What is the phospholipid bilayer?

The phospholipid bilayer is part of the Fluid Mosaic model forming part of the structure of the cell membrane. It plays a role in regulating the movement of substances across the cell membrane and makes up the the fluid part of the model. The phospholipid bilayer is made up of phospholipids which are fats and are described as Amphipathic. This means they have a hydrophobic and hydrophilic part. The hydrophobic part is the phospholipid tail, which moves away from water and the hydrophilic part is the head which moves towards water. The head can also be described as polar and the tail described as non-polar. When in contact with water, the phospholipids form a bilayer which consists of two layers of phospholipids with the tails pointing inwards and the heads pointing outwards.