Outline the effect of temperature and substrate concentration on the activity of enzymes.

Distinguish between competitive and non-competitive enzyme inhibition of chemical reactions, giving an example of each.

Explain the light-independent reactions of photosynthesis.

enzymes most active at one temperature/optimum temperature;
any deviation from that temperature lowers the enzyme activity;
denaturing/change in active site/no activity at higher temperatures / inactivated at (very) low temperatures;
increasing the substrate concentration increases the enzyme activity/more enzyme-substrate complex formed/more collisions between enzyme and substrate;
eventually no increase in enzyme activity with increased substrate concentration / plateau when enzymes are working to the maximum/when all active sites occupied/saturated;
Accept answers shown graphically.

example of competitive; (e.g. malonate competes with succinate dehydrogenase)
example of non-competitive; (e.g. opioids inhibit nitric oxide synthase)

Award [2 max] for examples and [1] for each correct paired statements up to [3 max].
Answers do not need to be shown in a table format.

take place in the stroma of the chloroplast;
produce carbohydrates;
ribulose bisphosphate/RuBP is a five carbon compound;
carbon dioxide fixed/added to RuBP / carboxylation;
by RuBP carboxylase (enzyme)/Rubisco;
forms unstable six carbon compound;
this splits into (two molecules of) glycerate-3-phosphate/GP;
ATP and NADPH produced in light-dependent reaction;
ATP provides the energy;
GP reduced to triose phosphate/TP;
NADPH provides hydrogen;
some three carbon sugars go to form hexose sugars;
some go to making more RuBP;
called the Calvin (Benson) cycle;

Was generally well answered with many candidates scoring marks by including annotated drawings of the changes in enzyme activity.

Was answered much more poorly, not due to a lack of understanding of the different types of inhibition, but due to not comparing equivalent factors. For example, most gained the mark for mp (c) for inhibitor attaching to the active site in competitive and to another site in non-competitive. However, many mentioned similar structure to the substrate in the first but there was no equivalent comment for the second, thus no mark. 

Few students could give specific examples of either. It was insufficient to say a heavy metal is a non-competitive inhibitor without specifying the metal and the enzyme. 

Was generally well answered, with students showing very good understanding of the light-independent reaction. Many included clear, annotated diagrams to support their answers. A few students mistakenly described the light dependent reaction and a few respiration.