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

Question 2

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

Answer 2

1. set up a water bath at 35c
2. add equal volumes of the yeast and glucose solution to three test tubes. place test tubes in the water bath and leave them to equilibrate for 10 minutes
3. add 2cm3 of methylene blue to the test tubes and start a timer. shake for 10 seconds and place test tube back in water bath. record how long it take for the colour of the dye to change from blue to colourless
4. repeat the experiment using temperatures of 40c, 50c, 60c, and 70c

Question 3

how are the results used to calculate the rate r respiration at each temp

Answer 3

rate= 1/ time taken for colour change

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 temp increases the rate of respiration increases to an optimum. this is because the rate of enzyme activity increases. beyond the optimum the enzymes become denatured so the activity decreases