1. Osmosis (Latin: Osmos – impulse, urge) is a special type of diffusion. It represents the movement of water or solvent molecules through a selectively permeable membrane from the place of its higher concentration (high water potential) to the place of its lower concentration (low water potential).
Types of Solutions based on concentration:
Hypertonic (Hyper = High; tonic = solute): This is a strong solution (low solvent / high solute / low Ψ) which attracts solvent from other solutions.
Hypotonic (Hypo – low; tonic = solute): This is a weak solution (high sol vent / low or zero solute/ high Ψ) and it diffuses water out to other solutions.
sotonic (Iso = identical; tonic = soute): It refers to two solutions having same concentration. In this condition the net movement of water molecule will be zero.
The term hyper, hypo and isotonic are relative terms which can be used only in comparison with another solution.
2. Types of osmosis: Based on the direction of movement of water or solvent in an osmotic system, two types of osmosis can occur, they are Endosmosis and Exosmosis.
Endosmosis: Endosmosis is defined as the osmotic entry of solvent into a cell or a system when it is placed in a pure water or hypotonic solution. eg: dry raisins . (high solute and low solvent) placed in the water, it swells up due to turgidity.
Exosmosis: Exosmosis is defined as the osmotic withdrawal of water from a cell or system when it is placed in a hypertonic solution. Exosmosis in a plant cell leads to plasmolysis.
