Question

What is an easy way to explain the function of the Plasma Membrane and the structure (including the Fluid-Mosiac model)?

Answer 1

OK. The plasma membrane is made up of two layers of phospholipids. Phospholipids are amphipathic - they have a polar (hydrophillic) phosphate group on one end and non-polar (hydrophobic) fatty acid groups on the other end which make bilayer formation energetically favourable.

Entropy is the main driver of this process: fewer water molecules exist in an ordered conformation around the membrane surface, so more water molecules can sample a greater variety of interactions with each other. By comparison, the noncovalent bonds between the phospholipids in the membrane are relatively weak, so enthalpic contributions to the system are very low.

Because they are so low - that is, because the phospholipids in the membrane are not covalently bonded to each other - they are free to diffuse within the membrane. In essence, that is what's meant by the "Fluid Mosaic Model."