Cpac 9- Respiraton In Single Celled Organisms

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 blue to colourless, indicating the end point

Question 2

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

Answer 2

Set up a water bath at 35ºc
Add equal volumes of the yeast and glucose solution to three test tubes and place test tubes in the water bath and leave them to equilibrate for 10 minutes
Add 2cm^3 of methylene blue to the test tubes and start the timer. Shake for 10 seconds and place the test tube back in water bath. Record how long it takes for the methylene blue to turn colourless from each test tube
Repeat the experiment using temperatures of 40ºc, 50ºc, 60ºc and 70ºc

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

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. This is because the rate of enzyme activity increases
Beyond the optimum, enzyme activity decreases as enzymes denature with high temperature