Difference Between Osmosis and Diffusion

Edited by Diffzy | Updated on: August 17, 2022


Difference Between Osmosis and Diffusion Difference Between Osmosis and Diffusion

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The two distinct passive transport processes of osmosis and diffusion are crucial for transporting molecules into and out of the cell. Students are typically asked to make a comparison of the two modes of transportation or to explain the differences and similarities between osmosis and diffusion.

Now, let’s understand the basic differences between osmosis and diffusion in a bit more detail.

Osmosis vs. Diffusion

Osmosis and diffusion differ primarily in their dependencies and prerequisites. The quantity of dissolved solute fragments in the solution is what drives osmosis. However, the diffusion depends on the presence of other elements. Water is required by the former for particle activity. The latter, though, may travel without any water.

Difference Between Osmosis and Diffusion in Tabular Form

Table: Osmosis vs. Diffusion
Parameters of Comparison
Pressure, solute potentials, and water
The solute potential is essential for this process to occur.
These three factors do not affect the diffusion process.
The dependence
Osmosis depends on the number of dissolved solute particles.
Diffusion is the process that depends on the presence of other molecules.
The medium
A liquid medium is a must for osmosis to take place.
This process can occur in all types of medium whether it’s a solid, liquid, or gaseous medium.
Hydrostatic pressure
This process is opposed by hydrostatic pressure.
Generally, hydrostatic pressure is not vital in diffusion processes.

What is Osmosis?

Osmosis is the spontaneous net flow or dispersion of solvent molecules through a selectively permeable membrane, in the direction that tends to balance the solute concentrations on the two sides, from an area of high water content (region of lower solute concentration) to an area of low water potential (region of higher solute concentration).

It can also refer to a physical procedure that separates two solutions with various concentrations by allowing any solvent to pass through a membrane that is selectively permeable (permeable to the solvent but not the solute). You can make osmosis work for you. The amount of external pressure needed to be applied to prevent any net solvent migration across the membrane is known as osmotic pressure. Osmotic pressure depends on the molar concentration of the solute but not on its identity because it is a colligative feature.

Due to the semipermeable nature of biological membranes, osmosis is an essential mechanism in biological systems. These membranes are often accessible to non-polar or hydrophobic compounds like lipids and also to small molecules like oxygen, carbon dioxide, nitrogen, and nitric oxide, but impenetrable to big and polar molecules like ions, proteins, and polysaccharides.

In addition to solute size, permeability is influenced by solubility, charge, or chemistry. Aquaporins allow water molecules to diffuse across the phospholipid bilayer and pass through the membranes of the organelle, tonoplast, and plasma. The main mechanism for bringing water into and out of cells is osmosis. Osmosis between a cell's interior and its comparatively hypotonic surroundings regulates a cell's turgor pressure in significant part.

Osmosis is the flow of a solvent toward a more concentrated solute through a semipermeable membrane. Although water is frequently the solvent in biological systems, osmosis can also take place in other liquids, supercritical liquids, and even gases. Water molecules move through the cell membrane when a cell is submerged in water, traveling from a region of low solute concentration to high solute concentration. For instance, water molecules leave the cell once it is submerged in saltwater. A cell will absorb water molecules if it is submerged in freshwater.

Water molecules move across the membrane in both directions at the same rate when there is a volume of clean water on both sides. The membrane does not allow for any net water flow. When potato slices are introduced to a solution with a lot of salt, osmosis may be seen in action. The potato shrinks and loses its "turgor pressure" as a result of the water from inside moving to the solution. The loss in size and weight of the potato slice increases with salt solution concentration.

Chemical gardens show how osmosis works in inorganic chemistry. In biology and chemistry textbooks, the mechanism underlying osmosis is typically described as either the dilution of water by a solute (resulting in a lower concentration of water on the higher solute concentration side of the membrane and subsequently a diffusion of water along a concentration gradient) or the attraction of a solute to water. These two ideas have been categorically debunked.

The ability of osmosis to push water over a membrane in the direction of a higher water concentration renders the diffusion process of osmosis unworkable. Osmosis is independent of the mass of the solute molecules—a collapsible property—or whether hydrophilic they are, which casts doubt on the "bound water" hypothesis.

Without a mechanical or thermodynamic explanation, it is challenging to explain osmosis, but in essence, there is a contract between the solute and water that opposes the pressure which otherwise free solute molecules would exert. One thing to keep in mind is that heat from the environment can be changed into mechanical energy (water rising).

Many thermodynamic explanations deal with the idea of chemical potential and how, because of the increased pressure and the solute's presence, the function of water in solutions changes from that of pure water while the chemical potential is maintained. In many plants, osmotic pressure serves as the primary source of support. The steady state is produced when the osmotic entry of water raises the turgor pressure acting on the cell wall until it matches the osmotic pressure.

Water travels out of a plant cell when it is placed in a solution that is hypertonic in comparison to the cytoplasm, and the cell contracts. The cell becomes flaccid as a result. In extreme circumstances, the cell can become plasmolyzed, where the lack of water pressure causes the cell membrane to separate from the cell wall.

A plant cell absorbs water when it is placed in a solution that is hypotonic to the cytoplasm, causing the cell to enlarge and become turgid. The capacity of plant roots to extract water from the soil is due to osmosis. Water enters the roots by osmosis, and plants concentrate solutes in their root cells through active transport. Osmosis is also in charge of regulating how guard cells move.

Osmosis can be exceedingly destructive to species in strange situations. For instance, freshwater and saltwater aquarium fish will perish fast, and saltwater fish will perish drastically if they are placed in water that is not the salinity to which they are acclimated. The application of table salt to eliminate leeches and slugs is another illustration of a negative osmotic effect.

Imagine submerging a plant or animal cell in a sugar or salt solution.

  • If the medium is hypotonic in comparison to the cytoplasm of the cell, the cell will osmotically absorb water.
  • There won't be a net migration of water across the cell membrane if the medium is isotonic.
  • The cell will osmotically lose water if the medium is hypertonic about the cytoplasm.

This means that a cell will shrink if it is placed in a solution with a solute concentration greater than its own, and it will swell and possibly burst if it is placed in a solution with a solute concentration lower than its own.

By increasing the pressure in the area of high solute concentration relative to that in the area of low solute concentration, osmosis may be prevented. The osmotic pressure of the solution, or turgor, is comparable to the force per unit area, or pressure, needed to prevent the flow of water (or any other high-liquidity solution), through a selectively permeable barrier and into a solution of greater concentration. Osmotic pressure is a colligative feature, which means that it depends on the solute's concentration rather than its composition or chemical identity.

What is Diffusion?

The net movement of anything (such as atoms, ions, molecules, or energy) from a location of higher concentration to a region of lower concentration is known as diffusion. A gradient in the Gibbs free energy or chemical potential drives diffusion. As with spinodal decomposition, it is conceivable for molecules to diffuse "uphill" from an area of lower concentration to one of higher concentration.

Many disciplines, including physics (particle diffusion), chemistry, biology, sociology, economics, and finance, employ the concept of diffusion extensively (diffusion of people, ideas, and price values). All of these share the fundamental principle of diffusion, which states that a substance or collection spreads out from a place or location where there is a larger concentration of that material or collection.

A gradient is a change in a quantity's value caused by a change in another variable, typically distance, such as concentration, pressure, or temperature. The terms "concentration gradient," "pressure gradient," and "temperature gradient" are used to describe changes in concentration, pressure, and temperature over a given distance.

Numerous disciplines, including physics (particle diffusion), chemistry, biology, sociology, economics, and finance, utilize the concept of diffusion (diffusion of people, ideas, and price values). The substance or collection that is diffusing, however, is always "spreading out" from a place or area where there is a larger concentration of that substance or collection.

The concept of diffusion can be introduced in two different ways: either through a phenomenological approach that starts with Fick's laws of diffusion and their mathematical ramifications or through a physical and atomistic approach that takes into account the random movement of the diffusing particles.

Diffusion, according to the phenomenological method, is the movement of a substance without a bulk motion from an area of high concentration to a region of low concentration. The diffusion flow is proportional to the negative gradient of concentrations, as stated by Fick's laws. From higher concentration areas to lower concentration areas, it moves. Later, different generalizations of Fick's laws within the context of thermodynamics and non-equilibrium thermodynamics were established.

Diffusion is viewed from an atomistic perspective as the outcome of the random movement of the diffusing particles. The moving molecules in molecular diffusion propel themselves using heat energy. Robert Brown first observed that minute particles floating in a liquid medium and just large enough to be seen under an optical microscope exhibit a rapid and continuously irregular motion of particles known as Brownian movement. Brown made this discovery in 1827. Albert Einstein created the atomistic basis of diffusion and the Brownian motion theory. Diffusion theory is often used for any topic requiring ensembles of individuals walking randomly.

Now, diffusion is the term used to describe how fluid molecules travel across porous substances in chemistry and materials science. When a collision with another molecule is more likely than a collision with the pore walls, molecular diffusion takes place. So, in these circumstances, the diffusivity is proportional to the mean open path and is comparable to that in a non-confined region. Plus, whenever the pore diameter is equal to or less than the mean free route of the molecule diffusing through the pore, Knudsen diffusion takes place. This circumstance results in a progressive increase in the likelihood of a collision with the pore walls and a decrease in diffusivity.

Finally, configurational diffusion occurs when the size of the molecules and the pore are similar. In this circumstance, the diffusivity is significantly lower than that of molecular diffusion, and tiny variations in the kinetic diameter of the molecule result in significant variations in the diffusivity.

Main Differences Between Osmosis and Diffusion In Points

  • While diffusion is characterized by solvent movement from higher to lower concentration regions, osmosis entails solvent movements from lower to higher concentration regions.
  • Osmosis can only be seen over a partially permeable membrane, whereas diffusion can be seen in any combination of a mixture, even across a partially permeable membrane.
  • Diffusion allows both solvent and solute materials to pass through the membrane, whereas osmosis only allows the solvent materials—in this case, water molecules—to pass through the membrane.
  • While particle movement occurs in all directions during diffusion, it only occurs in one direction during osmosis.


So now, we can say that we have gathered enough knowledge about the major differences between osmosis and diffusion.


  • Diffusion. (n.d.). Retrieved from WIKIPEDIA: https://en.wikipedia.org/wiki/Diffusion
  • Osmosis. (n.d.). Retrieved from WIKIPEDIA: https://en.wikipedia.org/wiki/Osmosis


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"Difference Between Osmosis and Diffusion." Diffzy.com, 2023. Thu. 23 Mar. 2023. <https://www.diffzy.com/article/difference-between-osmosis-and-diffusion-913>.

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