📚 IB & Edexcel Biology: Last-Minute Revision Notes | IB与Edexcel生物：考前冲刺笔记
Whether you are sitting the IB Biology exam or the Edexcel A-level Biology paper, these last-minute revision notes distill the essential concepts and high-yield topics into one powerful bilingual resource. Use this guide to quickly refresh your memory on cell biology, biochemistry, genetics, ecology, and more – with each point presented in English immediately followed by its Chinese translation for clarity and retention. Let’s dive into the critical content that will help you maximise your marks in the final hours before the test.
无论你参加的是IB生物还是Edexcel A-level生物考试，这份考前冲刺笔记都将核心概念和高频考点浓缩为一份高效的双语复习资料。笔记中每个要点都采用“先英文后中文”的对应形式，帮助你快速回顾细胞生物学、生物化学、遗传学、生态学等关键内容，在考前最后关头强化记忆、锁定得分。现在让我们一起梳理那些决定成绩的关键知识。
1. Key Cellular Structures and Functions | 关键细胞结构与功能
All living organisms are built from cells. Prokaryotic cells, such as bacteria, lack a membrane-bound nucleus and organelles, whereas eukaryotic cells (protists, fungi, plants, and animals) possess a true nucleus and compartmentalised organelles including mitochondria, the endoplasmic reticulum, and the Golgi apparatus. Plant cells are distinguished by a cellulose cell wall, a large permanent vacuole, and chloroplasts – the sites of photosynthesis.
所有生物体都由细胞构成。原核细胞（如细菌）没有膜包被的细胞核和细胞器，而真核细胞（原生生物、真菌、植物和动物）具有真正的细胞核以及线粒体、内质网、高尔基体等分隔化的细胞器。植物细胞的独特之处在于具有纤维素细胞壁、大型中央液泡和光合作用场所——叶绿体。
The fluid-mosaic model describes the plasma membrane as a phospholipid bilayer with embedded proteins, cholesterol (in animal cells), and glycoproteins. Membrane proteins serve as channels, pumps, receptors, and enzymes. Transport across the membrane includes simple diffusion, facilitated diffusion via channel or carrier proteins, osmosis (water movement), and active transport requiring ATP. Bulk transport occurs by endocytosis and exocytosis.
流动镶嵌模型将质膜描述为磷脂双分子层，其中嵌有蛋白质、胆固醇（动物细胞）和糖蛋白。膜蛋白充当通道、泵、受体和酶。跨膜运输包括简单扩散、借助通道或载体蛋白的易化扩散、渗透（水的运动）以及需要消耗ATP的主动运输。大块物质通过胞吞和胞吐作用进出细胞。
- Prokaryotic vs Eukaryotic comparison:
- 原核细胞与真核细胞的比较：
| Feature | Prokaryote | Eukaryote |
| Nucleus | Absent (nucleoid region) | Present |
| DNA | Circular, naked | Linear, histone-bound |
| Ribosomes | 70S | 80S |
| Membrane-bound organelles | None | Many |
| 特征 | 原核细胞 | 真核细胞 |
| 细胞核 | 无（拟核区） | 有 |
| DNA | 环状、裸露 | 线状、与组蛋白结合 |
| 核糖体 | 70S | 80S |
| 膜包细胞器 | 无 | 多种 |
2. Biological Molecules: The Building Blocks | 生物分子：构建基石
Carbohydrates, lipids, proteins, and nucleic acids are the four major groups of biological macromolecules. Carbohydrates include monosaccharides (e.g., glucose, C₆H₁₂O₆), disaccharides (sucrose, lactose), and polysaccharides (starch, glycogen, cellulose). They are composed of carbon, hydrogen, and oxygen in a 1:2:1 ratio and serve as immediate energy sources and structural components.
碳水化合物、脂质、蛋白质和核酸是四大类生物大分子。碳水化合物包括单糖（如葡萄糖，C₆H₁₂O₆）、二糖（蔗糖、乳糖）和多糖（淀粉、糖原、纤维素）。它们由碳、氢、氧按1:2:1的比例构成，是即时能量来源和结构组分。
Lipids are non-polar molecules including triglycerides (glycerol + three fatty acids) and phospholipids. Triglycerides are energy stores, whereas phospholipids form the bilayer of membranes. Steroids, such as cholesterol, are also lipids. Saturated fatty acids have no double bonds; unsaturated fatty acids contain one or more double bonds, which cause kinks and influence membrane fluidity.
脂质是非极性分子，包括甘油三酯（甘油+三个脂肪酸）和磷脂。甘油三酯用于能量储存，而磷脂构成生物膜的双分子层。类固醇（如胆固醇）也属于脂质。饱和脂肪酸不含双键，不饱和脂肪酸含有一个或多个双键，使链发生弯曲并影响膜的流动性。
Proteins are polymers of amino acids joined by peptide bonds. The primary structure is the linear sequence of amino acids; secondary structure includes alpha-helices and beta-pleated sheets formed by hydrogen bonding; tertiary structure is the overall 3D folding stabilised by hydrogen bonds, ionic bonds, hydrophobic interactions, and disulfide bridges; quaternary structure involves multiple polypeptide subunits (e.g., haemoglobin). Protein shape is critical for its function.
蛋白质是由氨基酸通过肽键连接而成的多聚体。一级结构是氨基酸的线性序列；二级结构包括由氢键形成的α-螺旋和β-折叠片；三级结构是氢键、离子键、疏水相互作用和二硫键稳定下的三维折叠；四级结构涉及多个多肽亚基（如血红蛋白）。蛋白质的形状对其功能至关重要。
Nucleic acids (DNA and RNA) are polymers of nucleotides. Each nucleotide consists of a pentose sugar, a phosphate group, and a nitrogenous base. DNA uses deoxyribose and the bases adenine, thymine, cytosine, and guanine; RNA contains ribose and uracil instead of thymine. The double helix structure of DNA enables semi-conservative replication and stores genetic information.
核酸（DNA和RNA）是核苷酸的多聚体。每个核苷酸由戊糖、磷酸基团和含氮碱基组成。DNA使用脱氧核糖和腺嘌呤、胸腺嘧啶、胞嘧啶、鸟嘌呤；RNA含有核糖，并以尿嘧啶代替胸腺嘧啶。DNA的双螺旋结构能够进行半保留复制并储存遗传信息。
3. Enzymes: Catalysts of Life | 酶：生命催化剂
Enzymes are globular proteins that act as biological catalysts, lowering activation energy without being consumed. The active site of an enzyme is a specific region that binds the substrate, forming an enzyme-substrate complex. The induced-fit model explains that the active site undergoes a conformational change upon substrate binding, optimising catalysis.
酶是球状蛋白，作为生物催化剂，能降低活化能而自身不被消耗。酶的活性部位是结合底物的特定区域，形成酶-底物复合物。诱导契合模型指出，活性部位在底物结合时发生构象改变，从而优化催化作用。
Enzyme activity is affected by temperature, pH, substrate concentration, and inhibitors. At extreme temperatures or pH values, enzymes denature – the active site loses its specific shape. Competitive inhibitors bind to the active site, competing with the substrate, while non-competitive inhibitors bind to an allosteric site, altering the active site’s shape. The Michaelis-Menten constant (Km) indicates the substrate concentration at half Vmax; a low Km means high affinity.
酶活性受温度、pH、底物浓度和抑制剂的影响。在极端温度或pH下，酶会变性——活性部位失去其特定形状。竞争性抑制剂与活性部位结合，与底物竞争；非竞争性抑制剂结合于别构部位，改变活性部位的形状。米氏常数（Km）表示达到最大反应速率一半时的底物浓度；Km值越小，亲和力越高。
4. Cell Respiration and Photosynthesis | 细胞呼吸与光合作用
Aerobic respiration uses glucose and oxygen to produce ATP, carbon dioxide, and water. The overall equation is:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP)
Respiration occurs in four stages: glycolysis (cytoplasm), link reaction, Krebs cycle (mitochondrial matrix), and the electron transport chain (inner mitochondrial membrane). Anaerobic respiration in animals produces lactate; in plants and yeast, it produces ethanol and CO₂.
有氧呼吸利用葡萄糖和氧气产生ATP、二氧化碳和水。总反应式为：
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 能量（ATP）
呼吸作用分为四个阶段：糖酵解（细胞质）、衔接反应、克雷布斯循环（线粒体基质）和电子传递链（线粒体内膜）。动物体内的无氧呼吸产生乳酸；植物和酵母中则产生乙醇和CO₂。
Photosynthesis converts light energy into chemical energy stored in glucose. The summary equation is:
6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂
It takes place in chloroplasts and includes the light-dependent reactions (thylakoid membrane) that produce ATP and NADPH, and the Calvin cycle (stroma) that fixes CO₂ using ATP and NADPH. The rate of photosynthesis is limited by light intensity, CO₂ concentration, and temperature.
光合作用将光能转化为储存在葡萄糖中的化学能。总反应式为：
6CO₂ + 6H₂O + 光 → C₆H₁₂O₆ + 6O₂
该过程发生在叶绿体中，包括光反应（类囊体膜）产生ATP和NADPH，以及卡尔文循环（基质）利用ATP和NADPH固定CO₂。光合作用速率受光照强度、CO₂浓度和温度的限制。
5. DNA Replication, Transcription & Translation | DNA复制、转录与翻译
DNA replication is semi-conservative: each new double helix consists of one original strand and one newly synthesised strand. The enzyme helicase unwinds the double helix, and DNA polymerase adds complementary nucleotides in the 5′ to 3′ direction. The leading strand is synthesised continuously, while the lagging strand is formed in Okazaki fragments, later joined by DNA ligase.
DNA复制是半保留的：每个新的双螺旋包含一条原始链和一条新合成的链。解旋酶解开双螺旋，DNA聚合酶以5’到3’的方向添加互补核苷酸。前导链连续合成，滞后链则通过冈崎片段合成，随后由DNA连接酶连接。
Transcription occurs in the nucleus: RNA polymerase binds to the promoter, unwinds DNA, and synthesises an mRNA strand complementary to the template strand. The mRNA undergoes post-transcriptional modification (5′ cap, poly-A tail, splicing) in eukaryotes. Translation takes place on ribosomes: the mRNA codons are read by tRNA anticodons, which bring specific amino acids. Peptide bonds form to build a polypeptide chain until a stop codon is reached.
转录发生在细胞核内：RNA聚合酶与启动子结合，解开DNA，并合成与模板链互补的mRNA链。真核生物中，mRNA需经过转录后修饰（5’帽子、poly-A尾巴、剪接）。翻译在核糖体上进行：mRNA上的密码子被tRNA的反密码子识别，tRNA携带特定的氨基酸。氨基酸间形成肽键，延伸多肽链，直至遇到终止密码子。
6. Cell Division: Mitosis and Meiosis | 细胞分裂：有丝分裂与减数分裂
Mitosis produces two genetically identical diploid daughter cells and is required for growth, repair, and asexual reproduction. It consists of prophase, metaphase, anaphase, and telophase (and cytokinesis). Meiosis produces four genetically non-identical haploid gametes and involves two successive divisions: meiosis I separates homologous chromosomes, and meiosis II separates sister chromatids. Crossing over in prophase I and independent assortment in metaphase I generate genetic variation.
有丝分裂产生两个遗传信息相同的二倍体子细胞，用于生长、修复和无性繁殖。其过程包括前期、中期、后期和末期（以及胞质分裂）。减数分裂产生四个遗传上不同的单倍体配子，包括两次连续分裂：减数第一次分裂分离同源染色体，减数第二次分裂分离姐妹染色单体。前期I的交叉互换和中期I的自由组合是遗传变异的来源。
| Feature | Mitosis | Meiosis |
| Number of divisions | One | Two |
| Daughter cell number | 2 | 4 |
| Ploidy | Diploid (2n) | Haploid (n) |
| Genetic variation | None (identical) | Yes (crossing over, independent assortment) |
| 特征 | 有丝分裂 | 减数分裂 |
| 分裂次数 | 一次 | 两次 |
| 子细胞数目 | 2 | 4 |
| 倍性 | 二倍体 (2n) | 单倍体 (n) |
| 遗传变异 | 无（相同子细胞） | 有（交叉互换、自由组合） |
7. Genetics and Inheritance | 遗传与变异
Mendelian genetics is founded on the principles of dominance, segregation, and independent assortment. A gene may exist in different alleles. The genotype is the combination of alleles (homozygous or heterozygous), and the phenotype is the observable trait. Monohybrid crosses predict a 3:1 phenotypic ratio in the F2 generation for a dominant-recessive trait; dihybrid crosses give a 9:3:3:1 ratio when genes are unlinked.
孟德尔遗传学建立在显性、分离和自由组合定律之上。基因可以以不同等位基因的形式存在。基因型是等位基因的组合（纯合或杂合），表型是可观察的性状。单因子杂交对于显-隐性性状在F2代中预期产生3:1的表型比例；当基因不连锁时，双因子杂交给出9:3:3:1的比例。
Some traits show co-dominance (both alleles expressed, e.g., AB blood type, IAIB) or incomplete dominance (blended phenotype). Sex-linked traits, usually carried on the X chromosome, display different patterns of inheritance between males and females. A chi-squared (χ²) test determines if observed ratios differ significantly from expected Mendelian ratios. The formula is:
χ² = Σ (O − E)² / E
某些性状表现为共显性（两个等位基因同时表达，如AB血型，IAIB）或不完全显性（表型混合）。伴性性状通常位于X染色体上，在男性和女性中表现出不同的遗传模式。卡方（χ²）检验用于判断观察值比例是否与预期孟德尔比例有显著差异。公式为：
χ² = Σ (O − E)² / E
8. Natural Selection and Evolution | 自然选择与进化
Darwin’s theory of evolution by natural selection requires variation within a population, overproduction of offspring, competition for limited resources, and differential survival and reproduction of individuals with advantageous traits. Over generations, allele frequencies change, leading to adaptation and evolution. Antibiotic resistance in bacteria is a well-documented example of natural selection under strong selective pressure.
达尔文自然选择进化论需要种群内存在变异、后代过量产生、对有限资源的竞争以及具有有利性状的个体存活和繁殖机会的差异。经多代传递，等位基因频率发生改变，导致适应和进化。细菌对抗生素产生耐药性是强大选择压下自然选择的经典实例。
Speciation occurs when populations become reproductively isolated. Allopatric speciation arises from geographical barriers (e.g., mountain ranges, rivers), while sympatric speciation occurs without physical separation, often due to behavioural or temporal isolation. Evidence for evolution includes fossil records, comparative anatomy (homologous and vestigial structures), molecular biology (DNA and protein similarities), and biogeography.
当种群之间出现生殖隔离时，物种形成便发生了。异域物种形成由地理屏障（山脉、河流）引起，而同域物种形成则在没有物理隔离的情况下出现，常源于行为或时间隔离。进化的证据包括化石记录、比较解剖学（同源器官和痕迹器官）、分子生物学（DNA和蛋白质的相似性）以及生物地理学。
9. Homeostasis and Negative Feedback | 稳态与负反馈
Homeostasis is the maintenance of a relatively stable internal environment. Negative feedback mechanisms detect deviations from a set point and initiate corrective responses. Key examples include thermoregulation (sweating, shivering, vasodilation, vasoconstriction) and blood glucose regulation (insulin and glucagon from the pancreas). Osmoregulation involves the kidney and antidiuretic hormone (ADH) to control water balance.
稳态是维持相对稳定的内环境。负反馈机制能够检测偏离设定点的变化并启动纠正性反应。典型例子包括体温调节（出汗、颤抖、血管舒张、血管收缩）和血糖调节（胰腺分泌的胰岛素和胰高血糖素）。渗透调节涉及肾脏和抗利尿激素（ADH）以控制水平衡。
In diabetes mellitus, blood glucose homeostasis is impaired. Type 1 diabetes results from destruction of β cells in the pancreas, leading to insufficient insulin; type 2 diabetes is characterised by insulin resistance. Controlling blood glucose is essential because chronic hyperglycaemia damages blood vessels and organs. Negative feedback also governs hormone secretion in the endocrine system, such as thyroxine regulation.
糖尿病患者的血糖稳态受损。1型糖尿病源于胰腺β细胞被破坏，导致胰岛素不足；2型糖尿病的特征是胰岛素抵抗。控制血糖至关重要，因为慢性高血糖会损害血管和器官。负反馈同样调控内分泌系统中的激素分泌，如甲状腺素的调节。
10. Ecology and Energy Transfer | 生态学与能量传递
An ecosystem consists of a community of living organisms interacting with the abiotic environment. Energy enters most ecosystems as sunlight and is captured by producers (plants, algae) during photosynthesis. Energy flows through trophic levels: producers → primary consumers → secondary consumers → tertiary consumers. At each level, approximately 10% of energy is transferred; the rest is lost as heat via respiration, waste, and uneaten materials.
生态系统由生物群落与非生物环境相互作用组成。能量以太阳光的形式进入大多数生态系统，通过光合作用被生产者（植物、藻类）捕获。能量沿营养级流动：生产者→初级消费者→次级消费者→三级消费者。每经过一个营养级，只有约10%的能量被传递，其余能量通过呼吸作用、废物和未被取食的部分以热的形式散失。
Food chains and food webs illustrate feeding relationships. Pyramids of energy, biomass, and numbers visually represent ecosystem structure. Productivity is measured as gross primary productivity (GPP) and net primary productivity (NPP = GPP − respiration). Nutrient cycles, including the carbon and nitrogen cycles, recycle matter. The carbon cycle involves photosynthesis, respiration, decomposition, combustion, and fossilisation. Human activities such as deforestation and burning fossil fuels increase atmospheric CO₂, contributing to global warming.
食物链和食物网显示了摄食关系。能量金字塔、生物量金字塔和数量金字塔直观地表示生态系统的结构。生产力可以用总初级生产力（GPP）和净初级生产力（NPP = GPP − 呼吸作用）来衡量。物质循环，包括碳循环和氮循环，实现物质的再利用。碳循环涉及光合作用、呼吸作用、分解作用、燃烧和化石形成。森林砍伐和化石燃料燃烧等人类活动增加了大气中的CO₂，导致全球变暖。
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