Respiration in yeast


Independent variable: Temperature
Dependent variable: Time taken for the redox indicator to turn red


Equipment list


  • Redox indicator - triphenyl tetrazolium chloride (TTC) solution
  • Water baths and refrigerators at the following temperatures - 15°C, 20°C, 25°C, 30°C and

35°C

  • Thermometer
  • Yeast suspension / dried yeast, glucose and distilled water
  • Distilled water
  • Pipettes
  • Test tubes
  • Test tube rack
  • Stopwatch
  • Stirring rods


Background information


During oxidative phosphorylation in aerobic respiration the hydrogen carriers, such as FAD and

NAD, are regenerated by being oxidised. In this experiment, the hydrogen carriers are oxidised

by a redox indicator (TTC) which is in turn reduced, causing a colour change to red. The time

taken for the colour change to occur can be used to indicate the rate of respiration.


Method


Preparing the yeast -

Add 10g of dried yeast and 50g of glucose to 1000 cm3 of distilled water, mixing thoroughly with a

stirring rod. Allow the yeast culture to stabilise for 24 hours before starting the experiment.


1. Set up the first water bath at 35°C

2. Use a pipette to place 10 cm3 of the yeast suspension into one test tube and 1 cm3 of

TTC into a different test tube.

3. Place both test tubes into the water bath and leave them for 5 minutes to allow them to

reach the temperature of the water bath.

4. Quickly pour the TTC solution into the test tube containing the yeast, give it a stir with the

glass stirring rod and start the stopwatch.

5. Stop timing once the solution has turned red and record the time taken in a suitable

table.

6. Repeat steps 1-5 with the remaining 4 temperatures.




2 graphs can be plotted from the results table.

  • A graph of temperature against time
  • A graph of temperature against rate of reaction (calculated using 1 / Time taken)