Experiments A2

Question 1

How can oxygen uptake be measured? What is it?

Answer 1

-A respirometer: the apparatus for measuring the rate of oxygen consumption in respiration or for finding the respiratory quotient
-A respirometer suitable for measuring the rate of oxygen consumption of seeds or small terrestrial invertebrates at different temperatures
(DIAGRAM)

Question 2

How can carbon dioxide produced in respiration be absorbed?

Answer 2

1. Soda lime

2. Concentrated solution of potassium hydroxide (KOH) or sodium hydroxide (NaOH)

Question 3

How can oxygen consumption be determined?

Answer 3

1. Any decrease in the volume of air surrounding the organisms results form their oxygen consumption
2. Oxygen consumption in unit time can be measured by reading the level of the manometer fluid against the scale

Question 4

Why must the temperature and pressure be kept constant while readings are taken? How could this be done?

Answer 4

• Changes in temperature and pressure alter the volume of air in the apparatus
• E.G use a thermostatically controlled water bath
• The presence of a control tube contains an equal volume of inert material to the volume of the organisms used helps to compensate for changes in atmospheric pressure

Question 5

What graph would you plot for the respiration?

Answer 5

1. Once a series of measurements have been taken at a series of temperatures
2. A graph can be plotted of oxygen consumption against temperature

Question 6

How can the same apparatus be used to measure the RQ of an organism?

Answer 6

1. First oxygen consumption at a particular temperature is found (xcm^3min-1)
2. Then the respirometer is set up with the same organism at the same temperature, but with no chemical to absorb carbon dioxide
3. The manometer scale will show whether the volumes of oxygen absorbed and carbon dioxide produce are the same

Question 7

What happens to the level of the manometer fluid when the volumes are the same?

Answer 7

Will not change and the RQ=1

Question 8

What happens to the level of the manometer fluid when more carbon dioxide is produced than oxygen absorbed? How can you calculate the RQ then?

Answer 8

1. The scale will show an increase in the volume of air in the respirometer by (ycm^3min-1)
2. RQ=CO2/O2-x+y/x

Question 9

What happens to the level of the manometer fluid when less carbon dioxide is produced than oxygen absorbed? How can you calculate the RQ then?

Answer 9

1. The volume of air in the respirometer will decrease (by zcm^3min-1)
2. RQ= CO2/O2-x-z/x

Question 10

What is another way of investigating the rate of respiration in yeast? Why are they good?

Answer 10

1. Use a redox dye such as a solution of CDPIP or of ethylene blue
2. These dyes do not damage cells and so can be added to a suspension of yeast cells
3. When reduced these blue dyes become colourless
4. The rate of change from blue to colourless is a measure of the rate of respiration of the years
   - This technique can be sued to investigate the effect of various factors on yeast respiration, such as temperature, substrate concentration or different substrates