RP 16: Rate of Respiration

• Describe how a respirometer works.

  A chamber is connected to a capillary tube with a drop of dye. As the organism in the chamber respires and uses oxygen, pressure decreases and the liquid moves in the capillary.
• What is the control for this practical (respiration)?

  Replace the organism with an inert object of the same mass.
• How do you use the volume of oxygen consumed using a respirometer?

  Place a fixed mass of soda lime in the respirometer with the organism. Measure the distance moved by the dye and calculate volume using distance * 𝛑r^2
• How can the volume of Carbon Dioxide produced be found?

  Perform two set-ups: one with soda-lime (A) and one without (B). Find the volume of gas used in the given time.

  Volume of carbon dioxide = volume of A - volume of B
• How is the rate of respiration calculated using data from the respirometer?

  rate = volume of oxygen used / mass of organism / time
• What is the risk of using soda-lime?

  The soda-lime is corrosive. Wear eye protection and handle with gloves.
• What are the control variables? (respiration)

  • Mass of organism
  • Temperature
  • Mass of soda lime
  • Apparatus must be airtight - replace between each set-up
• Formula for the respiratory quotient:

  Volume of carbon dioxide produced / Volume of oxygen absorbed