Technicians' information Assuming 16 pupils or working groups
NB Liquids 1 and 2 should be made up 30 minutes before the practical, and be shaken occasionally.
Cheek that the tubes do not have a cracked or chipped rim which can split the balloon.
Check balloons - it is not advisable to store them for many days after they have been used once. If new, inflate them once before issue.
Liquid 1 80 g dried yeast well dispersed in 1 dm3 of 10% glucose solution (enough to 2/3 fill thirty two 22 mm diameter test tubes).
Liquid 2 80 g dried yeast well dispersed in 0.5 dm3 of distilled water (enough to 2/3 fill sixteen 22 mm diameter test tubes).
Liquid 3 0. 5 dm3 of 10% glucose solution (enough to 2/3 fill sixteen 22 mm diameter test tubes).
Hot water supply.
Means of lighting Bunsen burners
Per Working Group
Bunsen burner and tripod
Beaker or can, to use as a water bath
4 identical spherical rubber balloons
2 tubes 2/3 filled with liquid 1, labelled A and B
1 tube 2/3 filled with liquid 2, labelled C
tube 2/3 filled with liquid 3, labelled D
Rack or other support, for test tubes
1. You are given two test tubes, A and B, each containing the same volume of yeast mixed with glucose solution.
2. Prepare a warm water bath between 35°C and 40°C. Keep the temperature as nearly constant as possible
3 Place a balloon carefully over the opening of each tube.
4. Leave tube A in the rack or other support at air temperature. Measure and record this temperature.
5 You are also given test tube C which contains yeast, but no glucose, and test tube D which contains glucose solution, but no yeast. Place a balloon carefully over the openings of each of
6. Place tubes B, C and D in the warm water bath.
7. After 1 5 minutes, record what has happened to each of the four balloons,
8. Explain what is shown by comparing the results for test tubes A and B.
9. Suggest why test tubes C and D were set up.