OSMOSIS
The movement of solvent molecules from the region of higher concentration to the region of lower concentration through semi permeable membrane is called osmosis.
Demonstration
A thistle funnel is filled with a concentrated solution of sucrose. Its mouth is closed with a rubber membrane. The thistle funnel is inverted in beaker containing water. The mouth of the thistle funnel dips under water. The level of sugar solution is marked. Again note down the level of sugar solution after about 24tours. It is observed that the level of sugar solution in the thistle funnel moved down ward. It shows that osmosis occur through the semi permeable membrane. After some time, the concentration of sugar molecules and water molecules will be the same both in the beaker and the thistle funnel. Therefore, the osmosis will stop.
diffusion Factors affecting the osmosis
- Osmotic pressure (OP)
The maximum pressure that develops when a solution is separated
from its solvent by a semi permeable membrane is called osmotic pressure. It is also called osmotic potential. It moves the solvent inward.
- Diffusion pressure (DP)
The diffusion pressure of water is more than the diffusion pressure of
solution. Therefore, osmosis occurs from higher diffusion pressure to lower diffusion pressure of solvent. The difference of diffusion pressures
of solvent molecules and its solution is called diffusion pressure deficit (DPD). Osmosis occurs only when the value of DPD is more than zero.
- Turgor pressure (TP)
The pressure exerted by the cell sap on the cell wall of plant cell is called turgor pressure. It opposes the process of osmosis. Thus there is following relations between DPD, OP and IP
DPD = OP — UP
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