Diffusion

Dissolved substances have to pass through the cell membrane to get into or out of a cell. Diffusion is one of the processes that allows this to happen.

      Diffusion occurs when particles spread.      They move from a region where they are in high concentration to a region where they are in low concentration.       Diffusion happens when the particles are free to move.     This is true in gases and for particles dissolved in solutions.        

Location                                      Particles move                                         From                                               To

GutLungs

Digested food ProductsOxygen

Gut cavityAlveolar air space

Blood in capillary of villusBlood circulating around the lungs

Remember, particles continue to move from a high to a low concentration while there is a concentration gradient.

In the lungs, the blood will continue to take in oxygen from the alveolar air spaces provided the concentration of oxygen there is greater than in the blood. Oxygen diffuses across the alveolar walls into the blood, and the circulation takes the oxygen-rich blood away.

Diffusion

Examples of Diffusion

Diffusion in the Lungs