📚 Designing Experiments to Investigate Respiration | 呼吸作用实验设计
Respiration is a fundamental biological process that releases energy from organic molecules. In the laboratory, we can design experiments to measure the rate of respiration, identify the substrates used, and investigate factors that affect it. This guide covers the key experimental techniques used in A‑Level Biology, focusing on respirometers, carbon dioxide detection, and the determination of the respiratory quotient.
呼吸作用是生物体释放能量的核心过程。在实验室中，我们可以设计实验测量呼吸速率，判断所用的呼吸底物，并探究影响呼吸作用的因素。本指南涵盖A‑Level生物学中关键的呼吸实验技术，重点介绍呼吸计的使用、二氧化碳检测以及呼吸商的测定。
1. Introduction to Respiration and Its Experimental Study | 呼吸作用及其实验研究简介
Respiration can be aerobic or anaerobic. In aerobic respiration, glucose is fully oxidised to carbon dioxide and water, releasing a large amount of ATP. Anaerobic respiration in yeast produces ethanol and carbon dioxide, while in mammalian muscle it produces lactate. Understanding these pathways allows us to design experiments that quantify gas exchange as a proxy for metabolic rate.
呼吸作用分为有氧呼吸和无氧呼吸。有氧呼吸中，葡萄糖被完全氧化为二氧化碳和水，释放大量ATP。酵母的无氧呼吸产生乙醇和二氧化碳，而哺乳动物肌肉的无氧呼吸产生乳酸。理解这些代谢途径以后，我们可以设计实验，通过测量气体交换来间接反映代谢速率。
2. Selecting Appropriate Organisms and Tissues | 选择适合的生物和組織
The choice of biological material is crucial. Germinating seeds (e.g. peas, beans) are excellent for measuring aerobic respiration because they respire actively but do not photosynthesise, eliminating the interference of gas exchange from photosynthesis. Yeast suspensions are ideal for studying both aerobic and anaerobic respiration, and they are easy to handle. Small invertebrates such as woodlice or insect larvae can also be used, provided ethical guidelines are followed.
生物材料的选择至关重要。萌发种子（如豌豆、蚕豆）是测量有氧呼吸的理想材料，因为它们呼吸旺盛但不进行光合作用，避免了光合气体交换的干扰。酵母悬液适用于有氧和无氧呼吸研究，且操作简便。也可以使用小型无脊椎动物，比如鼠妇或昆虫幼虫，但须遵守动物伦理规范。
3. Principles of Respirometry | 呼吸计量法原理
A respirometer measures the volume of oxygen consumed by a respiring sample over a period of time. Typically, the organism is placed in a sealed chamber containing a carbon dioxide absorbent (e.g. soda lime or potassium hydroxide solution). Any CO₂ produced is absorbed, so the decrease in gas volume or pressure inside the chamber directly reflects O₂ consumption. A control tube without organisms or with an equal volume of inert glass beads is set up to correct for changes in atmospheric pressure and temperature.
呼吸计通过测量一定时间内样本消耗的氧气体积来反映呼吸速率。通常将生物体放入含有二氧化碳吸收剂（如碱石灰或氢氧化钾溶液）的密闭容器中，呼吸产生的CO₂被吸收，因此容器内气体体积或压力的变化直接反映O₂的消耗量。同时设置对照管，管内不放生物或放入等体积惰性玻璃珠，用来校正外界气压和温度变化的影响。
4. Constructing a Simple Respirometer | 搭建简易呼吸计
A basic respirometer can be built using a test tube, a bung with two holes, a graduated capillary tube or manometer, and a syringe for resetting the liquid. In one hole, a capillary tube with a drop of coloured liquid acts as an indicator of volume change. The other hole is fitted with a three-way tap or syringe to allow the liquid to be pushed back to the starting point. The test tube contains a wire mesh platform to hold soda lime beneath the organisms.
简易呼吸计可以用一个试管、一个双孔橡皮塞、一根带刻度的毛细管或压力计，以及一个用于复位的注射器搭建。毛细管内的一滴有色液体作为体积变化的指示剂。另一个孔连接三通阀或注射器，用于将液滴推回起始位置。试管底部放一层金属网，上面放置萌发种子，网下则是碱石灰以吸收CO₂。
5. Measuring Oxygen Consumption with a Respirometer | 用呼吸计测量氧气消耗
To measure O₂ uptake, place a known mass of germinating seeds into the respirometer chamber with soda lime. Insert the bung, open the tap to the atmosphere, and use the syringe to adjust the manometer fluid to a marked zero. Close the tap, start the timer, and record the distance moved by the fluid every 30 seconds for 5–10 minutes. The rate of O₂ consumption (mm³ min⁻¹) is calculated from the slope of the volume‑time graph, correcting with the control. Results are expressed per gram of tissue.
测量O₂消耗时，将已知质量的萌发种子与碱石灰一同放入呼吸计小室。塞好瓶塞，将三通阀通大气，用注射器将压力计液面调至零点。关闭阀门，开始计时，每隔30秒记录有色液滴移动的距离，持续5–10分钟。根据体积—时间曲线斜率计算O₂消耗速率（mm³ min⁻¹），并用对照组数据进行校正，最终结果以每克组织的耗氧速率表示。
6. Measuring Carbon Dioxide Production | 测量二氧化碳的产生
Carbon dioxide production can be tracked using chemical indicators. A hydrogen carbonate indicator turns from red to yellow as CO₂ concentration increases. Alternatively, limewater turns milky due to the formation of insoluble calcium carbonate. In a fermentation tube with yeast, the volume of CO₂ gas collected over water or mineral oil gives a direct measure of anaerobic respiration rate. For aerobic experiments, a respirometer without CO₂ absorbent will show a smaller volume change (net gas exchange).
二氧化碳的产生可以通过化学指示剂检测。碳酸氢盐指示剂随CO₂浓度升高由红色变为黄色。石灰水则因生成不溶性碳酸钙而变浑浊。在酵母发酵管中，通过排水或排液体积法直接收集CO₂气体体积，即可测量无氧呼吸速率。在进行有氧实验时，不使用CO₂吸收剂的呼吸计会显示出净气体体积的变化（O₂消耗与CO₂释放的差值）。
7. Investigating the Effect of Temperature on Respiration Rate | 探究温度对呼吸速率的影响
Temperature is a key factor controlling enzyme‑catalysed reactions in respiration. To investigate its effect, water baths set at a range of temperatures (e.g. 10 °C, 20 °C, 30 °C, 40 °C) are used to equilibrate respirometers containing identical masses of seeds. The rate of O₂ uptake is measured at each temperature. The rate typically increases up to an optimal temperature, beyond which enzymes denature and the rate drops sharply. A graph of rate against temperature illustrates the Q₁₀ temperature coefficient.
温度是调控呼吸酶活性的关键因素。为探究温度影响，使用不同温度的水浴（如10 °C、20 °C、30 °C、40 °C）平衡含有等质量种子的呼吸计，分别测定各温度下的O₂消耗速率。速率通常随温度升高而加快，直至最适温度，之后因酶变性而急剧下降。绘制速率‑温度图可计算出温度系数Q₁₀。
8. Determining the Respiratory Quotient (RQ) | 测定呼吸商（RQ）
The respiratory quotient is the ratio of the volume of CO₂ produced to the volume of O₂ consumed over a set period. To determine RQ, set up two identical respirometers with the same mass of tissue: one with CO₂ absorbent (measuring O₂ uptake) and one without (measuring the net change in volume). The difference between the two readings gives CO₂ production. RQ is calculated using the formula:
RQ = volume of CO₂ produced / volume of O₂ consumed
With carbohydrates, RQ = 1.0; with lipids, RQ ≈ 0.7; with proteins, RQ ≈ 0.9. This method can reveal which substrate is being respired.
呼吸商是指一定时间内产生的CO₂体积与消耗的O₂体积之比。测定RQ时，需设置两个相同的呼吸计，放入等质量组织，其中一个含CO₂吸收剂（测得O₂消耗），另一个不含吸收剂（测得净体积变化）。两者的差值即为CO₂产生量。RQ计算公式如下：
RQ = 产生CO₂的体积 / 消耗O₂的体积
碳水化合物RQ=1.0；脂类RQ≈0.7；蛋白质RQ≈0.9。此法可以揭示当前被呼吸氧化的是哪类底物。
9. Using Metabolic Inhibitors to Study Pathways | 使用代谢抑制剂研究呼吸途径
Specific inhibitors can block steps in the electron transport chain or Krebs cycle, allowing us to deduce the order of reactions. For example, malonate is a competitive inhibitor of succinate dehydrogenase in the Krebs cycle. By adding malonate to a respiring tissue extract and measuring the accumulation of intermediates (e.g. succinate), we can identify the site of inhibition. Cyanide and DNP (2,4‑dinitrophenol) uncouple oxidative phosphorylation, causing a sharp increase in O₂ consumption and heat production without ATP synthesis.
特定的代谢抑制剂能够阻断电子传递链或克雷布斯循环的某些步骤，从而推断反应的顺序。例如，丙二酸是克雷布斯循环中琥珀酸脱氢酶的竞争性抑制剂。向呼吸组织提取液中加入丙二酸并检测中间产物（如琥珀酸）的积累，即可确定抑制位点。氰化物和DNP（2,4‑二硝基苯酚）能解除氧化磷酸化的偶联，导致耗氧量与产热量急剧增加，但不合成ATP。
10. Data Collection, Analysis and Evaluation | 数据收集、分析与评估
Reliable data require careful control of variables: temperature, mass of tissue, surface area, buffer pH, and equilibration time. Replicates should be performed to calculate mean rates and assess variability. A line graph of volume change against time is plotted, and the gradient calculated using linear regression. Sources of error include leaks in the apparatus, incomplete absorption of CO₂, and temperature fluctuations. Critical evaluation of the method and suggestions for improvement (e.g. using a pressure sensor and data logger) demonstrate higher‑level practical skills.
要获得可靠数据，需精细控制变量：温度、组织质量、表面积、缓冲液pH和平衡时间。应设置重复实验，计算平均速率并评估变异程度。绘制体积变化随时间变化的折线图，通过线性回归求出梯度（速率）。误差来源包括装置漏气、CO₂吸收不完全、温度波动等。对方法进行批判性评价并提出改进建议（如采用压力传感器和数据记录器），能够体现更高层次的实验技能。
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