Three-way Taps (AQA A Level Biology): Revision Note

Measuring air volume

• The volumes of air involved in gas exchange can be measured using a respirometer, an experimental set-up that measures oxygen consumption in living organisms

  • Respirometers measure changes in air pressure inside a container

  • As oxygen is consumed the air pressure decreases, causing a drop of coloured liquid to move towards the region of lower pressure

  • The distance moved by the coloured liquid in a given time can be used to calculate the volume of oxygen consumed

• Respirometers often contain equipment that aids their function, e.g.

  • three-way tap

  • manometer

Three-way taps

• Three-way taps can be opened to allow air into the respirometer, altering the internal pressure

• This enables the return of the liquid bead to the starting point to allow easy repeat readings

Manometers

• Manometers are narrow tubes that contain liquid, used to determine the difference in air pressure between two sealed containers

• The liquid in the tube is drawn towards the container where the pressure is lowest, and the distance moved by the fluid can be used to calculate the volume of gas removed