Practicals - Paper 1

Question 1

What do you do differently when testing for anaerobc respiration instead of aerobic respiration?

Answer 1

Place a layer of parrafin over the respiring yeast culture, so that oxygen cannot enter the solution.

Question 2

What are the first 4 steps for a practical when testing for rate of respiration of yeast? (aerobic or anaerobic)

Answer 2

1. Put a known volume + concentration of substrate (e.g. glucose) in a test tube
2. Add a known volume of buffer solution to keep the pH constant.
3. Place in water bath of 25C - ensures temp stays constant throughout experiment - leave for ten minutes to allow the temperature of the substrate to stabilise.
4. Add a known mass of dried yeast to the test tube and stir for two minutes.

Question 3

What would you do after stirring the yeast?

Answer 3

5. Place a bung on top of the test tube (that has the gas syringe set to 0 attatched)
6. Start stopwatch as soon as bung is attached.
7. At regular time intervals, record the volume of CO2 that is evolved (e.g. every minute for 20 minutes)

Question 4

what should you do to ensure the reliability of results?

Answer 4

Have a control set up where no yeast is present, where no CO2 should be formed.

Question 5

How does a respirometer work?

Answer 5

Measure the amount of oxygen consumed rather than the CO2 produced.

Question 6

Why does a respirometer contain KOH solution or soda lime?

Answer 6

to absorb the CO2 that is produced.

Question 7

What is the syringe used for in a respirometer?

Answer 7

To move the liquid in the manometer so that it is at a known volume.

Question 8

How would you produce 5 serial dilutions with a dilution factor of 2, starting with a 40M Glucose concentration

Answer 8

1. Have 5 test tubes, and fill 4 up 5cm3 with distilled water.
2. Fill the empty test tube to 10cm3 with the the 40M glucose solution
3. Using a pippette, draw 5cm3 from the initial test tube, add to test tube 2, and stir thoroughly - now have a 20M solution.
4. Repeat this process with the remaining test tubes to get concentrations of 10M, 5M, and 2.5M.

Question 9

How do you make a calibration curve?

Answer 9

1. Do a Benedict’s test on each serial diluted solution, with an extra control of pure water. (Use same vol of benedicts for all)
2. Remove precipitate (either by centrifuge or leaving for 24 hours)
3. Use a colorimeter with a red filter to measure the absorbance of Benedicts solution remaining in each tube.
4. Use results to make a calibration curve, showing absorbance against glucose concentration.

Question 10

How would you investigate how temperature affects beetroot membrane permeability?

Answer 10

1. Cut 5 equal sizes beetroot pieces and rinse them to remove excess pigment.
2. Place the 5 pieces in five different test tubes, each with 5cm3 of water.
3. Place each test tube in a water bath at a different temperature, e.g. 10, 20, 30, 40, 50 celsius for the same amount of time.
4. Remove each piece of beetroot from the test tubes, leaving only the coloured liquid.
5. Run each test tube through the colorimeter to test the absorbance - the more permeable the membrane (higher temp), the more pigment would have been released, so the higher the absorption.

Question 11

How does temperature affect membrane permeability?

Answer 11

the higher the temp, the more permeable the membrane.