RP 9

• What is the function of methylene blue in the practical?

  It acts as a redox dye and an alternate electron acceptor during ATP synthesis.
• What does the color change of methylene blue from blue to colorless indicate?

  It indicates the end point of the reaction.
• What is the procedure to investigate the effect of temperature on the rate of respiration of yeast?

  1. Set up a water bath at 35°C.
  2. Add equal volumes of yeast and glucose solution to three test tubes.
  3. Place test tubes in the water bath for 10 minutes.
  4. Add 2 cm³ of methylene blue and start the timer.
  5. Shake for 10 seconds and return to the water bath.
  6. Record the time taken for methylene blue to turn colorless.
  7. Repeat at temperatures of 40°C, 50°C, 60°C, and 70°C.
• How is the rate of respiration calculated at each temperature?

  The rate is calculated using the formula Rate = $\frac{1}{\text{time taken for methylene blue to decolourise}}$.
• Why does the yeast solution need to be buffered?

  To maintain a constant pH for optimal enzyme function.
• What is the effect of temperature on the rate of respiration?

  The rate of respiration increases with temperature to an optimum, then decreases as enzymes denature.
• What happens to enzyme activity beyond the optimum temperature?

  Enzyme activity decreases as enzymes denature with high temperature.