1. The Cell Membrane
All cells are separated from the external environment by a Plasma Membrane
 Membrane is pliable and semipermiable only allowing certain materials in/out of cells.
It is composed of many components.
Phospholipids
Cholsterol
Proteins
 Phospholipids
Very similar to triglycerides however, one of the fatty acid chains has been replaced by a very polar Phosphate group

2. Phospholipids & Water
This poses a problem for the molecule since the molecule is both polar and non-polar simultaneously.
It is therefore very unstable in water, polar end is attracted to it, non polar tails are repelled by it.
This forces the phospholipids to take an arrangement such that their tails face each other. This accomplishes 2 things..
The polar heads can be adjacent to polar water molecules
The non-polar tails can be adjacent to each other.

3. The Lipid Bilayer
As the layer enlarges it forms a bubble shape formed of a lipid bilayer which is the foundation of the plasma membrane

4. More Membrane Components
The membrane requires a few more components to make it complete:
Cholesterol
Functions to hold the membrane together like glue. Adds strength to the membrane.
Proteins (2 types)
Intrinsic Proteins
Extend into or through lipid bilayer
Often are channel proteins allowing large molecules in/out
Extrinsic Proteins
Exist only on surfaces of the bilayer
Often serve as receptor molecules
Glycoproteins serve as cellular markers (nametags)

5. The Fluid Mosaic Model
Entire model is referred to as the Fluid Mosaic model of the plasma membrane