📚 Year 12 AQA Biology: Core Knowledge Points | AQA 生物 Year 12：核心知识点梳理
Year 12 AQA Biology covers a wide range of fundamental topics that build the foundation for understanding living systems. From the chemistry of monomers and polymers to the complexity of gas exchange, immunity, and genetic diversity, these core ideas are essential for success in the AS and A-level examinations. This article provides a structured overview of the most important knowledge points, presented in a clear bilingual format to support learners in mastering both terminology and concepts.
AQA 生物 Year 12 涵盖了构建生命系统理解基础的广泛主题。从单体和聚合物的化学到气体交换、免疫和遗传多样性的复杂性，这些核心思想对于在 AS 和 A-level 考试中取得成功至关重要。本文以清晰的双语格式，对最重要的知识点进行了结构化概述，以支持学习者掌握术语和概念。
1. Monomers and Polymers | 单体与聚合物
Biological molecules are built from smaller units called monomers, which join together through condensation reactions to form polymers. In a condensation reaction, a water molecule is released, whereas hydrolysis requires the addition of water to break the bonds. This fundamental principle underpins the synthesis and breakdown of carbohydrates, proteins, and nucleic acids.
生物分子由称为单体的小单元构成，单体通过缩合反应连接形成聚合物。在缩合反应中，会释放一个水分子，而水解反应则需要加水来断裂化学键。这一基本原理是碳水化合物、蛋白质和核酸合成与分解的基础。
2. Carbohydrates | 碳水化合物
Monosaccharides, such as glucose, galactose, and fructose, are the simplest carbohydrates with the general formula (CH₂O)ₙ. Glucose exists as α-glucose and β-glucose, which differ only in the orientation of the hydroxyl group on carbon-1. Disaccharides are formed by glycosidic bonds: maltose (glucose + glucose), sucrose (glucose + fructose), and lactose (glucose + galactose). Polysaccharides like starch, glycogen, and cellulose are polymers of glucose. Starch is a storage molecule in plants, composed of amylose (coiled, unbranched) and amylopectin (branched), while glycogen is the animal storage equivalent, more highly branched. Cellulose provides structural support in plant cell walls, with long, straight chains linked by hydrogen bonds to form microfibrils.
单糖如葡萄糖、半乳糖和果糖是最简单的碳水化合物，通式为 (CH₂O)ₙ。葡萄糖以 α-葡萄糖和 β-葡萄糖两种形式存在，区别仅在于 1 号碳上羟基的取向。二糖通过糖苷键形成：麦芽糖（葡萄糖+葡萄糖）、蔗糖（葡萄糖+果糖）和乳糖（葡萄糖+半乳糖）。淀粉、糖原和纤维素等多糖都是葡萄糖的聚合物。淀粉是植物中的储存分子，由直链淀粉（螺旋、无支链）和支链淀粉（有支链）组成；而糖原是动物的储存等同物，支链更多。纤维素为植物细胞壁提供结构支撑，其长而直的链通过氢键连接形成微纤丝。
3. Lipids | 脂质
Triglycerides are composed of one glycerol molecule and three fatty acid chains, joined by ester bonds in a condensation reaction. They are important for energy storage, insulation, and protection. Fatty acids can be saturated (no double bonds) or unsaturated (one or more double bonds). Phospholipids have a phosphate group replacing one fatty acid, giving them a hydrophilic 'head' and hydrophobic 'tails', making them ideal for membrane formation. The emulsion test is used to detect lipids.
甘油三酯由一个甘油分子和三条脂肪酸链组成，通过缩合反应中的酯键连接。它们对于能量储存、绝缘和保护很重要。脂肪酸可以是饱和的（无双键）或不饱和的（一个或多个双键）。磷脂用一个磷酸基团取代了一条脂肪酸，使其具有亲水的“头部”和疏水的“尾部”，非常适合形成膜。乳液试验用于检测脂质。
4. Proteins and Enzymes | 蛋白质与酶
Proteins are polymers of amino acids, linked by peptide bonds. The primary structure is the sequence of amino acids; secondary structure includes α-helices and β-pleated sheets held by hydrogen bonds; tertiary structure is the overall 3D folding, stabilized by hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic interactions; quaternary structure involves more than one polypeptide chain. The structure determines the function. Enzymes are biological catalysts that lower activation energy, and their activity is explained by the 'induced fit' model. They are specific to substrates, affected by temperature and pH, and can be inhibited competitively or non-competitively.
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维持的 α-螺旋和 β-折叠；三级结构是整体的三维折叠，由氢键、离子键、二硫桥和疏水相互作用稳定；四级结构涉及不止一条多肽链。结构决定功能。酶是降低活化能的生物催化剂，其活性用“诱导契合”模型解释。酶对底物具有特异性，受温度和 pH 影响，可被竞争性或非竞争性抑制。
5. Nucleic Acids and DNA Replication | 核酸与 DNA 复制
DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are polymers of nucleotides. Each nucleotide consists of a pentose sugar, a phosphate group, and a nitrogenous base (adenine, thymine, guanine, cytosine in DNA; uracil replaces thymine in RNA). DNA is a double helix with complementary base pairing (A–T, G–C) and antiparallel strands. DNA replication is semi-conservative, involving the enzyme DNA helicase to unwind the helix and DNA polymerase to add complementary nucleotides using each original strand as a template. Meselson and Stahl demonstrated this mechanism using heavy and light nitrogen isotopes.
DNA（脱氧核糖核酸）和 RNA（核糖核酸）是核苷酸的聚合物。每个核苷酸由一个戊糖、一个磷酸基团和一个含氮碱基组成（DNA 中为腺嘌呤、胸腺嘧啶、鸟嘌呤、胞嘧啶；RNA 中用尿嘧啶代替胸腺嘧啶）。DNA 是双螺旋结构，通过互补碱基配对（A–T，G–C）和反平行链连接。DNA 复制是半保留的，需要 DNA 解旋酶解开螺旋，DNA 聚合酶以每条原始链为模板添加互补核苷酸。Meselson 和 Stahl 使用重氮和轻氮同位素证明了这一机制。
6. ATP, Water and Inorganic Ions | ATP、水和无机离子
Adenosine triphosphate (ATP) is the immediate energy currency of the cell, consisting of adenine, ribose, and three phosphate groups. Energy is released when ATP is hydrolysed to ADP and inorganic phosphate (Pᵢ), catalysed by ATP hydrolase. ATP can be resynthesised by ATP synthase during respiration and photosynthesis. Water has many properties crucial for life: it is a metabolite, a solvent, has a high specific heat capacity, a high latent heat of vaporisation, and exhibits strong cohesion. Inorganic ions such as iron (Fe²⁺ in haemoglobin), phosphate (in nucleotides), and sodium (co-transport) play specific vital roles.
三磷酸腺苷 (ATP) 是细胞的即时能量货币，由腺嘌呤、核糖和三个磷酸基团组成。在 ATP 水解酶的催化下，ATP 水解为 ADP 和无机磷酸 (Pᵢ) 时释放能量。在呼吸作用和光合作用过程中，ATP 合酶可重新合成 ATP。水具有许多对生命至关重要的特性：它是代谢物、溶剂，具有高比热容、高蒸发潜热，并表现出强内聚力。无机离子如铁（血红蛋白中的 Fe²⁺）、磷酸盐（核苷酸中）和钠（协同运输）都发挥着特定的重要作用。
7. Cell Structure and Microscopy | 细胞结构与显微镜
rganelles such as mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes. Prokaryotic cells are smaller, lack a nucleus, and have circular DNA in the cytosol, along with 70S ribosomes. Viruses are acellular and non-living. Microscopy techniques include light microscopes and electron microscopes (TEM and SEM). Magnification = image size ÷ actual size. Cell fractionation and ultracentrifugation are used to separate organelles.
所有细胞都有一些共同特征：细胞膜、细胞质、遗传物质和核糖体。真核细胞有细胞核和膜结合的细胞器，如线粒体、内质网、高尔基体和溶酶体。原核细胞较小，没有细胞核，在胞质溶胶中有环状 DNA，以及 70S 核糖体。病毒是非细胞和非生命的。显微镜技术包括光学显微镜和电子显微镜（TEM 和 SEM）。放大倍数 = 图像大小 ÷ 实际大小。细胞分级分离和超速离心用于分离细胞器。
8. Cell Membranes and Transport | 细胞膜与运输
The fluid mosaic model describes cell membranes as a phospholipid bilayer with embedded proteins, cholesterol, and glycoproteins. Transport across membranes occurs via diffusion (passive, down a concentration gradient), facilitated diffusion (through channel or carrier proteins), active transport (against a concentration gradient, using ATP), and co-transport (e.g., sodium-glucose co-transport in the ileum). Osmosis is the movement of water from a less negative water potential to a more negative water potential across a partially permeable membrane.
流动镶嵌模型将细胞膜描述为磷脂双层，其中嵌有蛋白质、胆固醇和糖蛋白。跨膜运输可通过扩散（被动，顺浓度梯度）、易化扩散（通过通道或载体蛋白）、主动运输（逆浓度梯度，利用 ATP）和协同运输（如回肠中的钠-葡萄糖协同运输）进行。渗透作用是水通过部分透性膜从水势较低的负值区域移动到水势更负的区域。
9. The Immune System | 免疫系统
The immune system defends the body against pathogens. Non-specific defences include physical barriers (skin, mucus) and phagocytosis by neutrophils and macrophages. Specific immunity involves B lymphocytes (humoral response) producing antibodies, and T lymphocytes (cell-mediated response) activating other cells or destroying infected cells. Antigens trigger clonal selection and the production of memory cells, leading to a faster secondary response. Antibodies are proteins with a specific variable region. Vaccination introduces antigens to stimulate memory cell production. Monoclonal antibodies can be used in pregnancy testing and cancer treatment. Human Immunodeficiency Virus (HIV) attacks helper T cells, compromising the immune system.
免疫系统保护身体免受病原体侵害。非特异性防御包括物理屏障（皮肤、粘液）以及中性粒细胞和巨噬细胞的吞噬作用。特异性免疫涉及 B 淋巴细胞（体液反应）产生抗体，以及 T 淋巴细胞（细胞介导反应）激活其他细胞或摧毁受感染细胞。抗原触发克隆选择和记忆细胞的产生，从而产生更快的二次反应。抗体是具有特定可变区的蛋白质。疫苗接种引入抗原来刺激记忆细胞的产生。单克隆抗体可用于验孕和癌症治疗。人类免疫缺陷病毒 (HIV) 攻击辅助性 T 细胞，破坏免疫系统。
10. Gas Exchange and Digestion | 气体交换与消化
Gas exchange surfaces require a large surface area, thin walls, good ventilation, and a rich blood supply. In mammals, alveoli in the lungs provide a vast surface area for diffusion of O₂ and CO₂. Ventilation is achieved by the diaphragm and intercostal muscles. In fish, countercurrent flow in gills maintains a steep concentration gradient. In insects, tracheae and tracheoles deliver oxygen directly to tissues. Digestion in mammals breaks down large molecules: carbohydrates by amylase and membrane-bound disaccharidases, proteins by endopeptidases and exopeptidases, and lipids by lipase and bile salts (emulsification). Products are absorbed in the ileum via diffusion and co-transport.
气体交换表面需要大面积、薄壁、良好的通风和丰富的血液供应。在哺乳动物中，肺部的肺泡为 O₂ 和 CO₂ 的扩散提供了巨大的表面积。通风通过膈肌和肋间肌实现。在鱼类中，鳃中的逆流交换维持了陡峭的浓度梯度。在昆虫中，气管和小气管将氧气直接输送到组织。哺乳动物的消化将大分子分解：碳水化合物由淀粉酶和膜结合二糖酶分解，蛋白质由内肽酶和外肽酶分解，脂质由脂肪酶和胆汁盐（乳化）分解。产物通过扩散和协同运输在回肠中被吸收。
11. Mass Transport in Animals and Plants | 动物与植物的质量运输
urve shows how saturation changes with partial pressure of oxygen. The Bohr effect (shift due to CO₂ or pH) promotes oxygen unloading in respiring tissues. The heart pumps blood through arteries, capillaries, and veins; cardiac output = stroke volume × heart rate. In plants, xylem transports water and minerals via the cohesion-tension theory, driven by transpiration. Phloem transports sucrose and amino acids by mass flow (pressure flow hypothesis) from sources to sinks, involving active loading at the source.
在动物中，循环系统运输氧气、营养物质和废物。血红蛋白协同结合氧气；氧解离曲线显示了饱和度如何随氧分压变化。波尔效应（由 CO₂ 或 pH 引起的偏移）促进呼吸组织中氧气的卸载。心脏将血液泵送通过动脉、毛细血管和静脉；心输出量 = 每搏输出量 × 心率。在植物中，木质部通过内聚力-张力理论运输水分和矿物质，由蒸腾作用驱动。韧皮部通过集流（压力流假说）将蔗糖和氨基酸从源运输到库，涉及在源处的主动装载。
12. DNA, Genes and Protein Synthesis | DNA、基因与蛋白质合成
A gene is a sequence of DNA bases that codes for a polypeptide or functional RNA. The genetic code is degenerate, universal, and non-overlapping. In eukaryotes, genes contain introns (non-coding) and exons (coding). Transcription produces pre-mRNA, which is spliced to remove introns. Translation occurs on ribosomes, where tRNA molecules with specific anticodons bring amino acids to the mRNA codon sequence. The sequence of bases determines the primary structure of proteins. Mutations in DNA can be substitution, deletion, or insertion, and may be silent, missense, nonsense, or frameshift.
基因是编码多肽或功能性 RNA 的 DNA 碱基序列。遗传密码具有简并性、通用性和非重叠性。在真核生物中，基因包含内含子（非编码）和外显子（编码）。转录产生前体 mRNA，经过剪接去除内含子。翻译在核糖体上进行，带有特定反密码子的 tRNA 分子将氨基酸带到 mRNA 的密码子序列。碱基序列决定了蛋白质的一级结构。DNA 突变可以是替换、缺失或插入，可能是沉默、错义、无义或移码突变。
13. Genetic Diversity and Adaptation | 遗传多样性与适应
Genetic diversity arises from differences in DNA sequences, mainly due to mutation and sexual reproduction (meiosis and random fertilisation). Crossing over during prophase I and independent assortment during metaphase I produce new combinations of alleles. Genetic bottlenecks and the founder effect can reduce genetic diversity. Adaptations are characteristics that increase an organism's chance of survival and reproduction; they can be anatomical, physiological, or behavioural. Natural selection acts on genetic variation to cause evolution. Antibiotic resistance in bacteria is an example of natural selection driven by human activity.
遗传多样性源于 DNA 序列的差异，主要是由于突变和有性生殖（减数分裂和随机受精）。前期 I 的交叉和中期 I 的独立分配产生新的等位基因组合。遗传瓶颈和奠基者效应会降低遗传多样性。适应是增加生物体生存和繁殖机会的特征；它们可以是解剖学上的、生理学上的或行为上的。自然选择作用于遗传变异引发进化。细菌的抗生素耐药性是人为活动驱动的自然选择的一个例子。
14. Species, Taxonomy and Investigating Diversity | 物种、分类与多样性调查
l system: domain, kingdom, phylum, class, order, family, genus, species. Phylogenetic trees show evolutionary relationships based on similarities and differences in DNA, RNA, or proteins. Biodiversity can be quantified by species richness and the index of diversity (D = N(N – 1) / Σ n(n – ersity can involve comparing observable characteristics, DNA sequences, or mRNA sequences.
物种是一组能够杂交产生可育后代的生物。分类学是对生物进行分类的科学，使用等级系统：域、界、门、纲、目、科、属、种。系统发育树根据 DNA、RNA 或蛋白质的相似性和差异显示进化关系。生物多样性可以通过物种丰富度和多样性指数 (D = N(N – 1) / Σ n(n – 1)) 来量化。农业技术会降低生物多样性，而保护工作旨在维持它。调查遗传多样性可以涉及比较可观察特征、DNA 序列或 mRNA 序列。
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