Respiration Exp.s Respirometer

Question 1

Describe how you would prepare the apparatus of a respirometer exp.

Answer 1

• Set up apparatus partially submerged in a water bath at 15°C.
  → to provide the optimum temp for the enzymes for resp. in woodlice.
• set up the control tube in exactly the same way but instead of woodlice, use glass beads of the same mass.
• leave the tap open and syringe unattached for 10 minutes to…
  → allow the apparatus to equilibrate ( to account for any expansion that might cause the pressure to change inside)
  → allow the resp. rate of the woodlice to stabilise in their new environment.
• After the 10 mins attach the close the tap and attach the syringe.
• Record the reading on the volume scale of the syringe.

Question 2

How does a respirometer work?

Answer 2

• rate of aerobic respiration is measured by the amount of oxygen consumed (over a period of time).
• As respiration occurs, the volume of the air in the test tube containing woodlice will decrease
  → as oxygen is consumed during respiration and all the CO2 produced is absorbed by the potassium hydroxide.
• The decrease in the volume of the air will reduce the pressure in the test tube, causing the coloured fluid in the capillary tube of the manometer to move towards it.
• After leaving the apparatus to run for a set period of time (e.g. 10 minutes) the reading on the syringe’s volume scale is recorded again.
• The difference between this figure and the figure taken at the start of the experiment is the oxygen consumption for this time period.
• The syringe is used to reset the manometer - so that the ends of the fluid are at the same level on either side of the U.

Question 3

Label this diagram of a respirometer.

Answer 3

Question 4

Why is it important that the temperature of the water bath is at 15°C?

Answer 4

to provide the optimum temperature for the enzymes involved in the woodlices’ respiration.

Question 5

What is the control in this experiment?

Answer 5

a control tube where the woodlice are substituted for glass beads of the same mass.

Question 6

Why is the tap left open and the syringe removed for ten minutes at the start of the experiment?

Answer 6

to allow the apparatus to equilibrate (to account for any expansion that might cause the pressure to change inside the capillary and test tubes).

to allow the resp. rate of the woodlice to stabilise.

Question 7

How could you inc. the precision of the results?

Answer 7

Repeat the exp. to calc. a mean vol. of O2 consumed.

Question 8

How else can O2 consumption be calculated from this exp?

Answer 8

Oxygen consumption can also be calculated by recording the movement of the fluid in the manometer read from the scale on the manometer itself.