The enzyme, E, hydrolyses (breaks down) the protein in milk. After the enzyme and milk are mixed, the protein is hydrolysed and the mixture will change from cloudy to clear. The end-point is reached when the mixture is clear. You are required to: make different concentrations of the enzyme solution, E investigate the effect of different concentrations of E, by finding the time taken to reach the end-point. You are provided with: labelled contents hazard volume /…

Biology 9700/34 — October/November 2012

Cambridge AS Level · Advanced Practical Skills · worked solutions for every part, with the mark scheme

questions

marks

120

minutes

Topics Manipulation, Measurement and Observation · Presentation of Data and Observations · Analysis, Conclusions and Evaluation · Use of the Light Microscope

Q1Manipulation, Measurement and ObservationPresentation of Data and ObservationsAnalysis, Conclusions and EvaluationFree sample

The enzyme, E, hydrolyses (breaks down) the protein in milk.

After the enzyme and milk are mixed, the protein is hydrolysed and the mixture will change from cloudy to clear. The end-point is reached when the mixture is clear.

You are required to:

make different concentrations of the enzyme solution, E
investigate the effect of different concentrations of E, by finding the time taken to reach the end-point.

You are provided with:

labelled	contents	hazard	volume / $\text{cm}^3$
E	1.0 % enzyme solution	irritant	20
W	distilled water	none	50
S	milk	none	50

(a)

(i)

You will need to make dilutions of the 1.0 % solution of E, so that the concentration of E is reduced by 0.2 % between each successive dilution.

You will need $5\ \text{cm}^3$ of each concentration.

Prepare the space below to show the:

concentrations of E
volumes of E
volumes of distilled water, W.

(ii)

Decide on a control you will use.

Describe how you will set up a control using the apparatus provided.

(iii)

Proceed as follows:

Prepare the concentrations of E and the control as decided in (a) (i) and (ii).
Set up a water-bath and adjust the temperature to between $35\ ^{\circ}\text{C}$ and $40\ ^{\circ}\text{C}$ . Maintain the temperature of the water-bath.
Put $1\ \text{cm}^3$ of the lowest concentration of E into a test-tube and put the test-tube into the water-bath.
Repeat step 3 for all the concentrations of E and the control prepared in step 1.
Leave the test-tubes for 2 minutes.
Remove the test-tubes containing the three highest concentrations of E.
Put $3\ \text{cm}^3$ of S into each test-tube and mix well.
Record the time taken for each test-tube to reach the end-point. If the end-point is not reached by 240 seconds, record ‘more than 240’.
Repeat steps 6 to 8 with the remaining test-tubes in the water-bath.

Prepare the space below and record your results.

(iv)

Identify a significant source of error in your investigation.

(v)

Suggest how you would modify this investigation to find the effect of pH on the rate of hydrolysis of the protein in milk.

(b)

Gelatine is made up of protein which is hydrolysed by the enzyme protease.

A student investigated the effect of pH 4.0 and pH 6.4 on the activity of protease.

One piece of gelatine, with an area of $200\ \text{mm}^2$ , was placed in a Petri dish and covered with a solution of protease maintained at pH 4.0.

The area of gelatine was recorded at intervals for 90 minutes.

The investigation was repeated with another piece of gelatine and a solution of protease maintained at pH 6.4.

The results of the student’s investigation are shown in Table 1.1.

Table 1.1

time / minutes	area of gelatine / $\text{mm}^2$ (pH 4.0)	area of gelatine / $\text{mm}^2$ (pH 6.4)
0	200	200
30	165	190
45	105	185
60	50	145
90	0	100

(i)

Plot a graph of the data shown in Table 1.1.

Graph grid 1b(i)

(ii)

Describe the trends shown by the data.

(iii)

Explain the difference in the effect of pH 4.0 and pH 6.4 on the activity of protease.

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Q2Use of the Light Microscope18M

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