The plasma membrane is the outermost covering of eukaryotic cells that allows the cell to transport nutrients, drugs, and objects into and out of the cell. The plasma membrane is essential for the proper functioning of all other membrane-bound organelles. Inside the plasma membrane of a single cell there are many different components that come together to help the cell complete all the functions it can perform. The basic, but most important, part of the plasma membrane is the fact that it is selectively permeable. Selectively permeable means that some substances can cross the membrane with ease, others with a little help, and some substances cannot cross it at all. The plasma membrane can be selectively permeable because it is made up of phospholipids and cholesterol. Cholesterol allows the membrane to be semi-fluid giving it the ability to prevent the entry of foreign bodies. Cholesterol is affected by