Phospholipids

• Phospholipids form a bilayer within cell membranes. They are formed from a hydrophilic phosphate 'head' and a hydrophobic lipid 'tail'.
• The hydrophilic heads of both phospholipid layers point to the outside of the cell-surface membrane (they are attracted to water).
• The hydrophobic tails of both phospholipid layers point into the centre of the cell-surface membrane (they are repelled by water).
• Phospholipids permit the movement of lipid-soluble substances into and out of the cell, whilst also preventing water-soluble substances from entering and leaving the cell.
• The phospholipid bilayer in the cell-surface membrane also makes the membrane flexible and self-sealing.