Simple Diffusion- Definition, Principle, Examples, Applications

Simple Diffusion 

  • As the name implies, a solute simply diffuses when the electrochemical potentials on the opposing sides of a permeable barrier are dissimilar. This is a type of passive transport.
  • Diffusion in biology refers to the selective permeation of a biological membrane, as opposed to the “spreading out” of molecules from a greater concentration in other scientific areas like chemistry.
  • Similar to all other passive transport processes, simple diffusion involves the passage of molecules down a concentration gradient until the solute concentration is balanced on both sides.

Principle of Simple Diffusion

How does simple diffusion work?

  • The solute particles travel randomly in free diffusion via a membrane, similar to how they behave in free solution.
  • These distinct movements are ultimately what cause the solute flux, a measured and repeatable quantity.
  • The aggregate of a huge number of these trajectories is fairly repeatable despite the fact that the path of a single solute particle cannot be anticipated.
  • The form suggested by Teorell (1953) may be used to express the flow of free diffusion very simply:
  • Flux = Mobility, Concentration, Driving Force
  • The flux is the quantity of solute molecules that traverse a membrane with an area of one square centimetre per second. 
  • The product of the solute mobility, which gauges how easily it can be transported, the concentration, which gauges how much material is available to take part in the operation, and the driving force determines the flux.
  • The solute is in equilibrium and its flow through the membrane is zero when its chemical potential is the same in the two phases enclosing the membrane.
  • A chemical gradient potential, which is what drives the flow of solute when the concentration is different develops when the concentration is different.
  • The permeability of the membrane should be measured scientifically for biological systems. The permeability of the membrane for that particular solute determines the solute’s movement.

Diffusion of electrolytes

  • Along with the concentration gradient, another force also acts on the diffusion of charged species.
  • When there are electrostatic potential gradients, charged solutes are susceptible to electrical forces.
  • As a result, rather than the chemical potential, the gradient of the electrochemical potential acts as the driving force for electrolyte movement.
  • There are always at least two solute species present in electrolyte solutions because they must have at least one anion and one cation, creating multiple fluxes.

Factors affecting Simple Diffusion

Numerous elements and characteristics impact the mechanism of diffusion because they alter the rate of diffusion.

  1. Concentration gradient
  • The force behind the diffusion of a non-electrolyte is the concentration gradient across a biological membrane.
  • Therefore the rate of diffusion will increase as the concentration difference across the membrane increases.
  • As molecules are distributed more uniformly across the membrane, the rate of diffusion decreases.
  • Diffusion stops until balance is preserved on both sides of the membrane.
  1. Mass/Size of the solute molecules
  • The size of the molecules has an impact on the rate of diffusion via a biological membrane.
  • The difficulty of moving over the membrane will increase with the size of the molecule, which will slow down the rate of diffusion.
  • Diffusion therefore occurs at a faster pace for smaller molecules and at a slower rate for bigger ones.
  1. Temperature
  • The simple diffusion process is also impacted by the system’s temperature.
  • While the temperature rises, the molecules’ energy rises as well.
  • Higher energy molecules may penetrate the membrane more quickly than lower energy particles, which travel more slowly.
  1. Solubility
  • The solubility of molecules in a medium has an impact on the rate of particle diffusion as well.
  • Lipid-soluble compounds may penetrate lipid layers quickly, including those in the plasma membrane.
  • Similar to how non-polar and polar molecules travel differently depending on the kind of biological membrane, so do polar and non-polar molecules.
  1. Solvent density
  • The rate of diffusion reduces as the solvent density rises.
  • The solute will find it more challenging to move about in a solvent that is more dense.
  • The transport of solute in the cytoplasm of the cell depends critically on the solvent density.
  • The flow of molecules and gases slows as cytoplasm density increases, and as the cytoplasm density falls, the opposite is true.
  1. Surface area and thickness of the biological membrane
  • The membrane’s surface area increases along with the rate of diffusion.
  • The molecules’ permeability, or mobility, rises due to the increase in surface area, since mobility is one of the variables causing the flow.
  • Similarly, when the membrane becomes thicker, the rate of diffusion is similarly slowed down.

Examples of Simple Diffusion

Oxygen and Carbon dioxide

  • The passage of gases through a membrane in an animal is one of the most well-known instances of simple diffusion.
  • Simple diffusion is used to transfer the dissolved oxygen and carbon dioxide in the blood.
  • The direction of gas flow is governed by the gradient in the concentrations of these gases within the cells.
  • The oxygen content in the alveoli is higher than that in the blood vessels that are being inhaled. As a result, oxygen is transferred from the alveoli to the blood.
  • Similar to this, during exhalation, more carbon dioxide is present in the blood than in the alveoli, which causes the gas to travel into the lungs.
  • A similar mechanism happens when blood and cells exchange gases.

Movement of waste materials

  • Simple diffusion allows the animals to remove waste products.
  • Urea is a waste product that the liver excretes into the blood through a simple diffusion mechanism.
  • The kidneys use simple diffusion in a manner comparable to this to eliminate waste products and toxins, and also to absorb water. Separate active transport is also active in some renal regions.

Nutrition in bacteria

  • It is unknown how bacteria and other prokaryotes move nutrients, water, gases, and various solutes around their bodies.
  • They thus rely on straightforward diffusion to move these molecules around in the cytoplasm.
  • Simple diffusion, which happens across the general body surface, also helps bacteria excrete waste products.

Application of Simple Diffusion

  • The idea of simple diffusion is used in a variety of contexts, including those involving food, medicine, and the environment.
  • The creation of the distinct flavour in beverages like tea and soda is greatly influenced by the diffusion of gases and chemicals from tea leaves.
  • The activity of medications in the body is governed by the basic diffusion mechanism. Once a drug has been consumed, simple diffusion causes the molecules to be released into the appropriate locations of action.
  • Another issue caused by diffusion is air pollution. Air pollution is caused by the dispersion of numerous gases emitted by industrial, mechanical, and agricultural operations.
  • Diffusion also leads to the creation of alloys. When two metals are exposed to one another over an extended period of time, the atoms diffuse from one metal to the other to fill the voids. Different alloys are created as a result of this.


  • Friedman, M. (2008). Principles and models of biological transport. Springer.
  • https://examples.yourdictionary.com/examples-of-diffusion.html
  • https://biologydictionary.net/simple-diffusion/
  • https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(Boundless)/5%3A_Structure_and_Function_of_Plasma_Membranes/5.2%3A_Passive_Transport/5.2C%3A_Diffusion


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