RP 9: Respiration Of Yeast

Question 1

How is a respirometer used to measure rate of aerobic respiration?

Answer 1

1) Add set mass of yeast to set volume / concentration of glucose

2) Add buffer to keep pH constant

3) Add chemical that absorbs CO2 (eg. NaOH)

4) Place in water bath at set temperature and allow to equilibriate

5) Measure distance moved by coloured liquid in a set time

Question 2

Why does the liquid move?

Answer 2

1) Yeast anaerobically respires –> takes in CO2

2) O2 is given out but absorbed by NaOH solution

3) Volume of gas and pressure in container decrease

4) Fluid in capillary tube moves further down a pressure gradient towards organism

Question 3

Why is respirometer left open for 10 minutes?

Answer 3

1) Allow apparatus to equilibriate

2) Allow overall pressure expansion

3) Allow respiration rate of organism to stabilise

Question 4

Why must apparatus be airtight?

Answer 4

Prevent air entering / leaving –> may change volume / pressure, affecting movement of liquid

Question 5

What is a more accurate way of measuring gas volume?

Answer 5

Gas syringe

Question 6

How to calculate rate of respiration?

Answer 6

1) Calculate volume of O2 / CO2 consumed / released (by calculating area of cylinder)

2) Divide by mass of organism and time taken

3) Units –> volume per time per unit mass (eg. cm^3 min^-1 g^-1)