Biology 5090/61 — May/June 2015

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

questions

marks

minutes

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

Q120MExperimental ContextsUse of Techniques, Apparatus and MaterialsObservations and MeasurementsAnalysis, Conclusions and EvaluationPlanning Experiments and InvestigationsFree sample

(a)

Describe how you would safely test a sample of milk for the presence of each of the following substances:

(i)

reducing sugars

(ii)

proteins.

(b)

Fromase® is an enzyme that is used in the production of cheese. It causes the proteins in milk to coagulate (clot) to form a solid ‘curd’.

A student investigated the time taken for milk to coagulate using Fromase® in the presence of calcium chloride solution. She used a range of concentrations of calcium chloride solution that were each added to $10\text{ cm}^3$ of milk and $1\text{ cm}^3$ of Fromase®.

For each concentration of calcium chloride solution, she recorded the time taken for the milk to coagulate.

Her record of results is shown below.

$0.0\text{ g per dm}^3$ , 230 seconds; $0.2\text{ g per dm}^3$ , 200 seconds;
$0.4\text{ g per dm}^3$ , 150 seconds; $0.6\text{ g per dm}^3$ , 50 seconds;
$0.8\text{ g per dm}^3$ , 30 seconds

(i)

Use these results to complete Table 1.1.

Table 1.1

concentration of calcium chloride solution / $\text{g per dm}^3$	time taken for milk to coagulate / seconds

(ii)

On the grid below, construct a line graph of the data in Table 1.1.
Join your points with ruled, straight lines.

Fig. 1.1

(iii)

Use your graph to find the time it will take for milk to coagulate in calcium chloride solution of concentration $0.7\text{ g per dm}^3$ .

______ seconds

(iv)

Describe the relationship between the concentration of calcium chloride solution and the time taken for the milk to coagulate.

______

(v)

During this experiment, the student kept the test-tubes at a constant temperature of $40\,^\circ\text{C}$ .

Suggest how she kept the temperature constant.

(c)

Design an experiment you could carry out in the laboratory to investigate the effect of pH on the time taken for milk to coagulate using Fromase®.

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