📚 Year 12 CAIE Science: Core Concepts Summary | Year 12 CAIE 科学：核心知识点梳理
This article consolidates the essential AS-Level knowledge across the three main CAIE science subjects – Physics, Chemistry and Biology. Whether you are preparing for mock exams or building a solid foundation ahead of Year 13, these core concepts are your toolkit for success.
本文梳理了 CAIE 物理、化学、生物三门主要科学学科在 AS 阶段的核心知识点。无论你正在备战模考，还是为 Year 13 打基础，这些核心概念都是你通向高分的工具箱。
1. Physics: Kinematics and Motion | 物理：运动学与运动
Displacement, velocity and acceleration are vector quantities that describe motion in one and two dimensions. The four suvat equations link these variables when acceleration is constant.
位移、速度和加速度都是矢量，用于描述一维和二维运动。当加速度恒定时，四个 suvat 方程将这些变量联系在一起。
v = u + at | s = ut + ½at² | v² = u² + 2as | s = ½(u+v)t
Distance–time and velocity–time graphs provide a visual way to extract displacement, speed and acceleration. The gradient of a distance–time graph gives speed; the gradient of a velocity–time graph gives acceleration, while the area under a velocity–time graph gives displacement.
距离–时间图和速度–时间图可以直观地提取位移、速率和加速度。距离–时间图的斜率表示速率；速度–时间图的斜率表示加速度，图线下的面积则表示位移。
Free-fall motion under gravity assumes negligible air resistance, so a = 9.81 m s⁻² vertically downward. Projectile motion is analysed by resolving the initial velocity into horizontal and vertical components; the horizontal component remains constant while the vertical component changes uniformly with g.
重力作用下的自由落体运动忽略空气阻力，加速度 a = 9.81 m s⁻² 竖直向下。抛体运动通过将初速度分解为水平和竖直分量来分析；水平分量保持不变，竖直分量在 g 的作用下均匀变化。
2. Physics: Forces, Energy and Momentum | 物理：力、能量与动量
Newton’s three laws form the backbone of mechanics: an object maintains its state of motion unless acted upon by a resultant force (inertia); the acceleration is directly proportional to the resultant force and inversely proportional to mass (F = ma); action and reaction forces are equal in magnitude and opposite in direction.
牛顿三定律构成了力学的支柱：物体在不受合外力作用时保持静止或匀速直线运动状态（惯性）；加速度与合外力成正比、与质量成反比（F = ma）；作用力与反作用力大小相等、方向相反。
Energy is conserved in any closed system. Kinetic energy (Eₖ = ½mv²), gravitational potential energy (Eₚ = mgh) and work done (W = Fd cosθ) are central to energy calculations. Power is the rate of doing work, P = W/t or P = Fv for constant velocity.
任何封闭系统内能量守恒。动能（Eₖ = ½mv²）、重力势能（Eₚ = mgh）和做功（W = Fd cosθ）是能量计算的核心。功率是做功的快慢，P = W/t，匀速运动时 P = Fv。
Momentum (p = mv) is conserved in collisions and explosions, provided no external resultant force acts. The impulse of a force (FΔt) equals the change in momentum, a crucial link for understanding safety features like airbags and crumple zones.
只要没有外力作用，动量（p = mv）在碰撞和爆炸过程中守恒。力的冲量（FΔt）等于动量的变化，这一关系对于理解气囊和溃缩区等安全设计至关重要。
3. Physics: Waves and Superposition | 物理：波与叠加
Progressive waves transfer energy without transferring matter. Transverse waves (e.g. light, water ripples) have oscillations perpendicular to the direction of propagation, while longitudinal waves (e.g. sound) have oscillations parallel to it. Key wave descriptors include amplitude, wavelength, frequency and wave speed (v = fλ).
行波传递能量而不传递物质。横波（如光、水波）的振动方向垂直于传播方向，纵波（如声波）的振动方向平行于传播方向。波的描述量包括振幅、波长、频率和波速（v = fλ）。
When two or more waves overlap, the principle of superposition applies, giving constructive or destructive interference. Stationary waves result from the superposition of two identical progressive waves travelling in opposite directions, displaying nodes (zero displacement) and antinodes (maximum displacement).
两个或多个波重叠时遵从叠加原理，产生相长干涉或相消干涉。驻波由两列相同的行波沿相反方向叠加形成，表现出波节（位移为零）和波腹（位移最大）。
Young’s double-slit experiment provides clear evidence for the wave nature of light. The fringe spacing Δx is given by Δx = λD / d, where D is the slit–screen distance and d is the slit separation. A diffraction grating produces sharper, brighter maxima described by d sinθ = nλ.
杨氏双缝实验为光的波动性提供了有力证据。条纹间距 Δx 由 Δx = λD / d 给出，其中 D 为双缝到屏幕距离，d 为双缝间距。衍射光栅产生更锐利、更亮的极大值，满足 d sinθ = nλ。
4. Physics: Electricity and DC Circuits | 物理：电流与直流电路
Electric current is the rate of flow of charge (I = ΔQ / Δt). In a metallic conductor, current is due to the movement of delocalised electrons. Potential difference (voltage) is the energy transferred per unit charge; electromotive force (e.m.f.) is the total energy supplied per unit charge by a source.
电流是电荷流动的快慢（I = ΔQ / Δt）。在金属导体中，电流由自由电子的定向移动形成。电势差（电压）是每单位电荷转移的能量；电动势（e.m.f.）是电源提供给每单位电荷的总能量。
Resistance R = V / I, and for an ohmic conductor at constant temperature, the I–V characteristic is a straight line. Resistivity (ρ) links the resistance of a wire to its length L and cross-sectional area A: R = ρL / A.
电阻 R = V / I，对于温度恒定的欧姆导体，其 I–V 特性为过原点的直线。电阻率 ρ 将导线的电阻与其长度 L 和横截面积 A 联系起来：R = ρL / A。
Kirchhoff’s two laws govern circuit analysis: the sum of currents entering a junction equals the sum leaving (charge conservation); the sum of e.m.f.s round a closed loop equals the sum of potential drops (energy conservation). These are used to calculate currents in series and parallel combinations, and to understand potential dividers.
基尔霍夫两条定律是电路分析的基础：流入节点的电流之和等于流出节点的电流之和（电荷守恒）；闭合回路中电动势之和等于电势降之和（能量守恒）。它们可用于计算串并联电路中的电流，并理解分压器原理。
5. Chemistry: Atomic Structure and Periodicity | 化学：原子结构与周期性
Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in discrete energy levels or shells. The atomic (proton) number Z defines the element, while the mass number A = protons + neutrons. Isotopes have the same Z but different numbers of neutrons.
原子由包含质子和中子的原子核以及分层排布的核外电子构成。原子序数（质子数）Z 决定了元素种类，质量数 A = 质子数 + 中子数。同位素具有相同的质子数但中子数不同。
Electron configuration follows the Aufbau principle, with orbitals filling in order of increasing energy: 1s, 2s, 2p, 3s, 3p, 4s, 3d. The shape of the periodic table reflects the sub-shell being filled; periodicity in atomic radius, ionisation energy and electronegativity arises from nuclear charge and shielding effects.
电子排布遵循构造原理，轨道按能量升高顺序填充：1s、2s、2p、3s、3p、4s、3d。元素周期表的形状反映了正在填充的亚层；原子半径、电离能和电负性的周期性变化源于核电荷与屏蔽效应。
First ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms, forming one mole of gaseous 1+ ions. A sharp decrease from Group 2 to Group 3 and Group 15 to 16 can be explained by sub-shell structure (p vs s) and electron–electron repulsion in orbitals.
第一电离能是指从一摩尔气态原子中移去一摩尔电子形成一摩尔气态 1+ 离子所需的能量。第 2 族到第 3 族、第 15 族到第 16 族之间的突然下降可以用亚层结构（p 轨道 vs s 轨道）和轨道内电子排斥来解释。
6. Chemistry: Chemical Bonding and Structure | 化学：化学键与结构
Ionic bonding involves the electrostatic attraction between oppositely charged ions, typically formed between a metal and a non-metal. Giant ionic lattices have high melting points and conduct electricity only when molten or dissolved, because ions become mobile.
离子键是带相反电荷离子之间的静电吸引，通常由金属和非金属形成。巨型离子晶格熔点高，且仅在熔融或溶于水时导电，因为此时离子可以自由移动。
Covalent bonding is the sharing of electron pairs between atoms. Simple molecular substances (e.g. I₂, H₂O) have low melting points and are non-conductors. Giant covalent structures (e.g. diamond, graphite, silicon dioxide) have very high melting points; graphite conducts electricity due to delocalised electrons between its layers.
共价键是原子间共用电子对。简单分子物质（如 I₂、H₂O）熔点低，不导电。巨型共价结构（如金刚石、石墨、二氧化硅）熔点极高；石墨因层间存在离域电子而能导电。
VSEPR theory predicts molecular shapes based on the repulsion between electron pairs around a central atom. Key geometries include linear (180°), trigonal planar (120°), tetrahedral (109.5°), bent/V-shaped and pyramidal. Bond polarity and molecular symmetry determine whether a molecule has a permanent dipole.
价层电子对互斥理论（VSEPR）通过中心原子周围电子对的排斥来预测分子形状。关键几何构型包括直线形（180°）、平面三角形（120°）、四面体形（109.5°）、角形/ V 形和三角锥形。键的极性和分子对称性决定了分子是否具有永久偶极。
7. Chemistry: Energetics and Chemical Equilibria | 化学：热化学与化学平衡
Enthalpy change ΔH is the heat energy transferred in a reaction at constant pressure. Exothermic reactions release energy (ΔH negative) while endothermic reactions absorb energy (ΔH positive). Standard enthalpy changes of combustion, formation and neutralisation are defined under standard conditions.
焓变 ΔH 是恒压条件下反应中传递的热能。放热反应释放能量（ΔH 为负），吸热反应吸收能量（ΔH 为正）。标准燃烧焓、标准生成焓和标准中和焓均在标准条件下定义。
Hess’s Law states that the total enthalpy change for a reaction is independent of the pathway, enabling indirect calculations from known enthalpy changes. Bond enthalpies provide an estimation of ΔH by comparing the energy absorbed in breaking bonds with the energy released when new bonds form.
赫斯定律指出，反应的总焓变与路径无关，这使得利用已知焓变进行间接计算成为可能。键焓通过比较断键吸收的能量和成键释放的能量，提供了一种估算 ΔH 的方法。
For a reversible reaction at equilibrium, the forward and backward rates are equal and the concentrations of reactants and products remain constant. The equilibrium constant Kc indicates the position of equilibrium; Le Chatelier’s principle predicts how a change in concentration, pressure or temperature shifts the equilibrium to counteract the change.
可逆反应达到平衡时，正、逆反应速率相等，反应物和产物浓度保持不变。平衡常数 Kc 表明了平衡的位置；勒夏特列原理可预测浓度、压力或温度的变化如何使平衡向抵消该变化的方向移动。
8. Biology: Cell Membranes and Transport | 生物：细胞膜与运输
All cells are surrounded by a plasma membrane composed of a phospholipid bilayer with embedded proteins, cholesterol (in animal cells) and glycoproteins. The fluid-mosaic model describes the membrane as a dynamic structure, with phospholipids and many proteins free to move laterally.
所有细胞都被质膜包裹，质膜由磷脂双分子层、镶嵌蛋白质、胆固醇（动物细胞）和糖蛋白构成。流动镶嵌模型描述了膜是一个动态结构，磷脂和许多蛋白质可以侧向移动。
Membranes are selectively permeable. Small, non-polar molecules (e.g. O₂, CO₂) diffuse freely through the bilayer, while ions and polar molecules require transport proteins. Passive transport includes simple diffusion and facilitated diffusion; both follow the concentration gradient and require no metabolic energy.
膜具有选择透过性。小分子非极性物质（如 O₂、CO₂）可自由扩散通过双分子层，而离子和极性分子则需要转运蛋白。被动运输包括简单扩散和易化扩散，两者均顺浓度梯度进行，不消耗代谢能量。
Active transport moves substances against the concentration gradient using energy from ATP, as seen in the sodium–potassium pump. Bulk transport (endocytosis and exocytosis) involves membrane folding and vesicle formation, allowing large molecules to enter or leave the cell.
主动运输利用 ATP 提供的能量将物质逆浓度梯度转运，如钠–钾泵。胞吞和胞吐这种大量运输涉及膜的折叠和囊泡形成，使大分子能够进出细胞。
9. Biology: Biological Molecules and Enzymes | 生物：生物分子与酶
Carbohydrates, lipids, proteins and nucleic acids are the four major classes of biological molecules. Monosaccharides (e.g. glucose) link via glycosidic bonds to form disaccharides (e.g. sucrose, maltose) and polysaccharides (starch, glycogen, cellulose). Triglycerides consist of glycerol esterified with three fatty acid chains.
糖类、脂质、蛋白质和核酸是四大类生物分子。单糖（如葡萄糖）通过糖苷键连接形成二糖（如蔗糖、麦芽糖）和多糖（淀粉、糖原、纤维素）。甘油三酯由一分子甘油与三分子脂肪酸酯化而成。
Proteins are polymers of amino acids joined by peptide bonds. Their primary structure is the sequence of amino acids; secondary structures (α-helix, β-pleated sheet) are stabilised by hydrogen bonds; tertiary structure determines overall 3D shape and is maintained by hydrophobic interactions, ionic bonds, hydrogen bonds and disulfide bridges.
蛋白质是由氨基酸通过肽键连接而成的聚合物。一级结构是氨基酸序列；二级结构（α 螺旋、β 折叠）由氢键稳定；三级结构决定整体三维形状，并由疏水相互作用、离子键、氢键和二硫键维持。
Enzymes are globular proteins that act as biological catalysts by lowering activation energy. The active site is specific to the substrate (lock-and-key / induced-fit models). Enzyme activity is affected by temperature, pH, enzyme concentration and substrate concentration; denaturation occurs when the tertiary structure is disrupted irreversibly.
酶是球状蛋白，通过降低活化能起生物催化剂作用。活性位点对底物具有专一性（锁钥模型 / 诱导契合模型）。酶活性受温度、pH、酶浓度和底物浓度影响；当三级结构被不可逆破坏时，酶发生变性。
10. Biology: Transport in Mammals and Plants | 生物：哺乳动物与植物的运输
The mammalian circulatory system is a closed, double circulation with blood passing twice through the heart per complete circuit. The heart’s own electrical conduction system initiates the cardiac cycle; SAN → AVN → Purkyne fibres coordinate atrial and ventricular contraction.
哺乳动物的循环系统是一个闭式双循环系统，血液完成一次全循环需两次流经心脏。心脏自身的电传导系统发起心动周期：窦房结 → 房室结 → 浦肯野纤维协调心房与心室的收缩。
Haemoglobin in red blood cells binds oxygen reversibly to form oxyhaemoglobin. The oxygen dissociation curve is sigmoidal, showing cooperative binding. Bohr effect describes the shift of the curve to the right at higher CO₂ concentrations, facilitating oxygen unloading in respiring tissues.
红细胞中的血红蛋白可逆地与氧结合形成氧合血红蛋白。氧解离曲线呈 S 形，体现了协同结合。波尔效应描述了高浓度 CO₂ 条件下曲线右移，从而促进氧气在呼吸组织处卸载。
In plants, xylem vessels transport water and dissolved minerals from the roots upwards. The cohesion–tension theory explains the ascent of water: transpiration at the leaves generates tension which pulls a continuous column of water, aided by strong cohesive and adhesive forces. Phloem sieve tubes transport sucrose and amino acids from sources to sinks via translocation, using active loading and pressure flow.
在植物中，木质部导管将水和溶解的矿物质从根部向上运输。内聚力–张力理论解释了水分上升的机制：叶片蒸腾作用产生张力，通过强大的内聚力和附着力拉动连续水柱上升。韧皮部筛管通过转运作用将蔗糖和氨基酸从源运至库，依赖主动装载和压力流动。
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