CourseCourseQuestionQuestionDocumentDocument

B2.1.10—Fluid mosaic model

The fluid mosaic model describes a mobile phospholipid bilayer containing embedded proteins, surface proteins, cholesterol, and carbohydrate-bearing components; Evidence and diagrams emphasize both component positions and lateral mobility.

Syllabus
First assessment 2025
Objective
B2.1.10
Level
SL

Exam analysis

Chance of appearing10%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper2
Typical marks1–4

Common command terms

  • Draw
  • Identify
  • Distinguish
  • State
  • Outline

Scoring notes

Common mistake
Drawing proteins only as external layers rather than embedded within the bilayer.

Recent exam appearances

November 2025Paper2 ["SL"] · TZ33(a)[ 1 ]B2.1.10—Fluid mosaic model
May 2025Paper1A ["SL"] · TZ310[ 1 ]B2.1.10—Fluid mosaic model
May 2024Paper1 ["SL"] · TZ14[ 1 ]B2.1.10—Fluid mosaic model
May 2024Paper1 ["SL"] · TZ23[ 1 ]B2.1.10—Fluid mosaic model
May 2023Paper3 ["SL"] · TZ12(a)[ 1 ]B2.1.10—Fluid mosaic model

Coverage 2011–2025 · Updated 15 Jul 2026

Evidence Supports a Fluid Protein Mosaic

The fluid mosaic model describes laterally mobile lipids and many proteins arranged asymmetrically in a phospholipid bilayer.

A labeled lipid bilayer shows a protein traversing the membrane, proteins attached to one side, and a channel protein forming a pore toward the cell interior.

freeze fracture → particles within membrane faces
protein extraction → integral vs peripheral attachment
fluorescent cell fusion → labelled proteins spread laterally

SL Summary: Choose a Membrane Route

Particle property → gradient → route → energy.
Non-polar: bilayer. Water: osmosis/aquaporin. Ion or polar solute downhill: channel/carrier. Uphill: ATP-coupled pump.

The bilayer creates the barrier; proteins make it selective; carbohydrates create an outward interface; component mobility makes the membrane adaptable.

Fluid mosaic model

[ 6 ]

Draw and label a diagram to show the structure of membranes.

Drawing canvas

Concept essentials

  • The fluid mosaic model contains a phospholipid bilayer with mobile lipids and proteins.
  • Integral proteins are embedded in the bilayer, while peripheral proteins sit at membrane surfaces.
  • Cholesterol lies among phospholipid tails and carbohydrate chains project outward.
  • Freeze-fracture and model-comparison evidence support embedded proteins rather than a protein sandwich.