The plasma membrane is the outermost covering of eukaryotic cells that allows the cell to transport nutrients, drugs, and objects in and out of the cell. The plasma membrane is essential for the proper functioning of all other membrane-bound organelles. In the plasma membrane of an individual cell, many different components come together to help the cell perform whatever functions it can perform. The most basic, yet important, part of the plasma membrane is the fact that it is selectively permeable. Selectively permeable means that some substances can pass through the membrane easily, others with a little help, and some substances cannot pass through the membrane at all. The plasma membrane can be selectively permeable because it is made of phospholipids and cholesterol. Cholesterol allows the membrane to be semi-fluid giving it the ability to keep foreign bodies out. Cholesterol is affected by