Syllabus Edition

First teaching 2023

First exams 2025

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The Fluid Mosaic Model: Skills (HL IB Biology)

Revision Note

Cara Head

Author

Cara Head

Last updated

The Fluid Mosaic Model

Membranes

  • Membranes form partially permeable barriers between the cell and its environment, between cytoplasm and organelles and also within organelles
  • Substances can cross membranes by diffusion, facilitated diffusion, osmosis and active transport
  • Membranes play a role in cell signalling by acting as an interface for communication between cells

Membranes in the cell, downloadable AS & A Level Biology revision notes

Membranes formed from phospholipid bilayers help to compartmentalise different regions within the cell, as well as forming the cell surface membrane

Fluid mosaic model

  • The fluid mosaic model of membranes was first outlined in 1972 by Singer and Nicolson and it explains how biological molecules are arranged to form cell membranes
  • The fluid mosaic model also helps to explain:
    • Passive and active movement between cells and their surroundings
    • Cell-to-cell interactions
    • Cell signalling
  • The fluid mosaic model describes cell membranes as ‘fluid’ because:
    • The phospholipids and proteins can move around within their own layers
  • The fluid mosaic model describes cell membranes as ‘mosaics’ because:
    • The scattered pattern produced by the proteins within the phospholipid bilayer looks somewhat like a mosaic when viewed from above
  • The fluid mosaic model of membranes includes four main components:
    • Phospholipids
    • Cholesterol
    • Glycoproteins and glycolipids
    • Integral and peripheral proteins

The fluid mosaic model diagram

Fluid mosaic model exam example, downloadable AS & A Level Biology revision notes

The distribution of the proteins within the membrane gives a mosaic appearance and the structure of the proteins determines their position in the membrane

Examiner Tip

You should be able to draw a two-dimensional diagram of the fluid mosaic model of membrane structure.

You should show and label the following:

  • The phospholipid bilayer, making it clear which part is the phosphate head and which parts are the hydrocarbon tails
  • Integral proteins, e.g. channel/carrier
  • Peripheral proteins that do not extend into the hydrophobic region
  • Glycoproteins with a carbohydrate attached
  • Cholesterol, with the OH group next to the phosphate heads and the rest positioned next to the tails

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Cara Head

Author: Cara Head

Expertise: Biology

Cara graduated from the University of Exeter in 2005 with a degree in Biological Sciences. She has fifteen years of experience teaching the Sciences at KS3 to KS5, and Psychology at A-Level. Cara has taught in a range of secondary schools across the South West of England before joining the team at SME. Cara is passionate about Biology and creating resources that bring the subject alive and deepen students' understanding