📚 A-Level WJEC Science: End-of-Term Revision Checklist | A-Level WJEC 科学：期末复习提纲
The WJEC A-Level Science course integrates key concepts from biology, chemistry and physics, while emphasising scientific methodology and practical skills. As the end-of-term assessment approaches, a structured revision checklist helps you consolidate knowledge across all three disciplines. This article provides a thorough review of the core topics and experimental techniques essential for success.
WJEC A-Level 科学课程融合了生物学、化学和物理学的关键概念，同时强调科学方法和实验技能。随着期末考试临近，一份结构化的复习提纲能帮助你巩固三个学科的知识。本文提供了核心主题和实验技巧的全面回顾，助你取得成功。
1. Scientific Inquiry and Experimental Design | 科学探究与实验设计
Every scientific investigation begins with a justified hypothesis that predicts a relationship between variables. The hypothesis must be testable and falsifiable.
每一项科学探究都始于一个有依据的假设，预测变量之间的关系。该假设必须是可检验且可证伪的。
The independent variable is deliberately changed by the experimenter, while the dependent variable is measured as the outcome. Control variables are kept constant to ensure a fair test; replicates improve reliability.
自变量由实验者刻意改变，因变量作为结果被测量。控制变量保持不变以确保公平测试；重复试验可提高可靠性。
Risk assessments identify hazards and describe precautions, such as wearing safety goggles or handling chemicals in a fume cupboard. All methods should be written to allow reproducibility by others.
风险评估识别危险并描述预防措施，例如佩戴护目镜或在通风橱中处理化学品。所有方法都应书写得让其他人能够再现。
2. Cells and Biological Molecules | 细胞与生物分子
Prokaryotic cells lack a membrane-bound nucleus and organelles such as mitochondria, whereas eukaryotic cells possess a true nucleus and compartmentalised organelles. Plant cells additionally have a cell wall, chloroplasts and a large vacuole.
原核细胞缺乏膜包裹的细胞核和线粒体等细胞器，而真核细胞具有真正的细胞核和区室化的细胞器。植物细胞还具有细胞壁、叶绿体和一个大液泡。
The four major classes of biological molecules are carbohydrates (sugars and starch), lipids (fats and oils), proteins (made of amino acids) and nucleic acids (DNA and RNA). Each has specific monomers and bonds, such as glycosidic bonds in carbohydrates and peptide bonds in proteins.
四大类生物分子是碳水化合物（糖和淀粉）、脂质（脂肪和油）、蛋白质（由氨基酸构成）和核酸（DNA 和 RNA）。每一类都有特定的单体与化学键，例如碳水化合物中的糖苷键和蛋白质中的肽键。
Enzymes are biological catalysts that lower activation energy. Their activity is affected by temperature, pH and substrate concentration; denaturation occurs when the active site loses its shape permanently.
酶是降低活化能的生物催化剂。它们的活性受温度、pH 和底物浓度影响；当活性中心永久性变形时，酶发生变性。
3. Genetics and DNA | 遗传与 DNA
DNA replicates semi-conservatively: each new double helix contains one original strand and one newly synthesised strand. Helicase unwinds the double helix, and DNA polymerase adds complementary nucleotides.
DNA 进行半保留复制：每条新的双螺旋含有一条原始链和一条新合成的链。解旋酶解开双螺旋，DNA 聚合酶添加互补核苷酸。
Transcription produces mRNA from a DNA template; translation uses ribosomes to assemble amino acids into a polypeptide according to the codon sequence. The genetic code is degenerate and universal.
转录以 DNA 为模板产生 mRNA；翻译利用核糖体根据密码子序列将氨基酸组装成多肽。遗传密码具有简并性和通用性。
Mendelian genetics describes inheritance through dominant and recessive alleles. Monohybrid crosses produce phenotypic ratios such as 3:1 in the F2 generation. Mutations introduce new alleles and are the raw material for natural selection and evolution.
孟德尔遗传学通过显性和隐性等位基因描述遗传。单基因杂交在 F2 代产生如 3:1 的表型比例。突变引入新的等位基因，是自然选择和进化的原材料。
4. Chemical Bonding and Structure | 化学键与结构
Ionic bonding occurs when electrons are transferred from a metal to a non-metal, forming a lattice of oppositely charged ions with strong electrostatic attraction. Compounds such as NaCl have high melting points and conduct electricity when molten.
离子键发生在电子从金属转移到非金属时，形成由带相反电荷离子构成的晶格，具有强静电引力。如 NaCl 等离子化合物熔点高，熔融时可导电。
Covalent bonding involves the sharing of electron pairs between non-metals. Molecules like H₂O have discrete shapes determined by VSEPR theory; giant covalent structures such as diamond have high hardness.
共价键涉及非金属原子间共用电子对。H₂O 等分子具有由 VSEPR 理论决定的特定形状；而金刚石等巨型共价结构硬度极高。
Metallic bonding consists of a lattice of positive ions surrounded by a sea of delocalised electrons, giving metals malleability and electrical conductivity. Intermolecular forces, including London forces and hydrogen bonds, determine physical properties like boiling points of molecular substances.
金属键由正离子晶格与离域电子海组成，赋予金属延展性和导电性。分子间作用力，包括伦敦力和氢键，决定分子物质的沸点等物理性质。
5. Quantitative Chemistry | 定量化学
The mole is the unit of amount of substance containing 6.02 × 10²³ particles. Molar mass (M) relates mass and moles through n = m / M; this fundamental relationship underpins all stoichiometric calculations.
摩尔是物质的量的单位，包含 6.02 × 10²³ 个粒子。摩尔质量 (M) 通过 n = m / M 关联质量和物质的量；这一基本关系是所有化学计量计算的基础。
n = m / M
Concentration (c) is calculated as c = n / V. Titration experiments use acid–base neutralisation to determine unknown concentrations via concordant results and indicators such as phenolphthalein.
浓度 (c) 的计算公式为 c = n / V。滴定实验利用酸碱中和，通过合量结果和指示剂（如酚酞）测定未知浓度。
Percentage yield and atom economy measure reaction efficiency. Yield compares actual mass to theoretical mass; atom economy helps design greener synthesis routes by minimising waste products.
产率和原子经济性衡量反应效率。产率比较实际质量与理论质量；原子经济性通过减少副产品来帮助设计更绿色的合成路线。
6. Forces and Motion | 力与运动
Velocity–time graphs illustrate acceleration, constant speed and deceleration; the gradient gives acceleration and the area under the graph represents displacement. Newton’s first law states that an object remains at rest or in uniform motion unless acted upon by a resultant force.
速度-时间图示意加速度、匀速和减速；斜率表示加速度，图线下的面积代表位移。牛顿第一定律指出，物体保持静止或匀速直线运动状态，除非受到合力作用。
F = m a
Newton’s second law quantifies this: F = m a. Momentum (p = m v) is conserved in collisions and explosions, provided no external resultant force acts. Impulse equals change in momentum and can be calculated from a force–time graph.
牛顿第二定律对此量化：F = m a。动量 (p = m v) 在碰撞和爆炸中守恒，前提是没有外力作用。冲量等于动量的变化，可通过力-时间图计算。
Free-body diagrams help resolve forces; friction opposes motion, and terminal velocity occurs when weight balances air resistance. Moments and levers are essential in equilibrium situations.
受力图有助于分解力；摩擦力阻碍运动，当重力与空气阻力平衡时达到终极速度。力矩和杠杆在平衡情境中至关重要。
7. Waves and the Electromagnetic Spectrum | 波与电磁波谱
Transverse waves oscillate perpendicular to energy transfer (e.g. light), while longitudinal waves oscillate parallel (e.g. sound). Key wave parameters include amplitude, wavelength (λ), frequency (f) and period (T).
横波的振动方向与能量传递方向垂直（如光），纵波则平行振动（如声）。关键波参数包括振幅、波长 (λ)、频率 (f) 和周期 (T)。
v = f λ
The wave equation v = f λ links speed, frequency and wavelength. The electromagnetic spectrum, in order of increasing frequency, runs: radio, microwave, infrared, visible, ultraviolet, X-ray, gamma ray. Each region has distinct medical and communication applications.
波动方程 v = f λ 将波速、频率和波长联系起来。电磁波谱按频率递增顺序为：无线电波、微波、红外线、可见光、紫外线、X 射线、伽马射线。各波段在医疗和通信中有不同应用。
Reflection, refraction and diffraction occur with all waves. Refractive index determines the bending of light at boundaries; diffraction is most pronounced when the gap size is comparable to the wavelength.
反射、折射和衍射发生在所有波中。折射率决定光在边界处的弯曲程度；当缝隙尺寸与波长相当时，衍射最为明显。
8. Energy and Enthalpy | 能量与焓
Energy cannot be created or destroyed, only transferred. In chemical systems, the enthalpy change (ΔH) measures heat transferred at constant pressure; exothermic reactions release heat (negative ΔH), while endothermic reactions absorb heat (positive ΔH).
能量既不能被创造也不能被消灭，只能被转移。在化学系统中，焓变 (ΔH) 测量恒压条件下的热量转移；放热反应释放热量 (ΔH 为负)，吸热反应吸收热量 (ΔH 为正)。
| Exothermic: ΔH < 0; surroundings warm up. | 放热：ΔH < 0；环境升温。 |
| Endothermic: ΔH > 0; surroundings cool down. | 吸热：ΔH > 0；环境降温。 |
Hess’s Law states that the total enthalpy change for a reaction is independent of the pathway taken. Bond energy calculations and enthalpy of combustion data are commonly used to find an unknown ΔH.
盖斯定律指出，反应的总焓变与所采取的途径无关。键能计算和燃烧焓数据常用于求算未知 ΔH。
Q = m c ΔT
In physics and applied science, the equation Q = m c ΔT is used to calculate heat energy transferred to a substance, where c is specific heat capacity. Efficiency of energy transfers can be evaluated in biological and technological contexts.
在物理和应用科学中，方程 Q = m c ΔT 用于计算传递给物质的热量，其中 c 为比热容。能量转移的效率可在生物和技术背景中评估。
9. Data Analysis and Error | 数据分析与误差
Accuracy is the closeness of a measurement to the true value, while precision indicates the spread of repeated readings. Systematic errors cause bias; random errors lead to uncertainty that can be reduced by averaging.
准确度是测量值与真实值的接近程度，精密度则反映多次读数的散布程度。系统误差造成偏倚；随机误差导致不确定度，可通过取均值来减小。
Uncertainty is often quoted as half the smallest scale division. Standard deviation quantifies the spread of data around the mean, and error bars on graphs help compare datasets visually. Correlation does not imply causation.
不确定度通常取最小分度值的一半。标准差量化数据围绕均值的分散程度，图上的误差棒有助于直观比较数据集。相关性并不表明因果关系。
Constructing appropriate tables and graphs (scatter plots, bar charts, histograms) is vital. A line of best fit should pass through as many points as possible, and anomalous results must be identified and excluded from analysis with justification.
构建合适的表格和图表（散点图、条形图、直方图）至关重要。最佳拟合线应尽可能通过更多的点，异常结果必须识别并给出理由才可从分析中剔除。
10. Practical Techniques and Safety | 实验技术及安全
Core practical skills include performing titrations with burettes and pipettes, using a colorimeter to measure absorbance, and preparing temporary mounts for light microscopy. All readings should be recorded to an appropriate number of significant figures.
核心实验技能包括使用滴定管和移液管进行滴定，使用比色计测量吸光度，以及制作光学显微镜临时装片。所有读数应以适当有效数字记录。
Microscope calibration involves using an eyepiece graticule and stage micrometer to measure cell sizes. Heating substances safely, using reflux apparatus, and carrying out recrystallisation are typical organic chemistry techniques that also require careful risk management.
显微镜校准需使用目镜测微尺和镜台测微尺来测量细胞大小。安全加热物质、使用回流装置和进行重结晶是典型的有机化学技术，也需要仔细的风险管理。
Always follow CLEAPSS guidance or school-based safety protocols. Wear eye protection, tie back long hair, and never eat or drink in the laboratory. Knowing the location of fire extinguishers, eyewash stations and first aid kits is compulsory.
始终遵循 CLEAPSS 指南或学校安全规程。佩戴护目镜，束起长发，严禁在实验室饮食。熟悉灭火器、洗眼器和急救箱的位置是强制要求。
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