The membranes surrounding the internal organelles, such as the endoplasmic reticulum, Golgi bodies, lysosomes and vacuoles use this action to help carry out their functions. The cell membrane is the border surrounding the entire cell. Obviously if food, oxygen, water and wastes are going to move in and out of the cell there has to be some way to do that. Read here about the ways that materials can move in and out of cells. If cells are going to fight off germ invaders they have to have a way to recognize which cells belong to you and which cells don't.
Cells identify themselves by marker molecules on the cell membrane.
Click here to find out more about your immune system. Click here to find out. Electron microscope picture of the cell membrane.