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 /cm³ 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. 1. Label four test-tubes, S1, S2, S3, and S4. 2. Put 1 cm³ of S1 into the test-tube labelled S1. 3. Repeat step 2 for S2, S3, and S4. 4. Put 1 cm³ of P into each test-tube. Shake gently to mix. 5. Put 1 cm³ of C into each test-tube. Shake gently to mix. 6. Leave the test-tubes for at least 1 minute. Shake gently to mix. 7. Observe the colour in each test-tube and record your observations in (a)(iii). 8. Identify the solution or solutions (S1, S2, S3, S4) that contain protein and record this in (a)(iv). 9. 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. 10. 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. 11. Observe the colour in each test-tube and record your observations in (a)(iii). 12. Identify the solution or solutions (S1, S2, S3, S4) that contain reducing sugar and record this in (a)(iv). 13. 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. 14. 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. 15. Observe the colour in each test-tube and record your observations in (a)(iii). 16. Identify the solution or solutions (S1, S2, S3, S4) that contain starch and record this in (a)(iv). 17. Identify the solution or solutions, if any, that do not contain protein, reducing sugar or starch. Record this as 'none' in (a)(iv). 18. Carry out the tests for protein, reducing sugar and starch using solution U. 19. Observe the colour from each test and record your observations in (a)(v).

1. (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.[3]
2. (a)(ii)State the reagent that is used to test for starch and the colour that is produced if starch is present. reagent ..................................................... colour .....................................................[1]
3. (a)(iii)Record your observations in an appropriate table.[4]
4. (a)(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 .....................................................[3]
5. (a)(v)Record the colours observed for each test for U. protein test ..................................................... reducing sugar test ..................................................... starch test .....................................................[1]
6. (a)(vi)Identify the biological molecules present in U.[1]
7. (b)(i)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. Describe the test for lipid and the expected observation if a lipid is present. observation if a lipid is present .....................................................[2]
8. (b)(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.[1]
9. (b)(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.[3]