Phospholipids
These are the main component in cell membranes – they form a phospholipid bilayer.
The phosphate head is hydrophilic, polar (like water) and faces outwards. The fatty acid tail is hydrophobic, non-polar (doesn’t like water) and therefore they face inwards.
A phospholipid can be formed when one of the fatty acids found in a triglyceride is replaced by a phosphate group.
Phospholipids are responsible for controlling what goes in and out of cells.