What is diffusion

What is diffusion? 

Answer: Diffusion is the net movement of molecules from high to regions of lower concentration as a result of random molecular motion. 

Diffusion tends to distribute molecules uniformly. Exchange of gases like CO2 and O2 in lungs, plants, blood cells, O2 entering stomata of leaves are examples of diffusion. 

Diffusion is  passive transport i.e. no external energy is provided for the movement of molecules. The natural kinetic energy of the particle supplies

the energy.