5.7.11 Investigating the rate of respiration

Question 1

What is a redox indicator

Answer 1

A substance that changes colour when reduce/oxidised

Question 2

Give examples of redox indicators

Answer 2

DCPIP and methylene blue
They are used to investigate the effects of temperature and substrate concentration on the rate of anaerobic respiration in yeast

Question 3

Why can DCPIP and methylene blue be added to a suspension of living yeast cells?

Answer 3

As they dont damage cells

Question 4

What are the roles of DCPIP and methylene blue in investigating anaerobic respiration in yeast?

Answer 4

When they are present they take up hydrogens from the organic compounds and get reduced instead of NAD.
They both undergo same colour change when reduced: Blue -> colourless

Question 5

What is the effect of a faster rate of respiration on the colour change of the redox indicators?

Answer 5

The faster the rate of respiration, the faster the rate of hydrogen release, and the faster the dyes get reduced and change colour (blue -> colourless)

Question 6

What does the rate of colour change correspond to?

Answer 6

The rate dehyodrgenase (catalyses prodction of NADH in glycolysis) would be working at and therefore the rate of respiration in yeast

Question 7

What is the rate of respiration inversely proportional to?

Answer 7

The time taken
Rate of respiration (sec-1) = 1/time (sec)

Question 8

What happens to the release of hydrogens as temperature increases?

Answer 8

As temp increases, rate of respiration increases so the time taken for the solution to go colourless reduces.
H are released more quickly = hence DCPIP accepts electrons/hydrogens more quickly until all molecules of DCPIP are reduced. (less time to turn from blue to colourless)

Question 9

What are the limitations of investigating anaerobic respiration in yeast?

Answer 9

• This experiment is measuring the rate of electron transfer instead of the rate of dehydrogenase activity
• Distinguishing the end of the reaction and the colour change is subjective - one person should be used
• Key to remember that the yeast suspension in the tube may have a slight colour (not completely colourless)

Question 10

How else can you investigate the effect of other factors on the rate of anaerobic respiration in yeast?

Answer 10

• Adding diff concentrations of substrate (recording the time taken for a colour change to occur once dye is added)
• Effect of different respiratory substrates (lipids/proteins) and recording time taken for colour change
• Temperature

Question 11

What are respirometers

Answer 11

They are used to measure and investigate the rate of oxygen consumption during aerobic respiration in organisms

Question 12

How can the effect of temperature on the rate of respiration be investigated using a respirometer?

Answer 12

By adding the apparatus to a thermostatically controlled water bath

Question 13

Describe the method of using a respirometer

Answer 13

1. measure O2 consumption - set up respirometer with both tubes in water bath. Use manometer reading to calculate change in gas volume within given time.
2. Reset apparatus - allow air to reenter tubes via screw cap and reset manometer fluid using syringe. Change temp of water bath and allow tubes to acclimatise, then close screw clip to begin experiment
3. Run experiment again - use manometer to calculate change in gas volume in given time
4. Repeat experiment several times at diff temps

Question 14

How can the volume of oxygen consumed be worked out?

Answer 14

Using the diameter of the capillary tube r (cm) and the distance moved by the manometer fluid h (cm) in a minute using formula:
πr2h