Interrelationship of OP, TP (WP) and DPD (SP)
The difference in the concentration of solutions, on two sides of a semipermeable membrane, results in the flow of water from solution of low concentration to solution of higher concentration. When a cell is placed in a hypotonic solution, water enters into the cell and the turgor pressure of the cell increases. As a result of increase in Tp, the wapressure of the cell also increases (equal in magnitude but opposite in direction).
Here, the value of diffusion pressure deficit or suction pressure (actual force responsible for entry of water into cell)
will be equal to osmotic pressure minus wall pressure.
ie.. DPD (SP) = OP-WP (as WP = TP) hence, DPD = OP-TP
In a flaccid cell, the TP is zero, therefore, DPD = OP-0 = 0P Thus, DPD will be equal to OP in case of flaccid cell, and the water will enter the cell with a force equal to the OP of the cell. When a flaccid cell is placed in water, endosmosis starts as a result of which, OP of the cell starts decreasing while TP starts increasing. A stage comes, when OP and TP become equal, so DPD becomes zero.
Now, the cell is said to be in fully turgid condition. In a turgid cell, the value of OP = TP ie, DPD OP-TP
So, DPD0 Thus, there will be no absorption water by the cell in a fully turgid condition
DPD or SP or suction pressure determines the direction of movement of water (water always moves from a cell of lower
DPD to a cell of higher DPD), e.g, if two cells, A and B have DPD 5 and 6 atm., water will flow from A to B.
Reverse osmosis-
Reverse osmosis is the expulsion of pure water from osmotically active solution, through a semipermeable membrane
under the influence of pressure higher than the osmotic pressure of the solution. It is used in removing salts from
saline water as well as in greater purification of water.
