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BIO3025 Human Biology

PRACTICAL 1: RESPIRATION OF YEAST

You are required to investigate the effect of glucose and sucrose on gas production by yeast in different conditions.You are provided with the following mixtures of a standard yeast suspension.

K1yeast suspension with an equal volume of 5% glucose solution

K2yeast suspension with an equal volume of 5% sucrose solution

K3yeast suspension with an equal volume of distilled water

Proceed as follows:

1. Half fill a beaker with water. Adjust the temperature to between 40 - 43C.

2. Maintain the water bath at this temperature.

3. Label 2 boiling tubes K1and K2respectively.

4. Stir suspensions K1 and K2 thoroughly using a glass rod. To one boiling tube add 20cm3of K1 and to the other

boiling tube add 20cm3of K2.

5. Fit both tubes with a bung and delivery tube. Ensure that the fitting is airtight. Place both tubes in the water bath.

Position the test tubes with water for each of the delivery tubes outside the water bath as shown in Fig 1.1.

Fig 1.1

6. Soon after you have set up the apparatus, bubbles of gas will emerge from the ends of the delivery tubes. After a

few minutes, when the bubbles appear regularly, count the number of bubbles produced in three successive one-

minute time intervals from both tubes. When you make a count, begin timing as soon as the bubble leaves the

delivery tube.

a)Record your results in the table provided. Calculate the mean bubbling rates for the first sets of readings (to the

nearest whole number).

PART B

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BIO3025 Human Biology

b)Remove both tubes from the water bath and put them to one side. Raise the temperature of the water bath by

approximately 10C and maintain it at this temperature. Return the apparatus containing K1to the water bath. Wait

for two minutes, and then take three successive readings of the bubbling rate at this temperature.

Add your results to the table and calculate the mean bubbling rate at this temperature.

c) Repeat the procedure using K3 at the same temperature as in (b)to obtain three readings with this mixture. You

can use either piece of apparatus that you have used before, but wash it thoroughly.

Add these results and their mean to the table.

bubbling rate / bubbles per minute

Reading K1(38-42C) K2(38-42C) K1 (plus 10C) K3

1

2

3

mean

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BIO3025 Human Biology

Name: ..

Date : ............................ Class: ................. MARK: [ 10 ]

(i) Give your reasons for the production of bubbles by K1 in (a).[3]

(ii) Explain the effect of raising the temperature by about 10C on the bubbling rate of K1. [3]

....

iii) What prediction about the bubbling rate would you make if you

(i) continued to measure the rate in (b) for the next hour or so,

(ii) raised the temperature in K1 to 80C?

State a reason for your answers. [4]

i.

ii.

..