📚 High-Frequency Exam Topics for IB and Edexcel Biology | IB 与 Edexcel 生物高频考点总结
Whether you are preparing for IB Biology or Edexcel A Level Biology, certain topics appear year after year in examinations. Mastering these high-frequency areas builds a solid foundation, saves revision time and sharpens your ability to tackle data-based and extended-response questions. This article summarises the most tested concepts, clarifies common misunderstandings and presents them in concise English–Chinese pairs to support bilingual learners.
无论你正在准备 IB 生物还是 Edexcel A Level 生物考试，总有一些主题每年都会以不同形式出现。掌握这些高频考点不仅能打下扎实的基础，还能节省复习时间，增强你应对数据分析题和长篇论述题的能力。本文以简洁的中英对照方式，梳理最常考的概念，澄清常见误解，助力双语学习者高效备考。
1. Cell Structure & Function | 细胞结构与功能
Prokaryotic cells lack a membrane-bound nucleus and organelles; their DNA is circular and free in the cytoplasm. Eukaryotic cells possess a true nucleus and compartmentalised organelles such as mitochondria, the endoplasmic reticulum and the Golgi apparatus.
原核细胞没有膜包被的细胞核和细胞器，其 DNA 呈环状，游离在细胞质中。真核细胞拥有真正的细胞核和分区化的细胞器，如线粒体、内质网和高尔基体。
The fluid mosaic model describes the cell membrane as a phospholipid bilayer with embedded proteins, cholesterol and glycoproteins. Membrane fluidity is affected by the proportion of unsaturated fatty acid tails and cholesterol content.
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。膜的流动性受不饱和脂肪酸尾部比例和胆固醇含量的影响。
Ribosomes (70S in prokaryotes, 80S in eukaryotes) are the sites of protein synthesis. The rough ER is studded with ribosomes and modifies proteins; the smooth ER synthesises lipids and detoxifies poisons.
核糖体（原核生物为 70S，真核生物为 80S）是蛋白质合成的场所。粗面内质网上附着核糖体，负责蛋白质修饰；滑面内质网合成脂质并参与解毒。
| Feature | Prokaryotes | Eukaryotes |
| Nucleus | Absent | Present |
| DNA | Circular, naked | Linear, histone-bound |
| Ribosomes | 70S | 80S |
| Membrane-bound organelles | None | Many |
2. Membrane Transport | 膜运输
Simple diffusion is the passive movement of molecules down a concentration gradient, requiring no energy or protein channels. Only small, non-polar molecules (e.g. O₂, CO₂) cross the lipid bilayer freely.
简单扩散是分子顺浓度梯度的被动运输，不需要能量或蛋白质通道。只有小的非极性分子（如 O₂、CO₂）能自由穿过脂双层。
Facilitated diffusion uses channel or carrier proteins to transport ions and larger polar molecules (e.g. glucose, Na⁺) down their gradient. It is specific, saturable and can be inhibited.
协助扩散利用通道蛋白或载体蛋白，顺浓度梯度运输离子和较大的极性分子（如葡萄糖、Na⁺）。该过程具有特异性、可饱和性，并可被抑制。
Active transport moves substances against their concentration gradient using energy from ATP. The sodium–potassium pump (Na⁺/K⁺-ATPase) is a classic example, expelling 3 Na⁺ and importing 2 K⁺ per ATP hydrolysed.
主动运输利用 ATP 水解释放的能量，逆浓度梯度转运物质。钠钾泵（Na⁺/K⁺-ATP酶）是典型例子：每水解一分子 ATP，泵出 3 个 Na⁺，泵入 2 个 K⁺。
Endocytosis and exocytosis involve the bulk transport of large particles via vesicles. Phagocytosis (‘cell eating’) and pinocytosis (‘cell drinking’) are important for immune defence and nutrient uptake.
胞吞和胞吐通过囊泡实现大颗粒物质的批量运输。吞噬（细胞吞噬）和胞饮（细胞饮用）对免疫防御和营养摄取至关重要。
3. Enzymes | 酶
Enzymes are globular proteins that act as biological catalysts, lowering activation energy without being consumed. The induced-fit model states that the active site changes shape to achieve a complementary fit with the substrate, stabilising the transition state.
酶是球状蛋白质，作为生物催化剂，降低活化能而自身不被消耗。诱导契合模型认为，活性部位通过改变构象与底物达到互补契合，稳定过渡态。
Temperature increases kinetic energy and collision frequency up to an optimum; beyond this, hydrogen bonds and hydrophobic interactions break, denaturing the enzyme irreversibly. pH changes alter the ionisation of active-site residues, also causing denaturation.
温度升高会增加动能和碰撞频率，直至最适温度；超过该温度，氢键和疏水相互作用被破坏，酶不可逆变性。pH 改变会改变活性部位残基的电离状态，同样可导致变性。
Initial rate analysis gives Vmax and Km. Competitive inhibitors bind to the active site, raising Km but Vmax unchanged. Non-competitive inhibitors bind at an allosteric site, leaving Km unchanged but lowering Vmax.
通过初速率分析可获得 Vmax 和 Km。竞争性抑制剂结合于活性位点，使 Km 增大而 Vmax 不变；非竞争性抑制剂结合于别构位点，Km 不变但 Vmax 下降。
E + S ⇌ ES → E + P
4. DNA Replication & Protein Synthesis | DNA 复制与蛋白质合成
DNA replication is semi-conservative, as proven by Meselson and Stahl. DNA helicase unwinds the double helix; DNA polymerase III adds nucleotides in the 5′ → 3′ direction. The leading strand is synthesised continuously, the lagging strand as Okazaki fragments, sealed by DNA ligase.
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 III 沿 5′ → 3′ 方向添加核苷酸。前导链连续合成，后随链以冈崎片段形式合成，由 DNA 连接酶连接。
Transcription produces mRNA complementary to the template strand. RNA polymerase binds to the promoter, unwinds DNA and synthesises mRNA. In eukaryotes, pre-mRNA undergoes splicing to remove introns.
转录产生与模板链互补的 mRNA。RNA 聚合酶与启动子结合，解开 DNA 并合成 mRNA。在真核生物中，前体 mRNA 经过剪接去除内含子。
Translation occurs on ribosomes: mRNA codons are recognised by tRNA anticodons carrying amino acids. The ribosome catalyses peptide bond formation; the process continues until a stop codon is reached. The genetic code is degenerate and universal.
翻译在核糖体上进行：mRNA 上的密码子被携带氨基酸的 tRNA 反密码子识别。核糖体催化肽键形成，直至遇到终止密码子。遗传密码具有简并性和通用性。
5. Genetics & Inheritance | 遗传与遗传规律
Monohybrid crosses follow Mendel’s law of segregation. A cross between two heterozygotes (Aa × Aa) gives a 3:1 phenotypic ratio for a dominant–recessive trait. Test crosses (Aa × aa) yield a 1:1 ratio and reveal unknown genotypes.
单基因杂交遵循孟德尔分离定律。两个杂合子（Aa × Aa）杂交，显隐性性状的表型比为 3:1。测交（Aa × aa）得到 1:1 的比例，可鉴定未知基因型。
Sex-linked inheritance involves genes on the X chromosome (e.g. haemophilia, colour blindness). Males are more frequently affected because they have only one X chromosome. Females can be carriers without showing symptoms.
伴性遗传涉及位于 X 染色体上的基因（如血友病、红绿色盲）。男性因只有一条 X 染色体，发病率更高。女性可能为携带者而无症状。
Codominance and multiple alleles are exemplified by the ABO blood group system. The alleles Iᴬ, Iᴮ are codominant, while i is recessive. Pedigree analysis helps deduce modes of inheritance.
共显性与复等位基因以 ABO 血型系统为代表。Iᴬ 与 Iᴮ 等位基因共显性，i 为隐性。系谱分析有助于推断遗传方式。
p² + 2pq + q² = 1 and p + q = 1
The chi-squared (χ²) test compares observed and expected ratios to determine if deviations are due to chance. A p-value < 0.05 leads to rejection of the null hypothesis.
卡方 (χ²) 检验比较观察值与期望值，判断偏差是否由偶然造成。p < 0.05 则拒绝原假设。
6. Evolution & Speciation | 进化与物种形成
Natural selection acts on phenotypic variation within a population. Individuals with advantageous alleles are more likely to survive and reproduce, increasing allele frequency over generations. Antibiotic resistance in bacteria is a vivid example.
自然选择作用于种群内的表型变异。携带有利等位基因的个体更可能存活并繁殖，使种群中等位基因频率逐代上升。细菌的抗生素耐药性就是生动实例。
The Hardy–Weinberg principle describes a non-evolving population where allele frequencies remain constant. The equations p² + 2pq + q² = 1 and p + q = 1 allow calculation of carrier frequencies.
哈代-温伯格定律描述无进化发生的理想群体，其等位基因频率保持恒定。利用公式 p² + 2pq + q² = 1 和 p + q = 1 可以计算携带者频率。
Speciation occurs when populations become reproductively isolated. Allopatric speciation results from geographical barriers; sympatric speciation arises within a shared habitat through behavioural, temporal or mechanical isolation.
当种群间形成生殖隔离时，物种形成发生。异域物种形成由地理障碍导致；同域物种形成在同一栖息地内，通过行为、时间或机械隔离完成。
7. Ecology & Energy Flow | 生态与能量流动
Energy enters ecosystems through photosynthesis and is transferred along food chains. Only about 10% of energy is passed to the next trophic level; the rest is lost as heat through respiration, movement and egestion.
能量通过光合作用进入生态系统，并沿食物链传递。只有大约 10% 的能量流入下一营养级，其余通过呼吸作用、运动和排遗以热的形式散失。
The carbon cycle involves photosynthesis, respiration, decomposition and combustion. Carbon is exchanged between the atmosphere, oceans, living organisms and fossil fuels. Deforestation and burning fossil fuels increase atmospheric CO₂.
碳循环包括光合作用、呼吸作用、分解作用和燃烧。碳在大气、海洋、生物体和化石燃料之间交换。森林砍伐和化石燃料燃烧增加了大气 CO₂ 浓度。
Nitrogen fixation converts atmospheric N₂ into ammonia (NH₃) via nitrogen-fixing bacteria. Nitrification and denitrification complete the cycle. Legumes form mutualistic relationships with Rhizobium in root nodules.
固氮作用通过固氮细菌将大气 N₂ 转化为氨 (NH₃)。硝化作用和反硝化作用完成整个循环。豆科植物与根瘤中的根瘤菌形成互利共生关系。
8. Human Physiology: Circulation & Respiration | 人体生理：循环与呼吸
The heart is a double pump: the right side delivers blood to the pulmonary circulation, the left to systemic circulation. The sinoatrial node initiates the heartbeat; the atrioventricular node delays impulses to allow ventricular filling.
心脏是一个双重泵：右侧将血液泵入肺循环，左侧泵入体循环。窦房结启动心跳，房室结延迟信号以保障心室充盈。
Gas exchange in alveoli relies on a steep concentration gradient maintained by ventilation and blood flow. Oxygen diffuses into capillaries and binds to haemoglobin, forming oxyhaemoglobin. The Bohr effect describes how increased CO₂ lowers haemoglobin’s affinity for O₂.
肺泡中的气体交换依赖通气和血流维持的陡峭浓度梯度。氧气扩散入毛细血管并与血红蛋白结合，形成氧合血红蛋白。波尔效应描述了 CO₂ 浓度升高如何降低血红蛋白对 O₂ 的亲和力。
The oxygen dissociation curve is sigmoidal due to cooperative binding. A rightward shift (e.g. during exercise) facilitates O₂ unloading to tissues. Myoglobin has a higher affinity and serves as an O₂ reserve in muscle.
由于协同结合，氧解离曲线呈 S 形。曲线右移（如运动时）有利于向组织释放 O₂。肌红蛋白亲和力更高，充当肌肉中的 O₂ 储备库。
9. Homeostasis & Excretion | 稳态与排泄
Negative feedback maintains internal stability. Blood glucose regulation involves insulin (lowering glucose) and glucagon (raising glucose), produced by pancreatic islets. Diabetes mellitus results from insulin deficiency or resistance.
负反馈维持内环境稳定。血糖调节涉及胰岛素（降低血糖）和胰高血糖素（升高血糖），由胰岛分泌。糖尿病源于胰岛素缺乏或抵抗。
The nephron is the functional unit of the kidney. Ultrafiltration in the glomerulus produces a filtrate free of cells and large proteins. Selective reabsorption occurs mainly in the proximal convoluted tubule, where glucose, amino acids and most salts are reclaimed.
肾单位是肾脏的功能单位。肾小球中的超滤作用产生不含细胞和大分子蛋白质的滤液。选择性重吸收主要发生在近曲小管，重吸收葡萄糖、氨基酸和大部分盐类。
Osmoregulation is controlled by antidiuretic hormone (ADH). When blood water potential is low, ADH increases the permeability of the collecting duct, allowing more water reabsorption and producing concentrated urine.
渗透调节由抗利尿激素 (ADH) 控制。当血液水势下降时，ADH 提高集合管通透性，促进更多水分重吸收，生成浓缩尿液。
10. Plant Biology | 植物生物学
6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂
Photosynthesis consists of light-dependent reactions (thylakoid membrane) and the Calvin cycle (stroma). Light energy splits water (photolysis), releasing O₂ and generating ATP and NADPH. The Calvin cycle fixes CO₂ into glucose using these products.
光合作用包括光反应（类囊体膜）和卡尔文循环（基质）。光能分解水（光解），释放 O₂，并产生 ATP 和 NADPH。卡尔文循环利用这些产物将 CO₂ 固定为葡萄糖。
Transpiration is the evaporation of water from leaves, driven by a water potential gradient. Cohesion–tension theory explains the ascent of xylem sap: water molecules form a continuous column under tension. Stomatal opening is regulated by guard cells and potassium ion fluxes.
蒸腾作用是叶片水分蒸发的过程，由水势梯度驱动。内聚力-张力理论解释了木质部汁液上升：水分子在张力下形成连续水柱。气孔开闭由保卫细胞和 K⁺ 离子流调控。
Phloem translocation moves sucrose from sources (leaves) to sinks (roots, fruits). The mass-flow hypothesis involves active loading of sucrose into sieve tubes, lowering water potential and drawing water in, creating hydrostatic pressure that drives flow.
韧皮部运输将蔗糖从源（叶片）运至库（根、果实）。压力流动假说认为，蔗糖被主动装载到筛管中，降低水势并吸水，产生静水压驱动汁液流动。
11. Immunology | 免疫学
Non-specific defences include skin barriers, mucous membranes, phagocytosis and inflammation. Phagocytes (e.g. neutrophils, macrophages) engulf pathogens and digest them using lysosomal enzymes.
非特异性防御包括皮肤屏障、粘膜、吞噬作用和炎症反应。吞噬细胞（如中性粒细胞、巨噬细胞）吞噬病原体并用溶酶体酶消化。
Specific immunity involves lymphocytes. B cells produce antibodies that neutralise extracellular pathogens. T helper cells activate B cells and cytotoxic T cells; cytotoxic T cells destroy virus-infected cells.
特异性免疫涉及淋巴细胞。B 细胞产生抗体，中和胞外病原体。辅助 T 细胞激活 B 细胞和细胞毒性 T 细胞；细胞毒性 T 细胞杀伤病毒感染的细胞。
Vaccination induces active immunity by exposing the body to antigens, generating memory cells for a rapid secondary response. Monoclonal antibodies are produced from a single clone of B cells and are used in diagnostics and targeted therapy.
疫苗接种通过暴露于抗原诱导主动免疫，产生记忆细胞以便快速二次应答。单克隆抗体由单一 B 细胞克隆产生，用于诊断和靶向治疗。
12. Molecular Biology & Biotechnology | 分子生物学与生物技术
Polymerase chain reaction (PCR) amplifies DNA in vitro. It requires Taq polymerase, primers, free nucleotides and thermal cycling: denaturation (95 °C), annealing (50–65 °C), extension (72 °C). Each cycle doubles the target DNA.
聚合酶链式反应 (PCR) 在体外扩增 DNA。需要 Taq 聚合酶、引物、游离核苷酸和热循环：变性 (95 °C)、退火 (50–65 °C)、延伸 (72 °C)。每个循环使目标 DNA 倍增。
Gel electrophoresis separates DNA fragments by size. DNA is loaded into a well, an electric current is applied, and negatively charged DNA moves towards the positive electrode. Smaller fragments travel faster and farther.
凝胶电泳根据大小分离 DNA 片段。DNA 加入点样孔，通电后带负电的 DNA 向正极移动。较小的片段迁移较快、较远。
Genetic engineering uses restriction endonucleases to cut DNA at specific sequences, producing sticky ends. DNA ligase seals foreign genes into plasmid vectors. Recombinant plasmids are introduced into host bacteria for insulin or growth hormone production.
基因工程使用限制性内切酶在特定序列切割 DNA，产生黏性末端。DNA 连接酶将外源基因封入质粒载体。重组质粒导入宿主细菌，用于生产胰岛素或生长激素。
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