Biology 3.5 The Cell-Surface Membrane

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  • Created by: Anna
  • Created on: 12-04-13 22:53

Known as plasma membrane, forms boundary between cell cytoplasm and environment.

Allows different conditions inside and outside cell and controls movement of substances in and out of cell.


Phospholipids form a bilayer sheet because:

  • One layer of phospholipids = hydrophilic heads pointing inwards (water inside cell cytoplasm)
  • Other layer has hydrophilic heads pointing outwards (to water outside the cells)
  • Hydrophobic tails of both layers point into centre of the membrane, protected from water on both sides.

Lipid soluble material moves through membrane via phospholipid portion. Function of membrane:

  • allow lipid-soluble materials in and out.
  • prevent water-soluble substances in and out.
  • make membrane flexible.

NB: phospholipid has…


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