Required Practical 9

Question 1

What is the function of methylene blue in this practical?

Answer 1

It is a redox dye and acts as an alternate electron acceptor of the electrons transferred during ATP synthesis. It turns from blue to colourless, indicating the end point.

Methylene blue is commonly used in biological experiments to visualize changes in redox states.

Question 2

Outline the procedure to investigate the effect of temperature on the rate of respiration of yeast.

Answer 2

1. Add equal volumes of yeast and glucose solution to three test tubes.
2. Place test tubes in the water bath and leave them to equilibrate for 10 minutes.
3. Add 2 cm3 of methylene blue to the test tubes and start the timer.
4. Shake for 10 seconds and place test tube back in water bath.
5. Record how long it takes for the methylene blue to decolourise at each temperature.

This procedure allows for the observation of the respiration rate by monitoring the decolourisation of methylene blue.

Question 3

How are the results used to calculate the rate of respiration at each temperature?

Answer 3

Rate = 1 / time taken for methylene blue to decolourise.

Question 4

Why does the yeast solution need to be buffered?

Answer 4

To maintain a constant pH so that the enzymes are functioning at their optimum pH.

Enzyme activity can be significantly affected by pH levels, hence buffering is essential in experiments.

Question 5

What is the effect of temperature on the rate of respiration?

Answer 5

As temperature increases, the rate of respiration increases to an optimum. Beyond the optimum, enzyme activity decreases as enzymes denature with high temperature.