A-LevelBiologyBiological molecules9700/33 · May/June 2017 · Q118 Marks
When a person eats food containing starch, the enzyme amylase is released to hydrolyse (break down) the starch into reducing sugar. As the food passes from the mouth to the stomach and then to the small intestine, amylase is released in the mouth and in the small intestine but is not released in the stomach.
- (a)Fig. 1.1 shows a sketch of the changes in the concentration of the biological molecule, starch, as it enters the mouth and passes to the small intestine. Sketch another line on the graph to show the changes in the concentration of reducing sugar as the starch enters the mouth and passes to the small intestine.[2]
- (b)(i)Decide how you will test each solution to show the relative concentration of starch present. State the reagent you will use Describe how you will carry out the test for starch. State what you will record. Describe how you will determine which solution has the highest concentration of starch present.[2]
- (b)(ii)Decide how you will test each solution to show the relative concentration of reducing sugar present. You may measure the time taken to the first colour change. State the reagent you will use When testing for reducing sugar the volume of the reagent should be equal to or more than the volume of the sample. Describe how you will carry out the test to measure the reducing sugar concentration. State how you will determine which solution has the highest concentration of reducing sugar present.[3]
- (b)(iii)Carry out the test for starch and the test for reducing sugar on each of the solutions, S1, S2, S3 and S4. If the time taken to the first colour change for the reducing sugar test is longer than 180 seconds then record 'more than 180'. Prepare the space below and record your results.[5]
- (b)(iv)Using your results in (b)(iii) and using the information on page 2, complete Table 1.1 to show the identification of the samples, S1, S2, S3 and S4.[2]
- (b)(v)Explain how you decided which sample was taken from the small intestine.[1]
- (c)A student wanted to obtain a quantitative estimate of the reducing sugar concentration in a sample. Describe how the student could obtain a quantitative estimate of the concentration of reducing sugar in a sample.[3]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.
- [2] 1 line for concentration of reducing sugar increases from zero ;
- 2 line for concentration of reducing sugar horizontal (where line for concentration of biological molecule horizontal);
- [2] 1 iodine solution + stated number of drops or stated volume ;
- 2 records colour + degree of colour (blue / black);
- [3] 1 states volume of sample + volume of Benedict's solution + equal volume or in excess;
- 2 states temperature (80°C or higher or boiling);
- 3 reference to shortest time to colour change ;
- [5] 1 table drawn + heading, colour (starch test) ;
- 2 heading, time + seconds (reducing sugar test);
- 3 records colours for at least four concentrations of samples (starch test) ;
- 4 records times for at least four concentrations of samples (reducing sugar test);
- 5 times recorded as whole seconds ;
- [2] 1 correct S2 + S4 ;
- 2 correct S1 + S3 ;
- [1] 1 no starch as hydrolysed or all reducing sugar from hydrolysis ;
- [3] 1 5 or more concentrations of reducing sugar ;
- 2 made by proportional dilution or simple dilution or serial dilution ;
- 3 reference to comparing results of unknown concentration to results for known concentrations or reference to drawing graph and reading off ;
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