Osmotic pressure

Osmosis

Diffusion of water across permeable or semipermeable membrane.

Osmosis term given by Nollet.

Characteristic of osmosis

• It is a type of diffusion.
• Response to driving force
• direction and rate of osmosis depend on pressure gradient and concentration gradient.
• At equilibrium two chamber same  water potential.

Osmotic pressure

Pressure develop in osmotically active solution.

Osmotic pressure is denoted by π.

Mathematical expression of osmotic pressure

π=iCRT

I ionization constant

C concentration.

R. Gas constant

T  absolute temperature

Osmotic pressure of pure water is taken to be 0 (zero).

Osmotic pressure is measured by osmometer.

Osmotic pressure of electrolyte is higher than non electrolyte.

Experimental demonstration of osmosis.

Taken solution of sucrose in water, taken in a funnel is separated from pure water  in a beaker through semi permeable membrane.

• Water move into the funnel and rising the level of solution in the funnel, continue till equillium.
• External pressure can we apply from the upper part of the funnel then no water move into the funnel to the membrane. Pressure required to prevent water from diffusing is called  osmotic pressure.

Turgor pressure

Hydrostatic pressure against the cell wall is called turgor pressure .

pressure exerted by the cell wall against turgid protoplast is called wall pressure.

• Turgor pressure is equal to wall pressure.

Characteristics of turgor pressure

• Turgor pressure for a plasmolysed cell is negative.
• Turgor pressure for flaccid cell is zero.

Significance of turgor pressure

1. Maintain shape of cell
2. Enlargement and  growth of cell

Frequently asked question

What would happen when RBC are palace in hypotonic solution?

Answer RBC will burst, because they lack cell wall.

Plasmolysis

Shrinkage of protoplast under the influence of hypertonic solution is called plasmolysis.

Characteristic of plasmolysis

1. Water move out from the cell due to hypertonic solution.
2. First water loss from the cytoplasmic then vacuole.
3. Plasmolysis is a property of living cell only.
4. Plasmolysis  is usually reversible.
5. Water move from high water potential to lower water potential.

Application of plasmolysis

1. Identification of living cells
2. Preservation of food.
3. Elimination of weeds

Diffusion pressure deficit. (DPD)

decrease in diffusion pressure of water or cell due to addition of solute.

Term coined by B.S Meyer in 1938.

• Diffusion pressure deficit is directly proportional to solute concentration.
• Water always move from low diffusion pressure deficit to high diffusion  pressure deficit.

Diffusion pressure deficit is also called suction pressure.

Turgor pressure of free solution is taken to be zero, so Diffusion pressure deficit is equal to osmotic pressure.

Water potential

Free energy of water is called water potential.

Pure water of water potential is zero.

0 is greater than water potential of water.

Two main component of determine water potential

1. Solute potential or osmotic potential
2. Pressure potential

Some solute is dissolved in pure water then decrease the water potential.

Decrease is due to dissolution of solute is called solute potential or osmotic potential.

 At Atmospheric pressure

• Water potential is equal to solute potential.
• Solute potential is always negative.
• Pressure potential is usually positive
• Water potential is affected by both solute and pressure potential.
• Water potential is equal to solute potential plus pressure potential.

Imbibition

It is a special type of diffusion.

It occur when water is absorbed by the solid or hydrophilic colloids.

Result of Imbibition

Volume increase

 pressure is exerted 

Characteristic Imbibition

affinity between absorbant and liquid is essential.

Pre-historic man split rock due to Imbibition

Swelling of the wood and exert pressure.

Fact

During rainy season doors are swell due to Imbibition.

Transport in plants