- phospholipid bilayer
- phosphate head is polar; one end is slightly positive, the other slightly negative. It attracts other polar molecules, like water, so is hydrophilic.
- phosphate tails are non-polar so are hydrophobic.
- In a cell, which are filled with watery/aqueous cytoplasm and surrounded by aqueous tissue fluid, phospholipids form a bilayer.
- the lipid bilayer is of critical biological importance, as it will close on itself so that there are no edges with exposed hydrogen chains- forms compartments.
- this avoids hydrophobic tails being in contact with the water on either side of the membrane and ensures the hydrophilic heads are in contact with the water.
- may also form micelles in water ( a layer on the surface) these are spherical clusters that do not occur in cells.