📚 A-Level CCEA Biology: End-of-Year Revision Guide | A-Level CCEA 生物：期末复习提纲
Preparing for your A-Level CCEA Biology exams requires a strategic approach that integrates deep understanding of core concepts with effective exam technique. This revision guide outlines the essential topics across AS and A2 units, offering a structured pathway to consolidate your knowledge and boost your confidence before the final assessments.
备战A-Level CCEA生物考试需要采取策略性的方法，将核心概念的深度理解与高效的应试技巧相结合。本复习提纲梳理了AS和A2各单元的重点内容，为你提供一条结构化的知识巩固路径，帮助你在最终评估前提升信心。
1. Mastering the CCEA Specification | 吃透CCEA考试大纲
The CCEA specification is your roadmap. Print it out and use it as a checklist to track your coverage of each learning outcome. Knowing exactly what examiners expect prevents wasted effort on irrelevant details.
CCEA课程大纲是你的路线图。请打印出来，把它当作清单来追踪每个学习目标的完成情况。准确了解考官的期望，可以避免在无关细节上浪费精力。
Highlight the command words in each topic – ‘describe’, ‘explain’, ‘evaluate’, ‘suggest’ – because they dictate the depth of answer required. Be aware that AS content is assumed knowledge at A2; many synoptic questions bridge the two years.
标记每个主题中的指令词——如“描述”、“解释”、“评估”、“建议”——因为它们决定了答案所需的深度。要清楚AS内容是A2的基础；许多综合性题目会串联起两个年级的知识。
2. AS Unit 1: Molecules and Cells | AS单元1：分子与细胞
Biological molecules form the foundation: understand the structure and function of carbohydrates, lipids, proteins and nucleic acids. Be able to describe the formation of glycosidic bonds, ester bonds and peptide bonds.
生物分子是基础：理解碳水化合物、脂质、蛋白质和核酸的结构与功能。要能够描述糖苷键、酯键和肽键的形成。
The table below summarises the key biological polymers, their monomers and the bonds holding them together:
下表总结了关键的生物聚合物、它们的单体以及将它们连接起来的化学键：
| Polymer | Monomer | Bond |
|---|---|---|
| Polysaccharide (starch, glycogen, cellulose) | Monosaccharide (e.g. glucose) | Glycosidic bond |
| Protein | Amino acid | Peptide bond |
| DNA / RNA | Nucleotide | Phosphodiester bond |
| Triglyceride (not a polymer) | Glycerol + 3 fatty acids | Ester bond |
Cell ultrastructure requires you to recognise organelles such as mitochondria, ribosomes, rough endoplasmic reticulum and Golgi apparatus, and link their structure to function. Prokaryotic cells lack membrane-bound organelles.
细胞超微结构要求你识别线粒体、核糖体、粗面内质网和高尔基体等细胞器，并将其结构与其功能联系起来。原核细胞缺少膜包围的细胞器。
Membrane transport processes – diffusion, facilitated diffusion, osmosis, active transport and bulk transport – must be explained with reference to the fluid-mosaic model. Use the terms hypertonic, hypotonic and isotonic accurately.
膜转运过程——扩散、协助扩散、渗透、主动运输和批量运输——必须结合流动镶嵌模型进行解释。请准确使用高渗、低渗和等渗这三个术语。
Enzymes are globular proteins that lower activation energy. Explore the induced-fit model, factors affecting rate (temperature, pH, substrate concentration), and the difference between competitive and non-competitive inhibition.
酶是降低活化能的球状蛋白质。探索诱导契合模型、影响反应速率的因素（温度、pH、底物浓度），以及竞争性抑制与非竞争性抑制的区别。
The cell cycle includes interphase (G₁, S, G₂) and mitosis (prophase, metaphase, anaphase, telophase). Be prepared to identify stages from micrographs and explain the significance of mitosis in growth and repair.
细胞周期包括间期（G₁期、S期、G₂期）和有丝分裂（前期、中期、后期、末期）。要能够从显微照片中辨认各个阶段，并解释有丝分裂在生长和修复中的意义。
DNA replication is semi-conservative; learn the roles of DNA helicase, DNA polymerase and ligase. Transcription (in the nucleus) and translation (on ribosomes) form the central dogma of molecular biology.
DNA复制是半保留复制；学习DNA解旋酶、DNA聚合酶和连接酶的作用。转录（在细胞核内）和翻译（在核糖体上）构成了分子生物学的中心法则。
3. AS Unit 2: Organisms and Biodiversity | AS单元2：生物体与生物多样性
Mass transport in animals: the structure of haemoglobin and its oxygen dissociation curve, the Bohr effect, and the mammalian circulatory system including the heart, arteries, veins and capillaries.
动物体内的物质运输：血红蛋白的结构及其氧解离曲线、玻尔效应，以及哺乳动物的循环系统，包括心脏、动脉、静脉和毛细血管。
In plants, the cohesion-tension theory explains water movement in the xylem; translocation in the phloem involves the mass flow hypothesis. Relate root pressure and transpiration pull to adaptations of xerophytes and hydrophytes.
植物中，内聚力-张力理论解释了木质部中水分的运输；韧皮部中的物质运输涉及压力流假说。将根压和蒸腾拉力与旱生植物和水生植物的适应性联系起来。
Gas exchange surfaces: countercurrent flow in fish gills, tracheae in insects, and the pathway of air in the human respiratory system (trachea → bronchi → bronchioles → alveoli). The role of surfactant and the mechanics of inhalation and exhalation.
气体交换表面：鱼鳃中的逆流交换、昆虫的气管以及人类呼吸系统中空气的通路（气管 → 支气管 → 细支气管 → 肺泡）。表面活性剂的作用以及吸气与呼气的机械过程。
Digestion: the breakdown of carbohydrates, proteins and lipids by enzymes at specific sites; the role of bile salts in emulsification; absorption of monomers including the co-transport of glucose and sodium ions in the ileum.
消化作用：酶在特定部位对碳水化合物、蛋白质和脂质的分解；胆汁盐在乳化中的作用；单体的吸收，包括回肠中葡萄糖与钠离子的协同转运。
Biodiversity can be measured using species richness and Simpson’s Index of Diversity. Natural selection requires variation, differential survival and reproduction. Be ready to recall examples such as antibiotic resistance in bacteria and peppered moth evolution.
生物多样性可使用物种丰富度和辛普森多样性指数来衡量。自然选择需要变异、差异性生存和繁殖。要能够回忆细菌抗生素耐药性及桦尺蠖进化等实例。
Classification follows a hierarchical system (domain, kingdom, phylum, class, order, family, genus, species). Phylogenetic trees represent evolutionary relationships; the more recent the common ancestor, the closer the relationship.
分类遵循层级系统（域、界、门、纲、目、科、属、种）。系统发生树表示进化关系；共同祖先越近，亲缘关系越密切。
4. A2 Unit 1: Physiology, Co-ordination and Ecosystems | A2单元1：生理学、协调与生态系统
Homeostasis involves negative feedback loops. Describe the role of the hypothalamus in thermoregulation and the actions of insulin and glucagon in blood glucose control. The kidney ultrafiltration mechanism in the Bowman’s capsule, selective reabsorption in the proximal convoluted tubule, and the countercurrent multiplier in the loop of Henle are central to osmoregulation.
体内稳态涉及负反馈回路。描述下丘脑在体温调节中的作用，以及胰岛素和胰高血糖素在血糖控制中的作用。鲍曼氏囊的超滤机制、近曲小管的选择性重吸收以及亨利氏袢的逆流倍增器是渗透调节的核心。
Nerve impulses: resting potential maintained by the sodium-potassium pump, depolarisation by voltage-gated Na+ channels, action potential propagation, saltatory conduction in myelinated axons, and synaptic transmission involving Ca2+ influx and exocytosis of acetylcholine. Summation and inhibitory synapses refine the signal.
神经冲动：钠钾泵维持静息电位，电压门控Na⁺通道引发去极化，动作电位的传播，有髓轴突中的跳跃传导，以及涉及Ca²⁺内流和乙酰胆碱胞吐的突触传递。总和作用与抑制性突触精细调节信号。
Muscle contraction relies on the sliding filament theory; Ca²⁺ and ATP power the cross-bridge cycle. Compare fast-twitch (anaerobic, fatigues quickly) and slow-twitch fibres (aerobic, myoglobin-rich).
肌肉收缩依赖于滑动丝理论；Ca²⁺和ATP驱动横桥循环。比较快缩肌纤维（无氧代谢，易疲劳）和慢缩肌纤维（有氧代谢，富含肌红蛋白）。
In ecosystems, energy flows through trophic levels. Use the equations to quantify productivity:
NPP = GPP – R
where GPP is gross primary productivity, NPP is net primary productivity, and R is respiratory loss. Energy transfer efficiency is typically about 10% between trophic levels.
生态系统中，能量在营养级之间流动。使用以下公式量化生产力：
NPP = GPP – R
其中GPP为总初级生产力，NPP为净初级生产力，R为呼吸消耗。营养级间的能量传递效率通常约为10%。
Nutrient cycles: describe the nitrogen cycle (including nitrogen fixation by Rhizobium, nitrification by Nitrosomonas and Nitrobacter, denitrification) and the carbon cycle. Ecological succession from pioneer species to climax community illustrates directional change over time.
营养循环：描述氮循环（包括根瘤菌的固氮作用、亚硝化单胞菌和硝化杆菌的硝化作用、反硝化作用）和碳循环。从先锋物种到顶级群落的生态演替说明了随时间发生的定向变化。
5. A2 Unit 2: Biochemistry, Genetics and Evolutionary Trends | A2单元2：生物化学、遗传学与进化趋势
Photosynthesis: the light-dependent reaction – including cyclic and non-cyclic photophosphorylation, photolysis of water – and the Calvin cycle (carbon fixation, GP reduction, RuBP regeneration). Limiting factors can be analysed using graphs of rate against light intensity, CO₂ concentration and temperature
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