碳和水转化为葡萄糖和氧气的过程。其平衡方程式如上所示。
Glucose is used for respiration, converted to starch for storage, synthesised into cellulose for cell walls or combined with nitrate ions to form amino acids. Limiting factors for photosynthesis are light intensity, carbon dioxide concentration and temperature. In a photosynthesis experiment, aquatic plants like Elodea can be used to count oxygen bubbles.
葡萄糖用于呼吸作用，转化为淀粉储存，合成纤维素构成细胞壁，或与硝酸根离子结合形成氨基酸。光合作用的限制因素有光照强度、二氧化碳浓度和温度。在光合作用实验中，可用伊乐藻等水生植物来计数氧气气泡。
| Mineral ion | Function |
| Nitrate (NO₃⁻) | Making amino acids and proteins |
| Magnesium (Mg²⁺) | Central atom of chlorophyll |
| 矿质离子 | 功能 |
| 硝酸根 (NO₃⁻) | 合成氨基酸和蛋白质 |
| 镁离子 (Mg²⁺) | 叶绿素中心原子 |
5. Chemical Bonding and Structure | 化学键与结构
Atoms bond to obtain a full outer shell. Ionic bonding occurs between metals and non-metals when electrons are transferred, forming oppositely charged ions held together by strong electrostatic forces. Sodium chloride has a giant ionic lattice with high melting point and conducts electricity when molten or dissolved.
原子通过键合获得满壳层。离子键发生在金属与非金属之间，通过电子转移形成带相反电荷的离子，由强静电引力结合在一起。氯化钠具有巨型离子晶格，熔点高，熔融或溶于水时可导电。
Covalent bonding involves sharing of electron pairs. Simple molecular substances like water and carbon dioxide have low boiling points due to weak intermolecular forces. Giant covalent structures such as diamond (each carbon atom bonded to four others) and graphite (layers of hexagonal rings) have very high melting points. Graphite conducts electricity because of delocalised electrons between layers.
共价键涉及电子对的共享。像水和二氧化碳这样的简单分子物质，因分子间作用力弱而沸点低。巨型共价结构如金刚石（每个碳原子与另外四个键合）和石墨（六角形环层状结构）熔点非常高。石墨能导电是因为层间有离域电子。
Metallic bonding consists of a lattice of positive ions surrounded by a sea of delocalised electrons, giving metals malleability and excellent electrical conductivity.
金属键由正离子晶格和周围的离域电子海构成，使金属具有延展性和优良的导电性。
6. Stoichiometry and the Mole | 化学计量与摩尔
The mole is the unit for amount of substance. One mole contains 6.02 × 10²³ particles (Avogadro constant). Molar mass is the mass of one mole of a substance in grams. Key formulas:
n = m / M
Concentration (mol/dm³) = n / V (dm³)
摩尔是物质的量的单位。一摩尔含有 6.02 × 10²³ 个粒子（阿伏伽德罗常数）。摩尔质量是一摩尔物质以克为单位的质量。关键公式如上所示。
Using a balanced equation, you can calculate reacting masses and volumes of gases. At room temperature and pressure, one mole of any gas occupies 24 dm³. Empirical formula is the simplest whole-number ratio of atoms; molecular formula is the actual number. Percentage yield = (actual yield / theoretical yield) × 100%.
利用配平方程式可以计算反应质量和气体体积。在常温常压下，任何气体一摩尔的体积均为 24 dm³。经验式是原子最简整数比；分子式是实际原子数。产率 =（实际产量 / 理论产量）× 100%。
7. Acids, Bases and Salts | 酸、碱与盐
An acid is a proton (H⁺) donor; a base is a proton acceptor. Common laboratory acids are hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃). Alkalis are soluble bases that release OH⁻ ions in water. The pH scale ranges from 0 (strongly acidic) to 14 (strongly alkaline), with 7 being neutral.
酸是质子（H⁺）供体；碱是质子受体。实验室常用酸有盐酸 (HCl)、硫酸 (H₂SO₄) 和硝酸 (HNO₃)。碱是可溶性的碱，在水中释放 OH⁻ 离子。pH 标度范围从 0（强酸性）到 14（强碱性），7 为中性。
Neutralisation: acid + base → salt + water. For example, H⁺ + OH⁻ → H₂O. With carbonates, a salt, water and carbon dioxide are produced. Titration can be used to find the concentration of an acid or alkali using an indicator like phenolphthalein or methyl orange.
中和反应：酸 + 碱 → 盐 + 水。例如，H⁺ + OH⁻ → H₂O。与碳酸盐反应则生成盐、水和二氧化碳。滴定法可用于用酚酞或甲基橙指示剂测定酸或碱的浓度。
Preparing a pure salt involves reacting an acid with an excess insoluble base, filtering off the excess, then evaporating the filtrate until crystallisation occurs.
制备纯盐时，用酸与过量不溶性碱反应，过滤除去过量物，然后蒸发滤液直至结晶析出。
8. Electricity and Magnetism | 电与磁
Electric current is the flow of charge. In metals, current is a flow of electrons. Conventional current flows from positive to negative. Key relationships:
Q = I × t
V = I × R
P = I × V
电流是电荷的流动。在金属中，电流是电子的流动。传统电流方向是从正到负。关键关系式如上。
In a series circuit, current is the same everywhere and voltage is shared. In parallel circuits, current splits while voltage remains the same across branches. Resistors in series add up; resistors in parallel have a combined resistance less than the smallest individual resistance.
在串联电路中，各处电流相同，电压被分配。并联电路中，电流分叉，各支路电压相同。串联电阻相加；并联电阻的总阻值小于最小的单个电阻。
Magnetism: like poles repel, unlike poles attract. An electromagnet is made by passing current through a coil of wire (solenoid) wound around an iron core. The motor effect: a current-carrying conductor in a magnetic field experiences a force, used in the d.c. motor. The generator effect produces a voltage when a conductor cuts magnetic field lines, used in alternators and dynamos.
磁学：同名磁极相斥，异名相吸。电磁铁是由绕在铁芯上的线圈（螺线管）通以电流构成。电动机效应：通电导体在磁场中受力，用于直流电动机。发电机效应是导体切割磁感线时产生电压，用于交流发电机和直流发电机。
9. Forces and Motion | 力与运动
Scalars have magnitude only (speed, distance, mass). Vectors have magnitude and direction (velocity, displacement, force). The equations of motion for uniform acceleration:
v = u + at
s = ut + ½at²
v² = u² + 2as
标量只有大小（速率、路程、质量）。矢量具有大小和方向（速度、位移、力）。匀加速运动方程如上。
Newton’s First Law: an object remains at rest or in uniform motion unless acted upon by a resultant force. Second Law: F = ma. Third Law: for every action, there is an equal and opposite reaction. Momentum = mass × velocity; in collisions, total momentum is conserved providing no external forces act.
牛顿第一定律：若无合力作用，物体保持静止或匀速直线运动。第二定律：F = ma。第三定律：每个作用力都有一个大小相等、方向相反的反作用力。动量 = 质量 × 速度；碰撞中若无外力，总动量守恒。
Terminal velocity occurs when air resistance balances weight, resulting in zero resultant force. Skydivers reach a steady speed when parachute opens increasing drag.
当空气阻力与重力平衡时，合力为零，达到终极速度。跳伞者打开降落伞后阻力增大，达到稳定速度。
10. Energy and Thermal Physics | 能量与热物理
Energy exists in many forms: kinetic, thermal, chemical, gravitational potential, elastic, nuclear and electromagnetic. The principle of conservation of energy states that energy cannot be created or destroyed, only transferred or stored. Sankey diagrams show energy transfers, with the useful energy output and wasted energy.
能量有多种形式：动能、热能、化学能、重力势能、弹性势能、核能和电磁能。能量守恒定律指出能量既不能被创造也不能被消灭，只能被转移或储存。桑基图显示能量传递，包括有用能量输出和浪费的能量。
Efficiency = (useful output energy / total input energy) × 100%. Work done = force × distance moved in the direction of the force. Kinetic energy = ½mv²; gravitational potential energy = mgh. Power = work done / time taken.
效率 =（有用输出能量 / 总输入能量）× 100%。做功 = 力 × 沿力方向移动的距离。动能 = ½mv²；重力势能 = mgh。功率 = 做功 / 时间。
Heat transfer occurs by conduction (mainly in solids), convection (in fluids due to density changes) and radiation (infrared waves that can travel through a vacuum). Conduction in metals is enhanced by free electrons. A vacuum flask minimises all three methods.
热传递通过传导（主要在固体）、对流（流体因密度变化引起）和辐射（能在真空中传播的红外波）进行。金属中的自由电子增强了传导。保温瓶能最大程度减少这三种传热方式。
11. Human Gas Exchange and Respiration | 人体气体交换与呼吸
During inhalation, the intercostal muscles and diaphragm contract, increasing the volume of the thoracic cavity. Pressure falls below atmospheric pressure, drawing air into the lungs. In the alveoli, oxygen diffuses into the blood while carbon dioxide diffuses out. Alveoli are adapted with thin walls, a large surface area and a rich capillary network.
吸气时，肋间肌和膈肌收缩，胸廓容积增大。压力降至大气压以下，空气被吸入肺中。在肺泡处，氧气扩散进入血液，二氧化碳扩散排出。肺泡适于气体交换，壁薄、表面积大且有丰富的毛细血管网。
Aerobic respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ ATP). Anaerobic respiration in muscles produces lactic acid and less ATP. In yeast, anaerobic respiration produces ethanol and carbon dioxide (fermentation).
有氧呼吸：C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ ATP)。肌肉缺氧呼吸产生乳酸和较少 ATP。酵母厌氧呼吸则产生乙醇和二氧化碳（发酵）。
12. Reproduction and Inheritance | 繁殖与遗传
Sexual reproduction involves the fusion of male and female gametes to produce genetically varied offspring. In humans, sperm and egg cells are haploid (23 chromosomes). DNA is a double helix made of nucleotides, and a gene is a section of DNA coding for a protein. Mitosis produces genetically identical diploid cells for growth; meiosis produces four haploid gametes.
有性繁殖涉及雌雄配子融合产生遗传变异的后代。人类精子与卵细胞均为单倍体（23 条染色体）。DNA 是由核苷酸构成的双螺旋，基因是编码蛋白质的 DNA 片段。分裂产生的二倍体子细胞用于生长；减数分裂产生四个单倍体配子。
Alleles are different forms of a gene. In a monohybrid cross, a dominant allele masks a recessive allele. The genotype determines the phenotype. Example: Tt × Tt produces a 3:1 phenotypic ratio of tall to short pea plants if T is dominant for tallness.
等位基因是同一基因的不同形式。在单基因杂交中，显性等位基因掩盖隐性等位基因。基因型决定表现型。例如：Tt × Tt 若 T 为高茎显性，则子代表现型高茎与矮茎比例为 3:1。
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