RP16

• Respirometer


  A piece of equipment which measures the rate of respiration
• How a respirometer works

  1. Addition of a drop of coloured liquid to a length of tubing

  2. As the organism respires and the volume of oxygen in the tube decreases, the pressure also decreases

  3. The liquid moves down the pressure gradient towards the respirometer
• Equipment


  • Respirometer
  • Actively respiring organisms
  • Soda lime
  • Coloured liquid
  • Pipette
  • Solvent
  • Cotton wool
  • Stop clock
• Procedure


  1. Assemble the respirometer

  2. Add 5g of one organism to the boiling tube and replace the bung

  3. Place a drop of coloured manometer fluid in the open end of the respirometer

  4. Use a syringe to draw the fluid as far from the respirometer as possible and record its starting position

  5. Close the tap, start the stop clock

  6. After five minutes, open the tap, record the end position of the coloured liquid

  7. Repeat the process for the other organism
• Hazards


  • Broken glass
  • Soda lime
  • Biohazard
• Safety precautions


  • Take care when handling glass objects; keep away from edge of desk
  • Wear eye protection; avoid contact with skin, keep away from edge of desk
  • Use disinfectant; wash hands with soap after handling organisms
• In emergency


  • Elevate cuts; apply pressure; do not remove glass from wound; seek medical assistance
  • Wash off skin immediately; flood eye/cuts with cold water
  • Seek assistance
• Analysis


  1. Convert distance moved by the liquid in the time into volume of gas by using the πD formula with the diameter of the respirometers tube to produce a cross-section and then multiplying by distance moved

  2. Convert volume into rate by dividing by five minutes

  3. Convert rate into rate per gram of organism by dividing by five grams
• Soda lime absorbs carbon dioxide that is given out during respiration, so any changes in volume are assumed to be only due to differences in oxygen uptake
• Gas exchange due to photosynthesis is ignored and all of the gas is assumed to be oxygen
• Different organisms have different rates of respiration


  The animals have a higher rate of respiration per gram than the plants, as they have a higher metabolic rate and require much more energy to be released for movement/reproduction/etc.