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Diffusion and Osmosis

Diffusion, also known as simple diffusion, is the net movement of molecules of a substance from a region of their higher concentration to a region of their lower concentration. In contrast, osmosis refers to the diffusion of solvents across a semipermeable membrane. Thus in osmosis, if a semipermeable membrane separates two solutions of different concentrations, the solvent will tend to diffuse across the membrane from the less concentrated to the more concentrated solution. This phenomenon best describes the main difference between diffusion and osmosis.

Compare and Contrast Between Diffusion and Osmosis

In biology, both diffusion and osmosis are important life processes that share many common properties, although being contrasting in many aspects.

Diffusion and Osmosis Difference

What are the Differences Between Diffusion and Osmosis

 Basis For Comparison  Diffusion  Osmosis
The Process The movement of molecules (solid, liquid or gases) from a region of higher concentration to the lower region concentration, but not necessarily through a semipermeable membrane The movement of solvent especially water from the higher region concentration to the region of lower concentration, through the semipermeable membrane
Medium Undertakes in any medium (solid, liquid, and gases) Undertakes in the liquid medium
Material Applied to all states of matter-solid, liquid, and gas Applied only for the solvent part of the solution
Properties of Molecules Depends on the size and electric charge of molecules Depends on the particle concentration
Concentration Gradient Moves from a high concentration gradient to a low concentration gradient Moves down concentration gradient
Semipermeable membrane (cell membrane) The motion is direct and does not always require the semipermeable membrane or cell membrane The motion is through the semipermeable membrane or cell membrane
Rate of the process Fast process Slow process
Free energy Only depends on the free energy of the substance Depends on the rate of reduction of the free energy of one solvent
Example The scent of perfume filling a whole room within seconds Plant root hairs taking up water from the soil
Purpose and Significance in living organisms 1. Important in animals for producing energy for the cell, during respiration it helps in the exchange of gases

2. In plants, it is helpful in the process of transpiration and photosynthesis

1. Important in animals for maintaining the water potential of the cell, transporting nutrients, and in cell-cell diffusion

2. In plants, it maintains turgidity, provides mechanical support, prevents excess water loss, and helps in the absorption of water from the soil

How are Diffusion and Osmosis Alike

  • Presence of concentration gradient between the participating regions is important in both diffusion and osmosis
  • Both diffusion and osmosis equalize the concentration of both the solutions participating in the process
  • Both diffusion and osmosis are spontaneous transport processes, which mean they do not require any input of extra energy to occur
  • In both diffusion and osmosis, particles move from an area of higher concentration to one of lower concentration
  • Internal factors like solute potential and water potential do not affect both osmosis and diffusion


Thus we can refer osmosis to be a special kind of diffusion in which the diffusion occurs across a semipermeable membrane where only the water or other solvent molecules participate in the movement.Since the two processes are not mutually exclusive, they can happen simultaneously in a living system, although there are cases when one of these two processes may happen exclusive of the other.

Article was last reviewed on Monday, February 17, 2020

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