📚 A-Level Biology: End-of-Term Revision Checklist | A-Level 生物：期末复习提纲
A-level Biology can feel overwhelming when you’re staring down an end-of-term exam. The syllabus spans everything from molecular bonds to whole ecosystems. This revision checklist breaks the core content into manageable sections, helping you identify what you know, what needs a quick refresh, and where to drill deeper. Use it alongside your notes and past papers to ensure no major topic is left behind.
A-Level 生物在期末复习时可能会让人感到无从下手。考纲涵盖从分子键到整个生态系统的所有内容。这份复习提纲将核心知识分成易于掌握的小节，帮助你识别哪些已经掌握、哪些需要快速回顾、哪些需要深入练习。结合笔记和历年真题使用，确保没有重大知识点被遗漏。
1. Biological Molecules | 生物分子
Carbohydrates consist of monosaccharides such as glucose, joined by glycosidic bonds to form disaccharides and polysaccharides including starch, glycogen and cellulose. You should be able to describe the ring structure of α- and β-glucose and how their different orientations affect polymer properties.
碳水化合物由葡萄糖等单糖组成，通过糖苷键连接形成二糖以及淀粉、糖原和纤维素等多糖。你需要能够描述 α- 和 β- 葡萄糖的环状结构，以及它们不同取向如何影响聚合物的性质。
Lipids are triglycerides made of glycerol and three fatty acids joined by ester bonds. Phospholipids replace one fatty acid with a phosphate group, giving them a hydrophilic head and hydrophobic tail, essential for membrane formation. Know the test for lipids using the emulsion test with ethanol.
脂质是由甘油和三个脂肪酸通过酯键连接而成的甘油三酯。磷脂用磷酸基团替代一个脂肪酸，形成亲水头部和疏水尾部，对膜的结构至关重要。掌握用乙醇乳化试验检测脂质的方法。
Proteins are polymers of amino acids linked by peptide bonds. Four levels of structure – primary sequence, secondary α-helices and β-pleated sheets, tertiary folding held by hydrogen bonds, ionic bonds, disulfide bridges and hydrophobic interactions, and quaternary association of multiple polypeptides – determine function. The biuret test detects peptide bonds.
蛋白质是由氨基酸通过肽键连接而成的多聚体。四级结构——一级序列、二级 α-螺旋和 β-折叠、由氢键、离子键、二硫键及疏水作用维持的三级折叠，以及多肽的四级联合——决定了其功能。双缩脲试验可用于检测肽键。
2. Cell Structure & Organelles | 细胞结构与细胞器
Prokaryotic cells lack a membrane-bound nucleus and organelles; their DNA is circular and free in the cytoplasm. Eukaryotic cells possess a true nucleus, linear DNA associated with histones, and membrane-bound organelles such as mitochondria, chloroplasts, endoplasmic reticulum and Golgi apparatus.
原核细胞没有膜包被的细胞核和细胞器；其 DNA 呈环状，游离于细胞质中。真核细胞拥有真正的细胞核、与组蛋白结合的线性 DNA，以及线粒体、叶绿体、内质网和高尔基体等膜包被细胞器。
Mitochondria are the site of aerobic respiration, with a double membrane; the inner membrane is folded into cristae to increase surface area for oxidative phosphorylation. Chloroplasts contain thylakoid membranes stacked into grana, where the light-dependent reactions of photosynthesis occur, surrounded by stroma for the Calvin cycle.
线粒体是有氧呼吸的场所，具有双层膜；内膜向内折叠形成嵴，以增加氧化磷酸化的表面积。叶绿体含有类囊体膜，堆叠成基粒，是光合作用光反应的发生地点，周围基质则是卡尔文循环的场所。
Be able to compare organelles visible under light and electron microscopes, and calculate actual sizes using magnification = image size / actual size.
能够比较在光学显微镜和电子显微镜下可见的细胞器，并使用放大倍数 = 图像大小 / 实际大小的公式计算实际尺寸。
3. Cell Membranes & Transport | 细胞膜与运输
The fluid mosaic model describes the membrane as a phospholipid bilayer with embedded proteins, cholesterol and glycoproteins. Phospholipids can move laterally, giving fluidity; cholesterol modulates fluidity and stability. Transport proteins include channel proteins and carrier proteins.
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。磷脂可侧向移动，赋予膜流动性；胆固醇调节流动性和稳定性。转运蛋白包括通道蛋白和载体蛋白。
Diffusion is the net movement of particles down a concentration gradient, passive and not requiring energy. Facilitated diffusion uses channel or carrier proteins for larger or polar molecules. Active transport moves substances against their gradient using ATP and carrier proteins. Osmosis is the movement of water across a partially permeable membrane from high to low water potential.
扩散是粒子顺浓度梯度的净移动，被动进行、不消耗能量。协助扩散利用通道蛋白或载体蛋白运输较大或极性分子。主动运输利用 ATP 和载体蛋白逆浓度梯度转运物质。渗透是水通过部分通透膜从高水势向低水势的移动。
Understand how to plot and interpret water potential calibration curves, and explain the effect of immersing plant and animal cells in solutions of different water potentials.
理解如何绘制和解释水势校准曲线，并能解释将植物和动物细胞置于不同水势溶液中的效果。
4. Enzymes | 酶
Enzymes are globular proteins that act as biological catalysts, lowering activation energy by forming an enzyme-substrate complex. The active site is specific to the substrate – the lock-and-key model and the induced-fit model explain this specificity. Enzyme activity is affected by temperature, pH, substrate concentration and inhibitors.
酶是球状蛋白质，作为生物催化剂，通过形成酶-底物复合物降低活化能。活性部位对底物具有特异性——锁钥模型和诱导契合模型解释了这种特异性。酶活性受温度、pH、底物浓度和抑制剂的影响。
Competitive inhibitors resemble the substrate and bind to the active site, overcome by increasing substrate concentration. Non-competitive inhibitors bind away from the active site, changing the enzyme’s shape and reducing Vmax without affecting Km. Be familiar with metabolic poisons and medicinal drugs that act as enzyme inhibitors.
竞争性抑制剂与底物相似，结合于活性位点，可通过提高底物浓度来克服。非竞争性抑制剂结合于活性位点以外的部位，改变酶的形状，降低 Vmax 但不影响 Km。要熟悉作为酶抑制剂的代谢毒物和医用药物。
Know how to design experiments to measure the initial rate of reaction, such as using catalase with hydrogen peroxide, and how to calculate the temperature coefficient Q₁₀.
了解如何设计实验测定反应初速率，例如使用过氧化氢酶与过氧化氢，以及如何计算温度系数 Q₁₀。
5. Cell Cycle & Division | 细胞周期与分裂
The cell cycle consists of interphase (G₁, S, G₂) and mitotic phase (mitosis and cytokinesis). DNA replicates during S phase, producing sister chromatids held at the centromere. Mitosis produces two genetically identical diploid daughter cells for growth and repair. Know the stages: prophase, metaphase, anaphase and telophase, and be able to recognise them in microscope images.
细胞周期由间期（G₁、S、G₂）和分裂期（有丝分裂和胞质分裂）组成。DNA 在 S 期复制，产生由着丝粒连接的姐妹染色单体。有丝分裂产生两个遗传上相同的二倍体子细胞，用于生长和修复。要了解前期、中期、后期和末期各个阶段，并能从显微镜图像中识别。
Meiosis produces haploid gametes through two divisions. In meiosis I, homologous chromosomes pair and crossing over occurs, generating genetic variation; they then segregate independently. Meiosis II separates sister chromatids. The result is four genetically distinct haploid cells. Compare mitosis and meiosis in terms of outcomes and significance.
减数分裂经过两次分裂产生单倍体配子。减数第一次分裂中，同源染色体配对并发生交叉互换，产生遗传变异；随后同源染色体独立分离。减数第二次分裂分离姐妹染色单体。最终形成四个遗传上不同的单倍体细胞。比较有丝分裂和减数分裂的结果与意义。
6. Nucleic Acids & Protein Synthesis | 核酸与蛋白质合成
DNA is a double helix of two antiparallel polynucleotide strands. Each nucleotide contains deoxyribose, a phosphate group and a nitrogenous base (A, T, C, G). Bases pair complementarily via hydrogen bonds – A with T (2 bonds), C with G (3 bonds). RNA contains ribose and uracil instead of thymine, and is usually single-stranded.
DNA 是由两条反向平行的多核苷酸链构成的双螺旋。每个核苷酸包含脱氧核糖、一个磷酸基团和一个含氮碱基（A、T、C、G）。碱基通过氢键互补配对——A 与 T 之间 2 个，C 与 G 之间 3 个。RNA 含有核糖，以尿嘧啶代替胸腺嘧啶，通常为单链。
DNA replication is semi-conservative, proven by Meselson and Stahl. Helicase unwinds the double helix, DNA polymerase adds nucleotides in the 5′ to 3′ direction, leading strand is continuous, lagging strand forms Okazaki fragments joined by ligase. Transcription produces mRNA as a complementary copy of a gene. Translation builds a polypeptide at the ribosome; tRNA anticodons match mRNA codons.
DNA 复制是半保留的，由 Meselson 和 Stahl 实验证实。解旋酶解开双螺旋，DNA 聚合酶沿 5′ 到 3′ 方向添加核苷酸，前导链连续合成，后随链形成由连接酶连接的冈崎片段。转录产生基因互补的 mRNA 拷贝。翻译在核糖体上构建多肽；tRNA 反密码子与 mRNA 密码子配对。
7. Genetics & Inheritance | 遗传与遗传规律
Monohybrid crosses illustrate Mendel’s law of segregation. Use Punnett squares to predict phenotypic ratios for dominant/recessive and codominant alleles. Be able to interpret pedigree diagrams to determine whether a condition is autosomal or sex-linked, dominant or recessive. Understand multiple alleles, as in the ABO blood group system.
单基因杂交体现了孟德尔的分离定律。用庞尼特方格预测显性/隐性以及共显性等位基因的表型比例。能够解读系谱图，判断某一性状是常染色体还是性连锁、显性还是隐性。理解复等位基因，例如 ABO 血型系统。
Dihybrid crosses can produce the 9:3:3:1 ratio if genes are unlinked and assort independently. Epistasis occurs when one gene masks the expression of another; know examples such as coat colour in Labrador retrievers. Linkage means alleles on the same chromosome do not assort independently; crossing over can produce recombinant phenotypes.
双基因杂交若基因不连锁且独立分配，可产生 9:3:3:1 的比率。当一个基因掩盖另一个基因的表达时发生上位效应；要了解拉布拉多犬毛色等例子。连锁意味着同一染色体上的等位基因不独立分配；交叉互换可产生重组表型。
Chi-squared (χ²) test is used to compare observed and expected frequencies and determine whether deviations are due to chance. Practice calculating χ² and interpreting probability values.
卡方（χ²）检验用于比较观察值与期望频率，判断偏差是否由偶然因素造成。练习计算 χ² 并解读概率值。
8. Evolution & Speciation | 进化与物种形成
Natural selection acts on genetic variation within a population. Individuals with phenotypes that increase fitness are more likely to survive, reproduce and pass on advantageous alleles. This leads to changes in allele frequency over time. Know examples like antibiotic resistance in bacteria and industrial melanism in moths.
自然选择作用于种群内的遗传变异。表型能提高适合度的个体更可能存活、繁殖并传递有利等位基因。这导致等位基因频率随时间改变。了解细菌的抗药性和桦尺蠖的工业黑化等实例。
Speciation occurs when populations become reproductively isolated. Allopatric speciation involves geographical barriers; sympatric speciation occurs without physical separation, often through behavioural or temporal isolation. Mechanisms of isolation prevent gene flow, allowing genetic differences to accumulate.
当种群之间产生生殖隔离时便会形成新物种。异域物种形成涉及地理障碍；同域物种形成则在没有物理隔离的情况下发生，通常通过行为或时间隔离实现。隔离机制阻止基因流动，使遗传差异得以积累。
9. Transport in Plants | 植物运输
Xylem transports water and mineral ions from roots to leaves. Water enters root hairs by osmosis and moves through the apoplast and symplast pathways. Transpiration, driven by evaporation from stomata, creates tension that pulls water up the xylem in unbroken columns – the cohesion-tension theory. The Casparian strip blocks apoplastic movement in the endodermis, forcing water into the symplast.
木质部将水和无机离子从根部运往叶片。水通过渗透进入根毛，并沿质外体及共质体途径移动。由气孔蒸发驱动的蒸腾作用产生张力，将水以连续水柱的形式拉上木质部——内聚力-张力理论。凯氏带阻断内皮层中的质外体移动，迫使水进入共质体。
Phloem transports sucrose and amino acids from sources to sinks by active loading and mass flow. Companion cells load sucrose using proton pumps and co-transport proteins; water follows by osmosis, raising hydrostatic pressure and driving sap towards regions of lower pressure (sinks). This is described by the pressure-flow hypothesis.
韧皮部通过主动装载和集流将蔗糖和氨基酸从源运至库。伴随细胞利用质子泵和协同运输蛋白装载蔗糖；水随后通过渗透流入，提升静水压力，驱使汁液流向压力较低的区域（库）。这可用压力流动假说解释。
10. Circulation, Respiration & Homeostasis | 循环、呼吸与稳态
Mammals have a closed, double circulatory system. The heart contains four chambers; the sinoatrial node initiates contraction, and the atrioventricular node delays impulses to ensure coordinated ventricular contraction. Haemoglobin associates with oxygen in the lungs and dissociates in respiring tissues. The oxygen dissociation curve shifts right with increased CO₂ (Bohr effect), facilitating oxygen unloading.
哺乳动物具有封闭的双循环系统。心脏有四个腔室；窦房结发起收缩，房室结延搁冲动以确保心室协调收缩。血红蛋白在肺部与氧结合，在呼吸组织释氧。氧解离曲线随 CO₂ 增加而右移（玻尔效应），有利于氧的卸载。
Aerobic respiration generates ATP through glycolysis, the link reaction, the Krebs cycle and oxidative phosphorylation. Glycolysis occurs in cytoplasm and yields a small amount of ATP and reduced NAD. The Krebs cycle in the mitochondrial matrix generates reduced coenzymes, CO₂ and ATP. In the electron transport chain, energy from reduced NAD and reduced FAD is used to make a large quantity of ATP via chemiosmosis. Anaerobic respiration in animals produces lactate; in plants and fungi, ethanol.
有氧呼吸通过糖酵解、连接反应、克雷布斯循环和氧化磷酸化生成 ATP。糖酵解发生于细胞质，产生少量 ATP 和还原型 NAD。线粒体基质中的克雷布斯循环生成还原型辅酶、CO₂ 和 ATP。在电子传递链中，来自还原型 NAD 和还原型 FAD 的能量通过化学渗透大量合成 ATP。动物无氧呼吸产生乳酸；植物和真菌则产生乙醇。
Homeostasis maintains internal conditions within narrow limits. The kidney regulates water potential through osmoregulation; ADH increases water reabsorption in the collecting duct. Blood glucose is controlled by insulin and glucagon, with the liver playing a central role. Thermoregulation involves vasodilation, vasoconstriction and shivering, coordinated by the hypothalamus.
稳态使内环境维持在狭窄范围内。肾脏通过渗透调节控制水势；抗利尿激素（ADH）增加集合管对水的重吸收。血糖由胰岛素和胰高血糖素调控，肝脏起核心作用。体温调节涉及血管舒张、血管收缩和战栗，由下丘脑协调。
11. Ecology & Ecosystems | 生态与生态系统
Ecosystems are characterised by energy flow and nutrient cycling. Energy enters through photosynthesis and is transferred through trophic levels, but around 90% is lost at each level mainly via respiration and waste. Pyramids of energy are always upright. Nutrients such as nitrogen and carbon are recycled through the actions of decomposers and microorganisms.
生态系统的特征在于能量流动和物质循环。能量通过光合作用进入，沿营养级传递，但在每一营养级约有 90% 因呼吸作用和废物而损耗。能量金字塔总是正立的。氮和碳等营养物质通过分解者和微生物的作用得以循环。
Abiotic and biotic factors influence population size. Use quadrats, transects and mark-release-recapture to estimate population sizes and distribution. Ecological succession describes the directional change in species composition over time, from pioneer communities to climax communities. Understand primary and secondary succession.
非生物因素和生物因素影响种群大小。使用样方、样线和标记-释放-重捕法估算种群大小和分布。生态演替描述了物种组成随时间的方向性变化，从先锋群落到顶极群落。理解初生演替和次生演替。
12. Gene Technology & Ethics | 基因技术与伦理
Recombinant DNA technology uses restriction enzymes to cut DNA at specific recognition sites, leaving sticky ends that can be joined by DNA ligase. Vectors such as plasmids carry the gene of interest into host cells. Genetic modification has applications in medicine (insulin production) and agriculture (pest-resistant crops).
重组 DNA 技术利用限制酶在特定识别位点切断 DNA，留下可被 DNA 连接酶连接的黏性末端。质粒等载体将目的基因带入宿主细胞。基因修饰在医学（胰岛素生产）和农业（抗虫作物）中有广泛应用。
Polymerase chain reaction (PCR) amplifies DNA fragments using repeated cycles of denaturation, annealing and extension. Gel electrophoresis separates DNA fragments by size; the pattern of bands can be used for DNA profiling in forensics and paternity testing. Understand the principles of DNA sequencing.
聚合酶链式反应（PCR）通过反复的变性、退火和延伸循环扩增 DNA 片段。凝胶电泳按大小分离 DNA 片段；条带图谱可用于法医学和亲子鉴定的 DNA 分析。理解 DNA 测序的基本原理。
Ethical considerations surround genetic screening, gene therapy, GMOs and cloning. Be able to discuss the balance between potential benefits and risks, including ecological impact and informed consent.
围绕基因筛查、基因治疗、转基因生物和克隆存在伦理考量。能够讨论潜在益处与风险之间的平衡，包括生态影响和知情同意等议题。
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