Year 13 OCR Biology: Core Knowledge Summary | Year 13 OCR 生物：核心知识点梳理

📚 Year 13 OCR Biology: Core Knowledge Summary | Year 13 OCR 生物：核心知识点梳理

Year 13 OCR A Level Biology delves into the intricate mechanisms that sustain life, from the rapid signalling of neurons to the delicate balance of ecosystems. Mastering these core topics provides a solid foundation for understanding how organisms function and interact, and it is essential for exam success. This article consolidates the key concepts from Modules 5 and 6, covering communication, homeostasis, energy, genetics, evolution and populations.

Year 13 OCR A Level 生物深入探讨从神经元的快速信号传导到生态系统微妙平衡等维持生命的复杂机制。掌握这些核心主题为理解生物体如何运作及互作提供了坚实基础，对考试成功至关重要。本文梳理了模块5和6的核心概念，涵盖通讯、稳态、能量、遗传、进化和种群等内容。

1. Neuronal Communication | 神经通讯

Resting membrane potential (around -70 mV) is established by the Na⁺/K⁺ pump, which actively transports 3 Na⁺ out and 2 K⁺ into the axon, and by K⁺ leak channels that allow K⁺ to diffuse out. When a stimulus depolarises the membrane to the threshold (-55 mV), voltage-gated Na⁺ channels open, causing a rapid Na⁺ influx that reverses the potential to about +40 mV. Shortly after, Na⁺ channels inactivate and voltage-gated K⁺ channels open, allowing K⁺ efflux to repolarise the membrane. The temporary hyperpolarisation and refractory period ensure unidirectional propagation of the impulse. The action potential is conducted more rapidly along myelinated axons through saltatory conduction, where depolarisation jumps between nodes of Ranvier.

静息膜电位（约 -70 mV）由钠钾泵主动转运（每消耗1分子ATP，泵出3个Na⁺、泵入2个K⁺）以及K⁺漏通道允许K⁺外流而建立。当刺激使膜去极化达到阈值（-55 mV），电压门控Na⁺通道开放，Na⁺快速内流将膜电位反转到约 +40 mV。稍后Na⁺通道失活，电压门控K⁺通道开放，K⁺外流使膜复极化。短暂的超极化和不应期确保冲动单向传导。在有髓鞘轴突上，动作电位通过跳跃传导在郎飞结之间跳跃，使传导速度大大加快。

In a cholinergic synapse, the arrival of an action potential at the presynaptic terminal opens voltage-gated Ca²⁺ channels; the influx of Ca²⁺ triggers synaptic vesicles to fuse with the membrane and release acetylcholine into the cleft. Acetylcholine binds to ligand-gated Na⁺ channels on the postsynaptic membrane, causing depolarisation (EPSP) if threshold is reached. The signal is terminated when acetylcholinesterase hydrolyses the neurotransmitter, ending the response and allowing the postsynaptic cell to reset.

在胆碱能突触中，动作电位到达突触前末梢后，电压门控Ca²⁺通道开放，Ca²⁺内流促使突触小泡与膜融合，释放乙酰胆碱至间隙。乙酰胆碱与突触后膜上配体门控Na⁺通道结合，若达到阈值则引起去极化（兴奋性突触后电位）。乙酰胆碱酶水解递质终止信号，让突触后细胞恢复静息状态。

2. Hormonal Communication | 激素通讯

Endocrine glands release hormones into the bloodstream to act on distant target cells. Peptide hormones (e.g. adrenaline, glucagon) are hydrophilic and bind to specific receptors on the cell surface, often activating second-messenger cascades such as cAMP which amplify the signal and trigger enzyme-driven responses. Steroid hormones (e.g. oestrogen) are lipid-soluble; they diffuse across the plasma membrane and bind to nuclear receptors, directly modulating gene transcription and protein synthesis.

内分泌腺将激素释放入血液，作用于远距离的靶细胞。肽类激素（如肾上腺素、胰高血糖素）亲水，与细胞表面特异性受体结合，通常激活cAMP等第二信使级联反应，放大信号并触发酶促响应。甾体类激素（如雌激素）脂溶，能穿越细胞膜并与核内受体结合，直接调节基因转录和蛋白质合成。

The adrenal medulla secretes adrenaline in response to stress, triggering hepatic glycogenolysis via cAMP to raise blood glucose for the ‘fight-or-flight’ response. Blood glucose homeostasis is managed by pancreatic cells: insulin (from β-cells) lowers blood glucose by promoting glucose uptake and glycogenesis, whereas glucagon (from α-cells) raises it by stimulating glycogenolysis and gluconeogenesis. Diabetes mellitus illustrates what happens when this feedback loop is disrupted.

肾上腺髓质在应激时分泌肾上腺素，通过cAMP促使肝糖原分解，升高血糖以支持“战或逃”反应。血糖稳态由胰岛细胞管理：胰岛素（β细胞分泌）通过促进葡萄糖摄取和糖原合成降低血糖，胰高血糖素（α细胞分泌）则通过刺激糖原分解和糖异生升高血糖。糖尿病正体现了这一反馈环路被破坏时的后果。

3. Homeostasis and Temperature Regulation | 稳态与体温调节

Homeostasis maintains a constant internal environment through negative feedback: any deviation from a set point triggers corrective responses. In thermoregulation, the hypothalamus acts as the control centre. A rise in core temperature leads to vasodilation of skin arterioles, increased sweat production, and lowered metabolic rate. A fall in temperature induces vasoconstriction, shivering (involuntary skeletal muscle contractions), activation of brown adipose tissue and behavioural adaptations such as huddling or seeking shelter.

稳态通过负反馈维持恒定内环境：任何偏离设定点的变化都会引发纠正反应。在体温调节中，下丘脑是控制中心。核心体温升高时，皮肤小动脉舒张、出汗增多、代谢率降低。体温下降则引起血管收缩、颤抖（不自主骨骼肌收缩）、激活棕色脂肪组织，以及蜷缩或寻找遮蔽处等行为适应。

Endotherms expend metabolic energy to maintain a stable core temperature. Piloerection, though less significant in humans, traps a layer of insulating air in furry mammals. Hormones such as thyroxine and adrenaline also modulate the metabolic rate over longer and shorter time scales respectively, contributing to thermal balance.

恒温动物消耗代谢能以维持稳定的核心体温。竖毛反射在人类身上意义不大，但在毛皮哺乳动物中可捕获一层隔热的空气。甲状腺素和肾上腺素等激素也在长短不同时间尺度上调节代谢率，共同维持热平衡。

4. Excretion and Kidney Function | 排泄与肾功能

The nephron is the functional unit of the kidney. Blood enters the glomerulus under high hydrostatic pressure, forcing water, ions, glucose and urea through the filtration barrier into Bowman’s capsule; this is ultrafiltration with the filtrate resembling plasma without large proteins or cells. In the proximal convoluted tubule, most glucose, amino acids and many ions are reabsorbed by active transport and co-transport, while urea and other wastes remain in the tubule. Water follows by osmosis, reducing the filtrate volume.

肾单位是肾脏的功能单位。血液在高压下进入肾小球，迫使水、离子、葡萄糖和尿素通过滤过屏障进入鲍曼氏囊，形成超滤液，其成分与血浆类似但缺乏大分子蛋白和血细胞。在近曲小管，绝大部分葡萄糖、氨基酸和许多离子通过主动转运和协同转运被重吸收，尿素等废物则留在小管液中，水以渗透方式跟随，滤液量减少。

The loop of Henle creates a hypertonic medullary interstitium via countercurrent multiplication. As filtrate descends, water leaves by osmosis; as it ascends, Na⁺ and Cl⁻ are actively transported out. The distal convoluted tubule and collecting duct fine-tune water and ion reabsorption under hormonal control. ADH, released from the posterior pituitary when blood water potential falls, inserts aquaporins into the collecting duct membrane, increasing water reabsorption and producing a small volume of concentrated urine. This osmoregulatory mechanism is vital for managing water balance.

亨氏袢通过逆流倍增机制在髓质建立高渗间质。滤液下行支水分子渗透外出；上行支Na⁺和Cl⁻被主动转运出。远曲小管和集合管在激素调控下精细调节水和离子重吸收。当血液水势下降，垂体后叶释放ADH，使集合管膜嵌入水通道蛋白，增加水重吸收，产生少量浓缩尿。这一渗透调节机制对水平衡至关重要。

5. Photosynthesis | 光合作用

The overall photosynthesis equation is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Light-dependent reactions occur in the thylakoid membranes. Light energy excites chlorophyll electrons, driving photolysis of water (2H₂O → 4H⁺ + 4e⁻ + O₂). The electron transport chain generates a proton gradient across the thylakoid membrane, powering ATP synthase (chemiosmosis) to produce ATP. NADP⁺ is reduced to NADPH. These products are then used in the stroma for the Calvin cycle.

光合作用总方程式为6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。光反应发生在类囊体膜上。光能激发叶绿素电子，驱动水的光解（2H₂O → 4H⁺ + 4e⁻ + O₂）。电子传递链在类囊体膜两侧建立质子梯度，驱动ATP合酶（化学渗透）合成ATP，并将NADP⁺还原为NADPH。这些产物随后在基质中用于卡尔文循环。

The light-independent Calvin cycle fixes CO₂. RuBisCO catalyses carboxylation of ribulose bisphosphate (RuBP) to form an unstable 6C intermediate that splits into two 3-phosphoglycerate (GP) molecules. GP is phosphorylated by ATP and reduced by NADPH to triose phosphate (TP). Most TP is used to regenerate RuBP, while some is exported to synthesise glucose, sucrose, starch and other carbohydrates. In C4 and CAM plants, additional CO₂-concentrating mechanisms minimise wasteful photorespiration by spatially or temporally separating carbon fixation from the Calvin cycle.

暗反应卡尔文循环固定CO₂。RuBisCO催化核酮糖二磷酸（RuBP）的羧化，生成不稳定的六碳中间物，随后裂解为两个3-磷酸甘油酸（GP）。GP被ATP磷酸化，被NADPH还原成磷酸丙糖（TP）。大部分TP用于再生RuBP，其余输出合成葡萄糖、蔗糖、淀粉等糖类。在C4和CAM植物中，额外的CO₂浓缩机制通过空间或时间分离碳固定与卡尔文循环，减少浪费性的光呼吸。

6. Respiration | 呼吸作用

The overall aerobic respiration reaction is C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (as ATP). Glycolysis in the cytoplasm splits glucose (6C) into two pyruvate (3C) molecules, yielding a net 2 ATP and 2 reduced NAD. In the mitochondrial matrix, the link reaction decarboxylates pyruvate, producing acetyl-CoA (2C), releasing CO₂ and generating reduced NAD. The Krebs cycle then oxidises acetyl-CoA completely to CO₂ while producing reduced NAD, reduced FAD and a small amount of ATP (via GTP).

有氧呼吸总方程式为C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 能量（ATP）。细胞质中的糖酵解将葡萄糖（6C）分解为两分子丙酮酸（3C），净得2 ATP和2 还原态

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