Experiment on Yeast Respiration

Overview

• Measure the rate of respiration in yeast.
• Use a test tube with yeast and glucose solution.
• Yeast are unicellular fungi.
• Respiration involves carbon dioxide production and oxygen usage, which are not visible directly.

Glycolysis in Yeast

• Glucose is broken down into pyruvate.
• Requires 2 ATP and produces 4 ATP.
• Oxidation occurs: hydrogen atoms are released.
• Hydrogen atoms are accepted by NAD (forming reduced NAD).
• Cannot visibly see glycolysis or oxidation/reduction directly.

Using a Redox Indicator

• Redox stands for reduction and oxidation.
• Indicators: DCPIP (Dichlorophenolindophenol) or Methylene Blue.
• Indicators are not toxic to yeast.

DCPIP Experiment

• Add DCPIP to yeast and glucose solution.
• Original color of DCPIP is blue.
• When reduced (accepting hydrogen), it becomes colorless.
• This color change indicates the occurrence of glycolysis and respiration.

Experiment Setup

• Two test tubes with equal volumes of yeast and glucose.
• Add DCPIP or Methylene Blue to both.
• Place one test tube in 10°C water bath and another in 20°C water bath.

Temperature Effect

• Higher temperature leads to increased enzyme activity and faster respiration.
• Measure time taken for DCPIP to decolorize:
  • Slower at 10°C due to slower enzyme-substrate interaction.
  • Faster at 20°C due to higher kinetic energy and faster reaction.

Results

• Example: 10°C takes 150 seconds to decolorize; 20°C takes 40 seconds.
• Faster decolorization at higher temperature indicates higher respiration rate.

Conclusion

• Use of DCPIP or Methylene Blue as redox indicators effectively demonstrates yeast respiration.
• Observing color change helps prove respiration rate differences due to temperature.
• Method applicable in exams using either DCPIP or Methylene Blue.