📚 Year 13 OCR Biology: Speaking & Listening Revision Focus | Year 13 OCR 生物：口语/听力备考专项
This revision guide transforms key Year 13 OCR Biology topics into an oral-aural learning experience. By speaking explanations aloud and listening carefully to the phrasing, you reinforce neural pathways and deepen comprehension. Each section presents a concise English explanation followed by its Chinese equivalent, perfect for reciprocal practice. Read the English paragraph, then attempt to explain it verbally before checking the Chinese version. For listening practice, have a partner read the paragraphs while you listen and recall key points.
这本复习指南将 Year 13 OCR 生物的核心主题转变为口语与听力学习体验。通过大声说出解释并仔细聆听表达，你能够强化神经通路并加深理解。每个部分先给出简洁的英文解释，紧跟着对应的中文翻译，非常适合对练。先阅读英文段落，尝试口头复述，再对照中文检查。在进行听力训练时，让搭档朗读段落，你边听边回忆关键点。
1. Cell Signalling and Communication | 细胞信号传导与通讯
Cell signalling enables cells to coordinate activities. A signalling cell releases a ligand, which binds to a specific receptor on or in a target cell. Receptors can be membrane-bound, like G-protein coupled receptors, or intracellular, such as receptors for steroid hormones. This binding triggers a cascade of events, often involving second messengers like cyclic AMP, leading to a cellular response.
细胞信号传导使细胞能够协调活动。信号细胞释放配体，配体与靶细胞表面或内部的特定受体结合。受体可以是膜结合型，如G蛋白偶联受体，也可以是胞内受体，例如类固醇激素的受体。这种结合触发级联事件，常常涉及像环腺苷酸这样的第二信使，最终引起细胞反应。
2. Neurones and the Action Potential | 神经元与动作电位
Neurones have a resting potential around -70 mV, maintained by the sodium-potassium pump. When a stimulus reaches threshold, voltage-gated sodium channels open, Na⁺ rushes in and the membrane depolarises, peaking near +40 mV. Next, sodium channels inactivate and potassium channels open, K⁺ flows out, causing repolarisation. A temporary hyperpolarisation may occur before the pump restores resting conditions. The all-or-nothing action potential then propagates along the axon.
神经元具有约-70 mV的静息电位，由钠钾泵维持。当刺激达到阈值，电压门控钠通道开放，Na⁺大量内流，膜去极化，峰值接近+40 mV。接着钠通道失活，钾通道开放，K⁺外流，引起复极化。在泵恢复静息状态之前可能出现短暂的超极化。全或无的动作电位随后沿轴突传播。
3. Synaptic Transmission | 突触传递
At a cholinergic synapse, the arrival of an action potential opens voltage-gated Ca²⁺ channels, allowing Ca²⁺ to enter the presynaptic knob. Vesicles containing acetylcholine fuse with the membrane and release the neurotransmitter into the cleft. Acetylcholine binds to receptors on the postsynaptic membrane, opening ligand-gated Na⁺ channels. If threshold is reached, a new action potential is generated. Acetylcholinesterase then breaks down the neurotransmitter to stop the signal.
在胆碱能突触，动作电位的到来打开电压门控 Ca²⁺ 通道，使 Ca²⁺ 进入突触前结。含有乙酰胆碱的囊泡与膜融合，将神经递质释放到间隙。乙酰胆碱与突触后膜上的受体结合，开放配体门控 Na⁺ 通道。若达到阈值，则产生新的动作电位。随后乙酰胆碱酯酶分解神经递质以终止信号。
4. Muscle Contraction – The Sliding Filament Model | 肌肉收缩——滑动纤维丝模型
Contraction occurs when myosin heads bind to actin, forming cross-bridges, and pull the actin filaments towards the centre of the sarcomere. The process begins when Ca²⁺ binds to troponin, causing tropomyosin to move and expose binding sites. Myosin heads hydrolyse ATP to ADP + Pi, pivot, and release energy to execute the power stroke. Binding of new ATP allows detachment, ready for the next cycle. The sarcomere shortens without the filaments themselves changing length.
当肌球蛋白头部与肌动蛋白结合，形成横桥，并将肌动蛋白丝拉向肌节中心时，便发生收缩。过程始于 Ca²⁺ 与肌钙蛋白结合，引起原肌球蛋白移动并暴露结合位点。肌球蛋白头部水解 ATP 为 ADP 与 Pi，旋动，释放能量完成动力冲程。新的 ATP 结合使横桥脱离，为下一循环做好准备。肌节缩短，而纤维丝本身长度不变。
5. Homeostasis and Negative Feedback | 稳态与负反馈
Homeostasis maintains a stable internal environment. A negative feedback loop involves a stimulus, a receptor, a coordination centre and an effector. For example, when blood temperature rises, thermoreceptors detect the change, the hypothalamus triggers effectors such as sweat glands and arterioles in skin to dilate, promoting heat loss. As the parameter returns to set point, the corrective action reduces. Positive feedback, in contrast, amplifies a change.
稳态维持稳定的内部环境。负反馈回路包含刺激、感受器、协调中心和效应器。例如，当血液温度升高，温度感受器检测变化，下丘脑触发效应器，如汗腺和皮小动脉扩张，促进散热。当参数回归设定点，矫正作用减弱。相反，正反馈会放大变化。
6. The Kidney – Osmoregulation | 肾——渗透调节
The kidney regulates water potential via the loop of Henle and collecting duct. In the descending limb, water moves out by osmosis; in the ascending limb, Na⁺ and Cl⁻ are actively transported out, creating a high solute concentration in the medulla. ADH released from the posterior pituitary increases the permeability of the collecting duct to water, allowing more reabsorption. In low ADH, less water is reabsorbed, producing dilute urine.
肾通过亨勒袢和集合管调节水势。在降支，水通过渗透作用运出；在升支，Na⁺ 和 Cl⁻ 被主动转运出，使髓质形成高溶质浓度。由垂体后叶释放的 ADH 增加集合管对水的通透性，允许更多重吸收。ADH 低时，较少水被重吸收，产生稀释尿液。
7. Photosynthesis – Light-dependent and Light-independent Reactions | 光合作用——光反应与暗反应
The overall equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. In the light-dependent stage, light energy excites electrons in chlorophyll, which pass along an electron transport chain, generating ATP and reducing NADP to reduced NADP. Photolysis of water provides electrons and releases O₂. In the Calvin cycle, CO₂ combines with RuBP, catalysed by Rubisco, producing GP, which is then reduced to TP using ATP and reduced NADP. TP regenerates RuBP and can form glucose.
总反应式：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。在光反应阶段，光能激发叶绿素中的电子，电子沿电子传递链传递，生成 ATP 并将 NADP 还原为还原型 NADP。水的光解提供电子并释放 O₂。在卡尔文循环中，CO₂ 在 Rubisco 催化下与 RuBP 结合，生成 GP，然后利用 ATP 和还原型 NADP 将 GP 还原为 TP。TP 再生成 RuBP 并可形成葡萄糖。
8. Respiration – Aerobic Pathways | 呼吸作用——有氧途径
Glycolysis in the cytoplasm splits glucose into two pyruvate molecules, yielding a net gain of 2 ATP and reduced NAD. The link reaction converts pyruvate to acetyl CoA, releasing CO₂ and reducing NAD. The Krebs cycle in the mitochondrial matrix oxidises acetyl groups, producing ATP, reduced NAD, reduced FAD and CO₂. Finally, the electron transport chain uses the energy from reduced coenzymes to drive ATP synthesis via chemiosmosis, producing up to 34 ATP per original glucose.
细胞质中的糖酵解将葡萄糖分解为两个丙酮酸分子，净生成 2 个 ATP 和还原型 NAD。连接反应将丙酮酸转化为乙酰辅酶 A，释放 CO₂ 并还原 NAD。线粒体基质中的克雷布斯循环氧化乙酰基，产生 ATP、还原型 NAD、还原型 FAD 和 CO₂。最后，电子传递链利用还原型辅酶的能量，通过化学渗透驱动 ATP 合成，每个原始葡萄糖最多产生 34 个 ATP。
9. Genetics – Dihybrid Inheritance and Linkage | 遗传学——双因子杂交与连锁
For unlinked genes, dihybrid crosses yield a 9:3:3:1 phenotypic ratio in the F₂ generation. Linked genes, located close on the same chromosome, do not assort independently and tend to be inherited together. Recombinant phenotypes arise only from crossing over. The frequency of recombination can be used to map gene loci; a 1% recombination frequency equals one map unit.
对于非连锁基因，双因子杂交在 F₂ 代产生 9:3:3:1 的表型比例。连锁基因位于同一条染色体上且距离相近，不独立分配，倾向于一起遗传。重组表型仅来自交叉互换。重组频率可用于绘制基因座位图；1% 的重组频率相当于一个图距单位。
10. Biotechnology – PCR and Gel Electrophoresis | 生物技术——PCR 与凝胶电泳
The polymerase chain reaction (PCR) amplifies DNA fragments in vitro. Components include DNA template, primers, DNA polymerase (Taq), and free nucleotides. Cycles of denaturation (95 °C), annealing (55–65 °C) and extension (72 °C) multiply the target sequence. Gel electrophoresis separates DNA fragments by size: samples are loaded into an agarose gel and an electric current is applied, causing negatively charged DNA to move towards the positive end. Smaller fragments travel further, producing a banding pattern.
聚合酶链式反应 (PCR) 在体外扩增 DNA 片段。所需成分包括 DNA 模板、引物、DNA 聚合酶 (Taq) 和游离核苷酸。变性 (95 °C)、退火 (55–65 °C) 和延伸 (72 °C) 的循环使目标序列倍增。凝胶电泳按大小分离 DNA 片段：样品加入琼脂糖凝胶，施加电流使带负电的 DNA 向正极移动。较小片段迁移更远，产生条带图谱。
11. Ecosystems – Energy Transfer and Productivity | 生态系统——能量传递与生产力
Energy enters ecosystems via photosynthesis. Gross primary productivity (GPP) is the total light energy converted to chemical energy. Net primary productivity (NPP) = GPP − respiratory losses. Energy transfer between trophic levels is inefficient; typically only 10% passes to the next level. Losses occur through respiration, excretion and uneaten parts. Pyramids of energy, biomass and numbers reflect these relationships.
能量通过光合作用进入生态系统。总初级生产力 (GPP) 是转化为化学能的总光能。净初级生产力 (NPP) = GPP − 呼吸消耗。营养级之间的能量传递效率低；通常只有约 10% 传递到下一级。损失源于呼吸、排泄和未被取食的部分。能量金字塔、生物量金字塔和数量金字塔反映了这些关系。
12. Population Control and Sustainability | 种群控制与可持续性
Population size is determined by birth rate, death rate, immigration and emigration. Density-dependent factors like competition and disease regulate populations near carrying capacity. Conservation aims to maintain biodiversity through sustainable practices, such as controlled fishing quotas and habitat restoration. Keystone species have a disproportionately large effect on their ecosystem, and their removal can trigger a trophic cascade.
种群大小由出生率、死亡率、迁入和迁出决定。密度制约因素如竞争和疾病将种群调节在环境容纳量附近。保护工作旨在通过可持续实践（如捕捞配额控制和栖息地恢复）维持生物多样性。关键种对其生态系统具有不成比例的巨大影响，移除它们可能引发营养级联效应。
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