Amylase is an enzyme that catalyses the hydrolysis of starch into reducing sugars. A student carried out an experiment to investigate the hydrolysis of starch using immobilised amylase. Fig. 6.1 is a diagram of the apparatus that was used in the investigation. [Figure 6.1] The alginate beads were all the same size. Both taps were opened to allow the starch solution to flow down the column and for the product to be collected. The product was tested for the presence of reducing sugar and starch.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.

1. [3] 1 (open top tap and) keep bottom tap closed / close bottom tap for a longer time (and then open bottom tap to collect product) A close bottom tap for complete hydrolysis to occur
2. or
3. run starch solution through column, collect product, repeat (a number of times) / AW
4. or
5. only allow a small quantity of starch solution through at a time / AW ;
6. if a different idea suggested to set-up in Fig. 6.1, method must be related to an increase in contact time between beads and starch to award mp1
7. any two from:
8. 2 suggestion of modification to experimental set-up in Fig. 6.1 ; e.g. use smaller beads use more, beads / enzyme in beads I use more immobilised enzyme use of visking tubing attached to end of column (so only reducing sugar passes out) use longer, narrower column I ref. to filtering with filter paper / adding buffers to control pH
9. 3 test (sample of) product with iodine solution, qualified ; A iodine in potassium iodide solution / I in Kl solution e.g. to confirm no starch present stays orange (colour) does not change to blue-black (colour) to confirm no starch present
10. 4 ref. to using optimum temperature (for amylase) ; A e.g. 35 °C temperature
11. [1] any one from:
12. surface area to volume ratio / SA:V, decreases with increasing size / increases with decreasing size ;
13. SA:V ratio is different, with consequence ; e.g. smaller beads means increased contact of substrate with enzyme (in same conditions)
14. idea that overall, larger surface area exposed using smaller beads ; ora
15. (for the same experimental set up)
16. larger beads, slows rate of diffusion into beads / increases diffusion time to reach enzyme ; ora
17. larger beads will increase rate of flow through column ; ora