Question

Why DPD is equal to negetive of osmotic pressure. DPD = -OP?

Answer 1

To understand the DPD (Diffusion pressure deficit), we have to first understand the terms osmotic pressure and turgor pressure.

Osmotic pressure (OP) is the pressure required to prevent solvent from passing through a semipermeable membrane from a region of higher concentration of solute to lower concentration of solute.

Turgor pressure (TP) is the pressure of the cell contents against the cell wall in plant cells. In hypotonic solution, water diffuses into the cell and thereby, cell enlarge and extension growth occurs. As water diffuses in, cytoplasm builds up a pressure against the cell wall. This pressure is called turgor pressure.

Diffusion pressure deficit is the pressure which opposes the diffusion of water from the region of higher chemical potential to lower chemical potential.
The two factors which determine the DPD are osmotic pressure (OP) and turgor pressure (TP). The value of DPD for a cell is always positive. It is an index of the water absorbing capacity of cell.

DPD= OP-TP

In flaccid cell,TP=0; DPD=OP
In turgid cell, TP=OP; DPD=0