Simple Diffusion

Diffusion is the net movement of molecules from an area of high concentration to an area of low contraction

Passive because it doesn’t require energy

Only occurs in fluids (not solids)

Small non-polar molecules can diffuse across membranes because they can pass between the phospholipid molecules

The rate of diffusion depends on the concentration

Same concentration = rate of movement is equal (no net movement)

Difference in concentration = more molecules move form higher to lower (net movement)

Gas exchange by diffusion in lung alveoli cells is an example off simple diffusion of molecules into/out of cells

--> this process happens without any energy input required

As both carbon dioxide and oxygen are very small and non-polar, they can both diffuse passively across the cell membrane