📚 Year 13 CIE Biology: Key Knowledge Points Review | Year 13 CIE 生物：核心知识点梳理
Year 13 CIE Biology takes you deeper into the molecular mechanisms of life, from energy transduction and homeostasis to evolution and genetic technologies. This article systematically revisits the most tested core knowledge points, pairing every English explanation with a Chinese version to strengthen bilingual understanding and exam readiness.
Year 13 CIE 生物带你深入生命的分子机制，从能量转换与稳态到进化与基因技术。本文系统梳理最常考查的核心知识点，每个要点均提供英文与中文配对解读，以强化双语理解并提升备考效率。
1. Cellular Respiration: Glycolysis to Oxidative Phosphorylation | 细胞呼吸：从糖酵解到氧化磷酸化
Respiration is a multi‑step metabolic pathway that releases energy from glucose. Glycolysis occurs in the cytoplasm, splitting glucose (6C) into two molecules of pyruvate (3C), with a net gain of 2 ATP and 2 reduced NAD (NADH).
呼吸作用是一条多步代谢途径，从葡萄糖中释放能量。糖酵解发生在细胞质中，将葡萄糖（6C）分解为两分子丙酮酸（3C），净产生 2 ATP 和 2 个还原态 NAD（NADH）。
The link reaction takes pyruvate into the mitochondrial matrix, where each pyruvate loses a CO₂ and is oxidised to an acetyl group, carried by coenzyme A as acetyl‑CoA. One NADH is produced per pyruvate.
连接反应将丙酮酸带入线粒体基质，每个丙酮酸失去一个 CO₂ 并被氧化成乙酰基，由辅酶 A 携带形成乙酰辅酶 A。每分子丙酮酸生成一分子 NADH。
In the Krebs cycle, acetyl‑CoA combines with a 4C compound to form citrate (6C). A series of decarboxylations and oxidations regenerates the 4C acceptor, releasing 2 CO₂, 1 ATP (by substrate‑level phosphorylation), 3 NADH and 1 reduced FAD (FADH₂) per turn. Since one glucose yields two acetyl‑CoA, the cycle turns twice.
在克雷布斯循环中，乙酰辅酶 A 与一个 4C 化合物结合生成柠檬酸（6C）。经一系列脱羧和氧化反应后再生 4C 接受体，每圈释放 2 CO₂、1 ATP（底物水平磷酸化）、3 NADH 和 1 还原态 FAD（FADH₂）。由于一分子葡萄糖产生两分子乙酰辅酶 A，循环运转两圈。
Oxidative phosphorylation is the final stage. NADH and FADH₂ donate electrons to the electron transport chain on the inner mitochondrial membrane. As electrons pass through carriers, energy pumps protons into the intermembrane space, creating a proton gradient. Protons flow back through ATP synthase, driving ATP synthesis (chemiosmosis). Oxygen is the final electron acceptor, forming water.
氧化磷酸化是最后阶段。NADH 与 FADH₂ 将电子提供给线粒体内膜上的电子传递链。电子在载体间传递时释放的能量将质子泵入膜间隙，建立质子梯度。质子经 ATP 合酶回流，驱动 ATP 合成（化学渗透）。氧气是末端电子受体，生成水。
Respiratory quotient (RQ) = CO₂ produced / O₂ consumed. RQ values indicate the respiratory substrate: carbohydrate ~1.0, lipid ~0.7, protein ~0.9.
呼吸商 (RQ) = 产生的 CO₂ / 消耗的 O₂。RQ 数值可指示呼吸底物：碳水化合物约 1.0，脂类约 0.7，蛋白质约 0.9。
2. Photosynthesis: Light-Dependent and Light-Independent Reactions | 光合作用：光反应与暗反应
Photosynthesis takes place in chloroplasts. The light‑dependent reactions occur on the thylakoid membranes. Photosystem II (PSII) absorbs light, splits water (photolysis) to yield O₂, electrons and H⁺. Excited electrons travel through an electron transport chain to photosystem I (PSI), generating ATP via chemiosmosis. In non‑cyclic photophosphorylation, PSI reduces NADP⁺ to NADPH using electrons from the chain. Cyclic photophosphorylation involves only PSI, producing ATP but no NADPH or O₂.
光合作用在叶绿体中进行。光反应发生在类囊体膜上。光系统 II（PSII）吸收光能，裂解水（光解）产生 O₂、电子和 H⁺。激发态电子经电子传递链传递到光系统 I（PSI），通过化学渗透产生 ATP。在非循环光合磷酸化中，PSI 利用来自传递链的电子将 NADP⁺ 还原为 NADPH。循环光合磷酸化仅涉及 PSI，产生 ATP 但不生成 NADPH 或 O₂。
The light‑independent reactions (Calvin cycle) occur in the stroma. CO₂ is fixed by RuBisCO to ribulose bisphosphate (RuBP), forming an unstable 6C compound that splits into two molecules of glycerate‑3‑phosphate (GP). GP is reduced to triose phosphate (TP) using ATP and NADPH from the light reactions. Most TP is used to regenerate RuBP, while some is converted to glucose or other organic molecules. To make one glucose, 6 CO₂ molecules must enter the cycle, using 18 ATP and 12 NADPH.
暗反应（卡尔文循环）在基质中进行。CO₂ 被 RuBisCO 固定到核酮糖二磷酸（RuBP）上，形成不稳定的 6C 中间体，随即裂解为两分子甘油酸‑3‑磷酸（GP）。GP 利用光反应产生的 ATP 和 NADPH 还原为磷酸丙糖（TP）。大部分 TP 用于再生 RuBP，少部分转化为葡萄糖或其他有机物。合成一分子葡萄糖需要 6 个 CO₂ 进入循环，共消耗 18 ATP 和 12 NADPH。
In C4 plants (e.g. maize), CO₂ is initially fixed in mesophyll cells by PEP carboxylase to form a 4C compound, which then releases CO₂ in bundle‑sheath cells, concentrating CO₂ around RuBisCO and reducing photorespiration. This adaptation is advantageous in hot, dry conditions.
在 C4 植物（如玉米）中，CO₂ 先在叶肉细胞中被 PEP 羧化酶固定为 4C 化合物，随后在维管束鞘细胞中释放 CO₂，提高 RuBisCO 周围 CO₂ 浓度从而减少光呼吸。这一适应在炎热干燥条件下具有优势。
3. Homeostasis: Temperature and Blood Glucose Regulation | 稳态：体温与血糖调节
Homeostasis is the maintenance of a stable internal environment via negative feedback. Core mechanisms involve a stimulus, receptor, coordinator, effector and response that counteract the initial change.
稳态是通过负反馈维持内环境稳定的过程。核心机制包括刺激、感受器、协调中心、效应器以及抵抗初始变化的响应。
Thermoregulation in mammals is coordinated by the hypothalamus. When core temperature rises, skin arterioles dilate (vasodilation), sweat glands secrete sweat, and hair‑erector muscles relax. When temperature falls, vasoconstriction reduces heat loss, shivering generates heat, and hair erection traps insulating air.
哺乳动物的体温调节由下丘脑协调。核心温度升高时，皮肤小动脉舒张（血管舒张），汗腺分泌汗液，竖毛肌松弛。温度下降时，血管收缩减少散热，颤抖生热，立毛捕获保温空气。
Blood glucose regulation involves insulin and glucagon, produced by β‑ and α‑cells of the pancreatic islets respectively. After a meal, high blood glucose stimulates β‑cells to secrete insulin, which increases glucose uptake by cells and promotes glycogen synthesis in the liver. Between meals, low glucose triggers α‑cells to secrete glucagon, stimulating glycogenolysis and gluconeogenesis. Diabetes mellitus results from insufficient insulin secretion (type 1) or reduced responsiveness of target cells (type 2).
血糖调节涉及胰岛素和胰高血糖素，分别由胰岛的 β 细胞和 α 细胞分泌。餐后高血糖刺激 β 细胞分泌胰岛素，增加细胞对葡萄糖的摄取并促进肝脏合成糖原。空腹时低血糖触发 α 细胞分泌胰高血糖素，促进糖原分解和糖异生。糖尿病源于胰岛素分泌不足（1型）或靶细胞对胰岛素反应性降低（2型）。
4. Homeostasis: Kidney and Osmoregulation | 稳态：肾脏与渗透调节
The functional unit of the kidney is the nephron. Ultrafiltration occurs in the Bowman’s capsule, where high blood pressure forces water, ions, glucose and urea through the glomerular endothelial‑capillary‑basement‑membrane‑podocyte barrier, forming glomerular filtrate. Large molecules such as proteins and cells remain in the blood.
肾脏的功能单位是肾单位。超滤发生在鲍曼氏囊，高血压迫使水、离子、葡萄糖和尿素穿过肾小球内皮‑毛细血管基底膜‑足细胞屏障，形成肾小球滤液。蛋白质和细胞等大分子留在血液中。
Selective reabsorption largely takes place in the proximal convoluted tubule. All glucose, amino acids and most ions are reabsorbed by active transport and facilitated diffusion. Water follows by osmosis. The loop of Henlé creates a sodium ion gradient in the medulla, enabling water reabsorption from the collecting duct. ADH (antidiuretic hormone) is released by the posterior pituitary when blood water potential is low; it increases the permeability of the collecting duct to water, producing more concentrated urine.
选择性重吸收主要发生在近曲小管。所有葡萄糖、氨基酸和大部分离子通过主动运输和易化扩散被重吸收。水通过渗透作用跟随。髓袢在髓质建立钠离子梯度，使集合管能够重吸收水。当血液水势降低时，垂体后叶释放抗利尿激素（ADH），增加集合管对水的通透性，产生更浓缩的尿液。
Osmoregulation maintains the balance of water and solutes. The countercurrent multiplier system in the loop of Henlé, together with urea recycling, builds a hypertonic medulla, allowing the kidney to excrete urine of varying concentrations according to the body's needs.
渗透调节维持水与溶质的平衡。髓袢的逆流倍增系统与尿素再循环共同建立高渗髓质，使肾脏能够根据机体需求排出不同浓度的尿液。
5. Nervous Coordination and Muscle Contraction | 神经协调与肌肉收缩
Neurones transmit electrical impulses. The resting potential (~‑70 mV) is maintained by the Na⁺/K⁺ pump, which actively transports 3 Na⁺ out and 2 K⁺ in, and by the greater permeability of the membrane to K⁺ than Na⁺. An action potential begins when voltage‑gated Na⁺ channels open, causing depolarisation. At the peak, Na⁺ channels close and K⁺ channels open, causing repolarisation and a brief hyperpolarisation. Impulses are all‑or‑nothing and travel along myelinated axons by saltatory conduction.
神经元传递电冲动。静息电位（约‑70 mV）由 Na⁺/K⁺ 泵主动运出 3 Na⁺ 和运入 2 K⁺，以及膜对 K⁺ 的通透性大于 Na⁺ 来维持。当电压门控 Na⁺ 通道开放时产生动作电位，引起去极化。到达峰值时 Na⁺ 通道关闭，K⁺ 通道开放，导致复极化及短暂超极化。冲动是全或无的，并沿有髓轴突以跳跃传导方式传播。
At a cholinergic synapse, an action potential opens Ca²⁺ channels in the presynaptic knob, causing vesicles to fuse with the membrane and release acetylcholine (ACh). ACh diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane, opening Na⁺ channels and generating an excitatory postsynaptic potential. Acetylcholinesterase quickly breaks down ACh to terminate the signal.
在胆碱能突触中，动作电位打开突触前膜上的 Ca²⁺ 通道，促使囊泡与膜融合释放乙酰胆碱（ACh）。ACh 扩散通过突触间隙，与突触后膜受体结合，开放 Na⁺ 通道并产生兴奋性突触后电位。乙酰胆碱酯酶迅速分解 ACh 以终止信号。
Skeletal muscle contraction is explained by the sliding filament model. A motor neurone stimulates a muscle fibre at the neuromuscular junction, releasing ACh and triggering an action potential in the sarcolemma. This causes the sarcoplasmic reticulum to release Ca²⁺. Ca²⁺ binds to troponin, shifting tropomyosin to expose myosin‑binding sites on actin. Myosin heads bind, perform a power stroke using ATP, then detach and reattach further along the actin filament, shortening the sarcomere.
骨骼肌收缩可通过滑丝模型解释。运动神经元在神经肌肉接头处刺激肌纤维，释放 ACh 并在肌膜引发动作电位。这使肌质网释放 Ca²⁺。Ca²⁺ 与肌钙蛋白结合，使原肌球蛋白移位，暴露肌动蛋白上的肌球蛋白结合位点。肌球蛋白头部结合后利用 ATP 进行摆动，然后脱离并沿肌动蛋白丝重新结合，使肌小节缩短。
6. Endocrine and Cell Signalling | 内分泌与细胞信号
Hormones are chemical messengers produced by endocrine glands and transported in the blood to target cells. Steroid hormones, such as oestrogen, cross cell membranes and bind to intracellular receptors, directly influencing gene transcription. Peptide hormones, e.g. adrenaline and glucagon, bind to cell‑surface receptors and activate second messenger systems.
激素是由内分泌腺产生并通过血液运输到靶细胞的化学信使。类固醇激素如雌激素可穿过细胞膜，与胞内受体结合并直接影响基因转录。肽类激素如肾上腺素和胰高血糖素则与细胞表面受体结合，并激活第二信使系统。
A classic second messenger is cyclic AMP (cAMP). When adrenaline binds to its receptor, a G‑protein activates adenylyl cyclase, which converts ATP to cAMP. cAMP then activates protein kinase A, leading to a cascade of phosphorylation events, such as the activation of glycogen phosphorylase that breaks down glycogen to glucose. Signal amplification allows a single hormone molecule to trigger a large cellular response.
经典的第二信使是环腺苷酸（cAMP）。肾上腺素与其受体结合时，G 蛋白激活腺苷酸环化酶，将 ATP 转化为 cAMP。cAMP 进而激活蛋白激酶 A，引发磷酸化级联反应，如激活糖原磷酸化酶分解糖原为葡萄糖。信号放大使单个激素分子可以引发巨大的细胞应答。
7. Inheritance and the Chi‑Squared Test | 遗传与卡方检验
Monohybrid inheritance follows Mendel’s principles. Codominance occurs when both alleles are expressed equally in heterozygotes (e.g. AB blood group). Sex‑linked traits are carried on the X chromosome; males are more likely to express recessive X‑linked disorders such as haemophilia.
单基因遗传遵循孟德尔规律。共显性表现为杂合子中等位基因同时表达（如 AB 血型）。伴性性状位于 X 染色体上；男性更易表现隐性 X 连锁疾病如血友病。
Dihybrid crosses without gene linkage produce a 9:3:3:1 phenotypic ratio. When genes are linked on the same chromosome, the ratio deviates, with more parental‑type offspring and fewer recombinants. Crossing over during prophase I of meiosis can separate linked alleles, producing new combinations.
无连锁的双因子杂交产生 9:3:3:1 的表型比。当基因位于同一染色体上连锁时，比率偏离，亲本型后代增多而重组型减少。减数分裂前期 I 发生的交叉互换可以分开连锁的等位基因，产生新组合。
The chi‑ is compared to a critical value at p=0.05 for the appropriate degrees of freedom. If χ² > critical value, the null hypothesis is rejected.
卡方（χ²）检验比较观察频数与预期频数，判断偏离是否由偶然引起。χ² = Σ[(O − E)² / E]。将计算值与 p=0.05 下对应自由度的临界值比较。若 χ² > 临界值，拒绝零假设。
8. Population Genetics: Hardy‑Weinberg Principle | 种群遗传：哈迪‑温伯格原理
The Hardy‑Weinberg model describes a non‑ ies), where p is the frequency of the dominant allele and q the frequency of the recessive allele. The principle assumes a large, randomly mating population with no mutation, selection, gene flow or genetic drift.
哈迪‑温伯格模型描述一个不进化的种群。两个方程为：p + q = 1（等位基因频率）和 p² + 2pq + q² = 1（基因型频率），其中 p 为显性等位基因频率，q 为隐性等位基因频率。该原理假设种群大、随机交配、没有突变、选择、基因流或遗传漂变。
dition (q²) is 1 in 10,000, then q = 0.01 and carrier frequency (2pq) ≈ 0.0198, or about 2%.
该工具可计算遗传病携带者频率。例如，若某一隐性疾病的发病率（q²）为 1/10000，则 q=0.01，携带者频率（2pq）≈ 0.0198，即约 2%。
9. Evolution and Speciation | 进化与物种形成
Natural selection operates on phenotypic variation generated by mutation. Stabilising selection favours intermediate phenotypes, directional selection shifts the mean phenotype, and disruptive selection favours extremes. Geographic isolation (allopatric speciation) and reproductive isolation without physical barriers (sympatric speciation) are the two main routes to new species.
自然选择作用于由突变产生的表型变异。稳定化选择青睐中间表型，定向选择使平均表型移位，分裂化选择则青睐极端类型。地理隔离（异域物种形成）和没有物理障碍的生殖隔离（同域物种形成）是形成新物种的两条主要途径。
Allopatric speciation occurs when populations are separated by a geographical barrier, e.g. a mountain range or river, preventing gene flow. Over time, mutations and different selection pressures lead to genetic divergence, eventually resulting in reproductive isolation even if the populations meet again.
异域物种形成指种群被地理屏障（如山脉或河流）分隔，阻碍基因流动。随着时间推移，突变和不同的选择压力导致遗传分化，最终即使种群再次相遇也无法杂交，产生生殖隔离。
Sympatric speciation can arise through ecological niche differentiation or chromosomal mutations such as polyploidy. Polyploidy is common in plants and instantly creates a reproductively isolated lineage.
同域物种形成可通过生态位分化或染色体突变（如多倍体）发生。多倍体在植物中常见，可立即形成生殖隔离的谱系。
10. Classification and Biodiversity | 分类与生物多样性
Modern classification recognises three domains: Bacteria, Archaea and Eukarya, based on ribosomal RNA sequences and cell structure. Within Eukarya, organisms are classified into kingdoms using shared derived characteristics. The binomial naming system uses the genus and species name.
现代分类学根据核糖体 RNA 序列和细胞结构识别三个域：细菌域、古菌域和真核域。在真核域内，依据共有衍征将生物划分到不同的界。双名命名法使用属名和种名。
index of diversity (D = 1 − Σ(n/N)²). A higher value indicates greater diversity. Conservation strategies, including habitat preservation, seed banks and captive breeding programmes, rely on in‑depth understanding of a species’ ecological requirements and genetic diversity.
生物多样性可在基因、物种和生态系统三个层次评估。物种多样性常用物种丰富度和辛普森多样性指数（D = 1 − Σ(n/N)²）衡量，数值越高表示多样性越高。保护策略如栖息地保护、种子库和人工繁殖计划，均依赖于对物种生态需求和遗传多样性的深入了解。
11. Genetic Technology | 基因技术
Polymerase chain reaction (PCR) amplifies DNA in vitro. Each cycle consists of denaturation (94–98 °C), annealing (50–65 °C) of primers to the target sequence, and extension (72 °C) by Taq polymerase. After ~30 cycles, millions of copies of the target DNA are produced.
聚合酶链反应（PCR）在体外扩增 DNA。每个循环包括变性（94–98 °C）、引物与靶序列退火（50–65 °C）以及 Taq 聚合酶在 72°C 延伸。经过约 30 个循环，可获得数百万拷贝的目标 DNA。
Gel electrophoresis separates DNA fragments according to size. DNA samples are loaded into wells of an agarose gel and an electric current is applied. Negatively charged DNA moves towards the positive electrode; smaller fragments migrate faster. Bands are visualised under UV light after staining. This technique is essential for DNA profiling and restriction fragment length polymorphism (RFLP) analysis.
凝胶电泳根据片段大小分离 DNA。将 DNA 样品加入到琼脂糖凝胶的孔中并施加电场。带负电的 DNA 向正极移动；较小的片段迁移较快。染色后在紫外光下观察条带。该技术对 DNA 图谱分析和限制性片段长度多态性（RFLP）分析至关重要。
Genetic engineering makes use of restriction enzymes to cut DNA at specific palindromic sequences, producing sticky or blunt ends. DNA ligase joins fragments together to create recombinant DNA. Vectors such as plasmids or viruses carry the gene of interest into host cells. Transformed bacteria can be identified using antibiotic resistance marker genes.
基因工程利用限制性内切酶在特定回文序列处切割 DNA，产生黏性末端或平末端。DNA 连接酶将片段连接起来构建重组 DNA。载体如质粒或病毒将目的基因导入宿主细胞。转化成功的细菌可利用抗生素抗性标记基因进行筛选。
Gene therapy aims to treat genetic disorders by inserting a functional allele into a patient’s cells. Somatic gene therapy targets body cells and is not heritable, while germline gene therapy would affect future generations and raises complex ethical issues.
基因疗法旨在通过将功能正常的等位基因导入患者细胞来治疗遗传疾病。体细胞基因疗法靶向体细胞，不可遗传；而生殖系基因疗法会影响后代，并引发复杂的伦理问题。
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