Simple Diffusion vs. Facilitated Diffusion: 5 Different Things

The main difference between simple diffusion and facilitated diffusion is that simple diffusion is an unaided type of diffusion in which a particle moves from a higher concentration to a lower concentration across a membrane, while facilitated diffusion is the transport of substances across a biological membrane through a concentration gradient using a carrier molecule.

What Is Simple Diffusion?

A particle moves from a high concentration to a low concentration in simple diffusion, which is a type of diffusion that doesn’t need any help. The concentration gradient moves both without doing anything and in a certain direction.

Once all the molecules are spread out evenly, molecules on both sides of the cell membrane start to move toward a state called equilibrium, in which there is no net movement of molecules.

In general, it is easy for small, non-polar molecules like carbon dioxide, oxygen, and ethanol to move through the cell membrane.

Simple Diffusion vs. Facilitated Diffusion

The rate of diffusion varies with molecular size, temperature, and the steepness of the concentration gradient. The temperature of a solution changes the kinetic energy of the particles in it.

Some large particles are harder to solve than smaller ones. Also, more molecules continue to pass through the cell membrane when there is a strong concentration gradient.

What Is Facilitated Diffusion?

Facilitated diffusion is the process of substances moving through a biological membrane with the help of a concentration gradient and a carrier molecule.

During the process of “assisted diffusion,” many polar molecules and big ions continue to dissolve in water and are moved across the cell membrane in a controlled and passive way.

Polar ion diffusion occurs via big molecules, transmembrane channels, and transmembrane carrier proteins. These channel proteins help make hydrophobic tunnels across the membrane that let molecules that don’t like water through.

Some channel proteins, such as “gated” ion proteins, are always open, while others are always closed.

Carrier proteins, like permeases, can change the shape of their molecules when they move amino acids or glucose. Aquaporins are another type of protein that moves water quickly through this membrane.

What are the Similarities Between Simple Diffusion and Facilitated Diffusion?

  • Both simple diffusion and assisted diffusion don’t use any energy.
  • Both reactions happen along a line of different concentrations.
  • In addition, when equilibrium is established, the molecular movements in both processes cease.
  • Also, these things happen across the membranes of cells.
  • Simple diffusion and facilitated diffusion are very different in six important ways.

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

Simple diffusion is the movement of gases through the respiratory membranes of living things and the movement of chemicals from the blood to the cells through the interstitial fluid.

Facilitated Diffusion Examples

Some examples of assisted diffusion are the counter-transport of bicarbonate or chloride in the cotransport of sodium with carbohydrates like galactose, fructose, amino acids, and glucose, and renal tubular cells.

Simple Diffusion vs. Facilitated Diffusion


Molecules can move from one concentration to another through two passive processes: simple diffusion and enhanced diffusion. Transmembrane proteins do not help with simple diffusion.

On the other hand, proteins that act as carriers or channels help with diffusion. As a result, it serves as the primary distinction between simple and aided diffusion.

Also, simple diffusion happens through the phospholipid bilayer of the cell membrane, while assisted diffusion happens through the transmembrane proteins.

So, this is another way that simple diffusion is different from aided diffusion. With simple diffusion, only small molecules can get through the membrane. With assisted diffusion, both small and large molecules can get through.

This article does a great job of explaining the difference between simple diffusion and assisted diffusion.

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