Simple Diffusion vs. Facilitated Diffusion: What’s The Difference Between Simple Diffusion And Facilitated Diffusion?

What are the differences between simple diffusion and facilitated diffusion? What are some examples of each? Read on to learn more about the key distinctions between these two important processes.
Simple Diffusion vs. Facilitated Diffusion: 6 Key Differences, Examples, Similarities

Simple Diffusion vs. Facilitated Diffusion: There are two kinds of passive transport methods called simple diffusion and facilitated diffusion, in which the transport of molecules is done across the cell membranes. Here, the use of natural entropy is done to move the molecules to a lower concentration from a higher concentration until the concentration gets equalized.

Hence, there is no use of ATP energy for molecular transportation.

Four main types of transport are:

  1. Passive filtration,
  2. Simple diffusion,
  3. Facilitated diffusion, 
  4. Osmosis.

The key difference between facilitated diffusion and simple diffusion is that in facilitated diffusion, the transport of substances is done through a concentration gradient across a biological membrane by the means of a carrier molecule, whereas simple diffusion is a type of diffusion that is unassisted where a particle moves to a lower concentration from a higher concentration across a membrane.

What Is Simple Diffusion?

What Is Simple Diffusion? Simple diffusion is classified as an unassisted type of diffusion where a particle starts moving to a lower concentration from a higher concentration. There is passive and directional movement through the concentration gradient.  Once all the molecules are distributed evenly, all the molecules on both sides of the cell membrane start achieving an equilibrium where there is no net movement of molecules observed.

Simple diffusion is classified as an unassisted type of diffusion where a particle starts moving to a lower concentration from a higher concentration. There is passive and directional movement through the concentration gradient. 

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Once all the molecules are distributed evenly, all the molecules on both sides of the cell membrane start achieving an equilibrium where there is no net movement of molecules observed. 

Generally, some small and non-polar molecules like carbon dioxide, oxygen, and ethanol are freely diffused across the membrane of the cell. The rate of diffusion varies as per the molecular size, temperature, and the steepness of the gradient that is concentrated. In a solution, the kinetic energy of particles in solution is affected by the temperature. 

Some large particles are subject to higher resistance having a solution compared with the smaller particles. Also, during the case when there is a high concentration gradient, more molecules keep on passing through the cell membrane.

What Is Facilitated Diffusion?

What Is Facilitated Diffusion? Facilitated diffusion states the transport of substances across a biological membrane with the help of a concentration gradient and a carrier molecule. During the process of facilitated diffusion, many polar molecules and large ions keep on dissolving in water and are passively and specifically transported across the cell membrane.

Facilitated diffusion states the transport of substances across a biological membrane with the help of a concentration gradient and a carrier molecule. During the process of facilitated diffusion, many polar molecules and large ions keep on dissolving in water and are passively and specifically transported across the cell membrane.

The diffusion of polar ions occurs through large molecules, transmembrane channels, and transmembrane carrier proteins. These channel proteins are used in the making of hydrophobic tunnels across the membrane, which permits the selected hydrophobic molecules to pass through the membrane.

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There are some channel proteins like the ‘gated’ ion proteins and some which are ‘opened’ all the time. The carrier proteins, such as permeases, are capable of changing their molecular conformation, like the transport of amino acids or glucose through them. The other type of transport protein is called Aquaporins which allows the water to cross this membrane very quickly.

Similarities Between Simple Diffusion and Facilitated Diffusion

  • Both facilitated and simple diffusion occur down from a lower concentration of molecules to a higher concentration of molecules with the concentration gradients.
  • Both these types do not require any form of energy for molecular transportation.
  • The exact movement of these molecules on both sides of the cell membrane is nil at the state of equilibrium.

6 Main Differences Between Simple Diffusion And Facilitated Diffusion

BasisSimple DiffusionFacilitated Diffusion
DefinitionSimple diffusion is classified as an unassisted type of diffusion where the movement of a particle occurs from a higher concentration to a lower concentrationFacilitated diffusion means the transportation of substances across a membrane of biology with the help of a carrier molecule through a gradient of concentration
OccurrenceThe occurrence of Simple diffusion is found through the phospholipid bilayerThe occurrence of Facilitated diffusion is found on transmembrane proteins
Transported MoleculesThe transportation of Simple diffusion is done by non-polar and small particlesThe transportation of Facilitated diffusion transports are done by polar or large particles
Facilitator MoleculesThe occurrence of Simple diffusion is found directly through the cell membraneThe occurrence of Facilitated diffusion is found through the transmembrane integral proteins, which are specific facilitator molecules
Rate of DiffusionHere, the rate of simple diffusion directly affects the concentration gradient across its membrane and also the permeability of the membrane solute moleculeHere, the kinetics of carrier-mediated transport decide the rate of facilitated diffusion
Low Concentration GradientsWhen the solute concentration is low, the rate of simple diffusion is also lowWhen the solute concentration is low, the rate of facilitated diffusion is opposite, i.e., high in comparison to that of simple diffusion

Examples of Simple Diffusion And Facilitated Diffusion 

Simple Diffusion Examples

All the diffusion that occurs in gases across the respiratory membranes of living beings and the diffusion of molecules to the cells from the blood through the interstitial fluid are some examples of simple diffusion.

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Facilitated Diffusion Examples

All the counter-transport of bicarbonate/chloride in the cotransport of sodium with sugars like galactose, fructose, amino acids, and glucose and renal tubular cells are some examples of facilitated diffusion.

Comparison Chart

What are the differences between simple diffusion and facilitated diffusion? What are some examples of each? Read on to learn more about the key distinctions between these two important processes.

Comparison Video

Facilitated Diffusion vs Simple Diffusion

Final Words

Facilitated diffusion and simple diffusion are two of the transport methods that are passive and carry the molecules across their cell membranes. Both this simple and facilitated diffusion find their occurrence through a concentration gradient. The important difference between facilitated and simple diffusion is that their molecular transport mechanism is found across the cell membrane. Where simple diffusion permits molecular transportation across the cell membrane directly, the occurrence of facilitated diffusion is found via transmembrane proteins like aquaporins, channel proteins, and carrier proteins. The nonpolar molecules that are small in size are transported by the process of simple diffusion. Whereas the polar molecules that are larger in size are transported by the process of facilitated diffusion. The net molecular movement on both sides of the cell membrane is always nil at the state of equilibrium.

Alex Stantor

Author & Researcher @ Difference 101 Master in Philosophy & Data Analysis, Sorbonne Université (Graduated 2011) Lived in New York City

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