Diffusion Pressure: 17 Facts Most Beginner’s Don’t Know

In this article, we came to know about details fact about diffusion pressure, diffusion pressure deficits and their related facts.

Diffusion pressure is the potential ability of ions or molecules move from high concentration to low concentration under constant pressure called as diffusion pressure.

Diffusion pressure is known of capacity of ions or molecules to diffuse.

What is diffusion pressure?

It is the pressure possessed by the molecules (solids, liquids or gases) having capacity to diffuse from high concentration region to the low concentration region.

The water molecule will transport via the biomembrane from the high concentration to the lower concentration gradient. It is near to impossible to have more concentration than pure water i.e. in the pure water, the highest amount of water molecule, if we have any other solution, some amount of solute is present which reduce the water molecule concentration in the solution.

Diffusion of ions or molecules depend on the temperature, atmospheric pressure, molecule concentration of the substance and medium concentration.

diffusion pressure
Diffusion of purple dye from Wikipedia

What cause diffusion pressure?

Diffusion pressure is the hypothetical term coined by Meyer in 1938 to denote the ability of the molecule or ions to move or diffuse from the area of higher concentration to lower of the molecules.

Diffusion pressure of ions or molecules is directly proportional to the diffusing particles of ions or molecules. More the particles able to move more will be diffusing pressure.

How to calculate diffusion pressure?

Diffusion pressure is the passive process where no external energy is required to carry out the process. Diffusion process depend directly on the solute concentration.

If a solution having high concentration of solute then it exerts force to move to the other side solution which have solute concentration. This transfer of solute continue till the stage of equilibrium will achieved.

What happen when diffusion pressure is high and why?

When the diffusion pressure is high, the ions or molecules of solute start moving to the low without any energy usage. This movement of ions continue until diffusion potential of the both medium will be equal.

Movement of ions or molecule from high to low concentration gradient because the solute molecule concentration in high in the high diffusion pressure medium and on the other side, solute concentration is low so basically it has the more space for solute molecule to move that’s why ions move from high diffusion pressure medium to the low one.

What affects diffusion pressure?

The diffusion pressure is depending on the mass of molecules, their environments and its temperature.

  • Mass– when the molecule is heavier in mass, it will move with the slow speed, therefore diffuse slowly. For the lighter molecules reverse is true.
  • Environments– when there is large difference in concentration gradient, then diffusion of molecule is faster. When the distribution of molecules closer to equilibrium, the rate of diffusion getting slow.
  • Temperature – due to increase in the temperature, increase energy and thus increase the molecule movements and diffusion pressure. Lower temperature decreases the molecules energy thus the diffusion pressure decreases.

Change in diffusion pressure

Diffusion pressure created by the solute molecules present in the solution. So, if we add or increase the solute concentration into the solution, then the diffusion pressure will decrease.

For example, water solution is present across the membrane. If we start adding sugar to other side of membrane, then water start moving across the membrane to the sugar solution and move until equilibrium attained.

Diffusion pressure gradient

A gradient is known as change in the quantity value like temperature, pressure or concentration with respect to the distance. In the same way, change in the diffusion pressure with respect to the distance called as diffusion pressure gradient.

How does pressure gradient affect diffusion?

Diffusion is directly proportional to concentration gradient. In the same way partial pressure gradient is related to the gases. The rate of diffusion depends on the velocity of gas molecules present in the solution then the diffusion of gas particles depend on the temperature of solution or environment.

In a mixture of gases, the partial pressure gradient is an area having high concentration of particular gas. It will diffuse to high gas concentration area to the low gas concentration area.

What is diffusion pressure deficit?

The diffusion pressure deficit also known as suction pressure. It is the difference between diffusion pressure of pure solvent and solution where some solute is added. Deficit means reduction. Therefore decrease in the diffusion pressure of solvent in the solution when we will compare to the diffusion pressure of pure state of solvent.

Due to presence of solute in the pure solvent, that will oppose the diffusion and hence decrease in the diffusion pressure generated.

Diffusion pressure deficit formula

Diffusion pressure deficit with the reference of plant cells is expressed as

DPD= OP-TP where DPD stands for diffusion pressure deficit, OP stands for osmotic pressure, TP stands for turgor pressure.

How to calculate diffusion pressure deficit?

When the plant cell is placed in the hypotonic solution (low solute concentration in the solution) water will come inside the cell by the endosmosis (movement of water into the cell) process. Due to incoming water inside the cell, turgor pressure (TP) developed in the cell. the membrane of cell expands and osmotic pressure (OP) decreased.

Due increase in solvent in the cell, cell will stretch and experience turgor pressure and pressure applied by solvent become low thus osmotic pressure become low. When the plant cell become full turgid (cannot have more water, stretched maximum) then its OP is equal to TP and DPD is zero. In this state of full turgid cell, it cannot absorb more water.

DPD can be defined as actual cell thirst for water.


Diffusion pressure deficit examples

The concept of diffusion pressure deficit or low-side pressure is used in daily life in many appliances like

  • Refrigeration
  • Air conditioning
  • Wet bulb temperature

Diffusion pressure of pure water

Pure water has maximum diffusion pressure. If some kind of solute is added in it, then the solvent or water attained low diffusion pressure than pure solvent or water. In simple word, we can say that pure solvent always has high diffusion pressure than its impure solute added form.

The amount of decrease in diffusion pressure after adding the solute into solution called as diffusion pressure deficit or suction pressure. Pure water has maximum DPD equal to 1245.69 atm. If the water is pure then the value of DPD and diffusion pressure always equal. Osmotic pressure of a solution is equal to the diffusion pressure deficit i.e. DPD = OP.

Diffusion pressure of oxygen

Diffusion rate of any gas depend on the surface area available for diffusion. Larger the surface area more the gaseous diffusion done. Gaseous exchange like carbon dioxide and oxygen during the process of respiration commonly done by the diffusion.

In human body, blood having low level of oxygen concentration a high level of carbon dioxide concentration undergoes gaseous exchange with the atmospheric air present in the lungs. In the lungs, high concentration of oxygen than that of oxygen low blood and low concentration of carbon dioxide. This concentration gradient makes a pathway for gaseous exchange of oxygen during respiration.

Diffusion pressure of cell

When a plant cell is placed in the hypotonic (low solute concentration) solution, the solvent start moving inside the cell, the cell wall start expanding which further increase the turgor pressure in the cell which is in solution. And osmotic pressure of cell starts reducing.

When the plant cell become completely shrink, the turgor pressure become equal to osmotic pressure and diffusion pressure deficit become zero then the water cannot enter into the cell.


Where DPD – diffusion pressure deficit defined as difference in the diffusion pressure of two different solute in the solution, OP- osmotic pressure defined as the pressure exerted by the water when comes from high concentration to the low concentration, TP- turgor pressure defined as pressure developed due to plant cell stretching.

Which cell have maximum diffusion pressure deficit?

The flaccid cells have maximum diffusion pressure deficit. In the flaccid cell, there in no inward movement of water so no turgor pressure. This is meant turgor pressure is zero. Due to this, diffusion pressure deficit becomes equal to osmotic pressure.


There is no negative value present to reduce the value of DPD hence DPD is present in maximum value.

Diffusion pressure of pure solvent

Diffusion pressure of pure solvent is always higher when compare to its solution. After adding of any kind of solute in the solvent, it will decrease its diffusion pressure. That decrease of diffusion pressure is called as diffusion pressure deficit.

DPD of pure solvent = 1236 atm

Due to decrease in the diffusion pressure of solvent, it will start gaining water from the outside. So DPD require water thirst thus called as suction pressure.

Change in diffusion pressure of a pure solvent

When any kind of solute is added in the pure solvent, its DPD of the solution increase and water potential will decrease.The water potential of a solution is also called as chemical potential of water. The water potential depends on the water molecule present in the solution related to solute molecules. Thus, water potential is directly proportional to water molecules.

DPD is decrease in the diffusion pressure. The solvent particles of solution are responsible for diffusion pressure and decrease in diffusion pressure is responsible by the solute particles into the solutions. Thus, when solute is added, DPD will increase.


To wrap the article, we state that diffusion pressure, osmotic pressure, turgor pressure and diffusion pressure deficit all are necessary to carry out the vital functioning in plant as well as human body. Many kind of gaseous exchange, vitamin, minerals absorptions and water absorption are carried with the help of above explained terms.

Recent Posts