Osmosis and diffusion are two forms of passive transport that play an important role in the movement of molecules in and out of the cell.
What is Osmosis?
Osmosis is the process of movement of solute particles across a permeable membrane from concentrate to concentrate. The entire process requires no energy to occur.
For Example: the absorption of water molecules from the soil by plant roots.
What is Diffusion?
Diffusion: The process of moving particles from a high-density region to a low-density region until equilibrium is reached Simple diffusion requires no energy; however, ATP is required for easy diffusion.
For Example: perfume is dispersed in the air through the use of perfume sprays.
Difference between Osmosis and Diffusion
| Osmosis | Diffusion |
| It is limited only to the liquid medium. | Occurs in liquid, gas and even solids. |
| Requires a semipermeable membrane. | Does not require a semipermeable membrane. |
| Depends on the number of solute particles dissolved in the solvent. | Depends on the presence of other particles. |
| Requires water for the movement of particles. | Does not require water for the movement of particles. |
| Only the solvent molecules can diffuse. | Both the molecules of solute and solvent can diffuse. |
| The flow of particles occurs only in one direction. | The flow of particles occurs in all the directions. |
| The entire process can either be stopped or reversed by applying additional pressure on the solution side. | This process can neither be stopped nor reversed. |
| Occurs only between similar types of solutions. | Occurs between the similar and dissimilar types of solutions. |
| It involves the movement of only solvent molecules from one side to the other. | It involves the movement of all the particles from one region to the other. |
| The concentration of the solvent does not become equal on both sides of the membrane. | The concentration of the diffusion substance equalises to fill the available space. |
| Depends on solute potential. | Does not depend on solute potential, pressure potential, or water potential. |
| Only water or another solvent moves from a region of its high concentration to a region of its lower concentration. | Any type of substance moves from area of highest energy or concentration to region of lowest energy or concentration. |
| Not associated with uptake of minerals and nutrients. | It helps in the uptake of minerals and nutrients. |
Two types of transport systems exist namely movement of molecules in and out of the cell, namely osmosis and diffusion. These two mechanisms are passive transport mechanisms because they require no additional energy (but ATP is required for rapid diffusion).
The main point that distinguishes the two methods is the environment in which they are used. Osmosis can only work in a liquid medium, but diffusion can occur in any of the three mediums (solid, liquid, and gas).
Furthermore, osmosis requires a semi-permeable surface, while diffusion does not. Water absorption by plants is an example of osmosis. Adding a drop of food coloring to a glass of water shows dispersion, eventually all water is colored.
