Outline the role of hydrolysis in the relationships between monosaccharides, disaccharides and polysaccharides.

Describe the use of biotechnology in the production of lactose-free milk.

Explain the importance of enzymes to human digestion.

monosaccharides are single sugars and disaccharides are two sugars and polysaccharides are multiple sugars;
hydrolysis is the addition of water to split a molecule into smaller fragments;
–OH and –H are added to the fragments;
disaccharides are split/digested into two single sugars;
polysaccharides are broken/digested into smaller fragments (e.g. diasaccharides);
process depends on enzyme control (in organisms);

a particular yeast (growing in natural milk) contains lactase;
biotechnology companies can grow/culture the yeast;
lactase (an enzyme) is extracted from the yeast;
natural milk contains lactose/milk sugar;
when added directly to milk, lactase converts lactose into simpler forms;
same effect when milk is passed past immobilized (on surface or beads) lactase;
simpler forms of sugar (glucose and galactose) are easily absorbed (in the small intestine);
a commercial market exists for lactose-free milk / lactose-free milk is example of biotechnology’s economic impact;
some people are lactose intolerant/cannot digest lactose in milk/have lost lactase activity in intestinal cells;
consuming lactose-free milk allows lactose intolerant people to be nourished by milk without discomfort (abdominal cramps and diarrhoea);
many Asians are lactose intolerant whereas less common among other groups (northern Europeans and some Africans);
biotechnology produced in one part of world is more useful in another;

food must be in a small enough form to leave the gut and enter the bloodstream;
physical breakdown is not enough / chemical breakdown is necessary;
enzymes are required for the chemical breakdown of food;
enzymes increase the rate of digestion;
enzymes are biological catalysts;
enzymes allow digestion to occur at body temperature;
enzymatic digestion is a sequential process e.g. from protein to peptide to amino acid;
specific location for each reaction with specific conditions/environments e.g. stomach high acidity;
most enzymes work extracellularly / some enzymes work intracellularly;
variations in pH throughout digestive tract promote the activity of different digestive enzymes / different enzymes have different optimal pHs;
amylases digest carbohydrate to monosaccharides;
proteases digest proteins to amino acids;
lipases digest fats to fatty acids and glycerol;

Candidates generally understood the process of hydrolysis but had difficulty applying it to the relationship between monosaccharides, disaccharides and polysaccharides.

The production of lactose free milk was well understood by many candidates, but most left out basic points such as the fact that lactose is found in milk and that lactase is the enzyme that breaks it down. Sometime these fundamental points, which are worth marks, are skipped. Candidates should fully explain their answers and not take any response for granted as "too obvious for a mark‟.

This section was generally well done with candidates demonstrating a good understanding of enzyme function in the context of the human digestive tract. The best responses named specific enzymes, the location of release and the substrate and products of the reaction catalysed. As in 5 (b), many candidates did not indicate that enzymes are biological catalysts and that they increase the rate of digestion. Candidates should fully explain their answers and not take any response for granted as "too obvious for a mark‟.