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At the end of this lab, students should know...
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Q1: 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.
Q2: 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.
Q3: 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.
Q4: 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.
Q5: 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.
Q6: 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.
Q7: 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.