Now, depending on the type of cell and the activity of cell, the ratio of lipids to proteins to carbohydrates basically varies. Now property number three, the cell membrane consists of a phospholipid bilayer and that can be seen in the following diagram. Now, generally speaking, as we'll see in a future lecture, lipids are amphatic molecules and what that means is they contain both hydrophobic and hydrophilic regions, non polar and polar regions. Now, one part of that phospholipid found inside the membrane is polar and that is known as the polar head. And these are shown in blue. And the polar heads basically orient themselves to the outside or the inside because the outside and inside contains an aqueous polar environment.