📚 Year 12 WJEC Science: Core Concepts Review | 12年级 WJEC 科学：核心知识点梳理
Welcome to your focused revision guide for Year 12 WJEC Science. This article covers the essential core concepts from Biology, Chemistry and Physics, aligned with the WJEC AS specification. Use it to consolidate your understanding, identify links between topics, and build confidence for your examinations.
欢迎阅读这份专为 12 年级 WJEC 科学准备的复习指南。本文涵盖了生物学、化学和物理学的核心知识点，与 WJEC AS 教学大纲紧密衔接。通过这篇梳理，你将巩固理解、发现学科间的联系，并为考试树立信心。
1. Cell Structure and Function | 细胞结构与功能
All living organisms are made of cells, which can be classified as prokaryotic (e.g. bacteria) or eukaryotic (e.g. animal and plant cells). Eukaryotic cells contain membrane-bound organelles including the nucleus, mitochondria, endoplasmic reticulum and Golgi apparatus. Plant cells also possess a cellulose cell wall, chloroplasts and a large permanent vacuole.
所有生物体都由细胞构成，可分为原核细胞（如细菌）和真核细胞（如动植物细胞）。真核细胞含有膜包裹的细胞器，包括细胞核、线粒体、内质网和高尔基体。植物细胞还具有纤维素细胞壁、叶绿体和一个大液泡。
Microscopy techniques allow us to study cell structure. The light microscope has a lower resolution than the electron microscope, but is suitable for living specimens. Magnification is calculated using the formula:
magnification = image size / actual size
显微镜技术使我们能够研究细胞结构。光学显微镜的分辨率低于电子显微镜，但适合观察活体标本。放大倍数的计算公式为：放大倍数 = 图像大小 / 实际大小。务必统一单位，并能从比例尺图像推算实际大小。
2. Biological Molecules | 生物分子
Carbohydrates, lipids, proteins and nucleic acids are the four major groups of biological molecules. Monosaccharides such as glucose form disaccharides (e.g. maltose, sucrose) and polysaccharides (starch, glycogen, cellulose) through condensation reactions. The glycosidic bond is broken by hydrolysis.
碳水化合物、脂质、蛋白质和核酸是四类主要的生物分子。单糖如葡萄糖通过缩合反应生成二糖（如麦芽糖、蔗糖）和多糖（淀粉、糖原、纤维素）。糖苷键通过水解反应断裂。
Proteins are polymers of amino acids joined by peptide bonds. The primary structure is the sequence of amino acids; secondary structure includes alpha-helices and beta-pleated sheets held by hydrogen bonds; tertiary structure is the overall 3D shape maintained by hydrogen bonds, disulfide bridges, ionic bonds and hydrophobic interactions. Enzymes are globular proteins that lower activation energy.
蛋白质是由氨基酸通过肽键连接而成的多聚体。一级结构是氨基酸序列；二级结构包括由氢键维持的α-螺旋和β-折叠；三级结构是通过氢键、二硫桥、离子键和疏水相互作用维持的整体三维形状。酶是球状蛋白，能降低活化能。
3. Cell Membranes and Transport | 细胞膜与运输
The fluid mosaic model describes the cell membrane as a phospholipid bilayer with embedded proteins, cholesterol and glycoproteins. Phospholipids have hydrophilic heads and hydrophobic tails, forming a selectively permeable barrier. Membrane proteins function in transport, cell recognition and enzymatic activity.
流动镶嵌模型将细胞膜描述为由磷脂双分子层和嵌入的蛋白质、胆固醇及糖蛋白构成。磷脂的亲水头部和疏水尾部形成选择性通透屏障。膜蛋白具有运输、细胞识别和酶活性等功能。
Substances cross membranes by passive or active processes. Diffusion and facilitated diffusion move substances down a concentration gradient without energy. Osmosis is the net movement of water across a partially permeable membrane. Active transport uses ATP to move substances against the gradient, while endocytosis and exocytosis involve vesicle formation for bulk transport.
物质通过被动或主动过程穿过细胞膜。扩散和协助扩散沿浓度梯度移动物质，不耗能。渗透是水通过部分透膜的净移动。主动运输利用 ATP 逆浓度梯度转运物质；内吞和胞吐作用则通过形成囊泡进行大宗运输。
4. Atomic Structure and Periodicity | 原子结构与周期律
Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in energy levels. Atomic number (Z) defines the number of protons; mass number (A) is the sum of protons and neutrons. Isotopes have the same Z but different A. Relative atomic mass is a weighted average of isotopic masses.
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组成。原子序数（Z）等于质子数；质量数（A）是质子数与中子数之和。同位素具有相同的 Z 但不同的 A。相对原子质量是同位素质量的加权平均值。
The modern periodic table is arranged in order of increasing atomic number. Elements in the same group have similar chemical properties due to the same number of outer electrons. Trends across period 3 include increasing ionisation energy and decreasing atomic radius. The s-, p- and d-blocks correspond to electron subshell filling.
现代元素周期表按原子序数递增的顺序排列。同族元素因最外层电子数相同而具有相似的化学性质。第三周期从左到右，电离能增加，原子半径减小。s 区、p 区和 d 区分别对应电子亚层的填充。
5. Chemical Bonding and Structure | 化学键与结构
Ionic bonding occurs between metals and non-metals via electron transfer, forming a giant ionic lattice. The strong electrostatic forces result in high melting points and electrical conductivity when molten or dissolved. Covalent bonding involves the sharing of electron pairs, forming either simple molecular substances (e.g. H₂O, CO₂) or giant covalent structures (e.g. diamond, graphite, SiO₂).
离子键通过金属与非金属之间的电子转移形成，构成巨型离子晶格。强静电引力使得离子化合物具有高熔点，并在熔融或溶于水时导电。共价键涉及电子对的共用，可形成简单分子物质（如 H₂O、CO₂）或巨型共价结构（如金刚石、石墨、SiO₂）。
Metallic bonding consists of a lattice of positive ions in a 'sea' of delocalised electrons, explaining high electrical and thermal conductivity, malleability and ductility. Electronegativity differences determine bond polarity; polar molecules have an overall dipole. Intermolecular forces, including hydrogen bonds, affect physical properties like boiling point.
金属键由离域电子“海洋”中的正离子晶格构成，这解释了金属的高导电性、高导热性以及展性和延性。电负性差异决定键的极性；极性分子具有整体偶极矩。分子间作用力，包括氢键，会影响沸点等物理性质。
6. Energetics and Kinetics | 能量学与动力学
ions absorb energy (ΔH positive). Standard conditions are 298 K and 100 kPa. Calorimetry experiments allow calculation of enthalpy changes using q = mcΔT.
焓变（ΔH）是恒压下的热量变化。放热反应释放能量（ΔH 为负值），吸热反应吸收能量（ΔH 为正值）。标准条件为 298 K 和 100 kPa。量热实验利用 q = mcΔT 计算焓变。
Hess's Law states that the total enthalpy change is independent of the pathway. Born– lculate unknown ΔH values. Bond enthalpies provide another route: ΔH = sum of bonds broken – sum of bonds formed.
赫斯定律指出，总焓变与反应路径无关。通过波恩-哈伯循环或燃烧焓数据，可以计算未知的 ΔH 值。键焓提供另一种途径：ΔH = 反应物键断裂吸收的总能量 – 生成物键形成释放的总能量。
7. Forces and Motion | 力与运动
Kinematics describes motion using quantities such as displacement, velocity, acceleration and time. The equations of motion (SUVAT) apply for constant acceleration in a straight line:
v = u + at, s = ut + ½at², v² = u² + 2as
运动学用位移、速度、加速度和时间等物理量描述运动。匀加速直线运动可以使用运动学方程（SUVAT）：v = u + at, s = ut + ½at², v² = u² + 2as。需注意矢量方向的正负规定。
Newton' a, links resultant force to acceleration; the third law states that forces occur in action– nd momentum (p = mv) is conserved in collisions provided no external resultant force acts.
牛顿运动定律奠定了动力学基础。第一定律引入了惯性概念；第二定律 F = ma 将合力与加速度联系起来；第三定律表明力总是成对出现。受力分析图帮助分解力，动量（p = mv）在没有外力作用的碰撞中守恒。
8. Waves and Optics | 波与光学
n of travel; longitudinal waves (e.g. sound) have oscillations parallel. Key wave descriptors include wavelength λ, frequency f, amplitude and speed v = fλ.
波传递能量而不传递物质。横波（如光波、水波）的振动方向与传播方向垂直；纵波（如声波）的振动方向与传播方向平行。关键波参量包括波长 λ、频率 f、振幅和波速 v = fλ。
Reflection, refraction and diffraction are wave behaviours. Snell' avels from a denser to a rarer medium. Diffraction is most significant when the gap size is similar to the wavelength. In optics, lenses form real or virtual images described by the lens formula 1/f = 1/u + 1/v.
反射、折射和衍射是波的行为特征。斯涅耳定律 n₁ sinθ₁ = n₂ sinθ₂ 描述折射规律。当光从光密介质射向光疏介质，且入射角大于临界角时，发生全内反射。当缝隙尺寸与波长相当时，衍射最显著。在光学中，透镜所成的实像或虚像可用透镜公式 1/f = 1/u + 1/v 描述。
9. Electricity and Circuits | 电与电路
: I = ΔQ/Δt. Potential difference (voltage) is the energy transferred per unit charge. Ohm's law states that V ∝ an ohmic conductor at constant temperature. Resistance R = V/I, and resistivity ρ = RA/L.
电流是电荷流动的速率：I = ΔQ/Δt。电势差（电压）是单位电荷转移的能量。欧姆定律指出，在恒定温度下，欧姆导体的 V 与 I 成正比。电阻 R = V/I，电阻率 ρ = RA/L。
age is constant and current is divided. Power P = IV = I²R = V²/R. Electric circuits often include internal resistance r, reducing the terminal p.d.: V = ε – Ir.
串联和并联电路具有不同的电流和电压规律。串联电路中电流处处相等，电压分配；并联电路中电压相等，电流分配。功率 P = IV = I²R = V²/R。实际电路常包含内阻 r，使端电压降低：V = ε – Ir。
10. Practical Skills and Data Analysis | 实验技能与数据分析
Practical work is integral to WJEC Science. You are expected to identify independent, dependent and control variables, and to assess risks and hazards. Results should be recorded in clearly headed tables with appropriate units. Graphs should be plotted using smooth lines or lines of best fit, and gradients can be used to determine constants or relationships.
实验操作是 WJEC 科学的有机组成部分。你需要识别自变量、因变量和控制变量，并评估风险和危害。结果应记录在表头清晰、带单位的表格中。绘制图表时应使用平滑曲线或最佳拟合线，通过斜率可确定常量或物理关系。
Uncertainty and error analysis are essential. Calculate percentage uncertainty for single measurements and for repeated readings using range/2. Systematic errors affect accuracy; random errors affect precision. When evaluating an experiment, suggest specific improvements that reduce the largest source of uncertainty and explain how they would lead to more reliable data.
不确定度和误差分析至关重要。对单次测量计算百分不确定度，对重复读数使用 range/2。系统误差影响准确度；随机误差影响精密度。在评估实验时，应针对最大的不确定来源提出具体改进建议，并解释它们如何提高数据的可靠性。
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