1. 1
   A student tests a sample of fresh orange juice by adding Benedict's solution and heating the mixture in a water bath. The blue solution changes colour, indicating the presence of a certain type of biological molecule.

   (a)

   What colour change indicates a positive result when Benedict's solution is added to the orange juice and heated?

   [1 mark]

   • ABlue to brick-red precipitate
   • BYellow-brown to blue-black
   • CBlue to purple
   • DColourless to milky white

   (b)

   Which type of biological molecule does the Benedict's test detect?

   [1 mark]

   • AStarch
   • BReducing sugar
   • CProtein
   • DLipid

   (c)

   Describe the method the student should use to carry out the Benedict's test on the orange juice, and describe what the result would look like if reducing sugar were absent.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A food quality control laboratory receives an unlabelled white powder sample, thought to be either a starch-based thickener or a protein-based supplement, and needs to identify which one it is using appropriate chemical tests.

   (a)

   What colour change would confirm that the powder sample contains starch, when tested with iodine solution?

   [1 mark]

   • ABlue to brick-red precipitate
   • BColourless to milky white
   • CBlue to purple
   • DYellow-brown to blue-black

   (b)

   What colour change would confirm that the powder sample contains protein, when tested using the Biuret test?

   [1 mark]

   • ABlue to brick-red precipitate
   • BYellow-brown to blue-black
   • CBlue to purple
   • DColourless to milky white

   (c)

   Describe how the laboratory could use the iodine test and the Biuret test to determine whether the powder sample is the starch-based thickener or the protein-based supplement.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A quality control technician at a baby formula manufacturer uses the ethanol emulsion test to check for the presence of lipids in a new batch of formula milk, and also uses a colorimeter to measure the exact concentration of a nutrient in another sample.

   (a)

   Describe how the technician should carry out the ethanol emulsion test on the formula milk sample, and describe the result that would confirm the presence of lipid.

   [3 marks]

   (b)

   Explain how using a colorimeter allows the technician to measure the concentration of a nutrient more precisely than judging the colour of a food test result by eye.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A group of students is given four unlabelled test tubes, each containing a different unknown biological sample, and is asked to carry out a series of chemical tests to identify whether each sample contains reducing sugar, starch, protein or lipid.

   (a)

   Describe the method and expected positive result for each of the following food tests: the Benedict's test, the iodine test, the Biuret test and the ethanol emulsion test.

   [6 marks]

   (b)

   Describe how the students could carry out and interpret these food tests systematically and accurately, including the use of a colorimeter to improve the accuracy of interpreting results.

   [6 marks]

   Total for question 4: 12 marks

End of questions