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Difference Between Diffusion and Osmosis - Biology

Diffusion

Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration until the equilibrium is achieved. The diffused particles result in a pressure called diffusion pressure (DP), and is directly proportional to the number or concentration of the diffusing particles. The molecules move from higher DP to lower DP. Following are the key characteristics of diffusion -

  1. The direction of diffusion of one substance is independent of the movement of another substance.
  2. It is very important to plants since it is the only means for gaseous movement within the plant body.
  3. The process is slow and it does not depend on any living system. Diffusion is common in gases and liquids. Diffusion in solids is uncommon. Diffusion rates get affected by factors like the permeability of the membrane between them, the gradient of concentration, pressure, and temperature.
  4. The diffusion of any substance across a membrane also depends on its solubility in lipids, the major constituents of the membrane. Substance soluble in lipids diffuses through the membrane faster. A substance that has a hydrophilic moiety finds it difficult to pass through the membrane; its movement has to be facilitated.

Osmosis

The plant cell is surrounded by a cell membrane and a cell wall. The cell wall is freely permeable to water and a substance in solution hence is not a barrier to movement. The cell membrane of plant cells and tonoplast together play an important role in determining the movement of molecules in and out of the cell. Osmosis is the process of the passage of solvent molecules from a region of higher concentration to a region of lower concentration via a semi-permeable membrane. Osmosis occurs spontaneously in response to a driving force. Osmosis is regulated by -

  • The concentration of dissolved solutes in a solution
  • Pressure gradient

Osmotic pressure is defined as the hydrostatic pressure developed in a solution when it is separated from pure solvent by a semi-permeable membrane in a rigid vessel. It develops only in a confined system. Osmotic pressure is numerically equal to osmotic potential but has a positive sign. Osmotic potential is the lowering of the free energy of water in a system due to the presence of solute particles. Osmotic potential is present whether the solution occurs in a confined system or an open system. The value of osmotic potential is negative.

Difference between diffusion and osmosis

Diffusion Osmosis
It can be defined as the movement of particles from a region of higher concentration to a region of lower concentration. It is defined as the phenomenon of the movement of solvent particles across a semi-permeable form.
Diffusion can occur in liquids and gases. It takes place in a liquid medium only.
A semi-permeable membrane is not required. A semi-permeable membrane is required.
The constituent particles move randomly in all directions. The constituent particles move only in one direction.
Water is not essentially required. Water is required for the movement of particles.
Solute, as well as solvent molecules, can diffuse Only the solvent molecules move through the membrane.
It can occur between similar and dissimilar types of solutions. It occurs only between similar types of solutions.
The available space is filled up by the concentration of the diffused substance. The concentration of the solvent is not equal on both sides of the membrane.
It does not depend on pressure potential, solute potential, or water potential. It depends on solute potential.
It is associated with the uptake of minerals and nutrients. It is not responsible for the uptake of minerals and nutrients.
This is an irreversible process. This process can be stopped or reversed by applying pressure.

Despite certain similarities, there are several differences between the process of diffusion and osmosis. Both the process equalizes the concentration of two solutions. No extra energy is required for both the processes to occur. Particles move from a region of higher concentration to a region of lower concentration. But in osmosis, this movement takes place across a semi-permeable membrane while no membrane is required in diffusion. In diffusion, both solute and solvent particles move whereas movement of the only solvent is observed in the case of osmosis. The process of osmosis can be reversed by applying hydrostatic pressure on the solution side of the membrane. This process is known as reverse osmosis, it increases the escaping tendency of the solvent molecules. Diffusion is associated with random movement of solute particles, while the only solvent moves in a single direction in case of osmosis.

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