Tag: plant water relation

The amount by which the diffusion pressure of a solution is lower than that of the pure solvent is called as 'diffusion pressure deficit' (DPD). The term diffusion pressure deficit (DPD) was coined by B.S Meyer in 1938. Originally DPD was described as suction pressure by Renner (1915).

When a cell is immersed in water, then water enter into the cell because the osmotic pressure of the cell sap is higher. The cell content develops a pressure against the cell wall, which is called turgor pressure. If the given solution is of 25% concentration; then it can not represent TP(turgor pressure) because pressure cannot be expressed in terms of concentration.

In a fully turgid cell there will be no net movement of water. Neither water will move inside nor move outside. This is because DPD will be zero. DPD can be zero, when the osmotic pressure, which causes movement of water inside the cell equals to turgor pressure, which opposes the entry of water inside the cell.

When the mesophyll cells lose water the concentration of solutes will increase. Consequently, the OP will increase concomitantly, there will be a drop in turgor and TP will decrease. These changes will increase the DPD. Water moves from lower DPD to higher DPD, thus, water will gain entry into the cells, whose DPD has increased.

A turgid cell is one where the cell wall is stretched to its limit by the internal turgor pressure, which equals the osmotic pressure. Consequently, the Diffusion Pressure Deficit (DPD), which represents the water-absorbing capacity, is zero.

Water moves from a region of lower DPD to a region of higher DPD. Cell 1 has a DPD of 3 atm and Cell 2 has a DPD of 5 atm; therefore, water moves from Cell 1 to Cell 2.

Answer is option B i.e. "OP"
Hypotonic solution is one in which the solution kept outside the cell has lower solute concentration than the fluid inside the cell. The process being investigated is osmosis. Osmosis is the diffusion of water molecules across a semi-permeable membrane from a more dilute solution (with a lower solute concentration) to a less dilute solution (with a higher solute concentration). Therefore cell absorbs or sucks water with a force equal to O.P

Diffusion Pressure Deficit = osmotic pressure - wall pressure. Wall pressure is the same as Turgor pressure. When a cell is placed in a hypotonic solution water enters the cell. Hence its osmotic pressure decreases and the turgor pressure increases. In a fully turgid cell the turgor pressure becomes equal to the osmotic pressure. Hence the Diffusion Pressure Deficit becomes zero in a turgid cell. Thus the correct answer is option B.

Suction pressure is the decrease in the diffusion pressure of solution over its pure state due to the presence of solute particles in it. The concentration of solute is higher in root hair cells as compared to soil water. So suction pressure builds up and water is drawn towards root hair cells. These water molecules are transported to different parts of the plant. So, the correct answer is 'Suction pressure'.