📚 AQA AS Biology: Core Topics and Exam Skills | AQA AS 生物：核心主题与考试技能
The AQA AS Biology specification focuses on the fundamental concepts that underpin all living systems. This article reviews the key content areas, common exam questions and practical skills you need to master. Each section pairs English explanations with Chinese summaries to support bilingual learners.
AQA AS 生物课程聚焦于支撑所有生命系统的基本概念。本文回顾核心内容、常见考题和必须掌握的实验技能。每个小节采用英文解释与中文总结配对的形式，帮助双语学习者巩固知识。
1. Biological Molecules: Monomers and Polymers | 生物分子：单体与聚合物
Most large biological molecules are polymers built from smaller monomers by condensation reactions, which remove a water molecule. Hydrolysis reactions add water to break polymers back into monomers. Recognising these reactions helps explain how carbohydrates, proteins and nucleic acids are assembled and digested.
大多数生物大分子是由较小单体通过缩合反应连接而成的聚合物，缩合反应会脱去一分子水。水解反应则加入水将聚合物分解为单体。理解这两种反应有助于解释碳水化合物、蛋白质和核酸的合成与消化。
Common examples include monosaccharides forming polysaccharides, amino acids forming polypeptides, and nucleotides forming polynucleotides. The type of bond formed differs: glycosidic bonds link sugars, peptide bonds link amino acids, and phosphodiester bonds link nucleotides.
常见例子包括单糖形成多糖、氨基酸形成多肽、核苷酸形成多核苷酸。形成的化学键类型不同：糖苷键连接糖类，肽键连接氨基酸，磷酸二酯键连接核苷酸。
2. Carbohydrates and Lipids | 碳水化合物与脂质
Monosaccharides such as glucose are reducing sugars and can be detected using Benedict's solution with heating. Disaccharides include maltose, sucrose and lactose; each is formed from two monosaccharides joined by a glycosidic bond. Polysaccharides such as starch, glycogen and cellulose are polymers of glucose but differ in structure and function.
葡萄糖等单糖是还原糖，可使用本尼迪克特试剂加热检测。双糖包括麦芽糖、蔗糖和乳糖，各由两个单糖通过糖苷键连接。淀粉、糖原和纤维素等多糖都是葡萄糖聚合物，但结构和功能不同。
Starch is a compact storage molecule in plants made of amylose and amylopectin. Glycogen is more highly branched and stored in animal liver and muscle cells. Cellulose has straight chains with β-glucose monomers, allowing hydrogen bonds to form strong microfibrils for plant cell walls.
淀粉是植物中由直链淀粉和支链淀粉组成的紧凑储能分子。糖原分支更多，储存在动物肝脏和肌肉细胞中。纤维素由 β-葡萄糖单体形成直链，链间形成氢键构成坚固的微纤维，用于植物细胞壁。
Lipids include triglycerides, which contain one glycerol and three fatty acids joined by ester bonds. They are energy-dense, insoluble in water and important for insulation and protection. Phospholipids have a phosphate group instead of one fatty acid, making them amphipathic and ideal for membrane formation.
脂质包括甘油三酯，由一个甘油和三个脂肪酸通过酯键连接。它们能量密度高、不溶于水，具有保温和保护作用。磷脂用磷酸基团替代一个脂肪酸，具有两亲性，非常适合构成细胞膜。
The emulsion test can identify lipids: mix the sample with ethanol and then add water; a cloudy white emulsion indicates a positive result.
乳剂试验可鉴定脂质：将样品与乙醇混合后加水，若出现乳白色浑浊则为阳性。
3. Proteins and Enzymes | 蛋白质与酶
Proteins are made from amino acids joined 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 shape maintained by hydrogen bonds, ionic bonds, disulfide bridges and hydrophobic interactions. Quaternary structure occurs when more than one polypeptide chain associates.
蛋白质由氨基酸通过肽键连接而成。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。三级结构是由氢键、离子键、二硫键和疏水相互作用维持的整体三维形状。当多条多肽链结合时形成四级结构。
Enzymes are globular proteins that lower activation energy by forming enzyme-substrate complexes. The induced fit model states that the active site changes shape slightly to bind the substrate. Enzyme activity is affected by temperature, pH, enzyme concentration and substrate concentration. Denaturation disrupts the tertiary structure, so the active site loses its complementary shape.
酶是球状蛋白质，通过形成酶-底物复合物降低活化能。诱导契合模型认为活性部位会略微改变形状以结合底物。酶活性受温度、pH、酶浓度和底物浓度影响。变性会破坏三级结构，使活性部位失去互补形状。
Competitive inhibitors bind to the active site, while non-competitive inhibitors bind elsewhere and change the active site shape. Increasing substrate concentration can overcome competitive inhibition but not non-competitive inhibition.
竞争性抑制剂结合活性部位，而非竞争性抑制剂结合其他部位并改变活性部位形状。增加底物浓度可以克服竞争性抑制，但不能克服非竞争性抑制。
4. Nucleic Acids, ATP and DNA Replication | 核酸、ATP 与 DNA 复制
DNA and RNA are polynucleotides made of nucleotides. Each nucleotide contains a pentose sugar, a phosphate group and a nitrogenous base. DNA contains deoxyribose and bases adenine, thymine, cytosine and guanine; RNA contains ribose and replaces thymine with uracil. DNA is a double helix with complementary base pairing: A pairs with T by two hydrogen bonds, and C pairs with G by three hydrogen bonds.
DNA 和 RNA 是由核苷酸组成的多核苷酸。每个核苷酸含有一个五碳糖、一个磷酸基团和一个含氮碱基。DNA 含有脱氧核糖和腺嘌呤、胸腺嘧啶、胞嘧啶、鸟嘌呤；RNA 含有核糖，并用尿嘧啶代替胸腺嘧啶。DNA 是双螺旋结构，具有互补碱基配对：A 与
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