Respiration PAG

Question 1

What can respirometer be used to indicate?

Answer 1

Used to indicate the rate of aerobic respiration by measuring the amount of oxygen consumed by a respiring organism over a period of time

Question 2

How would you set up/ explain the apparatus set up of a respirometer?

Answer 2

2 tubes: control tube (contains glass beads same mass as organisms that are respiring) and test tube (e.g. wood lice or seedlings)
Each tube contains potassium hydroxide solution, which absorbs carbon dioxide.
Tubes are connected by a manometer (a capillary tube filled with coloured fluid, with a calibrated scale)

Coloured fluid is added to the manometer by dipping the end of the capillary tube into a small beaker of the fluid, and allowed to run (capillary action makes fluid move into tube)

Question 3

Limitations of using respirometer to investigate respiration rate?

Answer 3

• oxygen may leak from the connectors so reduce the gas movement
• difficult to read the meniscus (may be subjective)

Question 4

What other variables need to be controlled when investigating respiration rate?
How would you control them?

Answer 4

• mass of seeds (e.g.)
  Take mass of seedlings at the start
• temperature
  Allows apparatus to stabilise before taking readings

Question 5

How does this experiment work?
Steps

Answer 5

1) syringe is used to set the fluid to a known level
2) the apparatus is then left for a set period of time (e.g 20 mins).
During that time there will be a decrease in the volume of air in the test tube, due to oxygen consumption by all the woodlice.
The decrease in the volume of air will reduce the pressure in the tube and cause the coloured liquid to the capillary tube to move towards the test tube (and away from the control tube)
3) distance moved by liquid in a given time is measured. This value can then be used to calculate the volume oxygen taken in by the woollike per minute (YOU ALSO NEED TO KNOW THE DIAMETER OF TH CAPILLARY TUBE TO DO THIS)
4) any variables that may affect the results are controlled and kept the same (e.g. volume of potassium hydroxide and mass of woodlice)
5) to produce more precise results, the experiment is repeated and a mean volume of O2 is calculated