respiration

• CONTROL VARIABLES

  • Number of organisms – 5g of maggots will be used
  • Temperature – same temperature used for each setup
  • Time – Recordings of volume increase will take place every minute for 5 minutes
• CONTROL


  Experiment can be carried out with plastic beads in the tube as a negative control (as plastic beads shouldn’t respire).
• method

  1. Place 5g of the organism (maggots) into the tube and replace the bung.
  2. Introduce a drop of dye into the glass tube.
  3. Open the connection (three-way tap) to the syringe and move the fluid to a convenient place on the pipette 
  4. Mark the starting position of the fluid on the pipette tube with a permanent marker.
  5. Isolate the respirometer by closing the connection to the syringe and the atmosphere and immediately start the stopwatch.
  6. Mark the position of the fluid on the pipette at 1 minute intervals for 5 minutes.
• method continued


  7.At the end of 5 minutes open the connection to the outside air. Measure the distance travelled by the liquid during each minute 

  8.Record your results in a suitable table.
• conclusion


  Oxygen molecules are absorbed by the organism and used in respiration. The same number of carbon dioxide molecules are released but these are absorbed by the soda lime. This reduces the pressure inside the test tube (fewer molecules = lower pressure). Atmospheric pressure pushes the liquid along the tube, until the pressure in and outside the tube is equal.