All cells have a cell membrane. In animal cells the cell membrane is the outermost layer of the cell. In plant cells the cell membrane is located just beneath the cell wall. The cell membrane is semi permeable. This means that some selective substances are allowed to pass through while others are not. The cell membrane basically controls what substances come into and out of the cell. It is made of a flexible phospholipid bilayer. This bilayer is made up of two heads which are hydrophilic and two tails which are hydrophobic. The heads will face outwards to the outside and inside of the cell while the tails will face in towards each other. The hydrophilic heads are attracted to watery environment inside and outside the cell while the hydrophobic tails are repelled by water.
Substances that enter the cell through the cell membrane:
Substances that leave the cell through the cell membrane: