What materials do you need to assemble a microrespirometer?

A microrespirometer requires a tuberculin syringe, capillary tube, hot glue gun, manometer fluid (red food coloring mixed with soapy water), absorbent cotton, potassium hydroxide (KOH), nonabsorbent cotton, and glass beads. The syringe plunger is pushed in and the syringe end is cut off before inserting the capillary tube and sealing it with hot glue to create an airtight seal.

Why is detergent added to the manometer fluid?

Detergent is added to the manometer fluid because it coats the inside of the capillary tube, preventing the manometer fluid from sticking during the experiment. This coating ensures the fluid moves freely within the tube, allowing accurate measurement of gas volume changes as respiration occurs.

How should the cotton and potassium hydroxide be arranged inside the microrespirometer?

Absorbent cotton is inserted into the syringe barrel up to the 0 mL mark and packed firmly. A single drop of 15% KOH is added to this cotton, then nonabsorbent cotton is layered on top as a barrier to the seeds. The cotton should reach halfway between the 0 mL and 1 mL mark, and excess KOH is removed by pressing it out.

What is the role of potassium hydroxide in measuring cellular respiration?

Potassium hydroxide (KOH) absorbs carbon dioxide produced during cellular respiration. By removing CO2 from the system, any volume change in the capillary tube reflects only oxygen consumption, allowing direct measurement of respiration rate through the displacement of manometer fluid in the microrespirometer.

Why are two water baths set at different temperatures?

Two water baths at approximately 25°C and 40°C allow comparison of respiration rates at different temperatures. This experimental design tests how temperature affects cellular respiration in seeds, revealing the relationship between metabolic activity and environmental conditions in the microrespirometer setup.

What is the purpose of glass beads in the microrespirometer setup?

Glass beads serve as a control material in the microrespirometer. They are placed alongside seeds to account for any physical volume changes unrelated to respiration, ensuring that measured gas volume changes reflect only biological respiration rather than physical displacement or settling of materials.

How do you prepare the capillary tube before filling it with manometer fluid?

The capillary tube is inserted into the empty needle end of the syringe until it touches the plunger tip, then sealed with hot glue while standing straight. Once dry, the plunger is pulled back to verify the capillary tube is not plugged, ensuring it is ready for respiration quantification using microrespirometers procedure.

细胞呼吸

概念教师准备学生实验方案

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所有有生命的生物都需要能源来为其活动提供动力。归根结底，这种能源是太阳。那么，地球上的生物是如何利用这种能量的呢？这一切都始于光合作用。这些生物能够吸收二氧化碳和水，然后利用从太阳捕获的能量作为光子将这些分子推到一起，产生葡萄糖和氧气。葡萄糖是下一个关键步骤的关键，几乎所有生物体都以一种或另一种形式使用这一步骤——细胞呼吸。细胞呼吸由酶进行，无论是在原核生物的细胞膜中还是在真核生物的线粒体中。

化学反应首先使用氧气分解葡萄糖，再次产生二氧化碳和水，但在此过程中，最初用于制造葡萄糖分子的能量流向了两个新的地方。一种是合成 ATP 或三磷酸腺苷分子，这是一种细胞可以轻松使用的能源。其余的以热量的形式流失。到目前为止，我们一直在谈论一种使用氧气的细胞呼吸，这被称为有氧呼吸，但一些生物体和细胞能够在没有氧气的情况下进行呼吸。这称为无氧呼吸。这个过程不会产生二氧化碳和水，而是将乙醇作为副产品。发酵就是这种呼吸作用的一个例子。这就是酵母能够在密封容器中产生酒精的方式。我们可以使用一种称为呼吸计的工具来测量有氧呼吸。很简单，该设备测量生物体使用的氧气量，在这种情况下，植物种子发芽。发芽的种子正在呼吸，这意味着我们可以预期它们会耗尽氧气并释放二氧化碳。它们还没有绿色部分，所以它们没有进行光合作用。

在呼吸计中测量呼吸使用一种基于理想气体定律的巧妙方法，P 乘以 V 等于 n 乘以 R 乘以 T。V 是气体的体积。n 是存在的气体摩尔数。R 是理想气体常数，T 是绝对温度。简单地说，这意味着您可以通过测量样品的体积来计算出样品中存在多少个气体分子，前提是您知道压力和温度，因为 R 是一个常数。

呼吸计含有氢氧化钾，氢氧化钾以碳酸钾的形式捕获固体形式的二氧化碳。因此，由于细胞呼吸作用，密封管中的氧气被种子耗尽，它们释放出二氧化碳，而二氧化碳又被捕获为碳酸钾。因此，随着细胞呼吸的进行，系统内的气体总量减少。我们可以通过将呼吸计连接到称为压力计的设备上来量化这一点。在这里，随着氧分子的消耗，呼吸计腔室内的压力下降，微小毛细管内的有色液体被拉向压力降低的方向。然后，我们可以通过读取压力计水平上的值来估计呼吸计管中剩余的气体量。这种多功能系统可以设置许多不同的变量，例如不同的温度，并可用于测试许多不同类型的生物体的呼吸速率。

在本实验中，您将使用呼吸计和压力计来测量发芽种子的呼吸速率。