📚 Year 12 Edexcel Science: Core Concepts Revision | Edexcel 12年级科学核心知识点梳理
Welcome to the Year 12 Edexcel Science revision guide. This article brings together the most important ideas you will meet in Biology, Chemistry and Physics. We focus on the fundamental principles that underpin each subject and show how they connect across the sciences. Use this as a starting point for your own notes, flash cards and exam practice.
欢迎阅读 Edexcel 12 年级科学复习指南。本文汇集了生物、化学和物理三科中最核心的知识点，帮助你在跨学科框架中理解基本原理。你可以将这作为整理笔记、制作抽认卡和刷真题的起点。
1. Biological Molecules and Cells | 生物分子与细胞
The molecular building blocks of life include carbohydrates, lipids, proteins and nucleic acids. Monosaccharides such as glucose join by glycosidic bonds to form polysaccharides like starch and cellulose. Proteins are polymers of amino acids folded into specific three‑dimensional shapes determined by their primary sequence.
构成生命的大分子包括糖类、脂质、蛋白质和核酸。葡萄糖等单糖通过糖苷键连接形成淀粉和纤维素等多糖。蛋白质是由氨基酸组成的聚合物，其三维结构由一级序列决定。
Eukaryotic cells contain a membrane‑bound nucleus, mitochondria, endoplasmic reticulum and Golgi apparatus. Prokaryotic cells lack a nucleus and membrane‑bound organelles; their DNA is free in the cytoplasm. Key differences between plant and animal cells include the presence of a cellulose cell wall, chloroplasts and a large central vacuole in plants.
真核细胞拥有具膜包被的细胞核、线粒体、内质网和高尔基体。原核细胞没有细胞核和膜包被的细胞器，其 DNA 游离在细胞质中。动植物细胞的主要区别在于植物细胞含有纤维素细胞壁、叶绿体和中央大液泡。
2. Cell Membranes and Transport | 细胞膜与物质运输
The fluid‑mosaic model describes the cell membrane as a phospholipid bilayer with embedded proteins, cholesterol and glycoproteins. Phospholipids are amphipathic: their hydrophilic heads face outward and hydrophobic tails point inward, creating a selectively permeable barrier.
流动镶嵌模型将细胞膜描述为磷脂双分子层，上面镶嵌着蛋白质、胆固醇和糖蛋白。磷脂分子具有两亲性：亲水头部朝外、疏水尾部向内，形成选择性通透屏障。
Passive transport includes diffusion and facilitated diffusion through channel or carrier proteins; active transport requires ATP and moves substances against their concentration gradient. Osmosis is the net movement of water across a partially permeable membrane from a region of higher water potential to lower water potential.
被动运输包括简单扩散和借助通道蛋白或载体蛋白的协助扩散；主动运输需要 ATP 并逆浓度梯度运输物质。渗透是水分子通过半透膜从高水势区域向低水势区域的净移动。
3. Enzymes and Biological Reactions | 酶与生物反应
Enzymes are globular proteins that act as biological catalysts by lowering the activation energy of reactions. Each enzyme has an active site complementary to its substrate, described by the lock‑and‑key and induced‑fit models. Enzyme activity is affected by temperature, pH, substrate concentration and inhibitors.
酶是球状蛋白质，作为生物催化剂降低反应的活化能。每种酶的活性位点与底物互补，可用“锁钥模型”和“诱导契合模型”解释。酶活性受温度、pH、底物浓度和抑制剂的影响。
Competitive inhibitors resemble the substrate and bind reversibly to the active site; non‑competitive inhibitors bind elsewhere and change the shape of the active site. The initial rate of reaction can be measured by monitoring product formation or substrate disappearance over time.
竞争性抑制剂与底物结构相似，可逆地结合在活性位点；非竞争性抑制剂结合在其他部位，改变活性位点形状。反应的初始速率可通过监测产物生成或底物消耗随时间的变化来测定。
4. Nucleic Acids and DNA Replication | 核酸与 DNA 复制
DNA (deoxyribonucleic acid) is a double helix composed of nucleotides, each containing deoxyribose sugar, a phosphate group and a nitrogenous base (adenine, thymine, cytosine or guanine). Complementary base pairing holds the two strands together: A pairs with T via two hydrogen bonds, C pairs with G via three hydrogen bonds.
DNA（脱氧核糖核酸）是双螺旋结构，由核苷酸组成，每个核苷酸含脱氧核糖、磷酸基团和含氮碱基（腺嘌呤 A、胸腺嘧啶 T、胞嘧啶 C 或鸟嘌呤 G）。两条链通过互补碱基配对结合：A 与 T 形成两个氢键，C 与 G 形成三个氢键。
Semi‑conservative replication involves the enzyme helicase unwinding the double helix, DNA polymerase adding complementary nucleotides to each template strand, and ligase joining Okazaki fragments on the lagging strand. RNA differs from DNA by containing ribose sugar and uracil instead of thymine.
半保留复制过程中，解旋酶解开双螺旋，DNA 聚合酶以每条母链为模板添加互补核苷酸，连接酶将滞后链上的冈崎片段连接起来。RNA 与 DNA 的区别在于含有核糖和尿嘧啶 U 而非胸腺嘧啶 T。
5. Atomic Structure and Bonding | 原子结构与化学键
Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in energy levels or shells. Atomic number Z equals the number of protons; mass number A is the sum of protons and neutrons. Isotopes have the same Z but different A.
原子由包含质子和中子的原子核及核外分层排布的电子构成。原子序数 Z 等于质子数；质量数 A 为质子数与中子数之和。同位素具有相同的 Z 但不同的 A。
Ionic bonding involves electron transfer from a metal to a non‑metal, forming oppositely charged ions held together by strong electrostatic forces in a giant ionic lattice. Covalent bonds form when atoms share electron pairs; simple molecular substances have low melting points, while giant covalent structures like diamond and SiO₂ have very high melting points.
离子键是电子从金属转移到非金属，形成相反电荷的离子，通过离子晶格中的强静电吸引力结合。共价键通过原子间共用电子对形成；简单分子物质熔点低，而金刚石和 SiO₂ 等巨型共价结构熔点极高。
Metallic bonding consists of a lattice of positive metal ions surrounded by a sea of delocalised electrons, which explains electrical and thermal conductivity and malleability.
金属键由正金属离子的晶格及包围其的离域电子海构成，这解释了金属的导电性、导热性和延展性。
6. Chemical Reactions and Stoichiometry | 化学反应与计量学
The mole is the unit for amount of substance; one mole contains Avogadro’s number (6.02 × 10²³) of particles. The empirical formula is the simplest whole‑number ratio of atoms in a compound, while the molecular formula gives the actual number of each atom.
摩尔是物质的量的单位，1 摩尔含有阿伏伽德罗常数（6.02 × 10²³）个粒子。实验式是化合物中各原子最简整数比，而分子式给出每种原子的实际数目。
Balanced equations show the relative numbers of reactants and products. Calculations using mass, moles and concentration follow the relationships: n = m ÷ M, concentration = n ÷ V. Limiting reagents determine the maximum yield of product.
配平的化学方程式显示反应物与生成物的相对数量。利用质量、摩尔和浓度的计算遵循关系式：n = m ÷ M，浓度 = n ÷ V。限量试剂决定了产物的最大产量。
Percentage yield and atom economy assess the efficiency of a reaction. Atom economy = (molar mass of desired product ÷ sum of molar masses of all reactants) × 100%.
产率和原子经济性是衡量反应效率的指标。原子经济性 =（目标产物摩尔质量 ÷ 所有反应物摩尔质量之和）× 100%。
7. Energetics and Thermodynamics | 能量学与热力学
Enthalpy change ΔH is the heat energy transferred in a reaction at constant pressure. Exothermic reactions release energy (ΔH negative); endothermic reactions absorb energy (ΔH positive). Calorimetry experiments measure temperature change to calculate q = mcΔT and then ΔH.
焓变 ΔH 是恒压下反应中的热量变化。放热反应释放能量（ΔH 为负），吸热反应吸收能量（ΔH 为正）。量热实验通过测量温度变化，用 q = mcΔT 计算热量，再求出 ΔH。
Hess’s Law states that the total enthalpy change for a reaction is independent of the route taken. Bond enthalpies can be used to estimate ΔH: ΔH = Σ(bond energies broken) – Σ(bond energies formed). Standard conditions are 100 kPa, 298 K and solution concentrations of 1 mol dm⁻³.
盖斯定律指出，反应的总焓变与途径无关。可用键能估算 ΔH：ΔH = 反应物键能总和 – 生成物键能总和。标准条件为 100 kPa、298 K 及溶液浓度 1 mol dm⁻³。
8. Mechanics and Motion | 力学与运动
Kinematics describes motion using quantities: displacement (s), initial velocity (u), final velocity (v), acceleration (a) and time (t). The equations of motion for constant acceleration are: v = u + at, s = ½(u + v)t, s = ut + ½at², v² = u² + 2as.
运动学使用位移 s、初速度 u、末速度 v、加速度 a 和时间 t 描述运动。匀加速直线运动的公式为：v = u + at，s = ½(u + v)t，s = ut + ½at²，v² = u² + 2as。
Newton’s laws: First – an object remains at rest or in uniform motion unless acted on by a resultant force; Second – force F = ma; Third – every action has an equal and opposite reaction. Momentum p = mv is conserved in a closed system.
牛顿定律：第一定律——物体在无合外力作用下保持静止或匀速直线运动；第二定律——力 F = ma；第三定律——作用力与反作用力大小相等、方向相反。动量 p = mv 在封闭系统中守恒。
Work done = force × distance moved in the direction of the force; energy transforms between kinetic energy ½mv² and gravitational potential energy mgΔh.
做功 = 力 × 沿力方向移动的距离；能量可在动能 ½mv² 和重力势能 mgΔh 之间转化。
9. Waves and Electromagnetic Spectrum | 波与电磁波谱
Waves transfer energy without transferring matter. Transverse waves (e.g., light, water) have oscillations perpendicular to the direction of travel; longitudinal waves (e.g., sound) have oscillations parallel to the direction. Wave speed v = f λ.
波传递能量但不传递物质。横波（如光、水波）振动方向与传播方向垂直；纵波（如声波）振动方向与传播方向平行。波速 v = 频率 f × 波长 λ。
The electromagnetic spectrum, in order of increasing frequency, is: radio, microwave, infrared, visible, ultraviolet, X‑ray, gamma. All travel at 3.00 × 10⁸ m s⁻¹ in a vacuum. Refraction, reflection, diffraction and polarisation are key wave phenomena.
电磁波谱按频率递增的顺序为：无线电波、微波、红外线、可见光、紫外线、X 射线、伽马射线。它们在真空中传播速度均为 3.00 × 10⁸ m s⁻¹。折射、反射、衍射和偏振是关键的波动现象。
The photoelectric effect shows light behaving as particles (photons) with energy E = hf. The work function Φ is the minimum energy to release an electron; KEₘₐₓ = hf – Φ.
光电效应显示光具有粒子性（光子），能量 E = hf。功函数 Φ 是释放一个电子的最小能量；最大动能 KEₘₐₓ = hf – Φ。
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