Plasma Membrane

One of the main jobs of the plasma membrane is to keep Homeostasis. This is the process that keeps the balance inside of the cell. It works by its Selective Permeability, working like a filter, letting good things (like H2O, oxygen, and glucose) inside the cell, and bad things (like H20, waste, and CO2) out. Its structure is built by a phospholipid bilayer. First of all, a phospholipid is a molecule made up of glycerol, or phosphate, and 2 fatty acid chains. The head is is hydrophilic, meaning it is attracted to water, and the tain is hydrophobic, hates water. A phospholipid bilayer are 2 layers of phospholipids arranged tail to tail, so that the hydrophobic fatty acid chains never have to be exposed to H2O. The plasma membrane is not only made of the Phospholipid Bilayer, but of other things too. It includes proteins, carbohydrates and cholesterol. The proteins main purpose is to control what leaves and enters the cell. The Cholesterol, hydrophobic, is located between the tails of the phospholipids and it prevents the tails from sticking together. The carbohydrates are attached tot he proteins that stick out of the plasma membrane. They warn the cell of incoming bad things like disease cells, and also help to fight it off. The structure of the plasma membrane is many times described as a fluid mosaic. The phospholipids and proteins are able to move within the membrane, using constant motion. The different substances that move around make a pattern which resembles a mosaic (from where it got its name).