State how diffusion palys an imp. role in gaseous exchange between cell & external env.

Through respiration.

Eg- When carbon dioxide accumulates in high concentrations inside the cell, the concentration of carbon dioxide is low outside the cell as compared to the inside. Due to this difference of concentration, carbo dioxide moves out of the cell through diffusion. Thus carbon dioxide is excreted out of the cell. Similarly oxygen enters the cell by the process of diffusion.