Respiration exam q

Question 1

Investigating anaerobic respiration - why leave apparatus for an hour after culture has reached a constant temperature

Answer 1

Allow time for oxygen to be used/respired

Question 2

Respirometer apparatus is left open for 10 minutes. Explain why

Answer 2

Allow apparatus to equilibrate

Allow for overall pressure change throughout

Allow respiration rate of organisms to stabilise

Question 3

Explain why the apparatus must be airtight

Answer 3

Prevent air entering or leaving

Would change volume and pressure, affecting movement of liquid

Question 4

Describe a more accurate way to measure volume of gas

Answer 4

Use a gas syringe

Question 5

Why leave tubes in the water bath for 5 minutes

Answer 5

Allow for solution to equilibrate and reach the same temperature as the water bath

Question 6

Describe a control experiment and why it would be done

Answer 6

Add methylene blue to boiled/dead yeast

All other conditions the same

To show change is due to respiration in organisms

Question 7

Suggest and explain why you must not shake tubes containing methylene blue

Answer 7

Shaking would mix solution with oxygen

Which would oxidise methylene blue/cause it to lose its electrons

So methylene blue would turn back to its original blue colour

Question 8

Suggest one source of error in using methylene blue

Explain how this can be reduced

Answer 8

Subjective when determining colour change

Compare results to a colour standard

Or use a colorimeter for quantitative results