Diffusion: Definition, Formula and Examples

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What is Diffusion?

Diffusion is a process of passive transport predominant in root transferring water, minerals, and nutrients from soil to root by the difference between concentration gradient between root hairs and the soil. Diffusion is passive without powered by energy molecules – ATP; takes place in the absence of barriers (i.e.) cell wall specifically in plants and other living tissues and becomes effective in free space over a short distance.

Diffusion is a random motion of molecules in a free space without barriers of the molecules. Molecules above absolute zero in motion has a kinetic energy with heat and diffusion is a random motion in system to attain an equilibrium and hence the diffusion is governed by thermal agitation. Moles, atoms, or any particles in random motion is a medium collide with each other changing their course of motion in other random direction is diffusion.

Diffusion Formula

Diffusion was quantitatively measured by Adolf Fick in 1880’s determining the rate of diffusion to be the difference in the concentration gradient. The law formulated from Fick’s derivation is the “Fick’s first law” from the given equation

Js = -Ds ΔCs / Δ x

Js is the density of the diffusion at a unit area per time known as Density Flux

D is the diffusion coefficient of a substance over a medium, a proportionality constant depends on the medium in which the substance diffuses.

– negative sign indicates the rate of diffusion moves down a concentration gradient.

ΔCs is the concentration of the diffusing molecule Diffusion is slow over longer distances. This can be determined from the first law where the average time taken for a particle to diffuse over a distance id determined by the square of the distance L by the Diffusion coefficient. t= L2/Ds,

Diffusion Citations


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