Digestion

In the syllabus and the exam

Digestion is examined as a two-part process combining physical digestion, which increases surface area by chewing and churning food without changing its chemical identity, and chemical digestion, in which specific enzymes break large molecules into smaller soluble units. Candidates are expected to name the enzyme, its site of action and its substrate and product for each major food group, for example amylase converting starch to maltose in the mouth and small intestine, protease converting protein to amino acids in the stomach and small intestine, and lipase converting lipids to fatty acids and glycerol in the small intestine. A frequent exam trap asks why digestion is necessary at all, and the expected answer links back to absorption: large, insoluble food molecules cannot pass through the wall of the small intestine, so they must be broken down into small, soluble molecules first. Confusing digestion with absorption, or listing an enzyme without its correct substrate, are the errors markers most often flag.

Example

Digestion breaks the starch in rice down into glucose molecules small enough to be absorbed into the bloodstream.

Related terms

EnzymeVillusAssimilation

Source:SRC-DSKP-EN