Biology 5090/31 — May/June 2016

Cambridge O-Level · Practical Test · worked solutions for every part, with the mark scheme

questions

marks

minutes

Topics Experimental Contexts · Observations and Measurements · Analysis, Conclusions and Evaluation · Use of Techniques, Apparatus and Materials · Planning Experiments and Investigations · Microscopy and Biological Drawing

Q121MExperimental ContextsObservations and MeasurementsUse of Techniques, Apparatus and MaterialsPlanning Experiments and InvestigationsAnalysis, Conclusions and EvaluationFree sample

(a)

Dehydrogenase is an enzyme found in cells such as yeast.
Methylene blue is an indicator that can be used to show the activity of dehydrogenase.

In the presence of active dehydrogenase, methylene blue changes colour from blue to colourless.

You are required to carry out an experiment to investigate the effect of temperature on the activity of dehydrogenase in yeast cells.

You have been provided with two yeast suspensions, A and B. Yeast suspension B has been heated to boiling and then cooled.

Prepare a water bath by half filling a beaker with water and adjusting the temperature to $25\,^\circ\text{C}$ .
Label one test-tube A and one test-tube B.
Put $5\text{ cm}^3$ of yeast suspension A into the test-tube labelled A.
Put $5\text{ cm}^3$ of yeast suspension B into the test-tube labelled B.
Stand both test-tubes in the beaker of water kept at $25\,^\circ\text{C}$ . Leave the test-tubes in the water for 5 minutes.
After 5 minutes, add $1\text{ cm}^3$ of methylene blue solution to each test-tube, mix carefully and leave the test-tubes in the water.
Observe the colour of the contents of the test-tubes every minute for a period of 5 minutes, while keeping the water temperature at $25\,^\circ\text{C}$ .
Repeat this procedure using fresh yeast suspension and a beaker of water kept at $35\,^\circ\text{C}$ .

(i)

Record all your observations in Table 1.1.

Table 1.1

temperature of water / $^\circ\text{C}$	test-tube	observations at 1 min	observations at 2 mins	observations at 3 mins	observations at 4 mins	observations at 5 mins
25	A
25	B
35	A
35	B

(ii)

Explain how you were able to check the temperature of the water in the beaker.

______

(iii)

Explain how you kept the temperature of the water in the beaker at $25\,^\circ\text{C}$ and at $35\,^\circ\text{C}$ .

______

(iv)

Explain why the test-tubes were left in the beaker of water for 5 minutes before adding methylene blue solution.

______

(v)

Suggest an explanation for your observations.

______

(b)

Giving full experimental details, describe an experiment you could carry out to investigate the effect of pH on the activity of dehydrogenase, using yeast suspension and methylene blue solution.

(c)

Yeast is used for the production of alcohol in the brewing industry.

In an investigation, the production of alcohol by yeast was recorded every 5 hours for 25 hours.

The results are shown in Table 1.2.

Table 1.2

time / hr	alcohol concentration / $\text{g per dm}^3$
0	0.0
5	3.7
10	5.6
15	6.8
20	7.5
25	7.8

(i)

Construct a line graph of the data in Table 1.2 on the grid below.
Draw a smooth curve through your points.

grid-1

(ii)

Use your graph to find the concentration of alcohol after 12 hours.

concentration = ______

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2 more questions

Q2Microscopy and Biological Drawing · Experimental Contexts · Observations and Measurements13M
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