The cell membrane is made up of fats, proteins, lipids, and carbohydrates, and is a permeable structure. However, this permeation is very discerning because it only lets certain things pass through it. The cell membrane has a layer of phospholipids with hydrophobic ends and hydrophilic tops. The “tails” are made out of phosphate, while the “heads” are made up of two strings of fatty acids. There are two layers of these phospholipids, called the “bilayer”, and the tips of each phospholipid are facing outwards (that is, into the cell and out of the cell) while the ends of the phospholipids are touching. The phospholipids have a layer of protein on top of them. Proteins move within and out of the cell through the cell membrane. Depending on what type of cell it is, these proteins vary. These proteins can be set in the cell membrane, or floating in the cell, or outside of the cell. The cell membrane is a barricade between the inside and the outside of the cell. The function of the cell membrane is transportation; there are two different forms of this transport: the “passive transport process” and the “active transport process”. The passive transport works when the cell membrane lets in certain substances without using any energy from the cell. Contrasting with this, the active transport is when the cell membrane lets in substances using a power supply from the cell. The cell membrane works as a way to keep the shape of the cell and secure the cell’s cytoskeleton. Imbedded inside the cell membrane, the proteins convey messages from outside the cell to the organelles inside the cell and also receive messages. The cell membrane also protects the inside of the cell from harmful outside agents. The cell membrane assists with important energy procedures, like photosynthesis and oxidative phosphorylation.