Paper 2: Respiration

Question 1

State the apparatus used to measure the rate of respiration of a small organism.

Answer 1

A respirometer

Question 2

Why is soda lime added to the respirometer?

Answer 2

To absorb carbon dioxide in the respirometer so that the only change in volume results from change in oxygen volume.

Question 3

How does the respirometer measure the rate of respiration?

Answer 3

The change in position of a drop of dye in the capillary tube indicates the volume of oxygen consumed for respiration. The rate of oxygen consumption is proportional to the rate of respiration.

Question 4

State the controlled variables of this practical.

Answer 4

Temperature
Mass of soda lime
Time

Question 5

How is the rate of respiration calculated?

Answer 5

Rate of respiration = volume of oxygen consumed / mass of organism cm3 g-1

Question 6

State a source of error in this practical

Answer 6

If using animals, stress in captivity may affect the rate of photosynthesis.
The apparatus may not be airtight which may affect the movement of the dye

Question 7

How is the volume of oxygen consumed measured?

Answer 7

By reading off the markings of the capillary tube, or measuring the distance moved by the dye and find volume using πr2.

Question 8

How can the reliability of this practical be improved?

Answer 8

By repeating the practical at least 3 times to find the mean volume of oxygen consumed and calculate a mean rate.