Diffusion, diffusion pressure, diffusion pressure deficit

Diffusion, DP and DPD

1. Diffusion, diffusion pressure (DP) and diffusion pressure deficit (DPD) Dhole N. A. Department of Botany, Digambarrao Bindu ACS College, Bhokar

2. Diffusion: In a gas or solution that has an area of high numbers of particles and an area of lower number of particles, the particle will diffuse or move, from the area of higher to the area of lower concentration. This is known as simple diffusion. In other words, the movement of solute particles or molecules moves from a region of higher concentration to a region of their lower concentration is called diffusion .

3. This movement is takes place till the concentration of two regions become equal or at equilibrium. The movement of particle takes place due to their own kinetic energy . Diffusion takes place in all state of molecules i.e. gas, solid & liquid. The rate of diffusion of gases is faster than liquids and solids. The diffusion particles have a certain pressure called diffusion pressure. Example: If a gas containing bottle opened at a corner of room, immediately gas molecules distributed through the room. If a solute ( Suger ) is placed in its solvent (water), it is dissolved and solute (sugar) particles spread all over the solvent.

4. Significance of diffusion in plants: It helps in exchange of gases during photosynthesis and respiration. Mineral nutrition uptake by plants is possible because of diffusion. The opening and closing of stomata or transpiration process is depends upon diffusion. The movement of food and minerals in plant body takes place because of diffusion. Distribution of hormones in plants through diffusion.

5. Diffusion pressure (DP): The term diffusion pressure is coined by Meyer (1938). The diffusion pressure denotes the potential ability of the molecules or ions of any substances to diffuse from an area of their higher concentration to that of their lower concentration. The diffusing particles have certain pressure is called as diffusion pressure. Diffusion pressure is directly proportional to the concentration of solute particles. Higher the solute particles, diffusion pressure is higher and vice versa.

6. The diffusion pressure of pure water is maximum.

7. Diffusion Pressure Deficit (DPD) : The term diffusion pressure deficit was proposed by Meyer (1938). The diffusing particles have certain pressure which is called as diffusion pressure (DP). It is believed that the pure solvent have the maximum diffusion pressure. Addition of solutes resulted in a decrease in the diffusion pressure. This deficit was termed diffusion pressure deficit (DPD) or suction pressure (SP). DPD is measured in atmosphere.

8. The term Suction pressure (SP) was coined by Renner. The greater the concentration of a solution, greater the is its diffusion pressure deficit or suction pressure. In other words, osmosis takes place from a region of lower diffusion pressure deficit to region of higher diffusion pressure deficit. In simple words, water moves from lower DPD to higher DPD.

9. Usually, DPD = OP – TP (OP = Osmotic pressure, TP = Turger pressure) If WP = TP (WP = Wall pressure) Then DPD = OP – WP When a flaccid cell was placed in pure water TP = 0 DPD = OP – 0 = OP DPD = OP

10. But when the cell became turgid OP = TP DPD = OP – TP = 0 DPD = 0 On full turgidity of the cell, DPD will be zero. So water does not enter inside the cell. In plasmolysed cell, DPD is maximum because TP is negative.

11. If both the solution and pure water are subjected to the same pressure, then the difference in diffusion pressure between the two systems is exactly to the osmotic pressure of the solution. Thus, diffusion pressure deficit of a solution is equivalent to its osmotic pressure which is…. D.P.D. = O.P. When water enters into a plant cell by osmosis, turger pressure develops in the cell.

12. The cell membrane gets stretched and osmotic pressure of the cell decreases. As cell absorbs more and more water its T.P. increases and O.P. decreases. When the cell is fully turgid, its O.P. is equal to T.P. and D.P.D. is zero. The turgid cell cannot absorb any more water. Thus with reference to plant cell , D.P.D. = O.P. – T. P. Hence, D.P.D. represents water absorbing ability of the cell.

13. Thank you