Why is diffusion important to a living cell?

Diffusion plays a vital role in permitting molecules to enter and leave a cell in maintenance of homeostasis. Oxygen diffuses from the bloodstream, where it dwells in greater concentration. From the bloodstream, the oxygen enters the fluid surrounding a cell, then into the cell itself, where it is far less concentrated. In this manner, the flow of the blood through the lungs and bloodstream provides a continous supply of oxygen to the cells. Once oxygen has entered a cell, it is utilized in metabolic activities.