Suction pressure is also called Diffusion Pressure Deficit. If some solute is dissolved in solvent, its diffusion pressure decreases. The difference between diffusion pressure of pure solvent and solution is called diffusion pressure deficit (DPD). It is a reduction in the diffusion pressure of solvent in the solution over its pure state due to the presence of solutes in it and forces opposing diffusion.
When a plant cell is placed in a
hypotonic
In chemical biology, tonicity is a measure of the effective osmotic pressure gradient; the water potential of two solutions separated by a partially-permeable cell membrane. Tonicity depends on the relative concentration of selective memb ...
solution, water enters into a cell by
endosmosis
Osmosis (, ) is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region of ...
and as a result
turgor pressure
Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall.
It is also called ''hydrostatic pressure'', and is defined as the pressure in a fluid measured at a certain point within itself when at equilibri ...
(TP) develops in the cell. The cell membrane becomes stretched and the
osmotic pressure
Osmotic pressure is the minimum pressure which needs to be applied to a Solution (chemistry), solution to prevent the inward flow of its pure solvent across a semipermeable membrane.
It is also defined as the measure of the tendency of a soluti ...
(OP) of the cell decreases. As the cell absorbs more and more water its turgor pressure increases and osmotic pressure decreases. When a cell is fully turgid, its OP is equal to TP and DPD is zero. Turgid cells cannot absorb any more water. Thus, with reference to plant cells, the DPD can be described as the actual thirst of a cell for water and can be expressed as :
Thus it is DPD that tends to equate and represents the water-absorbing ability of a cell, it is also called suction force (SF) or suction pressure (SP). The actual pressure with which a cell absorbs water is called "suction pressure".
Factors affecting DPD
* DPD is directly proportional to the height of the plant, tree or organism.
* DPD is governed by two factors i.e. turgor pressure and osmotic pressure. Turgor pressure can be denoted as wall pressure in some cases.
* DPD is directly proportional to the concentration of the solution. DPD decreases with dilution of the solution.
History
The term diffusion pressure deficit (DPD) was coined by
B.S. Meyer in 1938. Originally DPD was described as suction pressure by German botanist
Otto Renner
Otto Renner (25 April 1883 in Neu-Ulm – 8 July 1960) was a German plant geneticist. Following the work of Erwin Baur, Renner established the theory of maternal plastid inheritance as a widely accepted genetic theory.
He studied botany under K ...
in 1915.
Refrigeration
In
refrigeration
Refrigeration is any of various types of cooling of a space, substance, or system to lower and/or maintain its temperature below the ambient one (while the removed heat is ejected to a place of higher temperature).IIR International Dictionary of ...
and
air conditioning
Air conditioning, often abbreviated as A/C (US) or air con (UK), is the process of removing heat from an enclosed space to achieve a more comfortable interior temperature, and in some cases, also controlling the humidity of internal air. Air c ...
systems, the ''suction pressure (also called the low-side pressure) is the intake pressure generated by the system compressor while operating. The suction pressure, along with the suction temperature the
wet bulb temperature
The wet-bulb temperature is the lowest temperature that can be reached under current ambient conditions by the evaporation of water only. It is defined as the temperature of a parcel of air cooled to saturation (100% relative humidity) by the ...
of the discharge air are used to determine the correct refrigerant charge in a system.
Further reading
The measurement of Diffusion Pressure Deficit in plants by the method of Vapour Equilibrium (By R. O. SLATYER, 1958)
References
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Diffusion