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B1.1.3—Digestion by hydrolysis

Hydrolysis uses water to break covalent bonds in food macromolecules, producing soluble monomers that can be absorbed and reused by cells.

Syllabus
First assessment 2025
Objective
B1.1.3
Level
SL

Exam analysis

Chance of appearing11%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper1
Typical marks1–3

Common command terms

  • State
  • Outline
  • Describe
  • Explain
  • Identify

Scoring notes

Common mistake
Confusing hydrolysis with condensation when identifying reaction type.

Recent exam appearances

May 2025Paper2 ["SL"] · TZ14(a)[ 1 ]B1.1.3—Digestion by hydrolysis
May 2024Paper2 ["SL"] · TZ25(c)[ 7 ]B1.1.3—Digestion by hydrolysis
November 2023Paper1 ["SL"] · TZ225[ 1 ]B1.1.3—Digestion by hydrolysis
November 2022Paper2 ["SL"] · TZ07(a)[ 3 ]B1.1.3—Digestion by hydrolysis
November 2022Paper1 ["SL"] · TZ025[ 1 ]B1.1.3—Digestion by hydrolysis

Coverage 2010–2025 · Updated 15 Jul 2026

Hydrolysis uses water to release monomers

During hydrolysis:

  1. water is a reactant
  2. a covalent linkage breaks
  3. water supplies –H to one product and –OH to the other
  4. enzyme-catalysed repetitions release small, absorbable molecules
Enzyme class Bond-containing substrate Main small products
amylase starch shorter sugars, then glucose
protease polypeptide peptides and amino acids
nuclease nucleic acid nucleotides

Condensation produces water while forming a bond. Hydrolysis consumes water while breaking one. The reactions are reverse in chemistry but are controlled by different enzymes in cells.

Carbohydrate summary: follow monomer to biological job

Starting form Linkage or arrangement Emergent form Main job
α-glucose α-1,4 with optional α-1,6 branches amylose, amylopectin, glycogen energy storage
β-glucose alternating β-1,4 chain; hydrogen-bonded bundles cellulose fibres tensile support
short surface sugars attached to protein or lipid; exposed outside glycocalyx markers recognition, adhesion, signalling

Condensation builds a covalent linkage and releases water; hydrolysis consumes water and breaks that linkage. Which enzyme acts depends on the bond and substrate.

For a structure–function explanation:

  1. name the monomer or functional group
  2. identify the linkage and three-dimensional arrangement
  3. state the resulting property
  4. connect that property to the biological job

Digestion by hydrolysis

[ 6 ]

Describe the importance of hydrolysis in digestion.

Concept essentials

  • Hydrolysis breaks covalent bonds by adding water.
  • Digestion converts macromolecules into smaller soluble products for absorption.
  • Amylase, proteases and lipase catalyse hydrolysis of different food molecules.
  • Products of digestion can be absorbed through the small intestine.