📚 Year 12 WJEC Biology: Core Knowledge Review | WJEC 生物 Year 12：核心知识点梳理
Year 12 WJEC Biology covers fundamental topics in biochemistry, cell biology, and physiology. This revision guide distils the core knowledge required for the AS-level units, helping you consolidate key concepts and prepare effectively for assessments.
Year 12 WJEC 生物课程涵盖生物化学、细胞生物学和生理学基础。这份复习梳理提炼了AS阶段单元的核心知识，帮助你巩固关键概念，有效备考。
1. Biological Molecules: Carbohydrates and Lipids | 生物分子：碳水化合物与脂质
Carbohydrates are organic compounds with the general formula Cn(H2O)n. Monosaccharides such as glucose (C6H12O6) are simple sugars that provide energy and act as building blocks. Disaccharides, like maltose and sucrose, form through condensation reactions that release water; the reverse, hydrolysis, breaks them apart. Polysaccharides include starch (amylose and amylopectin) and glycogen for storage, and cellulose for structural support in plant cell walls.
碳水化合物通式为 Cn(H2O)n。葡萄糖（C6H12O6）等单糖是提供能量并作为构建单元的简单糖类。麦芽糖和蔗糖等二糖通过缩合反应释放水分子而形成；水解则将其分解。多糖包括用于储存的淀粉（直链淀粉和支链淀粉）和糖原，以及用于植物细胞壁结构支撑的纤维素。
Lipids are hydrophobic molecules. Triglycerides consist of glycerol bonded to three fatty acids via ester bonds; they serve as energy stores. Phospholipids replace one fatty acid with a phosphate group, creating an amphipathic molecule essential for cell membranes. Steroids, such as cholesterol, modulate membrane fluidity. Key biochemical tests include Benedict’s test for reducing sugars, the iodine test for starch, and the emulsion test for lipids.
脂质是疏水分子。甘油三酯由甘油与三个脂肪酸通过酯键连接而成，是能量储备。磷脂中一个脂肪酸被磷酸基团取代，形成两亲性分子，对细胞膜至关重要。类固醇（如胆固醇）调节膜的流动性。重要的生化检验包括：还原糖的本尼迪克特试验、淀粉的碘液试验和脂质的乳浊液试验。
2. Proteins and Enzymes | 蛋白质与酶
Proteins are polymers of amino acids joined by peptide bonds. The primary structure is the sequence of amino acids; secondary structures include alpha-helices and beta-pleated sheets formed by hydrogen bonds; tertiary structure involves further folding due to disulfide bridges, ionic bonds, and hydrophobic interactions; quaternary structure arises from multiple polypeptide subunits. The biuret test detects peptide bonds, giving a violet colour.
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；二级结构包括由氢键形成的α螺旋和β折叠；三级结构因二硫键、离子键和疏水作用进一步折叠；四级结构由多条多肽亚基产生。双缩脲试验检测肽键，呈紫色。
Enzymes are biological catalysts that lower activation energy. The ‘lock and key’ model suggests a rigid active site, while the ‘induced fit’ model describes a conformational change upon substrate binding. Activity is affected by temperature, pH, substrate concentration, and inhibitors. Competitive inhibitors bind to the active site; non-competitive inhibitors bind elsewhere, altering the enzyme’s shape.
酶是降低活化能的生物催化剂。”锁钥”模型认为活性部位是刚性的，而”诱导契合”模型描述了底物结合时构象发生改变。活性受温度、pH、底物浓度和抑制剂的影响。竞争性抑制剂与活性部位结合；非竞争性抑制剂在其他部位结合，改变酶的形状。
3. Nucleic Acids and DNA Replication | 核酸与DNA复制
DNA is a double helix composed of nucleotides, each containing deoxyribose, a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, guanine). Complementary base pairing (A-T, C-G) holds the strands together via hydrogen bonds. RNA differs by having ribose and uracil instead of thymine. ATP (adenosine triphosphate) is the energy currency, releasing energy when its terminal phosphate is hydrolysed.
DNA是由核苷酸组成的双螺旋，每个核苷酸含有脱氧核糖、磷酸基团和含氮碱基（腺嘌呤、胸腺嘧啶、胞嘧啶、鸟嘌呤）。互补碱基对（A-T，C-G）通过氢键将两条链连接在一起。RNA的区别在于含有核糖和尿嘧啶而非胸腺嘧啶。ATP（腺苷三磷酸）是能量通货，末端磷酸水解时释放能量。
DNA replication is semi-conservative: each new molecule contains one original strand and one newly synthesised strand. Helicase unwinds the double helix, single-strand binding proteins stabilise it, primase synthesises RNA primers, and DNA polymerase adds nucleotides in the 5′ to 3′ direction. DNA ligase seals the fragments on the lagging strand.
DNA复制是半保留的：每个新分子包含一条原有链和一条新合成链。解旋酶解开双螺旋，单链结合蛋白稳定它，引物酶合成RNA引物，DNA聚合酶沿5’到3’方向添加核苷酸。DNA连接酶将后随链上的片段连接起来。
4. Cell Structure and Microscopy | 细胞结构与显微镜术
Eukaryotic cells contain membrane-bound organelles: the nucleus houses DNA; mitochondria produce ATP via aerobic respiration; the rough endoplasmic reticulum synthesises and transports proteins; the smooth ER synthesises lipids; the Golgi apparatus modifies and packages proteins; lysosomes digest waste; ribosomes are the site of translation; chloroplasts (in plants) perform photosynthesis; and a large central vacuole and cell wall provide support.
真核细胞含有膜包被的细胞器：细胞核容纳DNA；线粒体通过有氧呼吸产生ATP；粗面内质网合成和运输蛋白质；滑面内质网合成脂质；高尔基体修饰和包装蛋白质；溶酶体消化废物；核糖体是翻译的场所；叶绿体（植物）进行光合作用；中央大液泡和细胞壁提供支撑。
Prokaryotic cells, such as bacteria, lack membrane-bound organelles. They have a cell wall, a circular DNA molecule in the nucleoid region, plasmids, and 70S ribosomes. Microscopy involves calculating total magnification (eyepiece × objective) and actual size of specimens: actual size = image size ÷ magnification. An eyepiece graticule must be calibrated using a stage micrometer.
原核细胞（如细菌）没有膜包被的细胞器。它们有细胞壁、拟核区的环状DNA、质粒和70S核糖体。显微镜术涉及计算总放大倍数（目镜×物镜）以及标本的实际尺寸：实际尺寸 = 图像尺寸 ÷ 放大倍数。目镜测微尺需用镜台测微尺进行校准。
5. Cell Membranes and Transport | 细胞膜与跨膜运输
The fluid mosaic model describes the plasma membrane as a phospholipid bilayer with embedded proteins, cholesterol, and glycoproteins. The phospholipids are free to move laterally, giving fluidity, while proteins function as channels, carriers, and receptors. Cholesterol maintains stability by restricting excessive movement.
流动镶嵌模型将质膜描述为具有嵌入蛋白质、胆固醇和糖蛋白的磷脂双分子层。磷脂可横向移动，赋予流动性，而蛋白质则作为通道、载体和受体发挥作用。胆固醇通过限制过度移动维持稳定性。
Passive transport includes simple diffusion (down a concentration gradient), facilitated diffusion via channel or carrier proteins, and osmosis (the net movement of water from higher to lower water potential through a partially permeable membrane). Active transport requires ATP to move substances against their concentration gradient, such as the Na⁺/K⁺ pump. Endocytosis and exocytosis allow bulk transport across the membrane.
被动运输包括简单扩散（顺浓度梯度）、由通道或载体蛋白介导的易化扩散，以及渗透（水分通过部分透性膜从较高水势向较低水势的净移动）。主动运输需要ATP逆浓度梯度运输物质，如Na⁺/K⁺泵。胞吞和胞吐实现跨膜的大批量运输。
6. The Cell Cycle and Mitosis | 细胞周期与有丝分裂
The cell cycle consists of interphase (G1 growth, S phase for DNA replication, G2 preparation) and the M phase (mitosis and cytokinesis). Mitosis produces two genetically identical daughter cells for growth, repair, and asexual reproduction. Stages are prophase (chromosomes condense, nuclear envelope breaks down), metaphase (chromosomes align at the equator), anaphase (sister chromatids separate), and telophase (nuclei reform). Cytokinesis divides the cytoplasm.
细胞周期包括间期（G1生长期、S期DNA复制、G2准备期）和M期（有丝分裂和胞质分裂）。有丝分裂产生两个遗传上相同的子细胞，用于生长、修复和无性生殖。阶段为前期（染色体凝聚，核膜解体）、中期（染色体排列在赤道板）、后期（姐妹染色单体分离）和末期（细胞核重新形成）。胞质分裂将细胞质分开。
Uncontrolled cell division can lead to cancer. Mutations in proto-oncogenes (which promote cell division) and tumour suppressor genes (which inhibit it) can disrupt the cell cycle checkpoints, allowing tumours to form. Understanding mitosis aids in cancer research and therapeutic strategies.
不受控制的细胞分裂可导致癌症。原癌基因（促进细胞分裂）和肿瘤抑制基因（抑制分裂）发生突变会破坏细胞周期检查点，使肿瘤形成。对有丝分裂的理解有助于癌症研究和治疗策略。
7. Classification and Biodiversity | 分类与生物多样性
Living organisms are classified into hierarchical groups: domain, kingdom, phylum, class, order, family, genus, and species. The binomial naming system uses the genus and species (e.g., Homo sapiens). The three domains are Bacteria, Archaea, and Eukarya. A species is often defined as a group of organisms that can interbreed to produce fertile offspring.
生物被划分为等级类群：域、界、门、纲、目、科、属、种。双名命名法使用属名和种名（如 Homo sapiens）。三个域为细菌域、古菌域和真核域。物种通常被定义为能够相互交配并产生可育后代的一群生物。
Biodiversity encompasses species richness (number of species) and evenness (relative abundance). Simpson’s diversity index (D = 1 − Σ (n/N)²) quantifies diversity, where n is the number of individuals of a particular species and N is the total number of individuals of all species. A higher D value indicates greater diversity. Evolution by natural selection drives adaptation and speciation, illustrated by phylogenetic trees.
生物多样性包括物种丰富度（物种数量）和均匀度（相对丰度）。辛普森多样性指数（D = 1 − Σ (n/N)²）量化多样性，其中 n 为某一物种的个体数，N 为所有物种的总个体数。D值越高表示多样性越大。自然选择驱动的进化导致适应和物种形成，系统发育树可以说明这一点。
8. Animal Transport: The Circulatory System | 动物运输：循环系统
The mammalian heart has four chambers: right and left atria, and right and left ventricles. Atrioventricular valves (tricuspid and bicuspid) prevent backflow into the atria, while semilunar valves guard the pulmonary artery and aorta. The cardiac cycle involves atrial systole, ventricular systole, and diastole, coordinated by the sinoatrial node (SAN), atrioventricular node (AVN), and Purkinje fibres.
哺乳动物心脏有四个腔室：左右心房和左右心室。房室瓣（三尖瓣和二尖瓣）防止血液倒流入心房，半月瓣守护肺动脉和主动脉。心动周期包括心房收缩、心室收缩和舒张，由窦房结（SAN）、房室结（AVN）和浦肯野纤维协调。
Arteries have thick muscular, elastic walls to withstand high pressure; veins have thinner walls and valves to prevent backflow; capillaries are one cell thick to allow efficient exchange. Blood consists of plasma, red blood cells (transporting oxygen via haemoglobin), white blood cells (defence), and platelets (clotting). The oxygen dissociation curve shows the relationship between oxygen saturation of haemoglobin and partial pressure of oxygen. A rightward shift (Bohr effect) occurs with increased CO₂ or lowered pH, facilitating oxygen unloading in respiring tissues.
动脉壁厚而有肌肉和弹性，能承受高压；静脉壁较薄，具有防止倒流的瓣膜；毛细血管仅一层细胞厚，利于高效交换。血液由血浆、红细胞（通过血红蛋白运输氧气）、白细胞（防御）和血小板（凝血）组成。氧解离曲线显示血红蛋白氧饱和度与氧分压之间的关系。曲线右移（波尔效应）发生在CO₂增加或pH降低时，促进氧气在呼吸组织中的卸载。
9. Plant Transport and Transpiration | 植物运输与蒸腾作用
Water and minerals move through xylem vessels from roots to leaves, driven mainly by transpiration pull. The cohesion-tension theory explains that water molecules cohere and adhere to the xylem walls, creating a continuous column under tension. Root pressure and capillary action contribute to a lesser extent.
水分和矿物质通过木质部导管从根部运输到叶片，主要由蒸腾拉力驱动。内聚力-张力理论认为水分子彼此内聚并与木质部壁附着，形成连续的水柱而产生拉力。根压和毛细管作用贡献较小。
Transpiration rate is influenced by light intensity (stomata open wider), temperature (increases evaporation), humidity (reduces gradient), and air movement (removes saturated air). A potometer measures water uptake, indirectly indicating transpiration rate.
蒸腾速率受光照强度（气孔张开更大）、温度（加速蒸发）、湿度（减小梯度）和空气流动（带走饱和空气）的影响。蒸腾计测量水分吸收，间接指示蒸腾速率。
Translocation in phloem transports sucrose and amino acids from sources (e.g., leaves) to sinks (e.g., roots) via the pressure-flow hypothesis. Active loading of sucrose into sieve tubes at the source lowers water potential, causing water to enter and generating hydrostatic pressure that pushes sap toward sinks where sucrose is unloaded.
韧皮部的易位通过压力流动假说将蔗糖和氨基酸从源（如叶片）运输到库（如根）。在源处主动装载蔗糖进入筛管降低水势，水分进入产生静水压，推动汁液流向卸出蔗糖的库。
10. Gas Exchange in Animals and Plants | 动物与植物的气体交换
Insects possess a tracheal system: air enters through spiracles and diffuses along tracheae and tracheoles directly to cells. Abdominal pumping ventilates the system. The moist tips of tracheoles enable gas exchange without a circulatory transport system.
昆虫拥有气管系统：空气经气门进入，沿气管和微气管直接扩散至细胞。腹部泵气运动实现通风。微气管湿润的末端使气体交换无需循环运输系统。
Fish gills use a countercurrent flow system: blood flows in the opposite direction to water over the gill lamellae, maintaining a concentration gradient that maximises oxygen uptake and carbon dioxide removal. The large surface area of the gill filaments further enhances efficiency.
鱼鳃采用逆流交换系统：血液流经鳃片的方向与水流方向相反，维持浓度梯度，最大化摄氧和排出二氧化碳。鳃丝的大表面积进一步提高效率。
Published by TutorHao | Year 12 Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导