Practical questions related to Respiration

• Describe how a respirometer can be used to measure the rate of aerobic respiration

  Measures O2 uptake:

  1. Add a set mass of single-celled organism eg. yeast to a set volume / concentration of substrate eg. glucose

  2. Add a buffer to keep pH constant

  3. Add a chemical that absorbs CO2 eg. sodium hydroxide

  4. Place in water bath at a set temperature and allow to equilibrate

  5. Measure distance moved by coloured liquid in a set time
• Common questions:

  Explain why the liquid moves.

  ● Organisms aerobically respire → take in O2

  ● CO2 given out but absorbed by sodium hydroxide solution

  ● So volume of gas and pressure in container decrease

  ● So fluid in capillary tube moves down a pressure gradient towards organism
• Describe a more accurate way

  to measure volume of gas.

  ● Use a gas syringe
• Explain why the apparatus must be airtight.

  ● Prevent air entering or leaving

  ● Would change volume and pressure, affecting movement of liquid
• Explain why the respirometer apparatus is left open for 10 minutes.

  ● Allow apparatus to equilibrate

  ● Allow for overall pressure expansion/change throughout

  ● Allow respiration rate of organisms to stabilise
• Describe how a respirometer can be used to measure the rate of anaerobic respiration

  • Explain why the apparatus is left for an hour after the culture has reached a constant temperature.
  • ● Allow time for oxygen to be used / respired
• IN ANAEROBIC RESPIRATION

  Explain why the liquid moves.

  ● Yeast anaerobically respire → release CO2

  ● So volume of gas and pressure in container increase

  ● So fluid in capillary tube moves down a pressure gradient away from organism
• MEASURING CO2 RELEASE IN ANAEROBIC RESPIRATION

  ● Repeat experiment as above but remove chemical that absorbs CO2

  • ● Make conditions anaerobic, for example:
  • ○ Layer of oil / liquid paraffin above yeast → stop O2 diffusing in
  • ○ Add a chemical that absorbs O2
  • ○ Leave for an hour to allow O2 to be respired and used up