📚 Core Knowledge Review for Year 12 Cambridge Science | 剑桥 Year 12 科学核心知识点梳理
This article provides a concise yet comprehensive overview of the core concepts in Biology, Chemistry, and Physics for Year 12 students following the Cambridge International AS Level syllabus. Designed as a bilingual revision aid, it covers key definitions, fundamental principles, and essential equations to help you consolidate your understanding and build a solid foundation for further study.
本文为学习剑桥国际 AS 课程的 Year 12 学生提供生物、化学和物理核心概念的简明而全面的梳理。作为中英双语的复习辅助资料，本文涵盖关键定义、基本原理和重要方程式，旨在帮助你巩固理解，为进一步学习打下坚实基础。
1. Cell Structure and Function | 细胞结构与功能
All living organisms are composed of cells, which may be prokaryotic (lacking a nucleus) or eukaryotic (with a membrane-bound nucleus). The major organelles include the nucleus, mitochondrion, ribosome, endoplasmic reticulum, Golgi apparatus, and chloroplast in plant cells. The cell surface membrane, composed of a phospholipid bilayer with embedded proteins, controls the movement of substances into and out of the cell.
所有生物都由细胞组成，细胞分为原核细胞（无细胞核）和真核细胞（有膜包被的细胞核）。主要的细胞器包括细胞核、线粒体、核糖体、内质网、高尔基体以及植物细胞中的叶绿体。由磷脂双分子层和嵌入蛋白质构成的细胞表面膜，控制着物质进出细胞。
- Prokaryotes: bacteria, small ribosomes (70S), circular DNA free in cytoplasm. 原核生物：细菌，核糖体较小（70S），环状 DNA 游离在细胞质中。
- Eukaryotes: protists, fungi, plants, animals; larger 80S ribosomes; DNA in nucleus. 真核生物：原生生物、真菌、植物、动物；较大的 80S 核糖体；DNA 在细胞核内。
The fluid mosaic model describes the cell membrane structure: phospholipids form a bilayer, proteins float like mosaic pieces, and some have carbohydrate chains for cell recognition. Diffusion, osmosis, and active transport are key processes for transport across membranes.
流动镶嵌模型描述细胞膜结构：磷脂形成双分子层，蛋白质如马赛克般漂浮其中，部分带有糖链用于细胞识别。扩散、渗透和主动运输是跨膜运输的关键过程。
2. Biological Molecules and Enzymes | 生物分子与酶
Carbohydrates, lipids, proteins, and nucleic acids are the four major classes of biological macromolecules. Carbohydrates consist of monosaccharides such as glucose (C₆H₁₂O₆) and form disaccharides (e.g. maltose, sucrose) and polysaccharides (starch, cellulose, glycogen). Lipids are composed of glycerol and three fatty acid chains; triglycerides serve as energy stores and phospholipids form cell membranes.
碳水化合物、脂质、蛋白质和核酸是四大类生物大分子。碳水化合物由单糖如葡萄糖（C₆H₁₂O₆）构成，并形成二糖（如麦芽糖、蔗糖）和多糖（淀粉、纤维素、糖原）。脂质由甘油和三个脂肪酸链组成；甘油三酯作为能量储存，磷脂构成细胞膜。
Proteins are polymers of amino acids linked by peptide bonds. The primary structure is the sequence of amino acids; secondary structures include α-helices and β-pleated sheets held by hydrogen bonds; the tertiary structure is the overall 3D folding maintained by hydrogen bonds, ionic bonds, hydrophobic interactions, and disulfide bridges.
蛋白质是由肽键连接的氨基酸聚合物。一级结构是氨基酸序列；二级结构包括由氢键维系的 α–螺旋和 β–折叠层；三级结构是由氢键、离子键、疏水相互作用和二硫键维持的整体三维折叠。
Enzymes are globular proteins that act as biological catalysts by lowering activation energy. The lock-and-key model and the induced-fit model explain enzyme–substrate specificity. Enzyme activity is affected by temperature, pH, substrate concentration, and inhibitors.
酶是球状蛋白，作为生物催化剂降低活化能。锁钥模型和诱导契合模型解释了酶与底物的专一性。酶活性受温度、pH、底物浓度和抑制剂的影响。
3. Cell Division and Genetics | 细胞分裂与遗传
Mitosis produces two genetically identical diploid daughter cells and is essential for growth and repair. The stages are prophase, metaphase, anaphase, and telophase, with cytokinesis following. Meiosis reduces the chromosome number by half to produce haploid gametes and introduces genetic variation through crossing over and independent assortment.
有丝分裂产生两个遗传学上完全相同的二倍体子细胞，对生长和修复至关重要。其阶段为前期、中期、后期和末期，随后是胞质分裂。减数分裂将染色体数目减半，产生单倍体配子，并通过交叉互换和自由组合引入遗传变异。
nd a nitrogenous base (adenine, thymine, cytosine, guanine). Complementary base pairing (A–T, C– is a sequence of DNA that codes for a polypeptide. The central dogma: DNA → RNA → protein.
DNA 结构是由核苷酸构成的双螺旋，每个核苷酸包含脱氧核糖、磷酸和含氮碱基（腺嘌呤、胸腺嘧啶、胞嘧啶、鸟嘌呤）。互补碱基配对（A–T，C–G）实现了半保留复制。基因是编码多肽的 DNA 序列。中心法则：DNA → RNA → 蛋白质。
Monohybrid inheritance can be explained using Punnett squares. Codominance and multiple alleles (e.g. ABO blood groups) show patterns beyond simple dominance. Sex linkage (e.g. haemophilia) involves genes on the X chromosome.
单基因遗传可用旁氏表解释。共显性和复等位基因（如 ABO 血型系统）显示超越简单显性的模式。伴性遗传（如血友病）涉及 X 染色体上的基因。
4. Atomic Structure and the Periodic Table | 原子结构与周期表
Atoms consist of protons (charge +1), neutrons (0), and electrons (−1). The number of protons defines the atomic number Z; the mass number A is the total of protons + neutrons. Isotopes have the same Z but different A. Electrons are arranged in shells or energy levels: 2, 8, 18, etc.
原子由质子（+1 电荷）、中子（0）和电子（−1）组成。质子数决定原子序数 Z；质量数 A 是质子与中子之和。同位素具有相同的 Z 但不同的 A。电子排布在壳层或能级中：2，8，18 等。
The periodic table is arranged in order of increasing atomic number. Periods are horizontal rows; groups are vertical columns. Elements in the same group have the same number of outer electrons and similar chemical properties. Trends across Period 3 include decreasing atomic radius, increasing ionisation energy, and changing metallic character.
周期表按原子序数递增排列。周期是横行；族是纵列。同族元素具有相同的外层电子数和相似的化学性质。第三周期的趋势包括原子半径减小、电离能增大和金属性变化。
- Group 1: alkali metals, very reactive, form +1 ions. 第 1 族：碱金属，非常活泼，形成 +1 离子。
- Group 17: halogens, diatomic non-metals, form −1 ions. 第 17 族：卤素，双原子非金属，形成 −1 离子。
- Group 18: noble gases, monatomic, very unreactive. 第 18 族：稀有气体，单原子，极不活泼。
5. Chemical Bonding and Structure | 化学键合与结构
Ionic bonding involves the transfer of electrons from a metal to a non-metal, forming a giant ionic lattice held by strong electrostatic forces. Compounds like NaCl have high melting points, are brittle, and conduct electricity when molten or dissolved. Covalent bonding involves sharing of electron pairs between non-metal atoms.
离子键涉及电子从金属转移到非金属，形成由强静电作用力维系的巨型离子晶格。像 NaCl 这样的化合物熔点高、脆，并在熔融或溶解时导电。共价键涉及非金属原子间共享电子对。
Simple molecular substances (e.g. H₂O, CO₂) have low melting points because of weak intermolecular forces (van der Waals or hydrogen bonds). Giant covalent structures (diamond, graphite, SiO₂) have very high melting points. Graphite conducts electricity due to delocalised electrons between layers.
简单分子物质（如 H₂O、CO₂）因分子间作用力（范德华力或氢键）弱而熔点低。巨型共价结构（金刚石、石墨、SiO₂）熔点极高。石墨由于层间离域电子而能导电。
Metallic bonding is the attraction between positive metal ions and a sea of delocalised electrons, giving metals malleability, ductility, and electrical conductivity. Dative covalent (coordinate) bonds involve one atom providing both electrons of the shared pair, as in the ammonium ion NH₄⁺.
金属键是正金属离子与离域电子海之间的吸引力，赋予金属延展性、可锻性和导电性。配位共价键（配位键）涉及一个原子提供共享电子对中的两个电子，如铵离子 NH₄⁺。
6. Stoichiometry and Chemical Reactions | 化学计量与化学反应
The mole is the unit of amount of substance, containing 6.02 × 10²³ entities (Avogadro' e-number ratio of atoms in a compound; molecular formula gives the actual number of atoms.
摩尔是物质的量的单位，含 6.02 × 10²³ 个微粒（阿伏伽德罗常数）。摩尔质量（g mol⁻¹）是 1 摩尔物质的质量。实验式表示化合物中原子的最简整数比；分子式给出原子的实际数目。
alanced chemical equation, the coefficients represent mole ratios. Limiting reactants and percentage yield calculations are essential skills.
关键方程式：n = m / M，常温常压下气体体积：体积 = n × 24 dm³（或 24 000 cm³）。浓度 c = n / V（mol dm⁻³）。在配平的化学方程式中，系数表示摩尔比。限制反应物和产率计算是关键技能。
Types of reactions: acid–base (proton transfer), redox (electron transfer, oxidation number changes), precipitation, and displacement. Oxidation is loss of electrons, reduction is gain of electrons (OIL RIG).
反应类型：酸碱（质子转移）、氧化还原（电子转移，氧化数变化）、沉淀和置换。氧化是失电子，还原是得电子（OIL RIG）。
7. Energetics and Equilibria | 能量学与平衡
nges can be calculated using q = mcΔT and then ΔH = −q/n (for reactions in solution). Hess' is independent of the pathway, allowing combination of known ΔH values to find an unknown.
放热反应向环境释放热能（ΔH 为负）；吸热反应吸收热量（ΔH 为正）。焓变可通过 q = mcΔT 计算，然后 ΔH = −q/n（适用于溶液反应）。盖斯定律指出总焓变与途径无关，可以组合已知的 ΔH 值求未知量。
− sum of bonds formed. In reversible reactions, dynamic equilibrium is reached when the forward and reverse rates are equal. Le Chatelier' m at equilibrium will shift to oppose a change in concentration, pressure, or temperature.
键焓：打破一摩尔键所需能量的平均值。ΔH ≈ 断裂键焓总和 − 形成键焓总和。在可逆反应中，当正逆反应速率相等时达到动态平衡。勒夏特列原理预测平衡体系会朝着抵消浓度、压强或温度变化的方向移动。
For the Haber process: N₂ + 3H₂ ⇌ re favours yield but rate is too slow, so compromise temperature (about 450 °C), high pressure (200 atm), and iron catalyst are used.
对于哈伯法合成氨：N₂ + 3H₂ ⇌ 2NH₃，ΔH = −92 kJ mol⁻¹；低温有利于产率但速率太慢，所以采用折中温度（约 450 °C）、高压（200 大气压）和铁催化剂。
8. Kinematics and Dynamics | 运动学与动力学
ght line are: v = u + at; s = ut + ½at²; v² = u² + 2as; s = (u+v)t/2. Graphs of displacement–time and velocity–time give gradient as velocity and acceleration, respectively, and area under a v–t graph gives displacement.
位移 s、速度 v、加速度 a 和时间 t 是矢量。匀加速直线运动的方程是：v = u + at；s = ut + ½at²；v² = u² + 2as；s = (u+v)t/2。位移–时间图和速度–时间图的梯度分别表示速度和加速度，v–t 图下方面积表示位移。
Newton's laws of motion: First law – ct remains at rest or in uniform motion unless acted upon by a resultant force. Second law – F = ma (resultant force = mass × acceleration). Third law – is an equal and opposite reaction. Free-body diagrams help resolve forces into components.
牛顿运动定律：第一定律 – 物体保持静止或匀速直线运动状态，除非受到合外力作用。第二定律 – F = ma（合外力 = 质量 × 加速度）。第三定律 – 每一个作用力都有一个大小相等、方向相反的反作用力。受力分析图有助于将力分解为分量。
collisions and explosions, provided no external resultant force acts. Impulse = FΔt = Δp.
重力 = mg；摩擦力是阻碍运动的力；摩擦系数 μ = F/R。动量 p = mv 在无外合力作用的碰撞和爆炸中守恒。冲量 = FΔt = Δp。
9. Electricity and Circuits | 电学与电路
l difference V is the energy transferred per unit charge: V = W/Q. Resistance R = V/I (Ohm' sistance to the dimensions of a conductor: R = ρL/A. Electrical power P = IV = I²R = V²/R.
电流 I 是电荷流动的速率：I = ΔQ/Δt。电势差 V 是单位电荷转移的能量：V = W/Q。电阻 R = V/I（适用于欧姆导体的欧姆定律）。电阻率 ρ 将电阻与导体的尺寸联系起来：R = ρL/A。电功率 P = IV = I²R = V²/R。
ts: same voltage across each branch, 1/Rₜ = 1/R₁ + 1/R₂ + ... ; current divides. Kirchhoff's laws: first law – sum of currents entering a junction = sum of currents leaving; second law – sum of e.m.f. = sum of p.d. around a closed loop.
串联电路：各元件电流相同，总电阻 Rₜ = R₁ + R₂ + ... ；电压分配。并联电路：各支路电压相同，1/Rₜ = 1/R₁ + 1/R₂ + ... ；电流分配。基尔霍夫定律：第一定律 – 流入节点的电流之和等于流出电流之和；第二定律 – 沿闭合回路的电动势之和等于电势差之和。
ge: Vₒᵤₜ = Vᵢₙ × (R₂/(R₁+R₂)). They are often used with sensors like LDRs and thermistors.
分压器使用两个串联电阻来提供输入电压的一部分：Vₒᵤₜ = Vᵢₙ × (R₂/(R₁+R₂))。它们常与光敏电阻和热敏电阻等传感器一同使用。
10. Waves and Optics | 波动与光学
. light, water ripples); longitudinal waves have oscillations parallel to the direction (e.g. sound). Key terms: displacement, amplitude A, wavelength λ, period T, frequency f = 1/T, wave speed v = fλ.
波传递能量而不引起物质的净移动。横波的振动方向与能量传播方向垂直（如光、水波）；纵波的振动方向与传播方向平行（如声波）。关键术语：位移、振幅 A、波长 λ、周期 T、频率 f = 1/T、波速 v = fλ。
Wave phenomena: reflection, refraction (due to speed change, following Snell' s produce stable interference patterns with constructive (path difference = nλ) and destructive (path difference = (n+½)λ) fringes.
波的现象：反射、折射（因波速改变，遵循斯涅尔定律：n₁ sin θ₁ = n₂ sin θ₂）、衍射（绕过障碍物或缝隙时扩展）和干涉（叠加原理）。两个相干波源产生稳定的干涉图样，包括加强干涉（程差 = nλ）和减弱干涉（程差 = (n+½)λ）。
Young' ction gratings produce sharper maxima with nλ = d sin θ. Standing (stationary) waves form when two identical waves travel in opposite directions, with nodes (zero displacement) and antinodes (maximum displacement).
杨氏双缝实验证实光的干涉：条纹间距 Δy = λD/d，其中 d 为双缝间距，D 为屏幕到缝的距离。衍射光栅产生更锐利的极大值，满足 nλ = d sin θ。当两个相同的波相向而行时形成驻波，具有波节（位移为零）和波腹（位移最大）。
11. Thermodynamics and Energy Transfer | 热力学与能量传递
e specific heat capacity c is the energy required to raise the temperature of 1 kg of substance by 1 K: Q = mcΔθ. The specific latent heat L is the energy per unit mass to change state at constant temperature: Q = mL.
温度是粒子平均无规则动能的量度。热量是因温差而传递的热能。比热容 c 是使 1 kg 物质升高 1 K 所需的能量：Q = mcΔθ。比潜热 L 是在恒定温度下单位质量物质改变状态所需能量：Q = mL。
ses obey pV = nRT and pV = NkT. For an isothermal change pV = constant; for adiabatic change pV^γ = constant.
热力学第一定律：ΔU = Q - W，其中 ΔU 为内能变化，Q 为系统吸收的热量，W 为系统对外做功。理想气体满足 pV = nRT 和 pV = NkT。等温变化 pV = 常数；绝热变化 pV^γ = 常数。
Conduction, convection, and radiation are three means of heat transfer. Conduction is the main mechanism in solids, through lattice vibrations and free electrons in metals. Convection occurs in fluids when heated regions expand and rise. Radiation is the transfer by electromagnetic waves, mainly infrared, and does not require a medium.
传导、对流和辐射是热传递的三种方式。传导是固体中的主要机制，通过晶格振动和金属中的自由电子实现。流体受热区域膨胀上升时发生对流。辐射是通过电磁波（主要是红外线）进行的传递，不需要介质。
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