WJEC生物生理 气体交换 循环 神经 备考
WJEC A-Level Biology Unit 2: Animal Physiology covers every major body system ： from gas exchange to immunity. This 6-week study plan helps you master all systems, understand exam command words, and avoid common pitfalls. WJEC A-Level生物第二单元：动物生理学 涵盖每一个主要身体系统 ：： 从气体交换到免疫。这份6周备考计划帮你掌握所有系统，理解考试指令词，避开常见陷阱。
1. Gas Exchange 气体交换
WJEC requires you to compare gas exchange surfaces across 4 organisms: human lungs, fish gills, insect tracheae, and plant leaves. Each surface follows Fick's Law ： rate of diffusion ∝ (surface area × concentration gradient) / diffusion distance. In human lungs, alveoli provide a large surface area (~70 m²), thin epithelium (0.2 μm), and a steep concentration gradient maintained by ventilation and blood flow. Fish gills use a countercurrent flow system where blood flows opposite to water, maintaining a gradient along the entire gill filament ： this achieves up to 80% oxygen extraction, compared to only 50% in parallel flow. WJEC特别强调对比四种气体交换表面：人肺、鱼鳃、昆虫气管和植物叶片。每个表面都遵循菲克定律。人肺的肺泡提供约70平方米的巨大表面积。鱼鳃的逆流交换系统使得氧气吸收率高达80%。重点掌握逆流vs并流的区别，这是高频考点。
2. Transport Systems 循环系统
The heart generates pressure to drive blood through a closed double circulatory system. Remember the cardiac cycle sequence: atrial systole → ventricular systole → diastole. The sinoatrial node (SAN) acts as the pacemaker, initiating electrical impulses that spread across the atria, pause at the atrioventricular node (AVN), then travel down the Bundle of His and Purkinje fibres to trigger ventricular contraction. WJEC also tests the Bohr effect: increased CO₂ lowers blood pH, causing haemoglobin to release more oxygen ： this is why actively respiring tissues receive more O₂. 心脏的节律性收缩驱动血液在闭合双循环系统中流动。记住心动周期的顺序：心房收缩→心室收缩→舒张期。窦房结是起搏器，电信号经房室结延迟后沿希氏束和浦肯野纤维传导。玻尔效应也是重点：二氧化碳升高降低pH值，促使血红蛋白释放更多氧气给活跃组织。
3. Digestion and Absorption 消化与吸收
Physical digestion begins with mastication in the mouth and continues with churning in the stomach. Chemical digestion uses enzymes: amylase (saliva, pancreas) breaks starch to maltose; endopeptidases cleave internal peptide bonds while exopeptidases remove terminal amino acids; lipase (pancreas, aided by bile salts that emulsify fats) hydrolyses triglycerides into monoglycerides and fatty acids. Absorption occurs primarily in the ileum, where villi and microvilli create a massive surface area (~200 m²). Glucose and amino acids are absorbed by co-transport with Na⁺, while fatty acids form micelles and diffuse across the membrane. 物理消化从口腔咀嚼开始，化学消化依赖酶的专一性作用。淀粉酶分解淀粉，肽链内切酶和外切酶联合消化蛋白质，脂肪酶在胆汁盐乳化作用下水解甘油三酯。吸收主要发生在回肠，绒毛和微绒毛将表面积扩大至约200平方米。葡萄糖和氨基酸通过钠离子协同转运吸收，脂肪酸形成微胶粒扩散入细胞。WJEC要求能解释协同转运机制。
4. Kidney Function 肾脏功能
The nephron is the functional unit of the kidney. Ultrafiltration occurs in the Bowman's capsule, where blood pressure forces water, ions, glucose, and urea through the basement membrane while retaining blood cells and large proteins. Selective reabsorption happens in the proximal convoluted tubule (PCT): all glucose, most amino acids, and ~85% of water and Na⁺ are reabsorbed via co-transport and osmosis. The loop of Henle uses a countercurrent multiplier to create a concentration gradient in the medulla ： Na⁺ and Cl⁻ are actively pumped out of the ascending limb, drawing water out of the descending limb by osmosis. ADH (antidiuretic hormone) controls the permeability of the collecting duct: more ADH → more aquaporins → more water reabsorbed → concentrated urine. 肾单位是肾脏的功能单位。超滤发生在肾小囊，血液压力将水、离子、葡萄糖和尿素挤过基底膜。近曲小管进行选择性重吸收：：全部葡萄糖和约85%的水钠被重吸收。亨勒袢的逆流倍增器在髓质建立浓度梯度。抗利尿激素ADH控制集合管的通透性：ADH增多→水通道蛋白增加→更多水重吸收→浓缩尿液。WJEC常见的6分大题：解释ADH如何调节水平衡。
5. The Nervous System 神经系统
A resting neurone maintains a potential difference of -70 mV across its membrane, established by the Na⁺/K⁺ pump (3 Na⁺ out, 2 K⁺ in) and the differential permeability to K⁺. An action potential is triggered when the membrane depolarises past the threshold (-55 mV), opening voltage-gated Na⁺ channels. The sequence: depolarisation (Na⁺ influx) → repolarisation (K⁺ efflux) → hyperpolarisation → return to resting potential. The refractory period ensures unidirectional propagation and limits maximum firing frequency. At a cholinergic synapse, the action potential opens Ca²⁺ channels in the presynaptic knob, triggering vesicle fusion and release of acetylcholine (ACh). ACh diffuses across the synaptic cleft, binds to receptors on the postsynaptic membrane, and opens Na⁺ channels. Acetylcholinesterase hydrolyses remaining ACh to prevent continuous stimulation. 静息神经元维持-70mV的膜电位，由钠钾泵和钾离子通透性建立。动作电位的序列：去极化→复极化→超极化→恢复静息。不应期确保单向传播并限制最大发放频率。在胆碱能突触中，动作电位触发钙离子内流，导致囊泡融合释放乙酰胆碱，ACh扩散至突触后膜并打开钠离子通道。乙酰胆碱酯酶水解残余ACh以防止持续刺激。
6. Muscles and Movement 肌肉与运动
The sliding filament theory explains muscle contraction. An action potential arriving at the neuromuscular junction triggers Ca²⁺ release from the sarcoplasmic reticulum. Ca²⁺ binds to troponin, causing a conformational change that moves tropomyosin away from the myosin-binding sites on actin. Myosin heads (with bound ADP + Pi) attach to actin, release ADP + Pi, and execute the power stroke ： pulling actin filaments toward the centre of the sarcomere. ATP binds to myosin, causing detachment, and is hydrolysed to re-cock the myosin head. When stimulation stops, Ca²⁺ is actively pumped back into the sarcoplasmic reticulum, tropomyosin re-blocks binding sites, and the muscle relaxes. WJEC requires you to interpret electron micrographs of sarcomeres in relaxed and contracted states. 肌丝滑动学说解释肌肉收缩机制。动作电位触发肌浆网释放钙离子，钙与肌钙蛋白结合引起构象变化，暴露出肌动蛋白上的结合位点。肌球蛋白头部完成强力收缩，拉动肌动蛋白丝向肌节中心滑动。ATP结合使肌球蛋白脱离，水解后重新蓄力。考试要求能解读松弛和收缩状态下的肌节电镜图，识别I带、A带和H区的变化。
7. Immune System 免疫系统
The immune system has two layers: innate (non-specific) and adaptive (specific). Innate defences include physical barriers (skin, mucus), phagocytes (neutrophils, macrophages) that engulf pathogens, and inflammation. The adaptive response involves lymphocytes: B cells produce antibodies (humoral response) while T cells attack infected cells (cell-mediated response). Antigen presentation is the bridge: macrophages display pathogen antigens on MHC Class II molecules, activating helper T cells, which in turn activate B cells and cytotoxic T cells. B cells differentiate into plasma cells that secrete antibodies and memory cells for long-term immunity. Vaccination exploits memory cell formation ： the primary response produces memory cells that enable a faster, stronger secondary response upon re-exposure. 免疫系统包含先天性和适应性两层防御。先天免疫包括物理屏障、吞噬细胞和炎症反应。适应性免疫涉及淋巴细胞：B细胞产生抗体（体液免疫），T细胞攻击感染细胞（细胞免疫）。抗原呈递是桥梁：巨噬细胞通过MHC II类分子展示抗原，激活辅助T细胞，进而激活B细胞和细胞毒性T细胞。疫苗接种利用记忆细胞：：初次应答产生记忆细胞，再暴露时触发更快更强烈的二次应答。
8. Homeostasis Integration 稳态整合
WJEC rewards answers that connect multiple systems. Homeostasis is the unifying theme across all Physiology topics. Thermoregulation involves the nervous system (hypothalamus detects blood temperature changes), muscles (shivering generates heat), transport system (vasodilation/vasoconstriction redirects blood), and glands (sweat cools by evaporation). Blood glucose regulation involves the pancreas (α-cells secrete glucagon, β-cells secrete insulin), the liver (glycogenesis, glycogenolysis, gluconeogenesis), and transport (blood distributes glucose). Osmoregulation integrates the kidney (nephron water reabsorption), pituitary gland (ADH release), and hypothalamus (osmoreceptors). When answering 6-mark questions, explicitly name the systems involved and trace the sequence from stimulus to response. WJEC评分倾向奖励连接多个系统的答案。稳态是所有生理学主题的统一概念。体温调节涉及神经系统（下丘脑检测血液温度）、肌肉（颤抖产热）、循环系统（血管舒张/收缩）和腺体（汗液蒸发散热）。血糖调节涉及胰腺、肝脏和循环系统的协同。渗透调节整合肾脏、垂体和下丘脑。回答6分大题时，明确指出涉及的系统并完整的从刺激到响应串联展开。
9. Six-Week Study Plan 六周备考计划
Week 1 第一周: Gas Exchange + Transport Systems. Draw labelled diagrams of alveoli, fish gills, and the cardiac cycle. Practise explaining the Bohr effect and countercurrent flow in your own words. 绘制肺泡、鱼鳃和心动周期的标注图，用自己的话解释玻尔效应和逆流交换。
Week 2 第二周: Digestion + Kidney. Create a flowchart of enzyme action (carbohydrases, proteases, lipases). Master the nephron diagram ： label Bowman's capsule, PCT, loop of Henle, DCT, and collecting duct. 制作酶作用的流程图，掌握肾单位标注图。
Week 3 第三周: Nervous System + Muscles. Draw and label an action potential graph (mV vs time). Practise the sliding filament sequence step by step. Write a 6-mark answer on synaptic transmission. 绘制动作电位图，逐步练习肌丝滑动顺序。写一篇关于突触传递的6分答案。
Week 4 第四周: Immune System + Cross-Topic Integration. Construct a comparison table of innate vs adaptive immunity. Draw antigen presentation and clonal selection. Practise linking transport (blood) to immunity (lymphocytes, antibodies). 构建先天性与适应性免疫对比表，绘制抗原呈递和克隆选择图。
Week 5 第五周: Past Papers. Complete WJEC Unit 2 papers from 2018-2024. Focus on 6-mark extended response questions ： practise the WJEC mark scheme structure: definition → mechanism → consequence → example. 完成2018-2024年WJEC第二单元真题，重点练习6分扩展题。
Week 6 第六周: Targeted Revision. Revisit weak areas identified from past papers. Time yourself on full papers. Create summary mind maps linking all systems ： for example, transport delivers oxygen (gas exchange), nutrients (digestion), and immune cells. 针对性复习薄弱环节，计时完成全卷，制作关联各系统的思维导图。
10. Exam Tips for WJEC Biology 考试技巧
Command words decode 指令词解码: "Describe" requires stating what you see or what happens ： no explanation needed. "Explain" demands reasons and mechanisms ： always include "because." "Compare" needs similarities AND differences ： use "whereas" or "while" to contrast. "Suggest" asks for applied reasoning ： use your scientific knowledge in an unfamiliar context. WJEC Paper-specific strategy: WJEC Unit 2 is a 2-hour paper worth 90 marks. The paper is structured with shorter 1-3 mark questions in Section A and extended 6-9 mark questions in Section B. Allocate roughly 1.3 minutes per mark： for a 6-mark question, spend no more than 8 minutes. Section B questions frequently ask you to analyse data from tables or graphs before explaining the underlying physiology： always quote data values in your answer. 6-mark extended responses: WJEC expects a logical sequence: state the observation → explain the mechanism → link to broader physiological context. Always include specific terminology (countercurrent, Bohr effect, action potential, co-transport) to hit mark scheme keywords. 描述题只要求陈述所见；解释题必须说明原因和机制；比较题同时要求异同；建议题考察应用推理。WJEC第二单元为2小时90分试卷。A部分为1-3分简答题，B部分为6-9分扩展题。每题分配约1.3分钟：6分题不超过8分钟。B部分常要求先分析图表数据再解释生理机制：务必引用具体数值。六分扩展题必须按逻辑展开，使用准确术语来命中评分关键词。
⚠️ 5 Common WJEC Biology Mistakes 五大常见错误:
1. Confusing countercurrent flow with concurrent flow in fish gills ： the gradient is maintained, not depleted.
2. Forgetting that the SAN initiates the heartbeat, not the AVN or brain ： the heart is myogenic.
3. Mixing up ADH effects: more ADH = more aquaporins = MORE water reabsorbed = concentrated urine (not dilute).
4. Stating Ca²⁺ binds to tropomyosin ： it binds to TROPONIN; tropomyosin is the protein that MOVES.
5. Writing "active transport of water" ： water moves by OSMOSIS, never active transport.
Key Bilingual Terms 关键双语术语
Countercurrent flow 逆流交换 | Fick's Law 菲克定律 | Alveoli 肺泡 | Tracheae 气管 | Bohr effect 玻尔效应 | Sinoatrial node (SAN) 窦房结 | Atrioventricular node (AVN) 房室结 | Bundle of His 希氏束 | Endopeptidase 肽链内切酶 | Exopeptidase 肽链外切酶 | Micelle 微胶粒 | Co-transport 协同转运 | Nephron 肾单位 | Bowman's capsule 肾小囊 | Ultrafiltration 超滤 | Proximal convoluted tubule 近曲小管 | Loop of Henle 亨勒袢 | Countercurrent multiplier 逆流倍增器 | Antidiuretic hormone (ADH) 抗利尿激素 | Aquaporin 水通道蛋白 | Depolarisation 去极化 | Repolarisation 复极化 | Refractory period 不应期 | Cholinergic synapse 胆碱能突触 | Acetylcholinesterase 乙酰胆碱酯酶 | Sarcoplasmic reticulum 肌浆网 | Troponin 肌钙蛋白 | Tropomyosin 原肌球蛋白 | Sarcomere 肌节 | Phagocyte 吞噬细胞 | Antigen presentation 抗原呈递 | MHC Class II 主要组织相容性复合体II类 | Plasma cell 浆细胞 | Memory cell 记忆细胞
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