Describe the structure of the cell membrane.

The cell membrane is a fluid matrix made of a phospholipid bilayer. Each lipid molecule has a hydrophilic, phosphorylated "head" and a hydrophobic, fatty acid "tail". The hydrophobic parts of the molecules on the bilayer face each other, whereas the hydrophilic parts form the inner and outer surfaces of the cell membrane. Small, hydrophobic molecules can traverse the cell membrane via simple diffusion.

Integrated into the membrane are protein molecules which may span the whole bilayer (and are thus known as transmembrane proteins) or just one layer. Some of these proteins act as channels for transport of ions and other particles that can not simply diffuse across the membrane. 

A number of sugar molecules are present on  the external surface of the cell membrane- this is known as the glycocalyx. Glucose that is attached to the phospholipid molecules is known as a glyolipid, whereas the glucose attached to proteins is known as a glycoprotein. Also interspersed within the phospholipids are molecules of cholesterol which give the membrane flexibility and fluidity.