Mark Scheme for Term 1 Assessment
1. (a) Amylase;
(Starch) to maltose:Maltase;
Maltose to glucose;
Hydrolysis;
(Of) glycosidic bond;
Q Do not penalise incorrect site for digestion or incorrect site of
enzyme production.
2. (a) (i) Increase to 30 °C/31 °C and then decreases / optimum or max
rate at 30 °C/31 °C;
Accept: peak at 30 °C/31 °C
(ii) 1. Enzyme denatured / hydrogen bonds/bonds holding tertiary
structure broken / tertiary structure changed;
2. Change in shape of active site (of enzymes);
3. Substrate / protein no longer fits / binds (into active site) / few or no ES
complexes;
4. More enzyme (molecules) denatured as temperature increased;
1. Reject: Peptide bonds broken
Denatures active site = 2 marks for mp 1 and 2
2. Q Only allow second point if active site is used correctly
Accept: active site no longer complementary
3. Accept: Substrate cannot bind to enzyme
3 max
(b) (i) Use buffer / test pH (at end/ at intervals);
Accept a method of measuring pH.
Reject litmus.
(ii) (30 °C/31 °C) Maximum rate / optimum temperature;
Accept other valid answers e.g. temp below
30 °C as enzyme not denatured.
1
(iii) Works best at pH 6 / at higher pH activity decreases;
Accept converse
Insufficient: pH 6 had largest clear area
1
3. (a) (i) Active site/enzyme not complementary;
Active site changes (shape)/is flexible;
(Change in enzyme allows) substrate to fit/E-S complex to form;
Active site becomes complementary/wraps around substrate = 2
marks
For mark point 2. allow ‘binding site’ but not ‘enzyme’
For mark point 2. can only have enzyme changes (shape) if active
site has been mentioned earlier
Final mark point must have context
Reject: active site on substrate for second marking point only
Accept: diagrams only if suitably labelled or annotated
2 max
(ii) Active site does not change (shape)/is fixed (shape)/is rigid/does
not wrap around substrate/(already) fits the substrate/is
complementary (before binding);
Assume that ‘it’ refers to lock and key
1
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(b) Similar structure/shape (to PABA)/both complementary;
Competes for/binds to active site/competitive inhibitor;
Less PABA binds/less E-S complexes;
OR
Specific reference to different structure/shape (to PABA)
using the diagram;
Binds to position other than active site/binds to allosteric
site/binds to inhibitor site/non-competitive inhibitor;
Changes the active site so substrate cannot bind/less PABA
binds/less E-S complexes;
Q Reject: same structure/shape
Note: competitive inhibitor binds to active site = 1 mark (same
mark point)
Assume that ‘it’ refers to sulfanilamide
Accept: PABA/substrate cannot bind
Neutral: less product produced as in question stem
Neutral: different structure/shape to PABA
Reject: active site on substrate for second marking point only
3 max
[6]
4. (a) (i) Increases then plateaus/constant/steady/rate does not change;
Neutral: ‘peaks’/‘reaches a maximum’/‘stops increasing’/‘no effect’
instead of ‘plateaus’
Reject: rate decreases/reaction stops
Correct reference. to 27/28 units;
e.g. increases up to/plateaus at 27/28
2
(ii) Substrate concentration/amount of substrate;
As substrate concentration increases, rate increases/positive
correlation (between rate and substrate concentration);
2
(iii) All active sites occupied/saturated/enzyme limiting (rate of
reaction)/maximum number of E-S complexes;
Reject: enzymes used up
Reject: substrate limits rate of reaction
Neutral: substrate no longer limits the reaction
Neutral: reference to temperature
1
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(b) Curve is lower and plateaus at a higher substrate concentration
(it must also start at zero);
Accept: curve lower and joins existing curve at final point (with no
plateau)
Reject: if curve plateaus before original
Reject: if curve plateaus lower than original
1
(c) (i) Methotrexate/drug is a similar shape/structure to substrate;
Q Reject: same structure/shape
Binds to/fits/is complementary to active site;
Q Reject: reacts with active site
Less substrate binds/less enzyme-substrate complexes formed;
Accept: substrate cannot bind/enzyme-substrate complex not
formed
2 max
(ii) Methotrexate/drug is only similar shape to specific substrate/
only fits this active site;
Assume that ‘it’ refers to the drug
OR
Methotrexate/drug is a different shape to other substrates/will
not fit other active sites;
1
[9]
5. (a) C
12
; H
22
O
11
;
2
(b) (i) heat with Benedict’s;
yellow/brown/orange/red;
2
(ii) (yes)
(may appear on second line)
more precipitate in sample B;
both sugars are reducing sugars/ give a positive test;
2
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