Describe and carry out investigations using redox indicators, including DCPIP and methylene blue, to determine the effects of temperature and substrate concentration on the rate of respiration of yeast

Sourav PanOctober 31, 2024

Answered

Investigation: Effects of Temperature and Substrate Concentration on Yeast Respiration using Redox Indicators (DCPIP and Methylene Blue)

Objective:
To investigate how temperature and substrate (glucose) concentration affect the rate of anaerobic respiration in yeast, utilizing the redox indicators DCPIP (2,6-Dichlorophenolindophenol) and Methylene Blue.

Theory:

• Redox Indicators:
  • DCPIP: Blue (oxidized) → Colorless (reduced)
  • Methylene Blue: Blue (oxidized) → Colorless (reduced)
• Yeast Anaerobic Respiration: Glucose → Ethanol + CO2 + Energy (with dehydrogenase enzymes)
• Variables:
  1. Temperature (°C): Affects enzyme activity and metabolic rate.
  2. Substrate (Glucose) Concentration (M): Influences the availability of energy source for respiration.

Investigation Setup:

Experiment 1: Effect of Temperature

Experiment 2: Effect of Substrate Concentration

Procedure:

1. Prepare Yeast Suspension: Mix active dry yeast with distilled water to create a uniform suspension.
2. Prepare Glucose Solutions: Dilute glucose to the required concentrations (0.1 M, 0.5 M, 1.0 M).
3. Add Reagents to Test Tubes:
   • Yeast suspension
   • Glucose solution (of specified concentration)
   • A few drops of DCPIP or Methylene Blue
4. Incubate at Specified Temperatures: Use water baths or incubators to maintain the desired temperatures.
5. Record Observations:
   • Time: Note the time taken for the color change from blue to colorless for each test tube.
   • Color Change: Observe and record any color changes, using the control tubes for comparison.

Data Analysis and Expected Results:

• Effect of Temperature:
  • Expected Outcome: Optimum temperature around 30-37°C for yeast respiration. Color change will be fastest at this temperature range.
  • Graph: Plot time taken for color change against temperature.
• Effect of Substrate Concentration:
  • Expected Outcome: Increase in glucose concentration will increase the rate of respiration up to a point, then plateau or decrease due to substrate saturation or inhibition.
  • Graph: Plot time taken for color change against glucose concentration.

Safety Precautions:

• Handle DCPIP and Methylene Blue with gloves; they can cause skin irritation.
• Ensure good ventilation when working with yeast to avoid inhaling spores.

Tips for Accurate Results:

• Use a consistent yeast suspension concentration across all experiments.
• Minimize exposure to light, as it can affect the redox indicators.
• Repeat experiments to ensure reliable results.