Phospholipids are a class of lipids, or fats, and are a major component of all biological membranes.
All phospholipids contain a diglyceride, a phosphate group, and a simple organic molecule such as choline. They form a lipid bilayer within a cell membrane. They also transport DNA.
The ‘head’ of a phospholipid is hydrophilic (attracted to water) wheras the hydrophobic ‘tails’ repel water. When placed in water, phospholipids form a variety of structures depending on the specific properties of the phospholipid. In biological systems, the phospholipids often occur with other molecules (e.g., proteins, glycolipids, cholesterol) in a bilayer such as a cell membrane.