Technicians' information Assuming 16 pupils or working groups.

NB The yeast suspension should be made up 30 minutes before the practical, and be shaken occasionally.

Per class

Yeast suspension

48 g dried yeast well dispersed in 0. 6 dm³ of distilled water,

10 cm³ syringes for dispensing the above.

Glucose solution

3 0 g glucose in 0. 6 dm³ of distilled water.

20 cm³ syringes for dispensing the above.

Per working group

Bunsen burner, tripod, gauze, bench mat, boss and clamp.

Thermometer

400 cm³ beaker, for use as a water bath.

2 wide test tubes, one fitted with bung, delivery tube, rubber connection and jet (see diagram).

Timer.

Graph paper.

Rack or other support, for test tubes.

Specimen results

Temperature (°C)	20	25	31	36	40	44	52
No. of gas bubbles per minute	3	5	7	6	14	20	1

2 Thermometer

3 400 cm³ beaker, for use as a water bath.

4 2 wide test tubes, one fitted with bung, delivery tube, rubber connection and jet (see diagram of assembled apparatus).

5 Timer

6 Graph paper.

7 Rack or other support, for test tubes.

8. Access to supplies of yeast suspension.

9. Access to supplies of 5% glucose solution.

Assembled apparatus

2 Read all the instructions before doing anything else.

3 Use a syringe to place 10 cm³ of yeast suspension and 20 cm³ of 5% glucose solution into one of the test tubes. Do not shake the mixture, now or later.

4. Assemble the apparatus as shown in the diagram. Do not light the Bunsen burner yet. Make sure that the bung fits tightly but do not take risks. ask your teacher to help if necessary.

5. Place the tube containing the yeast and glucose mixture in the water bath without heating and leave it for 3 minutes so that the mixture is at the same temperature as the water in the bath.

6. Count, and record in the table below the number of bubbles which come from the jet in exactly one minute (there may be none). Record the water bath temperature. Repeat your bubble count for another minute period and record it.

8 Repeat step 7, continuing to do this until you have one set of results at a temperature of 50°C or slightly higher.

9 Plot a line graph of your results.

10 Describe your results in words and state what conclusions can be drawn from them.

11. What readings, if any, do not fit into the general pattern?

12. What are the sources of error in this investigation?