AQA AS Biology: Key Concepts and Exam Strategies | AQA AS 生物：核心概念与考试策略

📚 AQA AS Biology: Key Concepts and Exam Strategies | AQA AS 生物：核心概念与考试策略

AQA AS Biology examines the molecular basis of life, the organisation of cells, transport mechanisms, and the flow of genetic information. This revision guide condenses the essential knowledge you need, with clear explanations, worked comparisons and exam-focused tips.

AQA AS 生物考查生命分子基础、细胞结构、物质运输机制以及遗传信息的流动。本复习指南浓缩了全部核心知识，配以清晰的讲解、对比和以考点为导向的提示。

1. Biological Molecules – Carbohydrates and Lipids | 生物分子——碳水化合物与脂质

Carbohydrates are sugars and their polymers. The most important monomer is glucose, C₆H₁₂O₆; its α and β isomers give rise to materials with very different functions. Two monosaccharides link by a condensation reaction to form a disaccharide, producing a glycosidic bond and releasing a water molecule. Hydrolysis is the reverse process, using water to break bonds.

碳水化合物是糖类及其聚合物。最重要的单体是葡萄糖（C₆H₁₂O₆），其α和β异构体能形成功能迥异的物质。两个单糖通过缩合反应生成双糖：形成糖苷键并释放一分子水。水解是其逆过程，利用水来断裂化学键。

Starch and glycogen store glucose: starch is a mixture of amylose (unbranched) and amylopectin (branched), while glycogen is highly branched, allowing rapid glucose release for energy. Cellulose is composed of β-glucose chains cross-linked by hydrogen bonds; these microfibrils provide tensile strength to plant cell walls.

淀粉和糖原用于储存葡萄糖：淀粉由直链淀粉（不分枝）和支链淀粉（分枝）组成，而糖原高度分枝，能快速释放葡萄糖供能。纤维素由β-葡萄糖链经氢键交联而成，这些微纤维为植物细胞壁提供抗张强度。

Lipids are not polymers. Triglycerides consist of glycerol and three fatty acids joined by ester bonds formed in condensation reactions. Saturated fatty acids lack double bonds and pack tightly; unsaturated fatty acids contain double bonds, introducing kinks. Phospholipids replace one fatty acid with a phosphate group, giving a hydrophilic head and two hydrophobic tails – this amphipathic character is fundamental to cell membranes.

脂质不是聚合物。甘油三酯由甘油和三个脂肪酸经缩合反应形成酯键连接而成。饱和脂肪酸不含双键，排列紧密；不饱和脂肪酸含双键，产生弯折。磷脂将其中一个脂肪酸替换为磷酸基团，形成亲水的头部和两条疏水的尾部——这种两亲性对细胞膜至关重要。

2. Proteins and Enzymes | 蛋白质与酶

Proteins are polymers of amino acids. Each amino acid contains an amino group (NH₂), a carboxyl group (COOH) and a variable R group. Amino acids join by condensation reactions to form peptide bonds. The sequence of amino acids is the primary structure; hydrogen bonds create α-helices and β-pleated sheets in the secondary structure. Further folding, including ionic and disulfide bonds, gives the three-dimensional tertiary structure. Proteins with multiple polypeptide chains have a quaternary structure.

蛋白质是氨基酸的聚合物。每个氨基酸包含氨基（NH₂）、羧基（COOH）和可变的R基团。氨基酸通过缩合反应形成肽键。氨基酸序列为一级结构；氢键在二级结构中形成α螺旋和β折叠片层。进一步折叠，包括离子键和二硫键，形成三维空间的三级结构。含多条多肽链的蛋白质还具有四级结构。

Enzymes are globular proteins with an active site complementary to their substrate. The induced-fit model states that the active site changes shape slightly on substrate binding, stressing bonds and lowering activation energy. Enzyme action is affected by temperature, pH and substrate or enzyme concentration.

酶是球状蛋白质，其活性位点与底物互补。诱导契合模型认为，底物结合时活性位点发生轻微形变，使化学键受力并降低活化能。温度、pH值以及底物或酶浓度都会影响酶的作用。

The Biuret test identifies proteins: sodium hydroxide and dilute copper(II) sulfate give a purple colour. In exams, remember that enzymes denature when bonds maintaining the tertiary structure break, especially at high temperatures or extreme pH – although the primary structure remains intact.

缩二脲试验用于鉴定蛋白质：加入氢氧化钠和稀硫酸铜后呈紫色。考试中需注意：当维持三级结构的化学键被破坏时，酶会变性，尤其是在高温或极端pH条件下——但一级结构仍然保持完整。

3. Cell Structure: Prokaryotes and Eukaryotes | 细胞结构：原核生物与真核生物

Eukaryotic cells contain membrane-bound organelles. The nucleus stores DNA and controls gene expression; the nucleolus makes ribosomes. Mitochondria carry out aerobic respiration, with a folded inner membrane (cristae) providing a large surface area for ATP synthesis. Rough endoplasmic reticulum (RER) modifies proteins, while the Golgi apparatus packages and secretes them.

真核细胞含有膜结合细胞器。细胞核储存DNA并控制基因表达；核仁制造核糖体。线粒体进行有氧呼吸，其折叠的内膜（嵴）为ATP合成提供巨大表面积。粗面内质网（RER）加工蛋白质，高尔基体则负责包装和分泌它们。

Prokaryotes differ in several key ways: they lack a nuclear envelope, have smaller 70S ribosomes, contain a single circular DNA molecule, and may carry plasmids. Their cell walls are made of peptidoglycan (murein), unlike plant cell walls made of cellulose. Viruses are not cells; they have no ribosomes or cytoplasm and must reproduce inside host cells.

原核生物在几个关键方面不同于真核生物：它们没有核膜，含有较小的70S核糖体，有一个环状DNA分子，并可能携带质粒。它们的细胞壁由肽聚糖（胞壁质）构成，而植物细胞壁则主要由纤维素构成。病毒不是细胞；它们没有核糖体和细胞质，必须在宿主细胞内繁殖。

When using a microscope in practical exams, calibrate with a stage micrometer, use the highest magnification to resolve organelles, and draw clearly labelled diagrams with size annotations in micrometres (μm).

在实验考试中使用显微镜时，要用载台测微尺校准，使用最高倍数分辨细胞器，并绘制清晰标注的示意图，以微米（μm）为单位注明尺寸。

4. Cell Membranes and Transport | 细胞膜与物质运输

The fluid mosaic model describes the membrane as a phospholipid bilayer with embedded proteins, cholesterol and glycoproteins. Phospholipids give flexibility; cholesterol stabilises the membrane; carrier and channel proteins allow specific molecules to cross; glycoproteins act in cell recognition.

流动镶嵌模型将细胞膜描述为磷脂双分子层，其中镶嵌着蛋白质、胆固醇和糖蛋白。磷脂提供柔韧性；胆固醇稳定膜结构；载体蛋白和通道蛋白允许特定分子通过；糖蛋白参与细胞识别。

Simple diffusion is the passive movement of small, non-polar molecules down their concentration gradient. Facilitated diffusion uses protein channels or carriers, also down the gradient, without ATP. Osmosis is the net movement of water across a partially permeable membrane from a higher to a lower water potential.

简单扩散是小型非极性分子顺浓度梯度的被动运动。协助扩散借助通道蛋白或载体蛋白，同样顺梯度进行，但不需要ATP。渗透作用是水分子通过半透膜从水势较高处向水势较低处的净移动。

Active transport moves solutes against their concentration gradient using carrier proteins and ATP. Large molecules are transported by endocytosis and exocytosis: the membrane folds round material to form vesicles, requiring energy and often involving membrane fluidity.Published by TutorHao | A-Level Biology Revision Series | aleveler.com

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