Introduction

 The movement of ions, gases, and solutes from their higher concentration to lower concentration is called diffusion. Eg:- If a drop of ink is dropped into the glass containing water,  very soon its molecules become distributed throughout the glass.

Experiment of diffusion

                         When a crystal of CuSO₄ is placed in a beaker containing water, a dense blue color is seen around the crystal. It decreases with an increase in distance from the Crystal representing the diffusion of the CuSO₄  molecules moving towards water and water moving toward the CuSO₄. Finally, the molecules of both water and CuSO₄  are distributed equally throughout the solution.

Diffusion pressure

                      The pressure exerted by the diffusing ions or molecules to diffuse from the area of its higher concentration to a lower concentration is called diffusion pressure.

Experiment of diffusion pressure:-

                   Fill a rubber balloon with any gas. The gas molecules are confined to space within the ballon and their molecules exert pressure on the wall of the ballon. Now, prick the balloon. Gases released immediately and collapsed the ballon. The pressure under which gas will be released from the ballon represents the diffusion pressure.

Factors affecting diffusion

            There are several factors affecting diffusion. These are as follows:-

1. Temperature: The rate of diffusion increases from the decrease of the temperature.

2. Diffusion pressure gradient: A higher diffusion pressure gradient increases the rate of diffusion.

3. Density of diffusing substance: The rate of diffusing decreases with the increase of density of diffusing substance.

4. Diffusing medium: A higher concentration of diffusing medium lowers the rate of diffusion.

Significance of diffusion:

I) Transpiration takes place due to the diffusion of water vapor.

ii) During photosynthesis and respiration, the exchange of oxygen and carbon dioxide takes place by the process of diffusion.

iii) The salt and ions are absorbed by the plant by the process of diffusion.

iv) Transport of substance within the cell or between the cells takes place by diffusion.

Diffusion pressure deficit (DPD):

            The amount by which the diffusion pressure of the solution is lower than that of the pure solvent is called diffusion pressure deficit.

Suction pressure:

             It is the force per unit area with which water comes inside a cell.