📚 Core Knowledge Review for Pre-U OCR Biology | Pre-U OCR 生物核心知识点梳理
Mastering the Pre-U OCR Biology syllabus requires a firm grasp of fundamental concepts spanning molecular biology, genetics, physiology, ecology, and evolution. This revision article condenses the essential knowledge into focused sections, pairing clear English explanations with Chinese translations to support bilingual learning. Each core area is presented with precision, mirroring the structure and depth expected in the examination.
掌握 Pre-U OCR 生物学大纲需要对涵盖分子生物学、遗传学、生理学、生态学和进化的基本概念有牢固的理解。这篇复习文章将核心知识浓缩到重点小节中，将清晰的英文解释与中文翻译配对，以支持双语学习。每个核心领域的呈现力求精准，贴合考试所要求的结构和深度。
1. Cell Structure and Function | 细胞结构与功能
All living organisms are composed of cells, which can be categorised as prokaryotic or eukaryotic. Eukaryotic cells contain a membrane-bound nucleus and organelles such as mitochondria, the endoplasmic reticulum, and the Golgi apparatus. Prokaryotic cells lack a nucleus and most membrane-bound organelles but possess a cell wall, circular DNA, and 70S ribosomes. The ultrastructure of cells can be revealed by electron microscopy, while optical microscopy remains useful for observing larger structures. Key distinctions include the presence of peptidoglycan in bacterial cell walls and cellulose in plant cell walls.
所有生物体都由细胞组成，细胞可分为原核细胞和真核细胞。真核细胞含有膜包围的细胞核以及线粒体、内质网和高尔基体等细胞器。原核细胞没有细胞核和大多数膜包围的细胞器，但具有细胞壁、环状DNA和70S核糖体。细胞的超微结构可通过电子显微镜揭示，而光学显微镜仍可用于观察较大结构。关键区别包括细菌细胞壁中存在的肽聚糖和植物细胞壁中存在的纤维素。
Organelles have specific functions: mitochondria are the sites of aerobic respiration, producing ATP; ribosomes synthesise proteins; the rough endoplasmic reticulum processes and transports proteins; and lysosomes contain hydrolytic enzymes for intracellular digestion. In plants, chloroplasts carry out photosynthesis, and a large permanent vacuole maintains turgor pressure. Viruses are acellular, consisting of genetic material enclosed in a protein coat, and they replicate only inside host cells.
细胞器具有特定功能：线粒体是有氧呼吸的场所，产生ATP；核糖体合成蛋白质；粗面内质网加工和运输蛋白质；溶酶体含有用于细胞内消化的水解酶。在植物中，叶绿体进行光合作用，而大型中央液泡维持膨胀压。病毒是非细胞的，由包裹在蛋白质外壳中的遗传物质组成，它们只能在宿主细胞内复制。
2. Biological Molecules | 生物分子
Living organisms are built from carbon-based compounds. Carbohydrates include monosaccharides (e.g., glucose, fructose), disaccharides (e.g., sucrose, lactose), and polysaccharides (e.g., starch, glycogen, cellulose). Glucose has isomers α-glucose and β-glucose, which determine the structure and function of polymers. Starch, a storage polysaccharide in plants, is a mixture of amylose (α-1,4 glycosidic bonds, helical) and amylopectin (α-1,4 and α-1,6 bonds, branched). Glycogen has more extensive branching, while cellulose, composed of β-glucose, forms straight chains with hydrogen bonds between parallel chains, providing structural strength.
生物体由碳基化合物构成。碳水化合物包括单糖（如葡萄糖、果糖）、二糖（如蔗糖、乳糖）和多糖（如淀粉、糖原、纤维素）。葡萄糖具有异构体α-葡萄糖和β-葡萄糖，这决定了聚合物的结构和功能。淀粉是植物中的储存多糖，由直链淀粉（α-1,4糖苷键，螺旋状）和支链淀粉（α-1,4和α-1,6键，分支状）的混合物组成。糖原分支更为广泛，而由β-葡萄糖构成的纤维素形成直链，平行链间有氢键，提供结构强度。
Lipids are diverse hydrophobic molecules. Triglycerides consist of one glycerol molecule esterified to three fatty acid tails; they function as energy stores and insulation. Phospholipids have a phosphate-containing head and two fatty acid tails, forming the bilayer of cell membranes. Steroids, such as cholesterol, modulate membrane fluidity and serve as precursors for hormones. Proteins are polymers of amino acids joined by peptide bonds. The primary structure is the amino acid sequence; secondary structures include α-helices and β-pleated sheets, stabilised by hydrogen bonds; tertiary structure is the overall 3D folding due to interactions between R-groups; quaternary structure involves multiple polypeptide subunits (e.g., haemoglobin).
脂质是多样的疏水分子。甘油三酯由一个甘油分子与三个脂肪酸尾酯化而成；它们用作能量储存和隔热。磷脂具有含磷酸基的头部和两条脂肪酸尾，形成细胞膜的双层。类固醇，如胆固醇，调节膜流动性并作为激素的前体。蛋白质是由氨基酸通过肽键连接而成的聚合物。一级结构是氨基酸序列；二级结构包括α-螺旋和β-折叠片，由氢键稳定；三级结构是由于R基团间相互作用形成的整体三维折叠；四级结构涉及多个多肽亚基（例如血红蛋白）。
3. Enzymes | 酶
Enzymes are globular proteins that act as biological catalysts, lowering activation energy without being consumed. Their activity depends on the specific three-dimensional shape of the active site, which is complementary to the substrate. The induced-fit model explains that the active site undergoes a conformational change upon substrate binding, stressing bonds and facilitating the reaction. Enzyme kinetics can be described by the Michaelis-Menten equation; Vmax represents the maximum rate when all active sites are saturated, and Km indicates the substrate concentration at half Vmax.
酶是球状蛋白质，作为生物催化剂，在降低活化能的同时自身不被消耗。它们的活性依赖于活性位点特定的三维形状，该形状与底物互补。诱导契合模型解释，活性位点在底物结合时发生构象变化，压迫键并促进反应。酶动力学可用米氏方程描述；Vmax代表所有活性位点饱和时的最大速率，Km表示半Vmax时的底物浓度。
Factors affecting enzyme activity include temperature, pH, enzyme concentration, and substrate concentration. Most enzymes have an optimum temperature and pH; deviations lead to reduced activity or irreversible denaturation. Competitive inhibitors bind to the active site, and their effect can be overcome by increasing substrate concentration. Non-competitive inhibitors bind elsewhere, altering the enzyme’s shape. End-product inhibition is a common regulatory mechanism in metabolic pathways.
影响酶活性的因素包括温度、pH、酶浓度和底物浓度。大多数酶有最适温度和pH；偏离会导致活性降低或不可逆变性。竞争性抑制剂与活性位点结合，其作用可通过增加底物浓度来克服。非竞争性抑制剂结合在别处，改变酶的形状。终产物抑制是代谢途径中常见的调控机制。
4. Cell Membranes and Transport | 细胞膜与运输
The fluid mosaic model describes cell membranes as phospholipid bilayers with embedded proteins, cholesterol, and glycocalyx. Phospholipids provide a selectively permeable barrier; their fatty acid tails face inward, while hydrophilic heads face the aqueous environments. Intrinsic proteins span the bilayer, functioning as channels, carriers, or pumps. Extrinsic proteins are peripheral and often involved in signalling. Cholesterol restricts phospholipid movement, maintaining membrane stability across temperature changes.
流动镶嵌模型将细胞膜描述为嵌入蛋白质、胆固醇和糖被的磷脂双分子层。磷脂提供选择性渗透屏障；其脂肪酸尾朝向内部，而亲水头部朝向水相环境。内在蛋白横跨双分子层，起到通道、载体或泵的作用。外在蛋白是外周蛋白，常参与信号传导。胆固醇限制磷脂运动，在温度变化时维持膜稳定性。
Transport across membranes occurs by passive and active mechanisms. Simple diffusion involves movement of small, non-polar molecules down their concentration gradient. Facilitated diffusion uses channel proteins or carrier proteins without energy input. Osmosis is the net movement of water across a partially permeable membrane from a region of higher water potential to lower water potential. Active transport requires ATP and carrier proteins to move substances against their concentration gradient. Bulk transport includes endocytosis (phagocytosis, pinocytosis) and exocytosis.
跨膜运输通过被动和主动机制进行。简单扩散涉及小的非极性分子沿其浓度梯度移动。易化扩散使用通道蛋白或载体蛋白，无需能量输入。渗透是水通过部分透性膜的净移动，从较高水势区域向较低水势区域。主动运输需要ATP和载体蛋白将物质逆浓度梯度移动。大量运输包括胞吞作用（吞噬、胞饮）和胞吐作用。
5. The Cell Cycle and Mitosis | 细胞周期与有丝分裂
The cell cycle consists of interphase (G1, S, G2) and the mitotic phase (mitosis and cytokinesis). During G1, the cell grows and synthesises proteins. In S phase, DNA is replicated, resulting in two identical sister chromatids held together at the centromere. G2 involves further growth and preparation for division. Mitosis ensures genetic continuity: prophase (chromosomes condense, nuclear envelope breaks down), metaphase (chromosomes align at the equator), anaphase (sister chromatids separate to opposite poles), and telophase (nuclear envelopes reform). Cytokinesis divides the cytoplasm, producing two genetically identical daughter cells.
细胞周期包括间期（G1、S、G2）和有丝分裂期（有丝分裂和胞质分裂）。在G1期，细胞生长并合成蛋白质。S期DNA复制，产生两个相同姐妹染色单体，由着丝粒连接。G2期涉及进一步生长和分裂准备。有丝分裂确保遗传连续性：前期（染色体凝集，核膜解体），中期（染色体排列在赤道板），后期（姐妹染色单体分离到相反两极），末期（核膜重新形成）。胞质分裂分割细胞质，产生两个基因相同的子细胞。
Mitosis is used for growth, tissue repair, and asexual reproduction. Control of the cell cycle is critical; checkpoints at G1/S and G2/M ensure fidelity. Cyclins and cyclin-dependent kinases regulate progression. Uncontrolled cell division can lead to cancer, characterised by mutations in proto-oncogenes or tumour suppressor genes.
有丝分裂用于生长、组织修复和无性繁殖。细胞周期的控制至关重要；G1/S和G2/M检查点确保准确性。细胞周期蛋白和细胞周期蛋白依赖性激酶调节进程。不受控制的细胞分裂可导致癌症，其特征是原癌基因或肿瘤抑制基因的突变。
6. DNA Replication and Protein Synthesis | DNA复制与蛋白质合成
DNA replication is semi-conservative, as demonstrated by Meselson and Stahl. The enzyme DNA helicase unwinds the double helix, and single-strand binding proteins stabilise the separated strands. DNA polymerase synthesises new strands in the 5′ to 3′ direction, requiring a primer. The leading strand is replicated continuously; the lagging strand is synthesised in short Okazaki fragments, later joined by DNA ligase. Proofreading mechanisms ensure high fidelity.
DNA复制是半保留的，由Meselson和Stahl的实验所证实。DNA解旋酶解开双螺旋，单链结合蛋白稳定分开的链。DNA聚合酶从5’向3’方向合成新链，需要引物。前导链连续复制；后随链以短的冈崎片段合成，随后由DNA连接酶连接。校对机制确保高保真度。
Protein synthesis involves transcription and translation. During transcription, RNA polymerase binds to a promoter and synthesises a complementary mRNA strand from the template DNA strand. In eukaryotes, pre-mRNA is processed: a 5′ cap and poly-A tail are added, and introns are spliced out. Translation occurs on ribosomes: mRNA codons are recognised by tRNA anticodons carrying specific amino acids. Peptide bond formation proceeds from the A site to the P site, producing a polypeptide chain. The genetic code is degenerate, universal, and non-overlapping.
蛋白质合成包括转录和翻译。在转录过程中，RNA聚合酶与启动子结合，以模板DNA链合成互补的mRNA链。在真核生物中，前体mRNA经过加工：添加5’帽子和poly-A尾巴，并剪接去除内含子。翻译在核糖体上进行：mRNA密码子由携带特定氨基酸的tRNA反密码子识别。肽键形成从A位到P位进行，产生多肽链。遗传密码是简并的、通用的和不重叠的。
7. Patterns of Inheritance | 遗传模式
Mendelian genetics describes the behaviour of alleles during monohybrid and dihybrid crosses. The law of segregation states that each gamete receives only one allele for each gene. The law of independent assortment applies to genes on different chromosomes. Genotype refers to the genetic makeup, while phenotype is the observable trait. Dominant alleles mask the effect of recessive alleles in heterozygotes. Codominance occurs when both alleles are expressed equally (e.g., AB blood group). Incomplete dominance results in an intermediate phenotype.
孟德尔遗传学描述了单杂交和双杂交中等位基因的行为。分离定律指出每个配子只获得每个基因的一个等位基因。自由组合定律适用于不同染色体上的基因。基因型指遗传组成，表型是观察到的性状。显性等位基因在杂合子中掩盖隐性等位基因的效应。共显性发生在两个等位基因同等表达时（例如AB血型）。不完全显性导致中间表型。
Sex linkage refers to genes located on sex chromosomes, most often the X chromosome. Examples include haemophilia and red-green colour blindness. Because males are hemizygous for X-linked loci, recessive traits appear more frequently in males. Autosomal linkage occurs when genes are on the same chromosome and tend to be inherited together, unless separated by crossing over. Chi-squared tests can assess the significance of deviations from expected ratios. Pedigree analysis reveals inheritance patterns.
伴性遗传指位于性染色体（通常是X染色体）上的基因。例子包括血友病和红绿色盲。由于男性对于X连锁基因座是半合子，隐性性状在男性中更频繁出现。常染色体连锁发生在基因位于同一染色体上且倾向于一起遗传时，除非通过交换分离。卡方检验可以评估偏离预期比例的显著性。系谱分析揭示遗传模式。
8. Evolution and Speciation | 进化与物种形成
Evolution is the change in allele frequencies in a population over time. The Hardy–Weinberg principle predicts that allele and genotype frequencies remain constant from generation to generation in the absence of disturbing factors (large population, random mating, no mutation, no migration, no natural selection). The equation p² + 2pq + q² = 1 describes genotype frequencies, where p and q are frequencies of two alleles. Deviations from Hardy–Weinberg equilibrium imply evolutionary forces at work.
进化是种群中等位基因频率随时间的变化。哈代–温伯格原理预测，在没有干扰因素（大种群、随机交配、无突变、无迁移、无自然选择）的情况下，等位基因和基因型频率在代际间保持恒定。方程p² + 2pq + q² = 1描述基因型频率，其中p和q是两个等位基因的频率。偏离哈代–温伯格平衡意味着进化力量的作用。
Natural selection acts on phenotypic variation conferred by alleles. Stabilising selection favours intermediate phenotypes; directional selection shifts the mean; disruptive selection favours extremes. Isolation mechanisms lead to speciation. Allopatric speciation occurs when populations are geographically separated, preventing gene flow. Sympatric speciation arises within a shared habitat, often through reproductive isolation mechanisms such as temporal, behavioural, or mechanical barriers. Postzygotic barriers include hybrid inviability or infertility.
自然选择作用于由等位基因赋予的表型变异。稳定化选择偏好中间表型；定向选择使均值偏移；分裂选择偏好极端表型。隔离机制导致物种形成。异域物种形成发生在种群被地理隔离，阻止基因流动时。同域物种形成在同一栖息地内发生，通常通过生殖隔离机制，如时间、行为或机械屏障。合子后屏障包括杂种不活或不育。
9. Energy Transfer and Nutrient Cycles | 能量传递与养分循环
Ecosystems depend on energy flow and nutrient recycling. Photosynthesis captures light energy to fix CO₂ into organic compounds. The light-dependent reactions in the thylakoid membrane generate ATP and reduced NADP. The light-independent reactions (Calvin cycle) use ATP and reduced NADP to synthesise triose phosphate, which can be converted to glucose, starch, and other carbohydrates. The overall equation is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
生态系统依赖能量流动和养分循环。光合作用捕获光能以将CO₂固定为有机化合物。类囊体膜上的光反应产生ATP和还原型NADP。暗反应（卡尔文循环）利用ATP和还原型NADP合成磷酸丙糖，后者可转化为葡萄糖、淀粉和其他碳水化合物。总体方程式为：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。
In respiration, glycolysis occurs in the cytoplasm, producing pyruvate, ATP, and reduced NAD. The link reaction converts pyruvate to acetyl CoA, releasing CO₂. The Krebs cycle in the mitochondrial matrix generates reduced NAD, reduced FAD, and ATP by substrate-level phosphorylation. The electron transport chain uses the reduced coenzymes to produce a large yield of ATP via oxidative phosphorylation. Anaerobic respiration in animals produces lactate; in yeasts, ethanol and CO₂.
在呼吸作用中，糖酵解在细胞质中进行，产生丙酮酸、ATP和还原型NAD。连接反应将丙酮酸转化为乙酰辅酶A，并释放CO₂。线粒体基质中的克雷布斯循环通过底物水平磷酸化产生还原型NAD、还原型FAD和ATP。电子传递链利用还原辅酶通过氧化磷酸化产生大量ATP。动物无氧呼吸产生乳酸；酵母产生乙醇和CO₂。
The carbon cycle involves photosynthesis, respiration, decomposition, combustion, and the formation of fossil fuels. The nitrogen cycle includes nitrogen fixation (by bacteria such as Rhizobium and Azotobacter), nitrification (ammonium to nitrite to nitrate by Nitrosomonas and Nitrobacter), assimilation, ammonification, and denitrification. Nitrogen-fixing bacteria convert N₂ gas into ammonium; nitrifying bacteria oxidise ammonium to nitrate, which plants absorb. Denitrifying bacteria return nitrogen gas to the atmosphere.
碳循环涉及光合作用、呼吸作用、分解作用、燃烧和化石燃料形成。氮循环包括固氮（由根瘤菌和固氮菌等细菌进行）、硝化作用（铵盐→亚硝酸盐→硝酸盐，由亚硝酸菌和硝化细菌进行）、同化作用、氨化作用和反硝化作用。固氮细菌将N₂气体转化为铵；硝化细菌将铵氧化为植物吸收的硝酸盐。反硝化细菌将氮气返回大气。
10. Nervous and Hormonal Communication | 神经与激素通讯
Organisms use nervous and endocrine systems to coordinate responses. The resting potential of a neuron is around –70 mV, maintained by the sodium-potassium pump (3Na⁺ out, 2K⁺ in) and differential permeability. An action potential is triggered when depolarisation reaches the threshold; voltage-gated Na⁺ channels open, causing rapid depolarisation, followed by inactivation of Na⁺ channels and opening of K⁺ channels for repolarisation. Saltatory conduction in myelinated axons increases speed by limiting depolarisation to nodes of Ranvier.
生物体使用神经系统和内分泌系统来协调反应。神经元的静息电位约为–70 mV，由钠钾泵（排出3个Na⁺，摄入2个K⁺）和差异通透性维持。当去极化达到阈值时触发动作电位；电压门控Na⁺通道开放，引起快速去极化，随后Na⁺通道失活，K⁺通道开放进行复极化。有髓轴突中的跳跃传导通过将去极化限制在郎飞结来提高速度。
Synaptic transmission involves calcium ion influx, vesicle exocytosis releasing neurotransmitter into the cleft, binding to postsynaptic receptors, and summation. Excitatory postsynaptic potentials (EPSPs) depolarise, while inhibitory postsynaptic potentials (IPSPs) hyperpolarise. Hormonal communication is slower but longer-lasting. Endocrine glands secrete hormones into the bloodstream; receptors are specific. Examples include adrenaline (fight-or-flight, binds to cell membrane receptors, activates cAMP second messenger) and steroid hormones (e.g., oestrogen, binds to intracellular receptors, modulating transcription).
突触传递涉及钙离子内流，囊泡胞吐释放神经递质到间隙，与突触后受体结合，以及总和作用。兴奋性突触后电位（EPSPs）去极化，而抑制性突触后电位（IPSPs）超极化。激素通讯较慢但更持久。内分泌腺分泌激素进入血液；受体是特异的。例子包括肾上腺素（战斗或逃跑，与细胞膜受体结合，激活cAMP第二信使）和类固醇激素（如雌激素，与细胞内受体结合，调节转录）。
11. Homeostasis and Excretion | 稳态与排泄
Homeostasis is the maintenance of a constant internal environment. Negative feedback mechanisms counteract deviations from a set point. The control of blood glucose involves insulin and glucagon. After a meal, β-cells in the islets of Langerhans secrete insulin, promoting glucose uptake and glycogenesis. When blood glucose falls, α-cells secrete glucagon, stimulating glycogenolysis and gluconeogenesis. Diabetes mellitus type 1 results from autoimmune destruction of β-cells; type 2 involves insulin resistance.
稳态是维持恒定内环境。负反馈机制对抗偏离设定点。血糖的控制涉及胰岛素和胰高血糖素。饭后，胰岛β细胞分泌胰岛素，促进葡萄糖摄取和糖原生成。当血糖下降时，α细胞分泌胰高血糖素，刺激糖原分解和糖异生。1型糖尿病源于β细胞自身免疫破坏；2型涉及胰岛素抵抗。
The kidneys excrete nitrogenous waste and regulate water potential. The nephron is the functional unit: ultrafiltration in the Bowman’s capsule produces glomerular filtrate. Selective reabsorption in the proximal convoluted tubule reclaims glucose, amino acids, ions, and water. The loop of Henle creates a concentration gradient in the medulla. Osmoregulation is controlled by ADH, which increases water permeability of the collecting duct. Excretion also involves the liver, which deaminates excess amino acids, producing urea for excretion.
肾脏排出含氮废物并调节水势。肾单位是功能单位：鲍曼囊的超滤产生肾小球滤液。近曲小管的选择性重吸收回收葡萄糖、氨基酸、离子和水。亨利袢在髓质中建立浓度梯度。渗透调节由ADH控制，增加集合管对水的通透性。排泄还涉及肝脏，肝脏将多余的氨基酸脱氨，产生尿素供排泄。
12. Biotechnology and Gene Technologies | 生物技术与基因技术
Recombinant DNA technology involves cutting DNA with restriction endonucleases at specific recognition sites, producing sticky or blunt ends. DNA ligase joins fragments. Vectors such as plasmids or bacteriophages carry the gene of interest into host cells. Transformation, electroporation, or transduction can introduce recombinant DNA. Gene cloning produces multiple copies of a gene; PCR (polymerase chain reaction) amplifies DNA in vitro using Taq polymerase, primers, and thermal cycling.
重组DNA技术涉及用限制性内切酶在特定识别位点切割DNA，产生黏性末端或平末端。DNA连接酶连接片段。载体如质粒或噬菌体将目的基因带入宿主细胞。转化、电穿孔或转导可引入重组DNA。基因克隆产生多个基因拷贝；PCR（聚合酶链式反应）在体外使用Taq聚合酶、引物和热循环扩增DNA。
Gel electrophoresis separates DNA fragments by size; smaller fragments migrate faster. DNA profiling uses short tandem repeats (STRs) for forensic identification. Genetic engineering has applications in producing human insulin, growth hormone, and genetically modified crops (e.g., Bt corn). Gene therapy aims to replace defective alleles. Ethical, social, and safety considerations are integral to biotechnological advances, including concerns about GMOs and gene editing techniques like CRISPR-Cas9.
凝胶电泳根据大小分离DNA片段；较小片段迁移更快。DNA图谱分析使用短串联重复序列（STRs）进行法医鉴定。基因工程在产生人胰岛素、生长激素和转基因作物（如Bt玉米）中有应用。基因疗法旨在替换有缺陷的等位基因。伦理、社会和安全考虑是生物技术进步不可分割的部分，包括对转基因生物和CRISPR-Cas9等基因编辑技术的担忧。
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