Respirometer

• what indicates rate of respiration?

  oxygen intake and volume of CO2 produced
• Respirometers are used to measure oxygen intake (aka, rate of aerobic respiration)
• Apparatus

  • Respirometer: Device to measure oxygen consumption.
  • Glass Beads: Used as a control to ensure that changes in gas volume are due to respiration.
  • Germinating Seeds: Actively respiring organisms consuming oxygen.
  • Test Tubes: Containers for the experiment.
  • Soda-Lime Pellets (or Potassium Hydroxide): Absorb carbon dioxide produced during respiration.
  • Stopwatch: To measure time intervals accurately.
  • Capillary Tube: Part of the respirometer to measure the movement of manometer fluid.
• Setting up the respirometer

  1. Place the germinating seeds in one test tube

  2. Place an equal volume of glass beads in the second test tube as a control
• Soda-lime pellets or potassium hydroxide


  Added to each test tube to absorb the CO2 produced during respiration
• Running the experiment


  1. Seal the test tubes with the respirometer apparatus

  2. Start the stopwatch and run the experiment for a set duration (e.g., 30 minutes)
• What happens in the test tube as seeds respire

  • Seeds consume oxygen, decreasing the air volume in the test tube
  • CO2 produced is absorbed by soda lime or KOH, reducing the pressure
• Manometer fluid movement


  Indicates the pressure change in the respirometer setup, moving towards the test tube containing the seeds
• Measuring the rate of oxygen consumption


  1. Measure the distance moved by the manometer fluid in a set time (e.g., 30 minutes)

  2. Use this distance to calculate the change in gas volume
• Resetting the respirometer apparatus

  1. Allow air to re-enter the tubes via the screw cap

  2. Use the syringe to reset the manometer fluid to its starting position
• Repeating the experiment


  • To ensure accuracy
  • Calculate the average volume of oxygen consumed across trials
• Formula for calculating the volume of oxygen consumed

  Volume = π(r²)h
• In the formula π(r²)h, 'r' represents

  Radius of the capillary tube (cm)
• In the formula π(r²)h, 'h' represents

  Distance moved by the manometer fluid (cm)
• Rate of respiration


  Volume of oxygen consumed per unit time (cm³ min⁻¹)