📚 Year 13 WJEC Biology: Essential Core Knowledge Review | Year 13 WJEC 生物：核心知识点梳理
The Year 13 WJEC Biology course builds upon AS topics and introduces advanced cellular processes, ecological relationships, and physiological mechanisms. Mastering these core concepts is essential for tackling data-analysis questions, extended responses, and synoptic essays. This review distils the key knowledge from Units 3 and 4, covering bioenergetics, microbiology, populations, nutrient cycles, homeostasis, nervous coordination, muscle contraction, and molecular genetics.
Year 13 WJEC 生物课程在 AS 基础上进一步深入，引入高级细胞过程、生态关系和生理机制。掌握这些核心概念对于应对数据分析题、长篇讨论题和综合性论文至关重要。本文梳理 Unit 3 和 Unit 4 的关键知识，涵盖生物能学、微生物学、种群、营养循环、稳态、神经协调、肌肉收缩和分子遗传学。
1. Cellular Respiration and ATP Synthesis | 细胞呼吸与ATP合成
Respiration is a series of metabolic pathways that release energy from respiratory substrates such as glucose. The energy is used to synthesise ATP, the universal energy currency. Aerobic respiration has four main stages: glycolysis, the link reaction, the Krebs cycle, and oxidative phosphorylation.
呼吸作用是一系列代谢途径，从葡萄糖等呼吸底物中释放能量，用于合成通用能量货币 ATP。有氧呼吸有四个主要阶段：糖酵解、连接反应、克雷布斯循环和氧化磷酸化。
Glycolysis occurs in the cytoplasm and splits glucose (6C) into two molecules of pyruvate (3C). It yields a net gain of 2 ATP and 2 reduced NAD (NADH). No oxygen is required at this stage.
糖酵解发生在细胞质中，将葡萄糖 (6C) 分解为两个丙酮酸分子 (3C)。净产生 2个 ATP 和 2个还原型 NAD (NADH)，此阶段无需氧气。
In the presence of oxygen, pyruvate enters the mitochondrial matrix for the link reaction. Each pyruvate is decarboxylated and dehydrogenated, combining with coenzyme A to form acetyl-CoA. This produces CO₂ and reduced NAD.
在有氧条件下，丙酮酸进入线粒体基质进行连接反应。每个丙酮酸脱羧脱氢，与辅酶 A 结合形成乙酰辅酶 A，同时产生 CO₂ 和还原型 NAD。
The Krebs cycle (citric acid cycle) occurs in the matrix. Acetyl-CoA (2C) combines with a 4C compound (oxaloacetate) to form citrate (6C). Through a series of redox and decarboxylation steps, oxaloacetate is regenerated. For each acetyl group, 3 NADH, 1 FADH₂, 1 ATP (via substrate-level phosphorylation), and 2 CO₂ are produced.
克雷布斯循环（柠檬酸循环）在基质中进行。乙酰辅酶 A (2C) 与草酰乙酸 (4C) 结合生成柠檬酸 (6C)。通过一系列氧化还原和脱羧步骤，草酰乙酸再生。每个乙酰基产生 3个 NADH、1个 FADH₂、1个 ATP（经底物水平磷酸化）及 2个 CO₂。
Oxidative phosphorylation takes place on the inner mitochondrial membrane. Reduced coenzymes NADH and FADH₂ donate electrons to the electron transport chain. The energy released pumps H⁺ into the intermembrane space, creating a proton gradient. H⁺ flows back through ATP synthase, driving phosphorylation of ADP. Oxygen acts as the final electron acceptor, forming water. Total ATP yield per glucose is approximately 32–38 molecules.
氧化磷酸化发生在线粒体内膜。还原型辅酶 NADH 和 FADH₂ 将电子传递给电子传递链，释放的能量将 H⁺ 泵入膜间隙，形成质子梯度。H⁺ 通过 ATP 合酶回流，驱动 ADP 磷酸化。氧气作为最终电子受体生成水。每分子葡萄糖共产生约 32–38 个 ATP。
2. Photosynthesis | 光合作用
Photosynthesis converts light energy into chemical energy in the form of glucose. The overall equation is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. It consists of two sets of reactions: the light-dependent reactions and the light-independent reactions (Calvin cycle).
光合作用将光能转化为化学能储存在葡萄糖中。总反应式为：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。它包含两类反应：光依赖反应和光非依赖反应（卡尔文循环）。
Light-dependent reactions occur on the thylakoid membranes. Photosystems II and I absorb light, exciting electrons. Water is photolysed to release electrons, H⁺, and O₂. The electrons pass along an electron transport chain, generating ATP (chemiosmosis) and reducing NADP⁺ to NADPH. The products ATP and NADPH are essential for the Calvin cycle.
光依赖反应发生在类囊体薄膜上。光系统 II 和 I 吸收光能，激发电子。水光解释放电子、H⁺ 和 O₂。电子沿电子传递链传递，通过化学渗透生成 ATP，并将 NADP⁺ 还原为 NADPH。产物 ATP 和 NADPH 是卡尔文循环必需的。
The Calvin cycle takes place in the stroma. CO₂ is fixed to ribulose bisphosphate (RuBP) by the enzyme rubisco, forming two molecules of glycerate 3‑phosphate (GP). GP is reduced to triose phosphate (TP) using ATP and NADPH from the light-dependent stage. Some TP regenerates RuBP, while some is used to synthesise glucose, lipids, and amino acids.
卡尔文循环在基质中进行。CO₂ 被 Rubisco 酶固定于 1,5-二磷酸核酮糖 (RuBP)，生成两分子甘油酸-3-磷酸 (GP)。GP 利用光反应提供的 ATP 和 NADPH 还原为磷酸丙糖 (TP)。部分 TP 用于再生 RuBP，部分用于合成葡萄糖、脂肪和氨基酸。
3. Microbiology and Aseptic Technique | 微生物学与无菌技术
Microbiology involves the study of microorganisms such as bacteria and fungi. Key techniques include aseptic methods to prevent contamination, serial dilution for viable cell counts, and the measurement of growth curves.
微生物学研究细菌和真菌等微生物。关键技术包括防止污染的无菌操作、用于活菌计数的连续稀释以及生长曲线的测量。
Aseptic technique requires working near a Bunsen burner’s updraught, flaming culture bottle necks, and using sterile pipettes and spreaders. These steps prevent airborne contaminants from introducing unwanted microbes.
无菌技术要求在酒精灯上升气流旁操作、灼烧培养瓶口、使用无菌移液管和涂布棒。这些步骤可防止空气污染物引入不必要的微生物。
Total viable cell counts are often performed by serial dilution and plating on agar. Each colony arises from a single viable cell. Counts are expressed as colony-forming units (CFU) per cm³ of original culture. Only living cells that can divide are counted.
总活菌计数通常通过连续稀释和平板涂布进行。每个菌落源自单个活细胞。计数结果以原培养液每 cm³ 菌落形成单位 (CFU) 表示，只计数可分裂的活细胞。
The bacterial growth curve in a closed batch culture shows four phases: lag (adaptation), log/exponential (rapid division), stationary (nutrient depletion, waste accumulation), and death (cells die faster than they are produced). Knowledge of growth phases is critical for industrial fermentation.
封闭批培养中细菌生长曲线显示四个时期：延缓期（适应）、对数/指数期（快速分裂）、稳定期（营养耗尽、废物积累）和衰亡期（死亡速率超过繁殖速率）。了解生长时期对工业发酵至关重要。
4. Populations and Sampling | 种群与取样
Ecologists estimate population sizes using sampling techniques. For slow-moving or stationary organisms, quadrats are used. For motile animals, the mark-release-recapture method is applied.
生态学家利用取样技术估算种群大小。对于活动缓慢或不动的生物，使用样方；对于能自由活动的动物，采用标记重捕法。
A quadrat of known area is placed randomly within a habitat. The number of individuals (or percentage cover for plants) is recorded. Large sample sizes increase reliability. Population size is estimated as: mean count per quadrat × (total habitat area ÷ quadrat area).
将已知面积的样方随机放置在生境中，记录个体数量（或植物盖度百分比）。大样本量可提高可靠性。种群大小估算为：每样方平均计数 ×（总生境面积 ÷ 样方面积）。
Mark-release-recapture assumes that marking does not affect survival, marked individuals mix randomly, and the population is closed (no immigration/emigration). The Lincoln index is: N = (n₁ × n₂) ÷ m, where n₁ is number first caught and marked, n₂ is number in second catch, m is number of marked individuals recaptured.
标记重捕法假设标记不影响存活，标记个体随机混合，且种群封闭（无迁入迁出）。林肯指数公式为：N = (n₁ × n₂) ÷ m，其中 n₁ 为首次捕获并标记的数量，n₂ 为第二次捕获数量，m 为第二次捕获中已标记的个体数。
5. Ecosystems and Nutrient Cycles | 生态系统与营养循环
Energy flows through ecosystems in food chains, but nutrients cycle. The carbon cycle and nitrogen cycle are particularly important. Microorganisms play central roles in decomposition and nitrogen conversions.
能量通过食物链在生态系统中流动，但营养物质是循环的。碳循环和氮循环尤为重要。微生物在分解和氮素转化中发挥核心作用。
Carbon is exchanged between the atmosphere, organisms, and fossil reserves. Photosynthesis fixes CO₂ into organic compounds. Respiration, combustion, and decomposition release CO₂ back into the atmosphere. Decomposers break down dead organic matter, returning nutrients to the soil.
碳在大气、生物体和化石储备之间交换。光合作用将 CO₂ 固定为有机物；呼吸作用、燃烧和分解又将 CO₂ 释放回大气。分解者分解死亡有机物，使养分归还土壤。
The nitrogen cycle involves four main processes: nitrogen fixation (N₂ → NH₄⁺, by free-living or symbiotic bacteria), ammonification (organic N → NH₄⁺), nitrification (NH₄⁺ → NO₂⁻ → NO₃⁻, by Nitrosomonas and Nitrobacter), and denitrification (NO₃⁻ → N₂, by anaerobic bacteria). Plants absorb nitrate for protein and nucleic acid synthesis.
氮循环包括四个主要过程：固氮作用（N₂ → NH₄⁺，由自生或共生菌完成）、氨化作用（有机氮 → NH₄⁺）、硝化作用（NH₄⁺ → NO₂⁻ → NO₃⁻，由亚硝酸菌和硝酸菌完成）和反硝化作用（NO₃⁻ → N₂，由厌氧菌完成）。植物吸收硝酸盐用于合成蛋白质和核酸。
6. Homeostasis – Thermoregulation | 稳态——体温调节
Homeostasis is the maintenance of a stable internal environment. In mammals, core body temperature is kept close to 37°C. The hypothalamus acts as the thermoregulatory centre, receiving input from peripheral and central thermoreceptors.
稳态是内环境的稳定维持。哺乳动物的体核温度维持在 37°C 左右。下丘脑作为体温调节中枢，接收来自外周和中枢温度感受器的信号。
In response to cold, the hypothalamus triggers vasoconstriction of skin arterioles, shivering (involuntary muscle contractions), piloerection (raising of hairs), and increased metabolic rate via thyroxine secretion. These reduce heat loss and increase heat production.
寒冷时，下丘脑引发皮肤小动脉收缩、战栗（不自主肌肉收缩）、立毛（汗毛竖立）及通过甲状腺激素分泌提高代谢率。这些反应减少散热并增加产热。
In hot conditions, vasodilation of skin arterioles increases heat loss by radiation. Sweat glands secrete sweat, and evaporation removes latent heat. The metabolic rate may decrease, and behavioural changes (seeking shade, reducing activity) assist temperature control.
炎热条件下，皮肤小动脉舒张增加辐射散热；汗腺分泌汗液，蒸发带走潜热；代谢率可下降；行为改变（寻找阴凉处、减少活动）辅助体温调节。
7. Homeostasis – Blood Glucose Regulation | 稳态——血糖调节
Blood glucose concentration must be kept within a narrow range (approximately 90 mg per 100 cm³). The pancreas monitors glucose levels and secretes insulin and glucagon from the islets of Langerhans.
血糖浓度必须维持在狭窄范围内（约 90 mg/100 cm³）。胰岛监测血糖水平并分泌胰岛素和胰高血糖素。
When blood glucose rises, beta cells secrete insulin. Insulin increases the permeability of muscle and fat cells to glucose, stimulates glycogenesis (glucose → glycogen) in liver and muscle, and promotes glucose uptake. These actions lower blood glucose.
血糖升高时，β 细胞分泌胰岛素。胰岛素增加肌肉和脂肪细胞对葡萄糖的通透性，促进肝和肌糖元合成（葡萄糖→糖原），加快葡萄糖摄取，从而降低血糖。
When blood glucose falls, alpha cells release glucagon. Glucagon activates glycogenolysis (glycogen → glucose) and gluconeogenesis (formation of glucose from non-carbohydrate sources) in the liver. Adrenaline also promotes glycogenolysis in muscle. Diabetes mellitus is a disorder involving inadequate insulin production (Type 1) or reduced insulin sensitivity (Type 2).
血糖降低时，α 细胞分泌胰高血糖素。胰高血糖素激活肝糖原分解（糖原→葡萄糖）和糖异生（非糖物质转化为葡萄糖）。肾上腺素也促进肌糖原分解。糖尿病涉及胰岛素分泌不足（1型）或胰岛素敏感性降低（2型）。
8. Homeostasis – Kidney and Osmoregulation | 稳态——肾脏与渗透调节
The kidney regulates water, electrolyte, and urea balance. Each nephron filters blood in the Bowman’s capsule, producing glomerular filtrate. Selective reabsorption and secretion occur along the tubule.
肾脏调节水、电解质和尿素平衡。每个肾单位在鲍曼囊过滤血液形成肾小球滤液，沿肾小管进行选择性重吸收和分泌。
Ultrafiltration in the glomerulus is driven by hydrostatic pressure. Water, glucose, salts, and urea pass into the filtrate; blood cells and large proteins are retained. The proximal convoluted tubule reabsorbs all glucose, most water, and essential ions by active transport and co‑transport.
肾小球超滤由静水压驱动。水、葡萄糖、盐和尿素进入滤液；血细胞和大分子蛋白质被截留。近曲小管通过主动转运和协同转运重吸收全部葡萄糖、大部分水和必需离子。
The loop of Henle creates a concentration gradient in the medulla via the countercurrent multiplier system. The collecting duct regulates final water content under the influence of ADH (antidiuretic hormone). ADH increases aquaporin insertion, raising water reabsorption when the body is dehydrated. Osmoreceptors in the hypothalamus control ADH release.
髓袢通过逆流倍增系统在髓质建立浓度梯度。集合管在抗利尿激素 (ADH) 调控下调节最终含水量。脱水时 ADH 增加水通道蛋白的嵌入，促进水的重吸收。下丘脑渗透压感受器控制 ADH 的释放。
9. Nervous Communication | 神经通讯
Neurones transmit information as action potentials. The resting potential (–70 mV) is maintained by the Na⁺/K⁺ pump and differential membrane permeability. An action potential is a brief reversal of membrane potential caused by voltage‑gated ion channels.
神经元以动作电位形式传递信息。静息电位（约 –70 mV）由钠钾泵和膜对不同离子的通透性差异维持。动作电位是由电压门控离子通道介导的短暂电位反转。
During depolarisation, voltage‑gated Na⁺ channels open, Na⁺ enters, and the membrane potential becomes positive. Repolarisation occurs as K⁺ channels open and K⁺ leaves. Hyperpolarisation follows before the resting potential is restored. The refractory period ensures unidirectional propagation.
去极化时电压门控 Na⁺ 通道开放，Na⁺ 内流，膜电位变正。K⁺ 通道开放、K⁺ 外流导致复极化；随后出现超极化，直至恢复静息电位。不应期保证冲动单向传导。
At a cholinergic synapse, an action potential triggers Ca²⁺ entry, causing vesicles to release acetylcholine into the cleft. Acetylcholine binds to receptors on the postsynaptic membrane, opening Na⁺ channels and generating an excitatory postsynaptic potential. Acetylcholinesterase degrades the transmitter. Summation (temporal and spatial) determines whether an action potential fires.
在胆碱能突触，动作电位引发 Ca²⁺ 内流，导致突触小泡释放乙酰胆碱至间隙。乙酰胆碱与后膜受体结合，开放 Na⁺ 通道产生兴奋性突触后电位。乙酰胆碱酯酶降解递质。时间总和与空间总和决定是否爆发动作电位。
10. Muscle Contraction | 肌肉收缩
Skeletal muscle fibres contain myofibrils made of repeating sarcomeres. The sliding filament theory explains contraction: actin (thin) filaments slide over myosin (thick) filaments, shortening the sarcomere.
骨骼肌纤维含有由重复肌节组成的肌原纤维。肌丝滑动学说阐明收缩：肌动蛋白（细丝）在肌球蛋白（粗丝）上滑动，肌节缩短。
Myosin heads bind to actin forming cross‑bridges, then perform a power stroke using ATP hydrolysis. Tropomyosin blocks myosin‑binding sites on actin in a relaxed muscle. When Ca²⁺ ions bind to troponin, tropomyosin moves, exposing the binding sites.
肌球蛋白头部与肌动蛋白结合形成横桥，随后利用 ATP 水解执行动力冲程。松弛时，原肌球蛋白覆盖肌动蛋白上的肌球蛋白结合位点。Ca²⁺ 与肌钙蛋白结合后，原肌球蛋白移开，暴露结合位点。
The arrival of a nerve impulse at the neuromuscular junction triggers Ca²⁺ release from the sarcoplasmic reticulum. The Ca²⁺ binds to troponin, initiating the cross‑bridge cycle. ATP is required for myosin head detachment and for pumping Ca²⁺ back into the sarcoplasmic reticulum during relaxation.
神经冲动到达神经肌肉接头引发肌质网释放 Ca²⁺。Ca²⁺ 与肌钙蛋白结合，启动横桥循环。ATP 用于肌球蛋白头部脱离，并在舒张时将 Ca²⁺ 泵回肌质网。
11. Gene Expression and Protein Synthesis | 基因表达与蛋白质合成
Protein synthesis involves transcription (DNA → mRNA) and translation (mRNA → polypeptide). In eukaryotes, transcription occurs in the nucleus and translation on ribosomes in the cytoplasm.
蛋白质合成包括转录（DNA → mRNA）和翻译（mRNA → 多肽）。真核生物中转录在细胞核内进行，翻译在细胞质的核糖体上完成。
During transcription, RNA polymerase binds to the promoter region and unwinds the DNA. It synthesises a complementary mRNA strand using the template strand. The mRNA is modified (splicing to remove introns, addition of a 5′ cap and poly‑A tail) before leaving the nucleus.
转录时，RNA 聚合酶结合启动子区域并解旋 DNA，以模板链为模板合成互补的 mRNA。mRNA 经修饰（剪接去除内含子、添加 5′ 帽和 poly-A 尾）后离开细胞核。
In translation, ribosomes read the mRNA codons. tRNA molecules carrying specific amino acids bind via anticodons. Peptide bonds form between adjacent amino acids. The process continues until a stop codon is reached. The lac operon in E. coli demonstrates transcriptional control: when lactose is present, it binds the repressor, allowing transcription of genes for lactose metabolism.
翻译时核糖体阅读 mRNA 密码子，携带特定氨基酸的 tRNA 通过反密码子结合。相邻氨基酸间形成肽键，直至终止密码子。大肠杆菌乳糖操纵子展示转录调控：存在乳糖时，它与阻遏蛋白结合，允许乳糖代谢基因转录。
12. Inheritance and Gene Technology | 遗传与基因技术
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