Outline, with examples, the types of carbohydrate found in living organisms.

Describe the importance of hydrolysis in digestion.

Explain the effect of inhibitors on the activity of enzymes.

(mono-, di- and polysaccharides) consist of one, two and many units;
example of monosaccharide (e.g. glucose/ribose/galactose/fructose);
example of disaccharide (e.g. maltose/lactose/sucrose);
example of polysaccharide (e.g. starch/glycogen/cellulose)

digestion is the breakdown of large molecules into small molecules;
to allow diffusion / to make food soluble;
so foods can be absorbed into the bloodstream/body;
so foods can move from bloodstream into cells;
small molecules can be joined to form the organism’s (unique) macromolecules;
hydrolysis is aided by enzymes;
hydrolysis requires water;
polysaccharides (hydrolysed) to disaccharides/monosaccharides/specific example;
proteins/polypeptides (hydrolysed) to amino acids;
fats/lipids/triglycerides (hydrolysed) to fatty acids and glycerol;

inhibitors reduce enzyme activity/reduce the rate of reaction;

Competitive inhibitors:
have a similar shape to the substrate;
bind to/attach to/enter the active site;
block/compete for occupation of the active site / prevent substrate binding;
example (e.g. succinate dehydrogenase by malonate);
increase in substrate concentration reduces inhibition / graph showing this;

Non-competitive inhibitors:
not chemically similar / different shape to substrate;
attach to a different part of the enzyme/allosteric site;
shape of the active site changes preventing/reducing substrate binding;
example of non-competitive inhibition (e.g. respiratory enzymes by cyanide);
increases in substrate concentration do not reduce inhibition / graph showing this;
end-product inhibitors are non-competitive;

The types of carbohydrate referred to in this question were structural. Candidates who outlined monosaccharides, disaccharides and polysaccharides, with examples of each were able to score the marks quite easily. Those who classified carbohydrates according to function without any reference to structural differences did not fare so well.

The examining team adopted a broad interpretation of the meaning of this question, as it would have been difficult to sustain an answer of its literal meaning beyond a few marks. Many candidates wrote good answers, explaining both the need for digestion and the relationship between hydrolysis and digestion.  

This was well answered by many of the stronger candidates, with detailed accounts of competitive and non-competitive inhibition. The only common omissions were end product inhibitors and examples of each type of inhibitor. Although not specifically requested in this question, examples are always worth including and are often rewarded with marks.