Required Practical 9- Respiration

Question 1

you were told to leave the tubes in the water bath for 5 mins.

why?

Answer 1

allow apparatus to equilibriate

Question 2

describe how you monitored the water bath temp and kept it constant at 35 degrees?

Answer 2

-use thermometer - take reg readings
-add hot/cold water if needed - maintain constant temp

Question 3

describe the control experiment you would set up.

explain why this control experiment would be important?

Answer 3

test tube with ONLY glucose and methylene blue
OR

glucose. methylene blue and boiled yeast
ensures yeast causing colour change

Question 4

shaking the tubes would have caused the methylene blue to go blue again.

why?

Answer 4

-mixing with oxygen
-oxygen oxidises methylene blue

Question 5

respiration by yeast caused methylene blue to go colourless.

how?

Answer 5

-accepts electrons
-from glucose

Question 6

the yeast cultures in the conical flasks were set up some time before you carried out your investigation.

explain why?

Answer 6

allows yeast to be reproduced

Question 7

the conical flasks were stoppered with cotton wool.

explain why?

Answer 7

prevent contamination by bacteria
would compete with yeast for O2

Question 8

the flasks were loosely stoppered with cotton wool rather than with rubber bungs.

why?

Answer 8

allow O2 through