📚 3.2 Transport in Animals: Experimental Design | 动物体内的运输：实验设计
In the study of animal transport systems, well‑designed experiments allow us to explore how blood, oxygen, carbon dioxide and nutrients move, and how the heart and vessels respond to different conditions. The following collection of practical investigations covers the core principles of A‑level circulatory physiology, with clear aims, variables, procedures and common pitfalls.
在研究动物运输系统时，精心设计的实验能帮助我们探究血液、氧气、二氧化碳和营养物质如何流动，以及心脏和血管如何应对不同条件。以下一系列实践探究涵盖了A‑level循环生理学的核心原理，包括清晰的实验目的、变量、步骤与常见误区。
1. Investigating the effect of exercise on heart rate in humans | 探究运动对人体心率的影响
Aim: To measure the change in pulse rate before, during and after a period of standardised exercise, and to calculate the recovery time. This experiment illustrates how the cardiovascular system adjusts to increased oxygen demand.
目的：测量标准化运动前、中、后脉搏率的变化，并计算恢复时间。该实验展示了心血管系统如何适应增大的氧气需求。
Method: Measure resting heart rate for one minute using the radial or carotid pulse. Perform a set of 20 step‑ups onto a bench at a steady pace. Immediately after, record the pulse every minute until it returns to resting level. Plot pulse rate (y‑axis) against time (x‑axis).
方法：使用桡动脉或颈动脉脉搏测量安静状态下一分钟的心率。以稳定节奏完成20次登阶运动。运动停止后立即每分钟记录一次脉搏，直至回落到安静水平。以脉搏率（纵轴）对时间（横轴）作图。
Key controlled variables: type and duration of exercise, fitness level of the subject, environmental temperature, time of day. Reliability is improved by repeating with the same individual on different days or by using a larger sample.
关键控制变量：运动类型与持续时间、受试者体能水平、环境温度、一天中的时间。可通过同一人在不同日期重复测量或增加样本量来提高可靠性。
2. Measuring blood pressure using a sphygmomanometer | 使用血压计测量血压
Aim: To measure systolic and diastolic blood pressure at rest and after mild activity, linking the values to cardiac output and peripheral resistance.
目的：测量安静状态和轻度活动后的收缩压与舒张压，将数值与心输出量和外周阻力联系起来。
Method: Wrap the cuff around the upper arm at heart level. Inflate to about 180 mmHg, then slowly deflate while listening with a stethoscope placed over the brachial artery. The first tapping sound (Korotkoff sound) indicates systolic pressure; the point at which the sound disappears marks diastolic pressure. Repeat on the same arm after walking for two minutes.
方法：将袖带缠绕在上臂心脏水平位置。充气至约180 mmHg，然后缓慢放气，同时用听诊器置于肱动脉处听诊。第一次叩击声（柯氏音）指示收缩压；声音消失的点代表舒张压。步行两分钟后在同一手臂重复测量。
Controls: same arm, same posture, same time after exercise. It is vital to avoid talking or moving during measurement to prevent false readings.
控制：同一手臂，相同姿势，运动后相同间隔时间。测量期间避免说话或移动至关重要，以防止假读数。
3. Using a dye to trace circulation in a fish tail or frog web | 使用染料示踪鱼尾或蛙蹼中的循环
Aim: To observe blood flow in capillaries, arterioles and venules in a living transparent tissue, demonstrating the direction and velocity of blood movement.
目的：在活的透明组织中观察毛细血管、微动脉和微静脉中的血流，展示血液运动的方向与速度。
Method: A small fish (e.g., tadpole or small goldfish) is anaesthetised lightly and placed in a petri dish with a cotton wool bed, keeping the tail fin spread under a coverslip. A drop of methylene blue or ink injected upstream can be traced as it moves through the vessels. Alternatively, a pithed frog’s web can be examined under low‑power microscopy, where red blood cells are clearly visible without dye.
方法：将小鱼（如蝌蚪或小金鱼）轻度麻醉，置于带有棉絮床的培养皿中，使尾鳍在盖玻片下展平。在上游注射一滴亚甲蓝或墨水，可追踪它在血管中移动。此外，可在低倍显微镜下检查毁髓青蛙的趾蹼，其中红细胞无需染料就清晰可见。
Observations: blood flows fastest in arterioles, slowest in capillaries (often single file), and then accelerates again in venules. This supports Fick’s law by showing how slow capillary flow maximises exchange.
观察：血液在微动脉中流速最快，在毛细血管中最慢（常呈单行通过），然后在微静脉中再次加快。这支持了菲克定律，显示缓慢的毛细血管流动如何最大化物质交换。
4. Daphnia heart rate as a model for investigating chemical effects | 以水蚤心率作为化学物质影响的模型
Aim: To investigate the effect of caffeine, ethanol or temperature on the heart rate of Daphnia, a small freshwater crustacean with a transparent body.
目的：探究咖啡因、乙醇或温度对水蚤心率的影响。水蚤是一种身体透明的小型淡水甲壳动物。
Method: Place a single Daphnia on a cavity slide with a drop of pond water. Use cotton wool fibres to restrict movement. Count heart beats for 15 seconds under a microscope at low magnification, then multiply by four for beats per minute. Replace the water with a test solution (e.g., 0.1% caffeine) and repeat after a one‑minute equilibration. Wash and return to pond water to check recovery.
方法：将单只水蚤置于凹玻片上，加一滴池水。用棉絮纤维限制其运动。在低倍显微镜下计数15秒的心跳次数，乘以4得到每分钟心跳数。用测试溶液（如0.1%咖啡因）替换池水，平衡一分钟后重复。冲洗后放回池水中检查恢复情况。
Ethical note: Daphnia are invertebrates and not subject to the same legal protection as vertebrates, but care should be taken to minimise stress and to return healthy individuals to culture after the experiment.
伦理说明：水蚤为无脊椎动物，不受与脊椎动物相同的法律保护，但仍需小心减少应激，实验结束后将健康个体放回培养液中。
5. Dissection of a mammalian heart | 哺乳动物心脏解剖
Aim: To examine the external and internal structure of a sheep or pig heart, identifying chambers, valves, major blood vessels and the thickness of ventricular walls.
目的：检查羊心或猪心的外部和内部结构，识别心腔、瓣膜、主要血管以及心室壁厚度。
Method: Observe the outside of the heart, noting the coronary arteries on the surface, the floppy atria and the thicker ventricles. Make an incision along the right side to reveal the tricuspid valve and chordae tendineae. Open the left ventricle to see the thicker wall and the bicuspid (mitral) valve. Use a probe to trace the path of blood through the pulmonary artery and aorta. Compare wall thickness to relate structure to function.
方法：观察心脏外部，注意表面的冠状动脉、较软的心房和较厚的心室。沿右侧切开显露三尖瓣和腱索。打开左心室观察更厚的壁和二尖瓣。用探针沿肺动脉和主动脉追踪血液通路。比较壁厚以将结构与功能联系起来。
Safety: wear gloves and eye protection; disinfect surfaces. This is a foundational dissection that reinforces understanding of the double circulatory system.
安全措施：穿戴手套和护目镜；消毒台面。这是一项基础解剖，能强化对双循环系统的理解。
6. Investigating the effect of adrenaline on heart rate in a pithed frog | 探究肾上腺素对毁髓蛙心率的影响
Aim: To demonstrate the chronotropic (rate‑changing) effect of adrenaline on a vertebrate heart, keeping intrinsic pacemaking and sympathetic receptors intact.
目的：展示肾上腺素对脊椎动物心脏的变时作用，同时保持内在起搏和交感受体完整。
Method: A frog is double‑pithed to destroy brain and spinal cord, leaving the heart exposed. The beating heart is bathed in Ringer’s solution. Baseline heart rate is recorded. A few drops of dilute adrenaline solution (1:10 000) are applied directly to the heart, and the change in rate is recorded. The preparation is then washed with fresh Ringer’s to observe return to baseline.
方法：对青蛙进行双毁髓，破坏大脑和脊髓，暴露心脏。用任氏液浸泡跳动的心脏。记录基线心率。向心脏表面滴加几滴稀释肾上腺素溶液（1:10 000），记录心率变化。然后用新鲜任氏液冲洗，观察恢复至基线。
Results: adrenaline increases the frequency and force of contraction by binding to β₁‑adrenergic receptors, mimicking sympathetic stimulation. This experiment should only be performed where permitted and under strict ethical approval.
结果：肾上腺素通过结合β₁‑肾上腺素受体增加收缩频率和力度，模拟交感神经刺激。此实验仅应在允许且经严格伦理审批的条件下进行。
7. Measuring the oxygen content of water passing over fish gills | 测量流经鱼鳃水的含氧量
Aim: To quantify the efficiency of oxygen extraction at the gills by comparing O₂ concentration in inspired and expired water.
目的：通过比较吸入水与呼出水的O₂浓度，量化鳃的氧气提取效率。
Method: A fish is restrained in a divided chamber that separates water flowing into the mouth from water exiting the opercular cavity. Dissolved oxygen is measured using an oxygen electrode or Winkler’s titration before and after passing over the gills. The counter‑current flow system should result in a higher O₂ extraction than a parallel‑flow system would give.
方法：将鱼置于分隔室中，分离进入口腔的水与流出鳃腔的水。用氧电极或温克勒滴定法测量流经鳃之前和之后的溶解氧。逆流交换系统应比并流系统获得更高的O₂提取率。
Calculation: percentage extraction = (O₂ in inhalant – O₂ in exhalant) / O₂ in inhalant × 100%. Values often reach 80% in active fish, demonstrating a remarkably high efficiency.
计算：提取百分比 = （吸入水O₂ – 呼出水O₂）/ 吸入水O₂ × 100%。活泼鱼类该值常达80%，显示出极高的效率。
8. The effect of temperature on the rate of blood flow (model using visking tubing) | 温度对血液流速的影响（使用透析管模型）
Aim: To model how body temperature influences blood viscosity and flow rate, using a simple physical analogue.
目的：利用简单的物理模拟，建立体温如何影响血液黏度和流速的模型。
Method: Set up a reservoir of dyed water at a fixed height connected to a Visking tubing ‘vessel’. Measure the volume of liquid collected in 30 seconds. Repeat with water at 5 °C, 20 °C, 35 °C and 45 °C. Keep the pressure head constant. The flow rate increases with temperature because viscosity decreases. In a real animal system, enzymes and haemoglobin‑oxygen binding would also be affected, but this model isolates the physical factor.
方法：设置一个固定高度的染色水储液器，连接到透析管“血管”。测量30秒内收集的液体体积。分别使用5 °C、20 °C、35 °C和45 °C的水重复实验。保持压力水头恒定。流速随温度升高而增加，这是因为黏度降低。在真实动物系统中，酶和血红蛋白‑氧结合也会受影响，但此模型隔离了物理因素。
Limitation: no smooth muscle adjustment or vasodilation is represented. The model helps in understanding the principle that warmer animals may have a lower resistance to flow in vessels.
局限性：模型未体现平滑肌调节或血管舒张。该模型有助于理解原理：较暖的动物血管中流动阻力可能更低。
9. Investigating transpiration as an analogous transport process | 探究蒸腾作用作为类似的运输过程
Aim: Although transpiration occurs in plants, comparing it with capillary action and haemolymph flow helps students design controls and appreciate common physical principles.
目的：虽然蒸腾作用发生在植物中，将之与毛细作用和血淋巴流动进行比较，有助于学生设计对照，理解共同的物理原理。
Method: Use a potometer to measure water uptake in a leafy shoot under different conditions (wind, light, humidity). Draw parallels to the pulling force generated by evaporation in tracheoles of insects or the negative pressure in mammalian veins. Discuss how surface tension and cohesion are universal properties relevant to both phloem transport and blood movement in small vessels.
方法：使用蒸腾计测量带叶枝条在不同条件（风、光、湿度）下的吸水量。类比昆虫微气管中蒸发产生的拉力或哺乳动物静脉中的负压。讨论表面张力和内聚力这些普遍性质如何与韧皮部运输以及小血管中的血液流动都相关。
This cross‑topic investigation encourages thinking about transport as a physical process limited by similar constraints across living systems.
这一跨主题探究鼓励将运输视为受各生命系统类似限制的物理过程。
10. ECG recording and analysis of the cardiac cycle | 心电图记录与心动周期分析
Aim: To record a human electrocardiogram using surface electrodes and relate the P, QRS and T waves to atrial depolarisation, ventricular depolarisation and ventricular repolarisation respectively.
目的：使用表面电极记录人体心电图，并将P波、QRS波和T波分别与心房去极化、心室去极化和心室复极化联系起来。
Method: Electrodes are placed on the wrists and ankle (Einthoven’s triangle). The subject sits still and breathes normally. The trace is observed on a computer interface. Calculate heart rate from the R–R interval and identify any irregularities. This non‑invasive technique directly visualises the electrical conduction system of the heart.
方法：将电极放置于手腕和脚踝（艾因特霍芬三角）。受试者静坐，正常呼吸。在计算机界面上观察迹线。根据R–R间期计算心率，识别任何不规则。这项非侵入性技术直接可视化心脏的电传导系统。
Safety: low‑voltage equipment only; never use mains‑powered apparatus without isolation. Ensure electrodes are not placed over broken skin.
安全措施：仅使用低电压设备；切勿使用无隔离的市电供电仪器。确保电极不放置在破损皮肤上。
11. Constructing a closed circulatory system model | 构建闭式循环系统模型
Aim: To build a working physical model demonstrating the roles of a pump, valves and elastic vessels in sustaining unidirectional flow.
目的：建立一个可运行的物理模型，展示泵、瓣膜和弹性血管在维持单向流动中的作用。
Method: Use two syringes connected by plastic tubing to represent the heart and arteries; insert one‑way valves (e.g., from commercial water pumps) to prevent backflow. A balloon inside a rigid chamber can mimic the elasticity of the aorta. Pumping water through the circuit demonstrates how the pressure pulse is damped and how valves ensure net forward movement. This model helps to visualise why a four‑chambered heart is more efficient than a two‑chambered one.
方法：使用两个注射器通过塑料管连接，代表心脏和动脉；插入单向阀（如商用抽水泵中的阀门）防止逆流。刚性腔室内的气球可模拟主动脉弹性。通过回路泵送水，展示压力脉冲如何被衰减，以及瓣膜如何确保净向前运动。该模型有助于直观理解四腔心脏为何比两腔心脏更高效。
Extension: measure flow rate with and without ‘aortic’ elasticity to quantify the Windkessel effect.
扩展：测量有和没有“主动脉”弹性时的流速，量化风力室效应。
12. Measuring the effect of altitude simulation on oxygen saturation | 测量模拟海拔高度对血氧饱和度的影响
Aim: To investigate how reduced oxygen partial pressure affects haemoglobin saturation, using a pulse oximeter and a controlled‑gas mixture.
目的：使用脉搏血氧仪和可控气体混合物，研究氧分压降低如何影响血红蛋白饱和度。
Method: A subject breathes normally through a mask connected to a Douglas bag containing 15% O₂ (simulating ~3000 m altitude). Monitor SpO₂ every minute for ten minutes. Compare with baseline readings. The drop in saturation demonstrates the shape of the oxygen‑haemoglobin dissociation curve and the physiological trigger for increased ventilation and erythropoietin release.
方法：受试者通过面罩正常呼吸，面罩连接含有15% O₂（模拟约3000米海拔）的道格拉斯气袋。每十分钟监测一次SpO₂，持续十分钟。与基线读数比较。饱和度下降展示了氧合血红蛋白解离曲线的形状，以及增加通气和促红细胞生成素释放的生理触发因素。
Safety: have a medical‑grade oxygen supply on standby. Never use pure nitrogen. The experiment must be stopped if SpO₂ falls below 80% or the subject feels dizzy.
安全措施：备有医用级氧气供给。切勿使用纯氮。如果SpO₂降至80%以下或受试者感到头晕，必须立即停止实验。
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