Topic 7

Question 1

What does a respirometer measure?

Answer 1

Volume of oxygen taken up in a given time

Question 2

How does volume of oxygen taken up in a given time affect rate of respiration?

Answer 2

The higher the volume of oxygen taken up in a given time, the higher the rate of respiration

Question 3

Explain how to carry out a respirometer practical - 8

Answer 3

• 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

Question 4

How can distance moved be converted into volume of oxygen used?

Answer 4

Do πr2 × distance moved, where r = the radius of the hole in the pipette

Question 5

Why is there a decrease of air volume in the test tube?

Answer 5

Oxygen consumed by woodlice and all CO2 produced is absorbed by sodalime

Question 6

What factors need to be controlled in respirometer practical?

Answer 6

• Temperature

- Volume of sodalime in each test tube

Question 7

What can a spirometer measure? 4

Answer 7

Tidal volume and so:

• Breathing rate
• Oxygen consumption
• Respiratory minute ventilation

Question 8

Explain how to carry out spirometer practical - 13

Answer 8

• 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

Question 9

Why does the spirometer need to be calibrated?

Answer 9

So that the movement of the lid corresponds to a given volume

Question 10

Explain how to measure effect of exercise on breathing - 6

Answer 10

• 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

Question 11

Define tidal volume

Answer 11

Volume of air in each breath

Question 12

Define breathing rate

Answer 12

Number of breaths taken in a minute

Question 13

Define oxygen consumption

Answer 13

Volume of oxygen used by the body expressed as a rate

Question 14

Define respiratory minute ventilation

Answer 14

Volume of gas breathed in/out per minute

Question 15

Give formula for calculating respiratory minute ventillation

Answer 15

tital volume x breathing rate