Digestive Enzymes — Nutrition & Digestion | IGCSE Biology

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 16% of your exam marks.

stable

Very High

Stable16%

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

Carbohydrase chain: starch → glucose

Starch is broken down in two steps:

Amylase (in saliva, then in pancreatic juice in the duodenum) breaks starch into maltose (a disaccharide made of two glucose molecules).
Maltase (made by the small intestine) then breaks maltose into individual glucose molecules, which can be absorbed.

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.

Proteases

Pepsin in the stomach (optimum pH 2) breaks proteins into shorter chains called polypeptides.
Trypsin and other proteases from the pancreas and small intestine (optimum pH 8) then finish the job, breaking polypeptides into individual amino acids.

Lipases

Lipase from the pancreas works in the small intestine, breaking lipids into fatty acids and glycerol. Lipase needs the lipids to be in tiny droplets first, which is the job of bile (next section).