Structures and Functions in Living Organisms · 9 question types
Past paper frequency (2018 to 2024)
This topic accounts for approximately 16% of your exam marks.
Enzymes in digestion and the role of digestive structures appear regularly across both papers.
Digestive enzymes fall into three groups, each one catalysing the breakdown of a different nutrient:
| Enzyme group | What it digests | Into | Where it is made |
|---|---|---|---|
| Carbohydrases (amylase, maltase) | Carbohydrates | Simple sugars (e.g. glucose) | Salivary glands, pancreas, small intestine |
| Proteases (pepsin, trypsin) | Proteins | Amino acids | Stomach, pancreas, small intestine |
| Lipases | Lipids | Fatty acids and glycerol | Pancreas, small intestine |
Starch is broken down in two steps:
Note: the amylase in saliva gets denatured as soon as it enters the acidic stomach (pH 2 destroys its shape), so most starch digestion actually happens in the duodenum after pancreatic amylase is added.
Lipase from the pancreas works in the small intestine, breaking into fatty acids and glycerol. Lipase needs the lipids to be in tiny droplets first, which is the job of bile (next section).
Digestive enzymes: what each digests and what it produces
What comes up: A table to complete, or a question asking which enzyme digests a named substrate, or what products are released.
Write: Match enzyme to substrate to product: (1) amylase digests starch into maltose; (2) maltase digests maltose into glucose; (3) protease digests proteins (and polypeptides) into amino acids; (4) lipase digests lipids into fatty acids and glycerol.
Watch out: Amylase produces maltose, not glucose — glucose comes from a second step by maltase. A common error is writing "starch → glucose" in one step; the mark scheme credits starch → maltose for amylase. Also, the products of lipase are (both required for the mark) — writing only "fatty acids" or only "glycerol" will lose a mark.