T4- Cell Membrane and Transport (diagrams & illustrations & common p1 & p2 misconceptions)
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Cambridge AS Biology
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-AS Biology Cambridge Topic 2 full notes covering all points of the sylabus as you go on. contact us on:
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If phospholipids are mixed with water they form:
1. Micelles → ball like structures→ hydrophilic heads face outwards
2. Bilayers → sheet-like structures
Role of cell membrane:
1. Controls exchange of materials → nutrients & waste products between cell
& environment
2. Cell signaling
The fluid-mosaic model of membrane structure:
Fluid: The phospholipids and proteins can move around via diffusion mainly
sideways, within their own layers.
Mosaic: the scattered protein pattern within the phospholipid bilayer.
Describe the structure of phospholipid.
● Hydrophilic (polar) Phospholipid heads point outwards into the aqueous
solution that surrounds the membranes forming, stabilizing the
membrane by forming hydrogen bonds with water.
● Hydrophobic (non polar) phospholipid tails point inward facing each other
forming a hydrophobic core which acts as a barrier to hydrophilic
molecules & ions
Factors which impact membrane fluidity:
1. Increased percentage of ● Unsaturated fatty acids have C=C double bonds which causes kinks
unsaturated fatty acids (bending) in fatty acids → they fit together more loosely
present INCREASES
membrane fluidity
2. Tail length → The ● The longer the tail, the more bond interactions between fatty acids, holding
longer the tail the less them closer, so fluidity decreases
fluid the membrane
3. Temperature ● As temperature increases fluidity increases due to phospholipid molecules
having a greater kinetic energy.
4. Cholesterol (more detail ● Fits between phospholipid molecules
soon) ● At low temperatures, cholesterol increases the membrane fluidity →
cholesterol prevents phospholipids from packing close together
● At high temperatures, cholesterol decreases the membrane fluidity.
2
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