📚 A-Level WJEC Biology: Last-Minute Revision Notes | A-Level WJEC 生物考前冲刺笔记
These concise, exam-focused revision notes cover the essential topics for the WJEC A-Level Biology specification. Use them to reinforce key concepts, clarify common misconceptions, and build confidence before the exam. Each section pairs an English summary with a Chinese translation, helping bilingual learners consolidate terminology and processes.
这本精炼的考前冲刺笔记覆盖了 WJEC A-Level 生物考试的核心内容。用它们来巩固关键概念、澄清常见误区，并在考前建立信心。每个小节都提供了英文总结与中文译文，帮助双语学习者同步掌握术语与过程。
1. Cell Structure and Organelles | 细胞结构与细胞器
Eukaryotic cells contain membrane-bound organelles, each with a specific function. The nucleus stores genetic material, while mitochondria are the site of aerobic respiration, producing ATP. Ribosomes synthesise proteins, and the rough endoplasmic reticulum (RER) processes and transports these proteins. The Golgi apparatus modifies and packages proteins into vesicles for secretion. Lysosomes contain hydrolytic enzymes to break down waste. Plant cells also possess chloroplasts, a large permanent vacuole, and a cellulose cell wall.
真核细胞含有膜包围的细胞器，各有特定功能。细胞核储存遗传物质，线粒体是有氧呼吸的场所，产生 ATP。核糖体合成蛋白质，粗面内质网 (RER) 加工并运输这些蛋白质。高尔基体修饰蛋白质并将其包装成囊泡以进行分泌。溶酶体含有水解酶以分解废物。植物细胞还有叶绿体、大中央液泡和纤维素细胞壁。
- Nucleus: contains DNA organised into chromatin / 细胞核：含有以染色质形式存在的 DNA
- Mitochondria: double membrane, cristae increase surface area for oxidative phosphorylation / 线粒体：双层膜，嵴增大氧化磷酸化的表面积
- RER & Ribosomes: 80S ribosomes on RER synthesise proteins for export / 粗面内质网和核糖体：RER 上 80S 核糖体合成分泌蛋白
- Chloroplasts: site of photosynthesis, contain thylakoids and stroma / 叶绿体：光合作用场所，含有类囊体和基质
Prokaryotic cells differ: they lack a nucleus, have circular DNA, 70S ribosomes, and may have a capsule, plasmid, and flagellum. Binary fission is their method of reproduction.
原核细胞不同：它们没有细胞核，有环状 DNA、70S 核糖体，可能含有荚膜、质粒和鞭毛。二分裂是其繁殖方式。
2. Biological Molecules: Carbohydrates, Lipids, Proteins & Nucleic Acids | 生物分子：碳水化合物、脂质、蛋白质和核酸
Carbohydrates include monosaccharides (e.g., glucose), disaccharides (maltose, sucrose), and polysaccharides (starch, glycogen, cellulose). Glucose has isomers α-glucose and β-glucose, which affect polymer structure. Glycosidic bonds link monosaccharides. Lipids, mainly triglycerides, are formed from glycerol and three fatty acids by ester bonds. They are hydrophobic and used for energy storage, insulation, and cell membranes (phospholipids).
碳水化合物包括单糖（如葡萄糖）、二糖（麦芽糖、蔗糖）和多糖（淀粉、糖原、纤维素）。葡萄糖有 α-葡萄糖和 β-葡萄糖异构体，这会影响聚合物的结构。糖苷键连接单糖。脂质，主要是甘油三酯，由甘油和三个脂肪酸通过酯键形成。它们疏水，用于能量储存、保温及构成细胞膜（磷脂）。
- Starch: α-glucose polymer, amylose (coiled) and amylopectin (branched), used in plants / 淀粉：α-葡萄糖聚合物，直链淀粉（螺旋）和支链淀粉（分支），植物储能
- Glycogen: highly branched α-glucose polymer in animals, stored in liver and muscles / 糖原：动物体内高度分支的 α-葡萄糖聚合物，储存在肝脏和肌肉
- Cellulose: β-glucose polymer, straight chains cross-linked by hydrogen bonds, structural / 纤维素：β-葡萄糖聚合物，直链通过氢键交联，结构成分
Proteins are polymers of amino acids. The primary structure is the sequence of amino acids; secondary structure includes α-helices and β-pleated sheets maintained by hydrogen bonds; tertiary structure is the 3D folding due to disulfide bridges, ionic bonds, and hydrophobic interactions; quaternary structure involves multiple polypeptide chains. Enzymes, antibodies, and haemoglobin are examples.
蛋白质是氨基酸的聚合物。一级结构是氨基酸序列；二级结构包括由氢键维持的 α-螺旋和 β-折叠；三级结构是由二硫键、离子键和疏水相互作用导致的三维折叠；四级结构涉及多条多肽链。酶、抗体和血红蛋白就是例子。
Nucleic acids: DNA and RNA. DNA is a double helix of deoxyribonucleotides with complementary base pairing (A-T, C-G). RNA is single-stranded, contains uracil instead of thymine, and comes in mRNA, tRNA, and rRNA. ATP is the immediate energy currency, releasing energy when hydrolysed to ADP + Pi.
核酸：DNA 和 RNA。DNA 是由脱氧核糖核苷酸组成的双螺旋，具有互补碱基配对（A-T，C-G）。RNA 是单链，含有尿嘧啶而不是胸腺嘧啶，有 mRNA、tRNA 和 rRNA。ATP 是即时能量货币，水解为 ADP + Pi 时释放能量。
3. Enzyme Action and Kinetics | 酶作用与动力学
Enzymes are biological catalysts that lower activation energy. The active site is complementary to the substrate, described by the lock and key model or the induced fit model. Enzyme activity is affected by temperature and pH: extreme conditions cause denaturation, changing the tertiary structure. At low temperatures, molecular motion is reduced, so reaction rates decrease.
酶是降低活化能的生物催化剂。活性位点与底物互补，可用锁钥模型或诱导契合模型描述。酶活性受温度和 pH 影响：极端条件导致变性，改变三级结构。低温时分子运动减少，因此反应速率降低。
- Temperature coefficient (Q₁₀): measures rate increase when temperature rises by 10°C, usually around 2 / 温度系数 (Q₁₀)：温度升高 10°C 时速率增加的倍数，通常约为 2
- Competitive inhibition: inhibitor resembles substrate, binds to active site; can be overcome by increasing substrate concentration / 竞争性抑制：抑制剂与底物相似，占据活性位点；增加底物浓度可以克服
- Non-competitive inhibition: inhibitor binds to allosteric site, changes shape of active site; Vmax reduced but Km unchanged / 非竞争性抑制：抑制剂结合别构位点，改变活性位点形状；Vmax 降低但 Km 不变
Initial rate of reaction is measured in the first few seconds; Michaelis-Menten kinetics describe the relationship between substrate concentration and rate. The Michaelis constant (Km) is the substrate concentration at half Vmax, indicating enzyme affinity.
初始反应速率在前几秒测量；米氏动力学描述了底物浓度与速率的关系。米氏常数 (Km) 是达到半 Vmax 时的底物浓度，表示酶的亲和力。
4. Membrane Structure and Transport | 膜结构与运输
The fluid mosaic model describes cell membranes as a phospholipid bilayer with embedded proteins, cholesterol, and glycoproteins. Phospholipids have hydrophilic heads and hydrophobic tails, forming a barrier to water-soluble molecules. Cholesterol regulates membrane fluidity. Transport mechanisms include passive diffusion, facilitated diffusion via channel/carrier proteins, and active transport requiring ATP. Osmosis is the net movement of water across a partially permeable membrane from a region of higher water potential to lower water potential.
流动镶嵌模型将细胞膜描述为嵌入蛋白质、胆固醇和糖蛋白的磷脂双分子层。磷脂具有亲水头部和疏水尾部，形成对水溶性分子的屏障。胆固醇调节膜的流动性。运输机制包括被动扩散、通过通道/载体蛋白的协助扩散以及需要 ATP 的主动运输。渗透作用是水通过半透膜从水势较高的区域向水势较低的区域净移动。
- Water potential (Ψ): Ψ = solute potential + pressure potential; water moves to more negative Ψ / 水势 (Ψ)：Ψ = 溶质势 + 压力势；水向更负的 Ψ 移动
- Cotransport: e.g., sodium-glucose cotransporter in small intestine, using Na⁺ gradient to move glucose against its gradient / 协同运输：例如小肠中的钠-葡萄糖协同转运蛋白，利用 Na⁺ 梯度逆浓度转运葡萄糖
- Endocytosis/exocytosis: bulk transport using vesicles, requiring energy / 胞吞/胞吐作用：利用囊泡的大量运输，需要能量
5. Cell Division and the Cell Cycle | 细胞分裂与细胞周期
The cell cycle consists of interphase (G₁, S, G₂) and mitosis. DNA replicates during S phase. Mitosis produces two genetically identical diploid cells: prophase (chromosomes condense, spindle forms), metaphase (chromosomes align at equator), anaphase (sister chromatids separate), telophase (nuclear envelope reforms). Cytokinesis divides the cytoplasm. Meiosis produces four haploid gametes, involving two divisions and crossing over in prophase I, which increases genetic variation.
细胞周期包括间期（G₁、S、G₂）和有丝分裂。DNA 在 S 期复制。有丝分裂产生两个遗传相同的二倍体细胞：前期（染色体凝集，纺锤体形成），中期（染色体排列在赤道板），后期（姐妹染色单体分离），末期（核膜重新形成）。胞质分裂分割细胞质。减数分裂产生四个单倍体配子，涉及两次分裂，前期 I 发生交叉互换，增加遗传变异。
- Checkpoints: G₁, G₂, and metaphase checkpoints control progression / 检查点：G₁、G₂ 和中期检查点控制细胞周期进程
- Cancer: arises from uncontrolled cell division, often due to mutations in proto-oncogenes or tumour suppressor genes / 癌症：由失控的细胞分裂引起，通常由于原癌基因或抑癌基因突变
Apoptosis is programmed cell death, essential for development and elimination of damaged cells.
凋亡是程序性细胞死亡，对发育和去除受损细胞至关重要。
6. DNA Replication and Protein Synthesis | DNA复制与蛋白质合成
DNA replication is semi-conservative, proven by Meselson and Stahl. DNA helicase unzips the double helix, and DNA polymerase synthesises new strands in the 5' to 3' direction, using the original strands as templates. The leading strand is continuous; the lagging strand is formed in Okazaki fragments, joined by DNA ligase. Transcription: RNA polymerase synthesises mRNA complementary to the template strand of DNA. In eukaryotes, pre-mRNA is spliced to remove introns. Translation: ribosomes read the mRNA codons; tRNA anticodons bring specific amino acids, and peptide bonds form, producing a polypeptide.
DNA 复制是半保留的，由 Meselson 和 Stahl 证明。DNA 解旋酶解开双螺旋，DNA 聚合酶从 5' 到 3' 合成新链，以原有链为模板。前导链连续合成；滞后链形成冈崎片段，由 DNA 连接酶连接。转录：RNA 聚合酶合成与 DNA 模板链互补的 mRNA。在真核生物中，前体 mRNA 经过剪接去除内含子。翻译：核糖体读取 mRNA 密码子；tRNA 反密码子携带特定氨基酸，形成肽键，产生多肽。
- Genetic code: degenerate (multiple codons for one amino acid), universal, non-overlapping / 遗传密码：简并性（一个氨基酸多个密码子），通用性，非重叠性
- Mutations: substitution (silent, missense, nonsense), insertion/deletion cause frameshift / 突变：替换（沉默、错义、无义），插入/缺失导致移码突变
7. Genetics and Inheritance Patterns | 遗传学与遗传模式
Monohybrid crosses follow Mendel's law of segregation; dihybrid crosses illustrate independent assortment. Phenotype ratios can be predicted using Punnett squares. Codominance (both alleles expressed, e.g., AB blood group) and incomplete dominance (blended phenotype) extend Mendelian patterns. Sex linkage is shown by genes on the X chromosome, e.g., haemophilia and colour blindness, more common in males.
单杂交遵循孟德尔分离定律；双杂交说明自由组合。表型比可通过旁氏表预测。共显性（两个等位基因都表达，如 AB 血型）和不完全显性（混合表型）扩展了孟德尔模式。伴性遗传由 X 染色体上的基因引起，如血友病和色盲，男性更常见。
- Epistasis: one gene masks the expression of another; e.g., coat colour in Labrador retrievers / 上位效应：一个基因掩盖另一个基因的表达；例如拉布拉多犬的毛色
- Chi-squared test: Σ (O-E)² / E, used to test goodness of fit between observed and expected ratios / 卡方检验：Σ (O-E)² / E，用于检验观察值与期望值比率的拟合优度
e frequencies in a population, assuming no mutation, migration, selection, large population, and random mating.
哈代-温伯格原理：p + q = 1，p² + 2pq + q² = 1，用于计算种群中的等位基因频率，假设没有突变、迁移、选择、大种群和随机交配。
8. Evolution and Natural Selection | 进化与自然选择
Evolution is a change in allele frequency in a population over time. Darwin's theory of natural selection states that individuals with advantageous alleles are more likely to survive and reproduce, passing on these alleles. Variation arises from mutation, meiosis (crossing over, independent assortment), and random fertilisation. Selection can be stabilising, directional, or disruptive. Speciation requires reproductive isolation (geographical or temporal) leading to accumulation of genetic differences.
进化是种群中等位基因频率随时间的变化。达尔文的自然选择理论认为，具有有利等位基因的个体更可能生存和繁殖，将这些等位基因传递下去。变异来源于突变、减数分裂（交叉互换、自由组合）和随机受精。选择可以是稳定性、定向性或分裂性。物种形成需要生殖隔离（地理或时间隔离）导致遗传差异的积累。
- Antibiotic resistance: example of directional selection; bacteria with resistance genes survive and multiply / 抗生素耐药性：定向选择的一个例子；具有耐药基因的细菌存活并繁殖
- Allopatric vs sympatric speciation: geographic barrier vs reproductive isolation within same area / 异域与同域物种形成：地理障碍 vs 同一区域内的生殖隔离
9. Ecosystems and Energy Transfer | 生态系统与能量传递
energy. Energy is transferred along food chains through trophic levels, but only about 10% GPP) - respiratory losses. Pyramids of energy are always upright. Nutrient cycles, such as the nitrogen cycle and carbon cycle, involve decomposition, nitrification, denitrification, and fixation.
能量通过光合作用进入生态系统。生产者（自养生物）将光能转化为化学能。能量沿食物链通过营养级传递，但只有约 10% 传递到下一级；其余以热量形式通过呼吸损失，或以粪便和未被摄食部分损失。净初级生产力 (NPP) = 总初级生产力 (GPP) - 呼吸损失。能量金字塔总是正立的。养分循环，如氮循环和碳循环，涉及分解作用、硝化作用、反硝化作用和固氮作用。
- Calculating energy efficiency: (energy in biomass at higher level / energy in biomass at lower level) × 100 / 能量效率计算：(较高营养级生物量能量 / 较低营养级生物量能量) × 100
- Carbon cycle: photosynthesis fixes CO₂; respiration, combustion, and decomposition release CO₂ / 碳循环：光合作用固定 CO₂；呼吸作用、燃烧和分解作用释放 CO₂
- Nitrogen cycle: nitrogen fixation (bacteria like Rhizobium), nitrification (Nitrosomonas, Nitrobacter), denitrification / 氮循环：固氮作用（根瘤菌等细菌），硝化作用（亚硝化单胞菌、硝化杆菌），反硝化作用
10. Homeostasis and the Kidney | 稳态与肾脏
Homeostasis is the maintenance of a stable internal environment, using negative feedback systems. Blood glucose regulation involves insulin and glucagon from the pancreas. Insulin lowers blood glucose by increasing cell uptake and glycogenesis; glucagon raises it by glycogenolysis and gluconeogenesis. Osmoregulation is controlled by the kidneys: when water potential is low, ADH is released from the pituitary gland, increasing the permeability of collecting ducts to water, so more water is reabsorbed and urine becomes concentrated.
稳态是通过负反馈系统维持稳定内环境。血糖调节涉及胰腺分泌的胰岛素和胰高血糖素。胰岛素通过增加细胞摄取和糖原生成降低血糖；胰高血糖素通过糖原分解和糖异生升高血糖。渗透调节由肾脏控制：当水势低时，垂体释放 ADH，增加集合管对水的通透性，因此更多的水被重吸收，尿浓缩。
- Nephron structure: Bowman's capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule, collecting duct / 肾单位结构：鲍曼囊，近曲小管，亨氏袢，远曲小管，集合管
- Ultrafiltration: occurs in Bowman's capsule, driven by high hydrostatic pressure; filtrate contains water, glucose, ions, urea / 超滤作用：发生在鲍曼囊，由高静水压驱动；滤液含有水、葡萄糖、离子、尿素
- Selective reabsorption: in proximal convoluted tubule, all glucose and most ions are reabsorbed by active transport and co-transport / 选择性重吸收：在近曲小管，所有葡萄糖和大部分离子通过主动运输和协同运输被重吸收
The loop of Henle creates a concentration gradient in the medulla, enabling further water reabsorption from the collecting duct under ADH control. Osmoreceptors in the hypothalamus detect changes in blood water potential and regulate ADH secretion.
亨氏袢在髓质建立浓度梯度，使得在 ADH 控制下更多水分从集合管重吸收。下丘脑的渗透压感受器检测血液水势的变化并调节 ADH 分泌。
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