- It is a special type of diffusion, which involves the movement of water through a semi-permeable membrane (differentially permeable membrane).
- The movement of molecules takes place from the region of higher concentration of water (dilute solution) to the region of lower concentration of water (stronger solution) until the equilibrium.
- It can also be defined as the movement of water or solvent from its higher chemical potential to its lower chemical potential through a semi-permeable membrane.
- The free energy per mole of any substance in a chemical system is referred to as its chemical potential.
- The higher the chemical potential of a substance, the greater will be its tendency to undergo chemical reactions, including processes like diffusion and osmosis.
- The membrane which allows the movement of water molecules and certain solutes but holds back the large solute particles is called semi-permeable membrane.
- For examples: plasma membrane, egg membrane, parchment paper, fish bladder, animal bladder, etc.
Types of osmosis
Osmosis can be classified into two types. They are:
- When a living plant is placed in a solution having high osmotic pressure (hypertonic solution) than that of the cell sap, the water molecules move outward from the cell. The outward movement of water from a cell under the influence of concentrated solution is called ex-osmosis.
- The osmotic entry of water inside the cell, when it is placed in a hypotonic solution is called endosmosis.
- A solution having low osmotic potential in comparison to the other is said to be hypotonic solution, while a solution having higher osmotic potential is said to be hypertonic solution.
- The solutions having the same osmotic potential are termed as isotonic solutions.
- Plant absorbs water from the soil solution by osmosis.
- The cell to cell movement of water within the plant body is performed by osmosis.
- The turgor pressure of cells resulting from osmosis maintain the definite shape and turgidity of living cells mainly in soft organs like fruits, leaves, young stems , etc.
- It is also responsible for the growth of radical and plumule during seed germination as it is the source of the forces used by growing tissues.
- It plays a key role in the penetration of young roots into the soil.
- A high osmotic pressure of the cell plays an important role in the protection of the plants against drought and frost injury.
- Also prevents and controls dehiscence of fruits and sporangia.
Osmosis: introduction, types and significance