Edexcel A (SNAB) A Level Biology

Revision Notes

7.2.6 Practical: Investigating the Rate of Respiration

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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

Apparatus

  • 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

Respirometer

A respirometer set up to measure the rate of respiration

Method

  • 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

Calculations

  • 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:

 πr2h

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. 

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Marlene

Author: Marlene

Marlene graduated from Stellenbosch University, South Africa, in 2002 with a degree in Biodiversity and Ecology. After completing a PGCE (Postgraduate certificate in education) in 2003 she taught high school Biology for over 10 years at various schools across South Africa before returning to Stellenbosch University in 2014 to obtain an Honours degree in Biological Sciences. With over 16 years of teaching experience, of which the past 3 years were spent teaching IGCSE and A level Biology, Marlene is passionate about Biology and making it more approachable to her students.