What is the Cell Membrane?

All cells have a Cell Membrane on the outside, it is also called the plasma membrane. In a plant cell it is very hard to see because it is right up against a Cell Wall. The plasma membrane is a very thin layer made upof Proteins and Fats. It is very important because the it determines what goes in and come out of the cell. It is said to be Partially Permeable, which means that it will let some substances through but not others.