A number of marine organisms are able to fix themselves onto hard surfaces, including rocks and the outer surfaces of ships. These are called fouling organisms.
The larva of the acorn barnacle, Amphibalanus amphitrite, is one such fouling organism. One barnacle larva is shown in Fig. 3.1.
Larvae of A. amphitrite use a protein to bind to ship surfaces.
Getting fouling organisms off ships is costly. Scientists have produced substances that stop larvae attaching. However, some of these substances are toxic and have caused a reduction in marine biodiversity.
Scientists examined the effect of using an immobilised protease, subtilisin A, to stop the larvae of A. amphitrite attaching to surfaces.
The scientists tested 4 different concentrations of subtilisin A that had been immobilised on the surface of a polymer film. As a control they used denatured subtilisin A immobilised on the surface of the same polymer. Glass slides were also used as a control.
The larvae were placed into 6 tanks of artificial sea water:
• 4 tanks, each with a polymer surface and a different concentration of immobilised subtilisin A
• 1 tank with a polymer surface and denatured immobilised subtilisin A
• 1 tank with glass slides rather than a polymer surface.
After 24 hours and then again after 48 hours, the number of larvae attached to the different surfaces in the tanks was counted.
For each tank, the number of attached larvae was given as a percentage of the total number of larvae released into that tank. The results are shown in Fig. 3.2.
(a)[3]
Describe how the induced-fit hypothesis explains enzyme action.
(b(i))[4]
With reference to the data in Fig. 3.2, discuss how effective subtilisin A is at preventing larval attachment.
(b(ii))[2]
The scientists extended their investigation by coating the outside of the bottom of small ships with the polymer containing immobilised subtilisin A.
Two factors that must be considered in this type of investigation are the temperature and pH of the sea water.
Outline two other factors that must be considered when investigating the suitability of immobilised subtilisin A as an anti-fouling agent for ships.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Active site and substrate are only partly / not complementary” …