The cell membrane’s primary purpose is to contain the contents of the cell and provide structural integrity to the entire unit. Additionally, the cell membrane must allow resources, such as water and oxygen, to permeate the membrane while excluding harmful objects from entering the cell. The cell membrane is made up of a phospholipid bilayer. Additionally, the cell membrane serves as the attachment site for some cell components.
Cell membranes are common to most forms of life. Prokaryotes, fungi, plants and animals all have membrane-bound cells. Additionally, some cells, like those of plants, have another type of barrier, called the cell wall. Most other life forms lack cell walls.
Cell membranes permit substances to enter or exit the cell through the process of diffusion. The cell membrane’s bilayer is constructed of paired molecules that have both water-repellant and water-soluble ends. When lined up to form a cell membrane, the water-soluble ends face outward, while the water-repellent sides face each other.
Proteins also help provide the structure of the cell membrane. Some of these proteins sit on the outside of the cell membrane and work as receptor cells. These cells exist only to detect the presence of various chemicals, which will cause the cell to react accordingly, when they are detected.