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B1.1.5—Polysaccharides as energy storage

Starch and glycogen are glucose polysaccharides adapted for energy storage through compact, insoluble, branched or helical molecular structures in organisms.

Syllabus
First assessment 2025
Objective
B1.1.5
Level
SL

Exam analysis

Chance of appearing6%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper2
Typical marks1–3

Common command terms

  • Outline
  • Describe
  • Distinguish
  • Compare

Scoring notes

Common mistake
Confusing glycogen with glucagon or glucose.

Recent exam appearances

May 2025Paper2 ["SL"] · TZ27(a)[ 3 ]B1.1.5—Polysaccharides as energy storage
May 2021Paper2 ["SL"] · TZ25(a)[ 5 ]B1.1.5—Polysaccharides as energy storage
May 2019Paper1 ["SL"] · TZ27[ 1 ]B1.1.5—Polysaccharides as energy storage
November 2018Paper3 ["SL"] · TZ09(a)[ 2 ]B1.1.5—Polysaccharides as energy storage
May 2018Paper2 ["SL"] · TZ12(a)(i)[ 1 ]B1.1.5—Polysaccharides as energy storage

Coverage 2011–2025 · Updated 15 Jul 2026

Branching controls access to stored glucose

Starch and glycogen are compact, insoluble stores of α-glucose. Their large molecules do not diffuse away and have far less osmotic effect than the same number of separate glucose molecules.

Store Main structure What the structure changes
amylose in plant starch mostly unbranched α-1,4 chain, coiled compact but relatively few chain ends
amylopectin in plant starch α-1,4 chains with α-1,6 branches more ends available for enzyme action
glycogen in animals and fungi more frequent α-1,6 branching many ends allow rapid glucose release

Branching does not add more energy to each glucose unit. It increases the number of chain ends that enzymes can hydrolyse at the same time, so stored fuel can be mobilised faster.

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

Polysaccharides as energy storage

[ 4 ]

Outline how and where energy is stored in plants.

Concept essentials

  • Starch stores glucose energy in plants as amylose and amylopectin.
  • Glycogen is a branched glucose storage polysaccharide in animals and fungi.
  • Amylose is mostly unbranched and helical, while amylopectin is branched.
  • Storage polysaccharides are compact and poorly soluble, reducing osmotic effects.