Respected sir/mam, 

I didn't undsrstood that what is diffusion and for what is it's function? Can you explain me with an example please?

Diffusion is a process by which the molecules move from a region of higher concentration to a region of lower concentration.

It should be noted that diffusion is different from osmosis as osmosis exclusively includes movement of water, whereas diffusion involves the movement of particles generally through a membrane.

 

The following example explains the significance of diffusion of gases in water :

 

       Breathing :

• While we breathe in, the oxygen from the air which we breathe diffuses from the lungs to the bloodstream.
• The oxygen which was breathed in the gaseous state is now in the liquid state mixed in the bloodstream. 
• Thus making diffusion of gases in liquid (oxygen gas from our lungs to the bloodstream) one of the essential phenomena