Imbibition & Plasmolysis | Biology for JAMB PDF Download

Plasmolysis

If a plant cell placed in a hypertonic solution, water molecules diffused out from the cell. As a result of exosmosis, the protoplasm of the cell detached from the cell wall and starts shrinking. This is called plasmolysis. 

• The various sequences of plasmolysis are as follows 

(i) In a turgid cell, the cell sap pushed away the protoplasm, so that it is in close contact with cell wall.

(ii) When it placed in a hypertonic solution, the volume of the cell reduces due to shrinking of cell because some amount of water of cell sap diffuses out by exosmosis. Turgor pressure decreases by which cell wall is not pushed by the protoplasm, so that shrinking cell membrane reduces in total volume of the cell.

This situation, is called the first stage of plasmolysis or limiting plasmolysis.

(iii) If the diffusion of water to the outside is continue by the exosmosis then central vacuole contracts and with this protoplasm also shrinks but cell wall is not contracting. So that protoplasm is seems to detach from the corners of cell wall. This condition is known as second phase of the plasmolysis or incipient plasmolysis.

(iv) The shrinking of protoplasm is continuous due to continuous exosmosis, it detaches from the cell wall and assumed a spherical shape. This phase is known as evident plasmolysis/full plasmolysis.

• Hypertonic solution is present in between the cell wall and protoplasm.

Plasmolysis : A–A cell in normal  stage, B–A. cell placed in pure water and resulting in increased turgor pressure and , C–A. cell placed in strong salt solution leading to plasmolysis.

Significance of plasmolysis : 

[i] A living cell is distinguished from the non living [dead] cell through the plasmolysis. Because plasmolysis does not occur in dead cell.

[ii] The osmotic pressure of any cell can be measured by incipient plasmolysis. 

[iii] If the plasmolysis remains for long duration in a cell then it dies. To destroy the weeds, salts puts in their roots.

[iv] Fishes and meat are prevented from spoilage by salting, which inhibits the growth of bacteria and fungus.

[v] Higher concentration of sugar in jams and jellies stops the growth of bacteria and fungus.

[vi] High amount of chemical fertilizers near the root causes death or browning of the plant due to plasmolysis.

[vii] The fresh water growing plants are either wilted or die when they are kept in marine water.

IMBIBITION

Adsorption of undissolved liquid by any solid material is called imbibition or adsorption of water by hydrophilic colloids is known as imbibition. 

• This is a physical process by which a dry solid colloid material swells up by adsorption of water.

• The cell wall is made up of colloidal substances as cellulose, pectin, hemicellulose etc. All they are in nature.

• Therefore they imbibe water.

• Proteins, Agar - agar, starch etc, these are all imbibant materials.

Agar - agar can adsorbs 99 times more water than that of its weight. Some of the proteins adsorb 15 times more water. Affinity must be between imbibant and liquid material and movement of water occurs in order of water potential gradient.

Imbibition power = Agar – Agar > Pectin > Protein > Starch > Cellulose

• The heat released during the imbibition is called heat of wetting.

• A huge pressure is developed in material due to imbibition.This pressure is called Imbibition pressure (IP).

• IP is also called as matric potential with respect to water potential. DPD=IP or Yw =Ym 

• Dry wood is filled in the natural grooves of rocks and watered them. The rocks are broken due to their swelling.

• The imbibition is less in compact arranged material like wood, and more in lighter or soft material like gelatin.

• Imbibition decreases with increasing pressure on imbibant material.

Significance of Imbibition :

(1) Absorption of water during the seed germination is only initiate through the imbibition.

(2) Breaking of seed coat during the seed germination is due to imbibition process. Proteins, fats and starch is present in the kernel. This kernel swells up more as compared to the seed coat which breaks the seed coat.

(3) Initial process of water absorption in roots by root hairs is imbibition.

(4) Resurrection in many plants like Selaginella, Lichen, takes place due to the process of imbibition. 

(5) The water enter into the aerial roots and dry fruits is due to imbibition.

(6) Newly formed wood swells up in rainy season.

Movement of water molecules :

• Higher D.P→ Lower D.P.
• Lower O.P.→Higher O.P.
• Lower DPD →Higher DPD
• Higher (less –ve) ψ_w → Lower (more –ve) ψ_w
• Higher T.P. → Lower T.P.
• Hypotonic →Hypertonic
• Lower conc. of solution → Higher conc. of solution.