Researchers isolated a sucrase enzyme from the bacterium Bacillus subtilis. They immobilised the enzyme in alginate beads. The researchers investigated the effects of temperature on the activity of the immobilised sucrase compared with the activity of the same enzyme free in solution. The results are shown in Fig. 3.1.

Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

1. [4] four from: activity increases and decreases / activity peaks, for both ; A both have maximum activity / optimum temperature, at 60 °C activity is 76% at 40 °C for both; (overall) activity decreases more steeply for free enzyme after, optimum / maximum / 60 °C; A ora at 80 °C free enzyme is inactive / (fully) denatured / 0%, but immobilised enzyme, is still active / is partially denatured / 27% ; for immobilised enzyme, activity is higher (than free enzyme) at all temperatures above 60 °C;
2. [2] two from: (alginate / immobilisation), is protective / has stabilising effect ; A enzyme, less / not, exposed (to solution) hydroxide ions do not penetrate the alginate beads ; shape of active site (of immobilised enzyme) is, less / not, disrupted / AW ; A active site is (more) complementary to substrate A few(er) active sites are, altered / changed few(er) bond's within (immobilised) enzyme break ; A hydrogen / ionic R peptide / disulfide at pH 8 immobilised enzyme is not fully denatured ; A pH 7/7.5
3. [2] explanation must match variable stated standardised variable concentration / volume, of, enzyme / substrate, solution; explanation for standardised variable idea that: concentration / volume, of, enzyme / substrate, influences the probability of collisions between enzyme and substrate molecules / formation of enzyme/substrate complexes ; A number of / frequency of, collisions between substrate and enzyme or standardised variable use the same method for determining enzyme activity; e.g. time when samples are taken explanation for standardised variable 3 ref. to how enzyme activity is measured by conversion of substrate to product;
4. [2] two from: 1 (may be able to) obtain more product (per unit time); 2 can use higher temperatures (to obtain more product) / still active at higher temperatures; A thermostable 3 does not denature (as easily as free) if temperatures increase / AW ; 4 immobilised enzyme can be reused/immobilised enzyme can be recovered ; 5 enzyme does not contaminate product; A no effect on quality of product, e.g. taste 6 less, purification (of product) / downstream processing, needed ; A idea that downstream processing less, complex / difficult 7 longer shelf-life of enzyme / AW ; A durability 8 AVP; e.g. allows continuous production (rather than batch) some enzymes are difficult to extract I ref. to cost/cost effective unqualified R reduces effect of end product inhibition