Cell membrane

Every living cell is surrounded by a cell membrane, also known as plasma membrane. It is precisely the boundary that delineates the intracellular medium from the extracellular medium/ environment. Interestingly the cells membrane itself is highly dynamic and all the cell-sustaining functions require contiguous interaction with the external environment.

There was an array of models proposed for the structure of the cell membrane, but the most widely accepted one is the Singer and Nicholson’s model Fluid Mosaic model of the cell membrane. According to the fluid mosaic model, the membrane is has a phospholipid bilayer and proteins are present both on the surface as well as embedded inside the bilayer.
An important feature of the bilayer is that it is always mobile and constantly the lipids are flipped, removed and added as confirmed by FRAP (Fluorescence recovery after photobleaching) experiments.