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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
HL

Exam analysis

Chance of appearing6%of analysed past papers
Latest appearanceMay 2024
Most common paperPaper2
Typical marks1–4

Common command terms

  • State
  • Outline
  • Describe
  • Explain
  • Identify

Scoring notes

Common mistake
Confusing hydrolysis with condensation when identifying reaction type.

Recent exam appearances

May 2024Paper1 ["HL"] · TZ124[ 1 ]B1.1.3—Digestion by hydrolysis
May 2022Paper2 ["HL"] · TZ26(c)[ 4 ]B1.1.3—Digestion by hydrolysis
May 2021Paper2 ["HL"] · TZ15(c)[ 2 ]B1.1.3—Digestion by hydrolysis
November 2020Paper2 ["HL"] · TZ06(b)[ 4 ]B1.1.3—Digestion by hydrolysis
November 2018Paper2 ["HL"] · TZ02(b)[ 2 ]B1.1.3—Digestion by hydrolysis
Practice this objective

Coverage 2015–2024 · Updated 15 Jul 2026

Hydrolysis Splits Biological Polymers

Hydrolysis breaks a covalent bond in a larger biological molecule by using water.

The water molecule separates into H and OH, which attach to the two products. This reverses the bond-forming logic of condensation and lets digestive enzymes release absorbable smaller molecules.

Trace the reaction as:

  • water enters the reaction
  • a polymer bond is cleaved
  • H and OH cap the two products

Hydrolysing a disaccharide produces two monosaccharides: one receives H and the other OH. The products are smaller than the starting molecule and can be transported for metabolism.

Hydrolysis is not the same as physically dissolving a food. It changes a covalent bond; water alone may be present, but enzymes usually control the biological rate.

Digestion by hydrolysis

Assessment in practice

1–3 marks
How it is assessed

This objective is assessed through structured response, commonly using State / Outline / Describe.

Command terms

State / Outline / Describe / Explain / Identify

What earns marks

Build the answer around this relationship: Hydrolysis breaks covalent bonds by adding water.

Watch for

Confusing hydrolysis with condensation when identifying reaction type.

Representative question

Question 1

[Maximum number: 6]

Describe the importance of hydrolysis in digestion.

Structure To Function

B1.1 becomes easy when every answer follows structure -> property -> function. Carbon skeletons and functional groups create molecular diversity. Condensation builds larger molecules and hydrolysis breaks them. Alpha-glucose stores energy as starch and glycogen; beta-glucose forms strong cellulose. Surface carbohydrates enable recognition. Lipids are hydrophobic, triglycerides store energy, phospholipids self-assemble into bilayers, and steroids cross membranes because they are mostly non-polar.

  • Carbon bonding and functional groups explain molecular diversity.
  • Condensation releases water; hydrolysis uses water.
  • Carbohydrates can store energy, build cell walls, and mark cell surfaces.
  • Lipids are hydrophobic and not true polymers.
  • Triglycerides store energy; phospholipids form membranes; steroids signal across membranes.

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.