Question

Amylase is an enzyme that breaks down starch into maltose. A student investigated the breakdown of starch into maltose. The student investigated the effect of pH on the activity of the amylase. This was the method used: Tubes containing starch and amylase were set up in a range of pH solutions. The same concentration of starch and amylase were used each time. A small sample of the solution was removed and tested for the presence of starch at 20 s intervals. The procedure was repeated three times and a mean was calculated for each pH. The student presented the results in table pH 4 5 6 7 8 9 Mean amylase activity(% of maximum) 27 68 96 100 50 29 (i) Another student wanted to replicate the investigation. Refine the method, by giving additional information, so that reproducible results would be obtained. …………………………………………………………………………………………………... …………………………………………………………………………………………………... ……………………………………………………………………………………………. [3] (ii) Explain, with reference to bonding, why amylase activity is low at pH 4. …………………………………………………………………………………………………... …………………………………………………………………………………………………... ……………………………………………………………………………………………. [4] (iii) The student concluded that the optimum pH for amylase was pH 7. A teacher made the following statement: ‘The results in Table 2.1 provide only weak support for the conclusion that the optimum pH for amylase is pH 7.0’ Evaluate the statement and suggest an improvement to the student’s procedure that would support the conclusion more strongly. Evaluation …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... Improvement …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... [3] (d) Amylase activity is increased in the presence of chloride ions. State the name given to any inorganic ion that increases the activity of an enzyme.

Answer 1

2 (a) (i) 32 
mmol dm–3 min–1 
2
ALLOW mmol dm–3
/ min’ or ‘mmol dm–3
per , min / minute
ALLOW 0.53 mmol dm–3
/ s
(ii) (initial rate likely to be) greater 
because…
higher concentration of, substrate / amylose, molecules (at
start) 
more chance of, substrate / AW, entering active site 
3
ALLOW ‘starch’
(b) (i) three from
competes (with substrate) / competitive 
enters / fits in / binds to / blocks, active site 
prevents substrate from entering active site 
(binds to active site) temporarily 
3
(ii) (at high substrate concentration) rate approaches rate in
absence of inhibitor 
1 IGNORE idea that increased substrate concentration
overcomes the inhibition as answer must refer to evidence
from the graph.
(c) (i) three from
specify volume of starch and amylase to be added to the
tubes 
specify volume (in ml) of the solution that should be
removed for testing 
stir before taking the sample 
test with iodine 
all carried out at same temperature 

(ii) four from
ionic / hydrogen, bonds, disrupted / broken 
(by) high concentration of, hydrogen ions / H+ 
tertiary structure / shape of active site, changed 
substrate no longer fits into active site 
(enzyme) denatured 
4
IGNORE active site denatured.
(iii) Evaluation, two from
idea that optimum could be anywhere between pH 6 and
pH 8 
only one value between pH 6 and pH 8 tested 
idea that shape of data implies optimum less than pH 7 
Improvement
repeat at more pH values between 6 and 8 
3
(d) cofactor  1 IGNORE coenzyme.