Movement of ions , gases, solute 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 sen around the crystal. It decrease with increase in distance from the Crystal representing the diffusion of the CuSO4 molecules moves towards water and water moves toward the CuSO4. Finally , the molecules of both water and CuSO4 are distributed equally throughout the solution.
The pressure exerted by the diffusing ions or molecules to diffuse from the area of its higher concentration to lower concentration is called diffusion pressure.
Experiment of diffusion pressure:-
Fill a rubber ballon with any gas. The gas molecules are confined to space within the ballon and their molecules exerts a pressure on the wall of the ballon. Now, prick the ballon. Gases released immediately and collapsed the ballon. The pressure under which gas will release from the ballon represents the diffusion pressure.
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.
It is the force per unit area with which water come inside a cell.
The movement of water or solvent from a region of its higher concentration to lower concentration through semi permeable membrane is called osmosis.
Osmotic pressure is defined as the pressure required to prevent the net movement of pure water into a solution.
It is the pressure developed inside a cell which press the protoplasm against the cell wall and cell become turgid.
The pressure exerted by the cell wall against protoplasm due to osmosis is called wall pressure.
When Tp = Wp; cell is turgid.
The shrinkage of protoplasm of plant cell due to the loss of water when placed in hypertonic solution is called Plasmolysis.
If we place the plasmolysed cell in a hypotonic solution, the water enters inside the cell and cell become turgid. This is called deplasmolysis.