Biology 9700/33 — May/June 2021

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

questions

marks

120

minutes

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

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

Some biological molecules produce a colour change when tested with a specific reagent.

You will investigate which biological molecules are present in four solutions, S1, S2, S3, and S4. Each solution contains one or none of the biological molecules: protein, starch, reducing sugar.

You will also investigate the contents of solution U which contains a mixture of biological molecules.

You are provided with the materials shown in Table 1.1.

Table 1.1

labelled	contents	hazard	volume / $\text{cm}^3$
C	0.15% copper sulfate solution	none	10
P	5% potassium hydroxide solution	harmful irritant	10
iodine	iodine solution	irritant	5
B	Benedict's solution	harmful irritant	20
S1	unknown solution	none	10
S2	unknown solution	none	10
S3	unknown solution	none	10
S4	unknown solution	none	10
U	unknown mixture of biological molecules	none	10

If any solution comes into contact with your skin, wash off immediately with cold water.

It is recommended that you wear suitable eye protection.

Carry out the test for protein on S1, S2, S3, and S4, using step 1 to step 9.

Label four test-tubes, S1, S2, S3, and S4.
Put $1\text{cm}^3$ of S1 into the test-tube labelled S1.
Repeat step 2 for S2, S3, and S4.
Put $1\text{cm}^3$ of P into each test-tube. Shake gently to mix.
Put $1\text{cm}^3$ of C into each test-tube. Shake gently to mix.
Leave the test-tubes for at least 1 minute. Shake gently to mix.
Observe the colour in each test-tube and record your observations in (a)(iii).
Identify the solution or solutions (S1, S2, S3, S4) that contain protein and record this in (a)(iv).
Keep any test-tubes from step 8 that contain protein. Empty the test-tubes that do not contain protein into the container labelled 'For waste'. Rinse the empty test-tubes for use in step 10.

(a)

(i)

State the reagent that is used to test for reducing sugar and the colour or colours produced if a reducing sugar is present.

reagent ______

colour or colours ______

Describe how you will use the reagent to carry out the test for reducing sugar.

(ii)

Carry out the test for reducing sugar on each of the solutions using the labelled test-tubes from step 9. You do not need to test any solutions identified as containing protein in step 8.
Observe the colour in each test-tube and record your observations in (a)(iii).
Identify the solution or solutions (S1, S2, S3, S4) that contain reducing sugar and record this in (a)(iv).
Keep any test-tubes from step 12 that contain reducing sugar. Empty the test-tubes that do not contain reducing sugar into the container labelled 'For waste'. Rinse the empty test-tubes for use in step 14.

State the reagent that is used to test for starch and the colour that is produced if starch is present.

reagent ______

colour ______

(iii)

Carry out the test for starch on each of the solutions using the labelled test-tubes from step 13. You do not need to test any solutions identified as containing protein or reducing sugar in step 8 and step 12.
Observe the colour in each test-tube and record your observations in (a)(iii).
Identify the solution or solutions (S1, S2, S3, S4) that contain starch and record this in (a)(iv).
Identify the solution or solutions, if any, that do not contain protein, reducing sugar or starch. Record this as 'none' in (a)(iv).

Record your observations in an appropriate table.

(iv)

Identify the biological molecules present in solutions S1, S2, S3 and S4. If any solution does not contain protein, reducing sugar or starch write the answer as 'none'.

S1 ______

S2 ______

S3 ______

S4 ______

(v)

Carry out the tests for protein, reducing sugar and starch using solution U.
Observe the colour from each test and record your observations in (a)(v).

Record the colours observed for each test for U.

protein test ______

reducing sugar test ______

starch test ______

(vi)

Identify the biological molecules present in U.

(b)

A student carries out the same tests for protein, reducing sugar and starch on two unknown solutions, Y and Z. The student also carries out the test for the presence of lipid.

(i)

Describe the test for lipid and the expected observation if a lipid is present.

observation if a lipid is present ______

(ii)

From the observations for each test, the student concludes:

solution Y contains protein and reducing sugar
solution Z contains protein and lipid.

The student also carries out the test for non-reducing sugar on solution Y and on solution Z.

The student observes a positive result for the presence of a non-reducing sugar in solution Y and in solution Z.

The student concludes that a non-reducing sugar is present in solution Y and in solution Z.

Suggest why the student's conclusion may not be correct for solution Y.

(iii)

The student thought that the protein in solution Z could be the enzyme amylase.

Describe how the student could determine whether the protein in solution Z is amylase.

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