Edexcel A (SNAB) A Level Biology:复习笔记7.2.6 Practical: Investigating the Rate of Respiration

Practical: Investigating the Rate of Respiration

  • Respirometers are used to measure and investigate the rate of oxygen consumption during aerobic respiration in organisms
  • The experiments usually involve organisms such as seeds or invertebrates


  • Respirometer
  • Glass beads
  • Germinating seeds
    • These will be actively respiring and consuming oxygen
  • Test tubes
  • Soda-lime pellets (or potassium hydroxide)
    • To absorb the carbon dioxide produced
  •  Stopwatch

A respirometer set up to measure the rate of respiration


  • Measure oxygen consumption: set up the respirometer and run the experiment with both tubes for a set amount of time (e.g. 30 minutes)
  • As the seeds consume oxygen, the volume of air in the test tube will decrease (CO2 produced during respiration is absorbed by soda lime or KOH)
  • This reduces the pressure in the capillary tube and manometer fluid will move towards the test tube containing the seeds
  • Measure the distance moved by the liquid in a given time
  • Use this measurement to calculate the change in gas volume within a given time, x cm3 min-1
  • Reset the apparatus: Allow air to re-enter the tubes via the screw cap and reset the manometer fluid using the syringe
  • Repeat experiment several times and calculate the average volume of oxygen consumed


  • The volume of oxygen consumed (cm3 min-1) can be worked out using:
    • The diameter of the capillary tube r (cm)
    • The distance moved by the manometer fluid h (cm) in a minute using the formula:


Exam Tip

It is important to note that when using living organisms such as woodlice or maggots you must treat them with respect and do not harm them.