📚 Year 12 CIE Biology: Core Concepts Review | Year 12 CIE 生物：核心知识点梳理
This article provides a structured review of the core concepts in the CIE AS Biology syllabus, covering cell structure, biological molecules, enzymes, membrane transport, cell division, molecular genetics, plant and mammalian physiology, gas exchange, infectious diseases, and immunity. Each section highlights essential knowledge paired with clear explanations to support Year 12 learners.
本文为CIE AS生物学课程的核心知识点提供了结构化梳理，涵盖细胞结构、生物分子、酶、膜运输、细胞分裂、分子遗传学、植物与哺乳动物生理、气体交换、传染病及免疫等内容。每一节都提炼了关键知识，并配以清晰的解释，帮助 Year 12 学生巩固基础。
1. Cell Structure and Function | 细胞结构与功能
Eukaryotic cells possess a true nucleus enclosed by a nuclear envelope, whereas prokaryotic cells contain a naked circular DNA molecule in a region called the nucleoid, without membrane-bound organelles.
真核细胞具有由核膜包裹的真正的细胞核，而原核细胞在称为类核的区域中含有裸露的环状DNA分子，没有膜包被的细胞器。
Key differences include size (eukaryotes typically 10–100 µm; prokaryotes 1–5 µm), ribosome size (80S in eukaryotes, 70S in prokaryotes), and cell wall composition (peptidoglycan in bacteria vs cellulose or chitin in plants and fungi).
关键区别包括尺寸（真核细胞通常10–100 µm，原核细胞1–5 µm）、核糖体大小（真核细胞80S，原核细胞70S）以及细胞壁组成（细菌为肽聚糖，植物为纤维素，真菌为几丁质）。
Organelles such as mitochondria carry out aerobic respiration; rough endoplasmic reticulum is studded with ribosomes and synthesises proteins; the Golgi apparatus modifies, sorts and packages proteins for secretion.
细胞器中，线粒体进行有氧呼吸；粗面内质网上附着核糖体，合成蛋白质；高尔基体对蛋白质进行修饰、分拣和包装，准备分泌。
2. Biological Molecules | 生物分子
Carbohydrates consist of carbon, hydrogen and oxygen in the ratio (CH₂O)ₙ. Monosaccharides are reducing sugars that give a brick‑red precipitate with Benedict's reagent upon heating.
碳水化合物由碳、氢、氧按(CH₂O)ₙ的比例组成。单糖是还原糖，与班氏试剂加热后产生砖红色沉淀。
Polysaccharides include starch (amylose and amylopectin) for energy storage in plants, glycogen in animals, and cellulose – a structural polymer with β-1,4 glycosidic bonds that forms plant cell walls.
多糖包括植物储存能量的淀粉（直链淀粉和支链淀粉）、动物体内的糖原，以及由β-1,4糖苷键连接而成的结构多聚物纤维素，构成植物细胞壁。
Lipids: triglycerides are esters of glycerol and three fatty acids; phospholipids have a hydrophilic phosphate head and hydrophobic tails, forming bilayers. Proteins: amino acids link via peptide bonds; primary, secondary, tertiary and quaternary structures determine their function.
脂质：甘油三酯是甘油与三个脂肪酸形成的酯；磷脂具有亲水磷酸头和疏水尾部，构成双分子层。蛋白质：氨基酸通过肽键连接，一级、二级、三级和四级结构决定其功能。
3. Enzymes | 酶
Enzymes are globular proteins that lower the activation energy by providing an alternative reaction pathway. The induced fit model states that the active site changes shape to accommodate the substrate.
酶是球状蛋白质，通过提供替代反应途径降低活化能。诱导契合模型指出，活性位点的形状会改变以结合底物。
Temperature and pH affect enzyme activity: extreme conditions cause denaturation and loss of function. Measuring initial reaction rates allows investigation of the effect of substrate concentration.
温度和pH影响酶活性：极端条件会导致变性，丧失功能。通过测量初始反应速率可以研究底物浓度的影响。
Competitive inhibitors bind to the active site, increasing apparent Kₘ without changing Vₘₐₓ. Non-competitive inhibitors bind to an allosteric site, reducing Vₘₐₓ while Kₘ remains unchanged.
竞争性抑制剂结合活性位点，提高表观Kₘ，但V
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