Osmosis:

Osmosis is defined as the movement of water from a region of its higher concentration to the region of lower concentration through semi-permeable membrane.

Types of Osmosis

a. Exosmosis: The outward movement of water from a cell, when it is placed in a hypertonic solution is called exosmosis. Due to exosmosis cell becomes flaccid.
b. Endosmosis: When a cell is placed in a hypotonic solution the water enters the cell and becomes turgid is called endosmosis.
Factors affecting Osmosis:
a. Temperature: At constant pressure & concentration of solution, the solvents moves from the side of higher temperature to the side lower temperature.
b. Pressure: Water molecules moves from the region of higher pressure to lower pressure.
c. Solute molecules: Water molecules moves from the region of its higher concentration to its lower concentration.

Significance of Osmosis:

• Plant root absorbs water by the process of osmosis.
• Osmosis is also utilized for cell to cell movement of water.
• Osmosis helps in growth of tissue.
• Osmosis regulates the guard cell movement in the plant i.e. opening and closing of stomata is due to the turgidity and flaccidity of guard cells due to osmosis.

Plasmolysis: 

Plasmolysis is the process in plant cell where the cytoplasm pulls away from the cell wall due to the loss of water through osmosis or when cell is placed in a hypertonic solution, exosmosis takes place. Due to the process of exosmosis the protoplasm of the plant cell shrinks. The shrinkage of protoplasm of plant cell due to the loss of water when it is placed in hypertonic solution is called plasmolysis.  

If we placed the plasmolysed cell in hypertonic solution, water again entered into the cell and the cell became turgid. This is called deplasmolysis. 

Significance of plasmolysis

• It proves the permeability of the cell wall and semipermeability of plasma membrane. 
• Plasmolysis explains the osmosis. 
• It helps to determine whether the cell is death or living. As plasmolysis does not take place in a dead cell. 
• It is also used to determine the osmotic pressure of cell. 

Difference between Osmosis and Diffusion:

Osmosis

• It occurs only in liquid medium. 
• Movement of only solvent molecules takes place. 
• A semipermeable membrane is required. 
• A turgorand hydrostatic pressure develops due to osmosis. 

Diffusion

• It occurs in all type of media. 
• The diffusing molecules may be liquid solid and gasses 
• A semipermeable membrane is not required 
• A turgor and hydrostatic pressure is not required.