Cambridge (CIE) AS Your notes
Biology
Fluid Mosaic Membranes
Contents
The Fluid Mosaic Model
Components of Cell Surface Membranes
The Cell Surface Membrane
Cell Signalling
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, The Fluid Mosaic Model
Your notes
The Fluid Mosaic Model of Membranes
Membranes are vital structures found in all cells
The cell surface membrane creates an enclosed space separating the internal cell
environment from the external environment
Intracellular membranes form compartments within the cell such as the nucleus,
mitochondria and RER
Membranes do not only separate different areas but also control the exchange of
materials across them, as well as acting as an interface for communication
Membranes are selectively permeable
Substances can cross membranes by diffusion, osmosis and active transport
Cellular membranes are formed from a bilayer of phospholipids which is roughly
7nm (7 × 10-9 metres) wide and therefore just visible under an electron microscope at
very high magnifications
The fluid mosaic model of the membrane was first outlined in 1972 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
Phospholipids
Phospholipids structurally contain two distinct regions: a polar head and two nonpolar
tails
The phosphate head of a phospholipid is polar (hydrophilic) and therefore soluble in
water
The lipid tail is non-polar (hydrophobic) and insoluble in water
If phospholipids are spread over the surface of water they form a single layer with the
hydrophilic phosphate heads in the water and the hydrophobic fatty acid tails sticking
up away from the water
This is called a phospholipid monolayer
Phospholipid Monolayer Diagram
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Biology
Fluid Mosaic Membranes
Contents
The Fluid Mosaic Model
Components of Cell Surface Membranes
The Cell Surface Membrane
Cell Signalling
© 2025 Save My Exams, Ltd. Get more and ace your exams at savemyexams.com 1
, The Fluid Mosaic Model
Your notes
The Fluid Mosaic Model of Membranes
Membranes are vital structures found in all cells
The cell surface membrane creates an enclosed space separating the internal cell
environment from the external environment
Intracellular membranes form compartments within the cell such as the nucleus,
mitochondria and RER
Membranes do not only separate different areas but also control the exchange of
materials across them, as well as acting as an interface for communication
Membranes are selectively permeable
Substances can cross membranes by diffusion, osmosis and active transport
Cellular membranes are formed from a bilayer of phospholipids which is roughly
7nm (7 × 10-9 metres) wide and therefore just visible under an electron microscope at
very high magnifications
The fluid mosaic model of the membrane was first outlined in 1972 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
Phospholipids
Phospholipids structurally contain two distinct regions: a polar head and two nonpolar
tails
The phosphate head of a phospholipid is polar (hydrophilic) and therefore soluble in
water
The lipid tail is non-polar (hydrophobic) and insoluble in water
If phospholipids are spread over the surface of water they form a single layer with the
hydrophilic phosphate heads in the water and the hydrophobic fatty acid tails sticking
up away from the water
This is called a phospholipid monolayer
Phospholipid Monolayer Diagram
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