📚 A-Level AQA Biology: Last-Minute Revision Notes | AQA生物考前冲刺笔记
These last-minute revision notes condense the core topics of AQA A-level Biology, focusing on key definitions, processes, and common exam traps. Use them to consolidate your understanding and to identify areas that require deeper review before the final assessment.
本考前冲刺笔记浓缩了AQA A-level生物的核心主题，聚焦关键定义、重要过程和高频易错点。用它来巩固理解，并在最终评估前找出需要深入复习的薄弱环节。
1. Monomers and Polymers | 单体与聚合物
Monomers are small, repeating units that can be covalently bonded to form long chains called polymers. The reaction that joins monomers is called condensation, which releases a water molecule; the reverse, breaking polymers into monomers, is hydrolysis, which consumes water.
单体是可以共价连接形成长链（聚合物）的小分子重复单元。连接单体的反应称为缩合，释放一分子水；而将聚合物分解为单体的逆反应是水解，消耗一分子水。
Key examples in biology include: amino acids are monomers of proteins, nucleotides are monomers of nucleic acids, and monosaccharides such as glucose are monomers of carbohydrates.
生物学中的关键例子有：氨基酸是蛋白质的单体，核苷酸是核酸的单体，而葡萄糖等单糖则是碳水化合物的单体。
2. Carbohydrates | 碳水化合物
Monosaccharides have the general formula (CH₂O)ₙ. Glucose can exist as α-glucose or β-glucose, differing in the orientation of the –OH group on carbon 1. A condensation reaction between two monosaccharides forms a disaccharide, linked by a glycosidic bond, e.g., maltose (glucose + glucose), sucrose (glucose + fructose), lactose (glucose + galactose).
单糖的通式为(CH₂O)ₙ。葡萄糖以α-葡萄糖或β-葡萄糖形式存在，差异在于1号碳上–OH的取向。两个单糖通过缩合反应形成二糖，由糖苷键连接，如麦芽糖（葡萄糖+葡萄糖）、蔗糖（葡萄糖+果糖）、乳糖（葡萄糖+半乳糖）。
Polysaccharides are polymers of monosaccharides. Their properties arise from the type of monomers and the extent of branching.
多糖是单糖的聚合物，其性质取决于单体类型和分支程度。
| Polysaccharide | Monomer & Bond | Structure & Function |
|---|---|---|
| Starch | α-glucose; 1,4 and 1,6 glycosidic bonds | Mixture of amylose (helical, unbranched) and amylopectin (branched); compact storage in plants, insoluble so no osmotic effect. |
| Glycogen | α-glucose; 1,4 and many 1,6 glycosidic bonds | Highly branched polymer; storage in animal liver and muscles, more rapidly mobilised than starch. |
| Cellulose | β-glucose; 1,4 glycosidic bonds | Straight chains, every alternate glucose inverted; hydrogen bonds form between parallel chains forming microfibrils, providing high tensile strength for plant cell walls. |
中文对照：淀粉（α-葡萄糖；1,4和1,6糖苷键；直链淀粉螺旋无分支，支链淀粉有分支；植物中致密储存，不溶故无渗透效应）、糖原（α-葡萄糖；1,4和大量1,6键，高度分支；动物肝脏和肌肉中储存，比淀粉更快速动员）、纤维素（β-葡萄糖；1,4糖苷键，直链且每隔一个葡萄糖反转；平行链间形成氢键构成微纤丝，为植物细胞壁提供高抗拉强度）。
3. Lipids | 脂质
acids have no double bonds between carbon atoms; unsaturated fatty acids have one or more C=C double bonds, causing a kink in the chain.
甘油三酯由一个甘油分子和三条脂肪酸链通过缩合反应形成的酯键连接而成。饱和脂肪酸的碳原子间无双键；不饱和脂肪酸含有一个或多个C=C双键，导致链弯曲。
Their key functions include energy storage (due to a high ratio of carbon–hydrogen to oxygen atoms, yielding more energy per gram than carbohydrates), thermal insulation, protection of organs, and water-proofing. Phospholipids replace one fatty acid with a phosphate group, giving a hydrophilic head and hydrophobic tails; this amphipathic nature is fundamental to membrane bilayer formation.
其主要功能包括能量储存（碳-氢与氧原子比例高，每克释放的能量比碳水化合物多）、保温、保护器官和防水。磷脂的一个脂肪酸被磷酸基取代，形成亲水头部和疏水尾部；这种两亲性是构成膜双分子层的基础。
4. Proteins | 蛋白质
Amino acids share a common backbone: a central carbon bonded to an amino group (–NH₂), a carboxyl group (–COOH), a hydrogen atom, and a variable R group. They are linked by peptide bonds (a type of amide bond) during condensation, forming polypeptides.
氨基酸具有共同骨架：中心碳连接氨基(–NH₂)、羧基(–COOH)、氢原子和可变R基团。它们在缩合过程中通过肽键（酰胺键）连接形成多肽。
Protein structure is described at four levels: Primary structure – linear sequence of amino acids. Secondary structure – local folding into α-helices or β-pleated sheets stabilised by hydrogen bonds. Tertiary structure – overall 3D folding held by hydrogen bonds, ionic bonds, disulphide bridges, and hydrophobic interactions. Quaternary structure – association of two or more polypeptide chains (e.g., haemoglobin is a tetramer with four subunits).
蛋白质结构分为四级：一级结构——氨基酸线性序列；二级结构——通过氢键稳定的α-螺旋或β-折叠局部折叠；三级结构——整体三维折叠，由氢键、离子键、二硫键和疏水相互作用维持；四级结构——两条或多条多肽链的结合（例如血红蛋白是由四个亚基组成的四聚体）。
5. Enzymes | 酶
Enzymes are biological catalysts that lower activation energy by providing an alternative reaction pathway. The induced-fit model proposes that the active site undergoes a conformational change upon substrate binding, straining bonds and stabilising the transition state.
酶是通过提供替代反应途径来降低活化能的生物催化剂。诱导契合模型认为，活性部位在底物结合时发生构象变化，使化学键受力并稳定过渡态。
Factors affecting enzyme activity include temperature (rate increases until optimum, then denaturation occurs), pH (changes ionisation of active site residues), enzyme concentration, and substrate concentration. Competitive inhibitors bind to the active site and can be overcome by increasing substrate concentration; non-competitive inhibitors bind at an allosteric site, changing the shape of the active site and reducing Vmax without affecting Km.
影响酶活性的因素包括温度（速率升至最适温度后发生变性）、pH（改变活性部位残基的电离状态）、酶浓度和底物浓度。竞争性抑制剂与活性部位结合，可通过增加底物浓度克服；非竞争性抑制剂结合在别构部位，改变活性部位形状，降低Vmax而不影响Km。
6. Cell Structure | 细胞结构
Eukaryotic cells contain membrane-bound organelles, while prokaryotic cells lack a nucleus and membrane-bound organelles. A typical animal cell features a nucleus (nuclear envelope, pores, nucleolus), rough and smooth endoplasmic reticulum, Golgi apparatus, mitochondria, ribosomes (80S), lysosomes, and centrioles. Plant cells additionally have a cellulose cell wall, a large permanent vacuole, and chloroplasts.
真核细胞含有膜包被的细胞器，而原核细胞没有细胞核及膜包被的细胞器。典型动物细胞包含细胞核（核膜、核孔、核仁）、粗面内质网与光面内质网、高尔基体、线粒体、核糖体（80S）、溶酶体和中心粒。植物细胞还具有纤维素细胞壁、一个大中央液泡和叶绿体。
| Organelle | Function |
|---|---|
| Mitochondrion | Site of aerobic respiration; double membrane, cristae for large surface area, matrix contains enzymes. |
| Chloroplast | Site of photosynthesis; double membrane, thylakoid membranes (grana) contain chlorophyll, stroma for light-independent reactions. |
| Rough ER | Synthesis and transport of proteins; ribosomes on surface. |
| Golgi apparatus | Modification, sorting, and packaging of proteins into vesicles for secretion or delivery. |
中文：线粒体（有氧呼吸场所；双膜，嵴增大表面积，基质含酶）、叶绿体（光合作用场所；双膜，类囊体膜（基粒）含叶绿素，基质进行暗反应）、粗面内质网（蛋白质合成与运输；表面有核糖体）、高尔基体（蛋白质的修饰、分选和包装进入囊泡用于分泌或递送）。
7. Cell Membranes and Transport | 细胞膜与运输
The fluid mosaic model describes the membrane as a phospholipid bilayer with embedded proteins, cholesterol (in animals), glycolipids, and glycoproteins. The 'fluid' nature arises because phospholipids can move laterally; 'mosaic' refers to the patchwork of proteins.
流动镶嵌模型将膜描述为嵌入蛋白质、胆固醇（动物）、糖脂和糖蛋白的磷脂双分子层。“流动性”源于磷脂可侧向移动，“镶嵌性”指蛋白质的散在分布。
Passive transport includes simple diffusion (small, non-polar molecules down concentration gradient), facilitated diffusion (via channel or carrier proteins, also down gradient), and osmosis (net movement of water through a partially permeable membrane from a region of higher water potential to lower water potential). Active transport requires carrier proteins and energy (ATP) to move substances against their concentration gradient. Co-transport couples the movement of one solute with another, e.g., absorption of glucose in the ileum uses sodium ion gradient generated by Na⁺/K⁺ pump.
被动运输包括简单扩散（小、非极性分子顺浓度梯度）、易化扩散（通过通道蛋白或载体蛋白，也顺梯度）和渗透（水通过半透膜从较高水势区域向较低水势区域的净移动）。主动运输需要载体蛋白和能量（ATP）以逆浓度梯度转运物质。协同转运将一种溶质的移动与另一种耦合，例如回肠吸收葡萄糖利用Na⁺/K⁺泵建立的钠离子梯度。
8. Cell Division (Mitosis) and Cell Cycle | 细胞分裂与细胞周期
The cell cycle consists of interphase (G₁, S, G₂) and the mitotic phase. DNA replication occurs during S phase. Mitosis produces two genetically identical diploid daughter cells and is used for growth, repair, and asexual reproduction.
细胞周期包括间期（G₁期、S期、G₂期）和分裂期。DNA复制发生在S期。有丝分裂产生两个遗传上相同的二倍体子细胞，用于生长、修复和无性繁殖。
Stages of mitosis: Prophase – chromosomes condense, nuclear envelope breaks down, spindle fibres form. Metaphase – chromosomes align at the equator, attached to spindle fibres via centromeres. Anaphase – sister chromatids are pulled to opposite poles by shortening spindle fibres. Telophase – nuclear envelopes reform, chromosomes decondense. Cytokinesis divides the cytoplasm.
有丝分裂各阶段：前期——染色体凝聚，核膜解体，纺锤体形成。中期——染色体排列在赤道板，通过着丝粒连接纺锤丝。后期——姐妹染色单体被缩短的纺锤丝拉向两极。末期——核膜重新形成，染色体解凝。胞质分裂分割细胞质。
9. DNA Replication and Protein Synthesis | DNA复制与蛋白质合成
unwinds the double helix and breaks hydrogen bonds. DNA polymerase synthesises the new strand in the 5'→3' hesised continuously, the lagging strand in Okazaki fragments, later joined by DNA ligase.
DNA复制是半保留的：每个新的双螺旋由一条旧（亲本）链和一条新合成链组成。DNA解旋酶解开双螺旋并断开氢键。DNA聚合酶沿5'→3'方向合成新链，需要引物；前导链连续合成，后随链以冈崎片段合成，随后由DNA连接酶连接。
Protein synthesis: Transcription occurs in the nucleus. RNA polymerase binds to the promoter, unwinds DNA, and builds a complementary mRNA strand using the template strand of DNA. In eukaryotes, pre-mRNA is spliced to remove introns. Translation occurs on ribosomes in the cytoplasm. mRNA codons are read in sequence; tRNA molecules carry specific amino acids and have anticodons complementary to codons, allowing peptide bonds to form.
蛋白质合成：转录发生在细胞核。RNA聚合酶结合启动子，解开DNA，以DNA模板链合成互补的mRNA链。真核生物中，前体mRNA经过剪接去除内含子。翻译在细胞质核糖体上进行。mRNA密码子依次被读取；tRNA携带特定氨基酸，其反密码子与密码子互补，使肽键得以形成。
10. Immune System | 免疫系统
The non-specific immune response includes physical barriers (skin, mucus) and phagocytosis. Phagocytes (neutrophils, macrophages) engulf pathogens, forming a phagosome, which fuses with a lysosome; lysozymes digest the pathogen, and antigens are presented on the surface (antigen-presenting cell).
非特异性免疫反应包括物理屏障（皮肤、黏液）和吞噬作用。吞噬细胞（中性粒细胞、巨噬细胞）吞噬病原体，形成吞噬体，与溶酶体融合；溶菌酶消化病原体，并在表面呈递抗原（抗原呈递细胞）。
The specific immune response involves lymphocytes. Cell-mediated response: T-helper cells (CD4⁺) bind to presented antigens on APCs, become activated, and release cytokines that stimulate B cells and cytotoxic T cells. Humoral response: B cells bind to specific antigens and, with T-helper cell signals, undergo clonal selection and expansion into plasma cells (producing antibodies) and memory cells (long-term immunity). Antibodies are Y-shaped proteins that agglutinate pathogens and mark them for destruction. Vaccination introduces a harmless antigen to generate memory cells.
特异性免疫反应涉及淋巴细胞。细胞免疫：T辅助细胞（CD4⁺）与APC呈递的抗原结合后被激活，释放细胞因子刺激B细胞和细胞毒性T细胞。体液免疫：B细胞结合特异性抗原，在T辅助细胞信号下经历克隆选择和扩增，分化为浆细胞（产生抗体）和记忆细胞（长期免疫）。抗体是Y形蛋白，凝集病原体并标记其供摧毁。疫苗接种通过引入无害抗原产生记忆细胞。
11. Gas Exchange | 气体交换
y have a squamous epithelial lining one cell thick, are surrounded by a dense capillary network, provide a large total surface area, and maintain a steep concentration gradient through ventilation and blood flow. Fick's law states that rate of diffusion ∝ (surface area × concentration difference) / diffusion distance.
人类体内，空气经气管进入，气管分支为支气管、细支气管，最后到达肺泡。肺泡是气体交换场所：内衬单层扁平上皮，周围密集毛细血管网，总表面积大，并通过通气和血流维持陡峭的浓度梯度。菲克定律指出扩散速率正比于（表面积×浓度差）/扩散距离。
Key adaptations: the short diffusion distance (endothelium and epithelium are flattened), rich blood supply maintaining a steep partial pressure gradient for O₂ and CO₂, and elastic fibres allow alveoli to recoil during expiration, expelling stale air.
关键适应特征：扩散距离短（内皮和上皮扁平），丰富血液供应维持O₂与CO₂的分压梯度，弹性纤维使肺泡在呼气时回弹排出废气。
12. Mass Transport in Animals and Plants | 动物和植物的物质运输
Animals: The heart is a double pump; the right side pumps deoxygenated blood to the lungs, the left side pumps oxygenated blood to the body. The cardiac cycle includes atrial systole, ventricular systole, and diastole. Haemoglobin is a quaternary protein with four haem groups that bind oxygen cooperatively. The oxygen dissociation curve shifts right (lower affinity) with increased CO₂ (Bohr effect), and during increased metabolic demand. Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin, allowing oxygen transfer across the placenta.
动物：心脏是双泵；右侧将缺氧血泵入肺部，左侧将含氧血泵入全身。心动周期包括心房收缩、心室收缩和舒张。血红蛋白是具有四个血红素基团的四级结构蛋白，协作性结合氧气。氧离曲线在CO₂增加（波尔效应）及代谢需求升高时右移（亲和力降低）。胎儿血红蛋白对氧的亲和力高于成人血红蛋白，允许跨胎盘氧气转运。
Plants: Xylem transports water and mineral ions from roots to leaves. Transpiration is the evaporation of water from mesophyll cells into air spaces and out through stomata. The cohesion-tension theory explains water movement: water molecules cohere (hydrogen bonds) and are pulled up under tension as a continuous column. Phloem transports sucrose by mass flow; at the source (e.g., leaves) sucrose is actively loaded into sieve tubes, lowering water potential, causing water to enter by osmosis, creating high pressure; at the sink, sucrose is unloaded, and water leaves, generating a pressure gradient that drives flow.
植物：木质部将水和矿质离子从根运输到叶。蒸腾作用是水从叶肉细胞蒸发进入气室并通过气孔逸出。内聚力-张力理论解释水分运动：水分子内聚（氢键），在张力下被拉成连续水柱。韧皮部通过压力流运输蔗糖；在源（如叶片）蔗糖被主动装载进筛管，降低水势，水渗透进入产生高压；在库，蔗糖卸载，水离去，形成驱动流的压力梯度。
Published by TutorHao | Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图