What does a respirometer measure?
Volume of oxygen taken up in a given time
How does volume of oxygen taken up in a given time affect rate of respiration?
The higher the volume of oxygen taken up in a given time, the higher the rate of respiration
Explain how to carry out a respirometer practical - 8
- Set up two tubes: both with soda lime, one control tube with glass beads weighing same as organism and one as a test tube
- Add a manometer containing fluid on a calibrated scale and use a syringe to set the fluid in the manometer to a known level
- Mark the starting position of the fluid with a permanent marker
- Place 5g of organism (maggots) into the tube and replace the bung
- Isolate the respirometer by closing the connection to the syringe and the atmosphere and immediately start the stop clock.
- Leave for 20 mins
- There will be a decrease in air in test tube, reducing pressure and moving coloured liquid to move towards test tube
- Measure distance moved by liquid and calculate volume of oxygen taken in by minute
- Repeat experiment and calculate mean volume of O2
How can distance moved be converted into volume of oxygen used?
Do πr2 × distance moved, where r = the radius of the hole in the pipette
Why is there a decrease of air volume in the test tube?
Oxygen consumed by woodlice and all CO2 produced is absorbed by sodalime
What factors need to be controlled in respirometer practical?
- Temperature
- Volume of sodalime in each test tube
What can a spirometer measure? 4
Tidal volume and so:
- Breathing rate
- Oxygen consumption
- Respiratory minute ventilation
Explain how to carry out spirometer practical - 13
- Spirometer has oxygen filled chamber with moveable lid
- Person breathes through tube connected to oxygen chamber
- As person breathes in lid of chamber moves down, breathing out moves it up
- These movements are recorded by a pen attached to the lid of the chamber
- Writes on a rotating drum to create a spirometer trace
- The volume of air the person inhales and exhales can be calculated from the distance the lid moves.
- Calibrate apparatus
- A canister containing soda lime is inserted between
the mouthpiece and the floating chamber to absorb the CO2 that the subject exhales. - The spirometer is filled with oxygen
- A disinfected mouthpiece is attached to the
tube, with the tap positioned so that the mouthpiece is connected to the outside air. - The subject to be tested puts a nose clip
on, places the mouthpiece in their mouth and breathes the outside air until they are comfortable with breathing through the tube. - After breathing normally the subject should
take as deep a breath as possible and then exhale as much air as possible before returning to normal breathing
Why does the spirometer need to be calibrated?
So that the movement of the lid corresponds to a given volume
Explain how to measure effect of exercise on breathing - 6
- Person breathes into spirometer at rest for a minute and recordings are taken
- Person than exercises for 2 minutes
- While person is exercising, spirometer is refilled with oxygen
- Immediately after person stops exercising, they breathe into spirometer again
- Recordings taken for another minute
- Compare recordings
Define tidal volume
Volume of air in each breath
Define breathing rate
Number of breaths taken in a minute
Define oxygen consumption
Volume of oxygen used by the body expressed as a rate
Define respiratory minute ventilation
Volume of gas breathed in/out per minute
Give formula for calculating respiratory minute ventillation
tital volume x breathing rate
