📚 Core Knowledge Review for AS AQA Biology | AS AQA 生物核心知识点梳理
This article distils the essential topics covered in the AS AQA Biology specification. It is designed to help you consolidate your understanding of biological molecules, cell structure, exchange and transport, and genetic information. Each section presents key concepts in clear English paragraphs, followed by their Chinese translations, to support bilingual learners or those seeking conceptual clarity.
本文梳理了 AS AQA 生物课程的核心主题，旨在帮助你巩固对生物分子、细胞结构、物质交换与运输以及遗传信息的理解。每个部分先用简明的英文段落呈现关键概念，再附上对应的中文翻译，以帮助双语学生或追求概念清晰的学习者。
1. Monomers and Polymers | 单体与多聚体
All large biological molecules are polymers built from smaller repeating units called monomers. Monomers are joined together by condensation reactions, where a water molecule is removed, and covalent bonds are formed. The reverse process, hydrolysis, breaks polymers down into monomers by adding water. Familiar pairs include monosaccharides forming polysaccharides, amino acids forming proteins, and nucleotides forming nucleic acids. Understanding these reactions underpins all of biochemistry.
所有生物大分子都是由称为单体的较小重复单元构建而成的多聚体。单体通过缩合反应连接，该反应脱去一分子水并形成共价键。逆反应即水解，通过加入水将多聚体分解为单体。常见的配对包括单糖形成多糖、氨基酸形成蛋白质以及核苷酸形成核酸。理解这些反应是通晓生物化学的基础。
| Monomer | Polymer | Bond Formed |
|---|---|---|
| Monosaccharide | Polysaccharide | Glycosidic bond |
| Amino acid | Polypeptide / Protein | Peptide bond |
| Nucleotide | Nucleic acid (DNA/RNA) | Phosphodiester bond |
缩合反应脱去水分子形成共价键；水解反应则加水断裂这些键。上表总结了生物学中最重要的单体–多聚体配对。
2. Carbohydrates | 碳水化合物
Carbohydrates are composed of carbon, hydrogen, and oxygen, with the general formula Cₓ(H₂O)ᵧ. Monosaccharides such as glucose, galactose, and fructose are reducing sugars. Glucose exists as two isomers: α-glucose and β-glucose, differing in the orientation of the —OH group on carbon-1. Disaccharides form when two monosaccharides undergo a condensation reaction, e.g. maltose (glucose + glucose), sucrose (glucose + fructose), and lactose (glucose + galactose). Polysaccharides serve as energy stores or structural components. Starch (amylose and amylopectin) and glycogen are storage polymers of α-glucose; cellulose is a structural polymer of β-glucose with β-1,4-glycosidic bonds, forming straight chains cross-linked by hydrogen bonds.
碳水化合物由碳、氢、氧组成，通式为 Cₓ(H₂O)ᵧ。葡萄糖、半乳糖和果糖等单糖是还原糖。葡萄糖以两种异构体存在：α-葡萄糖和β-葡萄糖，它们碳-1 上的 —OH 基团取向不同。两个单糖经缩合反应形成二糖，如麦芽糖（葡萄糖+葡萄糖）、蔗糖（葡萄糖+果糖）和乳糖（葡萄糖+半乳糖）。多糖用作储能物质或结构组分。淀粉（直链淀粉和支链淀粉）和糖原是由α-葡萄糖构成的储存型多聚体；纤维素是由β-葡萄糖通过β-1,4-糖苷键形成的结构型多聚体，形成直链并由氢键交联。
| Polysaccharide | Monomer | Bond / Structure | Function |
|---|---|---|---|
| Starch (amylose) | α-glucose | α-1,4-glycosidic; helical | Energy storage in plants |
| Starch (amylopectin) | α-glucose | α-1,4 and α-1,6; branched | Energy storage in plants |
| Glycogen | α-glucose | α-1,4 and α-1,6; highly branched | Energy storage in animals |
| Cellulose | β-glucose | β-1,4-glycosidic; straight chains | Structural component of plant cell walls |
淀粉、糖原和纤维素的功能差异直接源于其糖苷键类型和分支程度。
3. Lipids | 脂质
Lipids are a diverse group of hydrophobic molecules. Triglycerides consist of one glycerol molecule esterified to three fatty acid chains. Fatty acids can be saturated (no C=C double bonds) or unsaturated (one or more C=C bonds, causing kinks). Triglycerides are excellent energy stores because their long hydrocarbon tails yield more energy per gram than carbohydrates and they are insoluble, so they do not affect cell water potential. Phospholipids have one fatty acid replaced by a phosphate-containing group; they are amphipathic, forming the basis of cell membranes. The emulsion test (adding ethanol then water) identifies lipids by forming a milky-white emulsion.
脂质是一类多样化的疏水分子。甘油三酯由一个甘油分子与三条脂肪酸链酯化形成。脂肪酸可以是饱和的（不含C=C双键）或不饱和的（含一个或多个C=C双键，造成扭结）。甘油三酯是极好的储能物质，因为其长烃尾释放的能量比碳水化合物多，且不溶于水，因此不影响细胞水势。磷脂的一个脂肪酸被含磷酸基团取代；它们是两亲性分子，构成细胞膜的基础。乳液试验（先加乙醇再加水）通过生成乳白色乳状液来鉴定脂质。
4. Proteins | 蛋白质
Amino acids are the monomers of proteins. Each amino acid has a central carbon bonded to an amine group (—NH₂), a carboxyl group (—COOH), a hydrogen atom, and a variable R group. Amino acids link via peptide bonds (—CO—NH—) in condensation reactions. The primary structure is the sequence of amino acids. Secondary structure includes α-helices and β-pleated sheets held by hydrogen bonds. Tertiary structure relies on interactions between R groups: disulfide bridges, ionic bonds, hydrogen bonds, and hydrophobic interactions. Quaternary structure involves multiple polypeptide chains, as in haemoglobin. Protein function (enzymes, antibodies, transport, structural) depends on the precise 3D shape, which is determined by the amino acid sequence.
氨基酸是蛋白质的单体。每个氨基酸含有一个与中心碳原子相连的氨基（—NH₂）、一个羧基（—COOH）、一个氢原子和一个可变的R基团。氨基酸在缩合反应中通过肽键（—CO—NH—）连接。一级结构是氨基酸的排列序列。二级结构包括由氢键维持的α-螺旋和β-折叠片。三级结构依赖于R基团间的相互作用：二硫键、离子键、氢键和疏水作用。四级结构含有多条多肽链，如血红蛋白。蛋白质的功能（酶、抗体、运输、结构）取决于精确的三维形状，而形状由氨基酸序列决定。
5. Enzymes | 酶
Enzymes are biological catalysts, typically globular proteins, that lower activation energy without being consumed. Their action is explained by the induced-fit model: the active site is flexible and moulds around the substrate, forming enzyme-substrate complexes. Enzyme activity is affected by temperature (higher kinetic energy until denaturation), pH (alters ionic bonds and active site charge), enzyme concentration, and substrate concentration. Many enzymes require cofactors. The kinetics often follow the Michaelis-Menten model, with Vmax representing the maximum rate when all active sites are saturated. Competitive inhibitors resemble the substrate and bind to the active site; their effect can be overcome by increasing substrate concentration. Non-competitive inhibitors bind elsewhere and change the active site’s shape, reducing Vmax but not the affinity (Km may be unaffected).
酶是生物催化剂，通常为球状蛋白，能降低活化能而不被消耗。其作用可用“诱导契合模型”解释：活性部位具有可塑性，能够环绕底物形成酶-底物复合物。酶活性受温度（动能增加直至变性）、pH（改变离子键和活性部位电荷）、酶浓度和底物浓度的影响。许多酶需要辅因子。酶动力学通常遵循米氏模型，Vmax代表所有活性部位饱和时的最大速率。竞争性抑制剂结构与底物相似，结合在活性部位；其效应可通过增加底物浓度来克服。非竞争性抑制剂结合在别处，改变活性部位形状，使Vmax降低但亲和力（Km可不受影响）。
6. Nucleic Acids and ATP | 核酸与ATP
DNA and RNA are polymers of nucleotides. Each nucleotide comprises a phosphate group, a pentose sugar (deoxyribose in DNA, ribose in RNA), and a nitrogenous base. DNA bases are adenine, thymine, cytosine, and guanine; in RNA uracil replaces thymine. Nucleotides join by phosphodiester bonds forming a sugar-phosphate backbone. DNA is a double helix with complementary base pairing (A=T, C≡G) held by hydrogen bonds. DNA replication is semi-conservative, with each strand serving as a template. The enzyme DNA helicase unzips the helix, and DNA polymerase adds complementary nucleotides. ATP (adenosine triphosphate) is the universal energy currency, consisting of adenine, ribose, and three phosphate groups; energy is released when the terminal phosphate is hydrolysed to form ADP and inorganic phosphate (Pᵢ).
DNA和RNA是核苷酸的多聚体。每个核苷酸由磷酸基团、戊糖（DNA中为脱氧核糖，RNA中为核糖）和含氮碱基组成。DNA的碱基为腺嘌呤、胸腺嘧啶、胞嘧啶和鸟嘌呤；RNA中尿嘧啶取代胸腺嘧啶。核苷酸通过磷酸二酯键连接，形成糖-磷酸骨架。DNA为双螺旋结构，依靠氢键进行互补碱基配对（A=T, C≡G）。DNA复制是半保留的，每一条链都作为模板。DNA解旋酶解开螺旋，DNA聚合酶添加互补核苷酸。ATP（腺苷三磷酸）是通用的能量货币，由腺嘌呤、核糖和三个磷酸基团组成；末端磷酸水解生成ADP和无机磷酸（Pᵢ）时释放能量。
7. Water and Inorganic Ions | 水与无机离子
Water is a dipolar molecule, with oxygen slightly negative and hydrogen slightly positive, allowing it to form hydrogen bonds. This property gives water a high specific heat capacity, high latent heat of vaporisation, cohesion, adhesion, and excellent solvent capabilities. These features make water essential for life: it buffers temperature changes, cools organisms through evaporation, transports dissolved substances (e.g. in blood plasma and xylem), and acts as a metabolic reactant. Inorganic ions, though needed in small amounts, are crucial. Examples include Na⁺ for co-transport of glucose, Fe²⁺ as a component of haemoglobin, phosphate ions in ATP and nucleic acids, and H⁺ for maintaining pH gradients.
水是极性分子，氧略显负电，氢略显正电，使其能形成氢键。这些性质赋予水高比热容、高汽化热、内聚力、附着力和优良的溶剂能力。这些特征使水对生命至关重要：缓冲温度变化、通过蒸发降温、运输溶解物质（如血浆和木质部中）以及作为代谢反应物。无机离子虽然需求量少，但必不可少，如Na⁺参与葡萄糖的协同转运，Fe²⁺是血红蛋白组分，磷酸根存在于ATP和核酸中，H⁺维持pH梯度。
8. Cell Structure | 细胞结构
Eukaryotic cells contain membrane-bound organelles: nucleus (stores genetic material), mitochondria (site of aerobic respiration), ribosomes (80S, protein synthesis), endoplasmic reticulum (rough ER with ribosomes processes proteins; smooth ER synthesises lipids), Golgi apparatus (modifies and packages proteins), lysosomes (contain hydrolytic enzymes), and chloroplasts (in plants, photosynthesis). Prokaryotic cells are smaller, lack a true nucleus, and have circular DNA free in the cytoplasm, 70S ribosomes, and sometimes plasmids and a capsule. Viruses are acellular and consist of genetic material (DNA or RNA) enclosed in a protein capsid, sometimes with a lipid envelope. Cell fractionation and microscopy have revealed these structures.
真核细胞含有膜包被的细胞器：细胞核（储存遗传物质）、线粒体（有氧呼吸场所）、核糖体（80S，蛋白质合成）、内质网（粗面内质网附着核糖体，加工蛋白质；滑面内质网合成脂质）、高尔基体（修饰和包装蛋白质）、溶酶体（含水解酶）以及叶绿体（植物细胞，光合作用）。原核细胞较小，缺乏真正的细胞核，有游离在胞质中的环状DNA、70S核糖体，有时含有质粒和荚膜。病毒是非细胞结构，由遗传物质（DNA或RNA）包被于蛋白质衣壳中构成，有时还有脂膜。细胞分级分离和显微镜技术揭示了这些结构。
| Organelle | 细胞器 | Key Function |
|---|---|---|
| Nucleus | 细胞核 | Contains DNA; controls gene expression |
| Mitochondrion | 线粒体 | Site of aerobic respiration; produces ATP |
| Ribosome | 核糖体 | Protein synthesis |
| Rough ER | 粗面内质网 | Processes and transports proteins |
| Golgi apparatus | 高尔基体 | Modifies, sorts and packages proteins into vesicles |
| Chloroplast | 叶绿体 | Photosynthesis |
上表汇总了真核细胞中重要细胞器的核心功能对比。
9. Cell Membranes and Transport | 细胞膜与跨膜运输
The cell surface membrane is described by the fluid-mosaic model: a phospholipid bilayer with embedded proteins, cholesterol (in animal cells), and glycolipids/glycoproteins. Phospholipids provide a selectively permeable barrier; cholesterol maintains membrane fluidity. Membrane proteins function as channels, carriers, enzymes, or receptors. Small, non-polar molecules diffuse directly through the bilayer. Facilitated diffusion uses channel or carrier proteins, moving substances down their concentration gradient without ATP. Active transport uses carrier proteins and ATP to move substances against a gradient. Co-transport couples the movement of one solute to the downhill flow of another (e.g. sodium-glucose co-transport). Osmosis is the net movement of water from a region of higher water potential to lower water potential across a partially permeable membrane. Endocytosis and exocytosis involve the engulfment or secretion of large molecules via vesicles.
细胞膜由流动镶嵌模型描述：磷脂双分子层上镶嵌有蛋白质、胆固醇（动物细胞）以及糖脂/糖蛋白。磷脂提供选择性通透屏障；胆固醇调节膜流动性。膜蛋白的功能包括通道、载体、酶或受体。小的非极性分子可直接通过双层扩散。协助扩散使用通道或载体蛋白，沿浓度梯度移动物质，无需ATP。主动运输利用载体蛋白、消耗ATP逆浓度梯度移动溶质。协同转运将一种溶质的运输与另一种溶质的顺浓度流动耦合（如钠-葡萄糖协同转运）。渗透是水通过部分透膜从较高水势区域向较低水势区域的净移动。胞吞和胞吐通过囊泡吞噬或分泌大分子物质。
10. The Immune System | 免疫系统
The body defends against pathogens through non-specific barriers (skin, mucous membranes, phagocytosis) and specific immune responses. Phagocytes engulf pathogens and present antigens on their surface. T-lymphocytes include helper T cells (stimulate B cells and cytotoxic T cells) and cytotoxic T cells (kill infected cells). B-lymphocytes differentiate into plasma cells that secrete antibodies. Antibodies are Y-shaped proteins with variable regions that bind specific antigens, neutralising pathogens or marking them for destruction. The primary immune response is slow; memory cells produced during this response enable a faster, stronger secondary response. Vaccines contain antigens to stimulate memory cell production without causing illness. The human immunodeficiency virus (HIV) attacks helper T cells, compromising the immune system and leading to AIDS. Monoclonal antibodies are used in diagnosis (e.g. ELISA tests) and therapy.
机体通过非特异性屏障（皮肤、黏膜、吞噬作用）和特异性免疫反应来防御病原体。吞噬细胞吞噬病原体并将抗原呈递在表面。T淋巴细胞包括辅助T细胞（刺激B细胞和细胞毒性T细胞）和细胞毒性T细胞（杀伤感染细胞）。B淋巴细胞分化为浆细胞，分泌抗体。抗体是Y形蛋白，其可变区能结合特定抗原，中和病原体或标记其被清除。初次免疫反应较慢；此过程中产生的记忆细胞使得二次反应更快、更强。疫苗含有抗原，能刺激记忆细胞的生成而不致病。人类免疫缺陷病毒（HIV）攻击辅助T细胞，损害免疫系统，导致艾滋病。单克隆抗体被用于诊断（如ELISA检测）和治疗。
11. Gas Exchange, Digestion and Absorption | 气体交换、消化与吸收
All organisms must exchange gases with their environment. Mammalian lungs have alveoli with a large surface area, thin walls, and a rich blood supply for efficient gas exchange. Ventilation is driven by the diaphragm and intercostal muscles. Fish gills use a counter-current flow mechanism to maintain a steep concentration gradient for oxygen uptake. Insects have a tracheal system where oxygen diffuses directly to tissues, aided by rhythmic body movements. Digestion involves the breakdown of large, insoluble molecules into small, soluble ones. Carbohydrases (amylase, maltase) hydrolyse starch; proteases (pepsin, trypsin) break down proteins; lipase, aided by bile salts, digests lipids. Absorption of glucose and amino acids occurs in the small intestine, mainly via co-transport mechanisms, while monoglycerides and fatty acids diffuse into epithelial cells and are reformed into chylomicrons before entering lacteals.
所有生物都必须与环境交换气体。哺乳动物的肺具有肺泡，其表面积大、壁薄、血供丰富，可实现高效气体交换。通氣由膈肌和肋间肌驱动。鱼鳃借助逆流交换机制维持氧摄取的陡峭浓度梯度。昆虫有气管系统，氧气直接扩散到组织，并辅以节律性体动。消化是将大而不溶的分子分解为小而可溶的小分子。淀粉酶、麦芽糖酶等水解淀粉；胃蛋白酶、胰蛋白酶分解蛋白质；脂肪酶在胆汁盐的帮助下消化脂质。葡萄糖和氨基酸主要通过协同转运机制在小肠被吸收，而甘油一酯和脂肪酸扩散进入上皮细胞并重新合成乳糜微粒，随后进入乳糜管。
12. Genetic Information, Variation and Evolution | 遗传信息、变异与进化
Genes are sections of DNA that code for polypeptides or functional RNA. During transcription, RNA polymerase unwinds the gene and synthesises pre-mRNA, which is spliced to remove introns, leaving exons to form mature mRNA. Translation occurs at ribosomes, where tRNA molecules, each carrying a specific amino acid, bind to the mRNA codons via their anticodons. The sequence of bases in DNA determines the primary structure of proteins. Mutations are changes to the base sequence; substitution may cause a different amino acid to be inserted (missense) or create a premature stop codon (nonsense). In diploid organisms, alleles are different versions of the same gene. Genetic variation arises through mutation, meiosis (crossing over, independent assortment), and random fertilisation. Natural selection acts on this variation; individuals with advantageous alleles are more likely to survive and reproduce, increasing the frequency of those alleles in the population over generations. This process can lead to adaptation and the formation of new species.
基因是编码多肽或功能性RNA的DNA区段。转录时，RNA聚合酶解开基因并合成前体mRNA，后者经剪接去除内含子，外显子连接形成成熟mRNA。翻译在核糖体上进行，携带特定氨基酸的tRNA分子通过反密码子与mRNA上的密码子结合。DNA中的碱基序列决定蛋白质的一级结构。突变是碱基序列的改变；替换可能导致插入不同的氨基酸（错义突变）或生成提前的终止密码子（无义突变）。在二倍体生物中，等位基因是同一基因的不同版本。遗传变异源于突变、减数分裂（交叉互换、独立分配）和随机受精。自然选择作用于这些变异；拥有有利等位基因的个体更有可能生存和繁殖，从而使这些等位基因在种群中的频率逐代增加。此过程可导致适应和新物种的形成。
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