Permeability of a membrane:
- Permeable membrane: The membrane that allows free movement of water and solute into and out of the cell is called permeable membrane. Eg: Filter paper.
- Impermeable membrane: The membrane that doesn’t allow the passage of both water and solvent into and out of the cell is called an impermeable membrane. Eg: Rubber membrane.
3. Semi-permeable membrane: The membrane that allows passage of only limited molecules of solvent selectively is called a semi-permeable membrane. Eg: Plasma membrane.
Osmotic pressure:
Osmotic pressure is defined as the pressure required to prevent the net movement of pure water into a solution.
Turgor pressure:
It is the pressure developed inside a cell that presses the protoplasm against the cell wall and the cell becomes turgid.
Wall pressure:
The pressure exerted by the cell wall against protoplasm due to osmosis is called wall pressure.
When Tp = Wp; the cell is turgid.
Factors affecting osmosis:
- Temperature: At constant pressure, the water molecules move from their higher concentration to lower concentration.
- Pressure: At constant temperature, the water molecules move from their higher concentration to lower concentration.
- Solute molecules: As the difference between two solutions increases, the rate of osmosis also increases.
Significance of osmosis:
a) Plant roots absorb water by the process of osmosis.
b) Osmosis helps in the cell-to-cell movement of water.
c)Osmosis helps the growth of the tissue.
d) It helps in the opening and closing of stomata.
e) Turgidity of a cell resulting from osmosis maintains the shape of the organ and makes the organ rigid.
Plasmolysis:
The shrinkage of the protoplasm of plant cells due to the loss of water when placed ina hypertonic solution is called Plasmolysis.
Deplasmolysis:
If we place the plasmolyzed cell in a hypotonic solution, the water enters the cell, and the cell becomes turgid. This is called deplasmolysis.
Significance of plasmolysis
a) Plasmolysis is the character of living cells, deadcellsl can’t show plasmolysis.
b) It indicates the semi-permeability nature of the plasma.
c) It is used to determine the osmotic pressure of the cell sac.
d) It also helps in food preservation.
e) It checks the growth of bacteria and fungi in jams and jellies, as bacteria and fungal cells are plasmolyzed in a concentrated sugar solution.
Imbibition
The process of increasing the volume of a solid by soaking in water is called imbibition. Eg: Swelling of doors and windows, swelling of gums, resins, etc. Cellulose, pectic substance, protoplasmic proteins, and other organic compounds in plant cells show imbibition.
Significance of imbibition
a) It helps in the germination of seeds because the stored food or seed swells causing the seed coat to rapture.
b) Before absorption of water in root cause imbibition.
c) Bursting of pollen grains or pollen tubes inside the ovary is due to imbibition.
