3.1) Diffusion

3.1) Diffusion

Diffusion: is the net movement of molecules and ions from a region of their higher concentration to a region of their lower concentration down a concentration gradient, as a result of their random movement.


Diffusion always takes place down a concentration gradient, that means that the particles that diffuse try to spread evenly in all spaces, so it moves from where it’s very concentrated to where it’s not concentrated.


Substances move into and out of cells by diffusion through the cell membrane.


The importance of diffusion of gases and solutes:



  • (Animals) Necessary for gas exchange in all living organisms (O2 in, CO2 out)
  • (Plants) Necessary for obtaining Carbon Dioxide and releasing oxygen during photosynthesis.


Solutes (liquids)

  • Dissolved salts diffuse through root hair cell.
  • Absorption of dissolved food material in many organisms, like amoeba, bacteria and fungi is carried out through diffusion.
  • Some digested food material is absorbed by diffusion


Water as a solvent

  • Plants cannot obtain minerals unless they are dissolved in water
  • Enzymes and hormones cannot be secreted unless they are dissolved in water
  • Excretory products cannot be excreted unless they are dissolved in water.


Rates of diffusion

The energy for diffusion comes from the kinetic energy of random movement of molecules and ions.

Factors that influenced the rate of diffusion:

  • Surface area – The larger the surface area of the exchange membrane the faster particles diffuse.
  • Temperature – Increasing the temperature will give particles more kinetic energy, making them move faster, thus increasing the rate of diffusion.
  • Concentration gradient – The steeper the gradient the faster the particles diffuse.
  • Distance (Thickness of exchange membrane) – The thinner it is, the easier it will be for particles to go through it, the faster the diffusion rate.