1. The Respirometer

2. 1. What process does the apparatus measure?
Capillary tube
Question
1. What process does the apparatus measure?
Answer
1. Respirometers measure the rate oxygen uptake.

3. 2. i) In what units might the results be measured?
Oil droplet
Question
2. i) In what units might the results be measured?
Answer
2. There needs to be some measurement of volume, mass of the specimen and of time.
e.g. mm3 g-1 hour-1

4. Oil droplet
Question
3. Name substance A.
Answer
3. Soda lime A

5. 4. What is the function of the soda lime?
Oil droplet
Question
4. What is the function of the soda lime?
Answer
CO2
4. To absorb carbon dioxide.
Soda
lime

6. 5. Suggest reasons for absorbing carbon dioxide in this apparatus?
Oil droplet
Question
5. Suggest reasons for absorbing carbon dioxide in this apparatus?
Answer
CO2
5. Carbon dioxide is produced by respiration and affects the volume and pressure of gas in the tube. If the carbon dioxide is removed by the soda lime it allows you to measure the amount of oxygen used in aerobic respiration
Soda
lime

7. 6. In which direction will the oil drop move.
Oil droplet
Question
6. In which direction will the oil drop move.
Answer
6. Towards the test tube.

8. 7. Why does the oil droplet move towards the test tube? O2
Question
7. Why does the oil droplet move towards the test tube? O2
Answer
CO2
7. The pressure in the test tube falls as oxygen is taken up by aerobic respiration and the carbon dioxide that replaces it is absorbed by the soda lime
Soda
lime

9. Question
8. Give two reasons why the respirometer should be placed in a thermostatically controlled water bath.
Answer
8. i) A change in temperature would cause the gas pressure in the test tube to change. This will cause the oil droplet to move and give an incorrect reading.
8. ii) Respiration is controlled by enzymes and the rate of an enzyme reaction is effected by temperature.

10. Question
9. Suggest two reasons why the apparatus was left for ten minutes, with the tap open, when it was first placed in a water bath.
Answer
9. ii. It allows the specimen to reach the same temperature as the water bath
9. i. If the apparatus is placed in a water bath then changes in temperature will cause changes in air pressure. Leaving the tap open allows the pressure to equalise with the outside air

11. Question
10. If the specimen in the respirometer was a plant and not an animal what modifications to the equipment would you need to make.
Answer
10. The respirometer is for measuring respiration not photosynthesis so you have to stop photosynthesis by placing the apparatus in the dark.

12. The respirometer was used to measure the rate of respiration of germinating seeds in air. The distance moved by the oil drop was measured at 15 minute intervals for one hour. This was repeated with the air replaced by nitrogen gas. The rate of respiration of small insects in air was measured using the same apparatus.

13. The Table below shows results recorded by a student using this apparatus
Organism
Distance moved by liquid in 15 minute intervals/mm
Mean rate of respiration /mm min -1
Germinating seeds 7 6 5
Germinating seeds in nitrogen gas
Insects 12 11 13
0.4
0.8
Question 11
11. Calculate the mean rates of respiration expressed as movement of liquid in millimetres per minute.

14. Question
12. The seeds in the experiment with nitrogen gas continued to germinate. Suggest an explanation for the lack of movement of the liquid .
Answer
12. No oxygen is available for aerobic respiration. The seeds must be respiring anaerobically which does not require oxygen. The carbon dioxide produced is absorbed and therefore there is no net change in the volume /pressure of gas. Therefore the oil droplet will not move.

15. Question
13. Suggest reasons why a valid comparison cannot be made between the mean rate of respiration of the germinating seeds in air and the insects. For each reason suggest a modification that would allow a valid comparison.
Answer
13. i. The mass of the organisms are not stated and may differ. Either use the same mass of for each organism or express the results per unit mass e.g. e.g. mm3 g-1 hour-1.
13. iii. The external air pressure may have altered changing the gas volume/pressure. Use a control with no organisms at the same time.
13. ii. The temperature has not been controlled and may have changed during the course of the experiment changing the volume/pressure of gas. Control the temperature by using a water bath.

16. Question
14. What is the function of the Pottasium hydroxide (KOH) in this experiment
Answer
14. It absorbs the Carbon dioxide, (It is an alternative to soda lime.)
KOH

17. 15. What is the function of the roll of filter paper
Question
15. What is the function of the roll of filter paper
Answer
15. It increases the surface area of air in contact with sodium hydroxide and thus speeds up absorption of carbon dioxide.
Filter
paper

18. Complex Respirometers
Question
16. Suggest a function of the second test tube A in this more complex respirometer .
Answer
16. The second test tube acts as a control

19. Complex Respirometers
Question
17. Suggest how the syringe could be used to check for leaks.
Answer
17. The syringe is pressed down changing the level of the coloured oil. If there are leaks present the oil will gradually return to the original level.

20. Complex Respirometers
Question
18. Give another function of the syringe.
Answer
18. The syringe is used to reset the oil droplet to allow readings over a longer time period.

22. Not in SNAB Edexcel Biology
Respiratory Quotient
Not in SNAB Edexcel Biology

23. The respirometer opposite was used to determine the rate of respiration and the respiratory quotient of blowfly larvae. In the first experiment 5 cm3 of sodium hydroxide solution was placed in the test tube and blowflies were placed on the wire cage. The assembled apparatus was placed in a water bath at 20°C, with the tap left open. After ten minutes the tap was closed and the position of the bead of liquid was recorded at 1 minute intervals. A second experiment was carried out using 5cm3 of water instead of sodium hydroxide solution.

24. 10. What is the function of the Sodium hydroxide in this experiment
Question
10. What is the function of the Sodium hydroxide in this experiment
Answer
10. It absorbs the Carbon dioxide, (It is an alternative to soda lime.)
NaOH

25. 11. What is the function of the roll of filter paper
Question
11. What is the function of the roll of filter paper
Answer
11. It increases the surface area of air in contact with sodium hydroxide and thus speeds up absorption of carbon dioxide.
Filter
paper

26. Time/
minutes
1st experiment
2nd experiment 11 40 1 23 2 34 3 47 4 60 5 71
Position of liquid/mm
Question
12. Plot the results of the experiment on a graph

27. 20 30 40 50 60 70
Position of liquid/mm
1st experiment
Time/
minutes
1st experiment
2nd experiment 11 40 1 23 2 34 3 47 4 60 5 71
Position of liquid/mm
2nd experiment 1 2 3 4 5
Time/minutes

28. Question
13. Explain why the bead of liquid moved in the first experiment but not in the second
Answer
13. In the first experiment the pressure in the test tube falls as oxygen is taken up by aerobic respiration and the carbon dioxide that replaces it is absorbed by the NaOH. In the second experiment the oxygen taken up in respiration is replaced by an equal amount of carbon dioxide. There is no NaOH to absorb the carbon dioxide.
NaOH or
H2O

29. 14. Suggest a suitable control for this experiment.
Question
14. Suggest a suitable control for this experiment.
Answer
14. Replace the blowflies with glass beads (or something similar). The glass beads are not undergoing respiration and this will demonstrate that movement of the oil droplet is due to respiration and not some other factor.
NaOH or
H2O

30. Question
15. The cross sectional area of the capillary tube was 1 mm2, and the blowfly had a mass of 0.5g. Calculate the rate of oxygen consumption of the blowfly. Give your answer in mm3 g-1 hour-1.
Answer
15. The oil droplet moves 60 mm in five minutes ( 71-11). So that in 1 minute it would have moved 12mm (60/5). In one hour 0.5g blowflies will have consumed 720 mm2 of oxygen ( 12 x 60). Therefore the blowflies consume 1440 mm3 g-1 hour-1 , (720 x 2, there are two 0.5 g in a gram).

31. 16. Give the formulae used for calculating respiratory quotient.
Question
16. Give the formulae used for calculating respiratory quotient.
Answer
16.
Respiratory
quotient =
Volume of O2 consumed
Volume of CO2 produced
NaOH or
H2O

32. Question
17. Explain how the results of the second experiment give an RQ = 1 for the blowfly.
Answer
17. The oil droplet does not move throughout the 2nd experiment staying on 40mm. Indicating that the amount of CO2 produced is exactly equal to the amount of O2 consumed. We know the animal must be respiring from the first experiment.
NaOH or
H2O

33. 18. It suggests the substrate is a carbohydrate.
Question
18. What does the results of the second experiment indicate about the respiratory substrate of the blowfly?
Answer
18. It suggests the substrate is a carbohydrate.
C6H12O6 + 6O2 = 6H2O + 6CO2
NaOH or
H2O

34. Calculate the respiratory quotient (RQ) of this lipid.
Question
19. The equation represents oxidation of a lipid.
C57H104O6 + 80O2 = 52H2O + 57CO2
Calculate the respiratory quotient (RQ) of this lipid.
Answer
19. The RQ of this lipid =
C57H104O6 + 80O2 = 52H2O + 57CO2 57 80 =

35. Question
20. Suggest why the RQ of a normal healthy person varies over a 24 hour period.
Answer
20. After a meal when carbohydrates are abundant the RQ of the individual is likely to be high. At night carbohydrate levels fall and more fats are consumed and the RQ level falls.