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5090/61

Biology 5090/61 — May/June 2016

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

3
questions
40
marks
60
minutes

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

Q121MUse of Techniques, Apparatus and MaterialsPlanning Experiments and InvestigationsExperimental ContextsObservations and MeasurementsAnalysis, 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.

A student carried out an experiment to investigate the effect of temperature on the activity of dehydrogenase, using yeast suspension (yeast mixed with water).

They carefully measured 5 cm35\text{ cm}^3 of yeast suspension and placed this in a test-tube labelled A.

The student also measured 5 cm35\text{ cm}^3 of yeast suspension which had been boiled and then cooled, and placed this in a test-tube labelled B.

Both test-tubes were placed in a beaker of water kept at 25 ∘C25\,^\circ\text{C}. After 5 minutes, the student added 1 cm31\text{ cm}^3 of methylene blue solution to each test-tube and mixed the contents.

Then every minute for 10 minutes they observed the contents of the two test-tubes and recorded their observations.

The student then repeated this experiment at a temperature of 35 ∘C35\,^\circ\text{C}.

Their observations are shown in Table 1.1.

Table 1.1

temperature / ∘C^\circ\text{C}test-tubetime after adding methylene blue solution / min 12345678910
25A✓✓✓✓✓✓✓–––
B✓✓✓✓✓✓✓✓✓✓
35A✓✓✓✓––––––
B✓✓✓✓✓✓✓✓✓✓

key
✓ indicates the presence of a blue colour
– indicates the absence of a blue colour

(i)

Explain how you would be able to check that the temperature of the water in the beaker was at 25 ∘C25\,^\circ\text{C}.

______

1M
(ii)

Describe how you would adjust the temperature if it became higher or lower than 25 ∘C25\,^\circ\text{C}.

______

1M
(iii)

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

______

1M
(iv)

Using the information in Table 1.1, describe the student's observations.

______

3M
(v)

Suggest an explanation for their observations.

______

3M
(vi)

Suggest one way in which this experiment could be improved to increase the reliability of the results.

______

1M
(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.

5M
(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\text{hr}alcohol concentration / g per dm3\text{g}\text{ per }\text{dm}^3
00.0
53.7
105.6
156.8
207.5
257.8
(i)

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

4M
(ii)

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

concentration = ______

2M

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