Diffusion

Diffusion

Diffusion
  • The movement of materials in and out of the cells in plants takes place in solution or gaseous form. Although the exact process of this is not very clear, three physical processes i.e., diffusion, osmosis and imbibition are usually involved in it.
  • The movement of particles or molecules or ions from a region of higher concentrations to a region of lower concentration due to random kinetic motion of the particles is called as diffusion. The rate of diffusion of gases is faster than liquids or solutes.
  • The diffusing particles have a certain pressure called as the diffusion pressure which is directly proportional to the number or concentration of the diffusing particles. Therefore the diffusion takes place always from a region of higher diffusion pressure to a region of lower diffusion pressure i.e., along a diffusion pressure gradient.

Factors influencing diffusion:

  1. Spatial factors
    • Path length of diffusion
    • Area through which diffusion is occurring.
    • Resistance against free diffusion.
  2. Higher temperature will increase the diffusion rate.
  3. Pressure.
  4. Molecular weight: lighter molecules will diffuse faster than the heaver molecules.

The rate of diffusion increases if,

  • The diffusion pressure gradient is steeper
  • The temperature is increased
  • The density of the differing particles is lesser
  • The medium through which diffusion occurs is less concentrated.

Diffusion of more than one substance at the same time and place may be at different rates and in different direction, but is independent of each other. A very common example of this is the gaseous (CO2 and O2) exchange in plants. Besides osmotic diffusion, the above mentioned simple diffusion also plays a very important role in the life of the plants.

Significance of diffusion

  1. It is an essential step in the exchange of gases during respiration and photosynthesis
  2. During passive salt uptake, the ions are absorbed by diffusion
  3. It is important in stomatal transpiration as the last step in the process where, diffusion of water vapour from the intercellular space into the outer atmosphere occurs through open stomata.

Animation: How Diffusion Works

Last modified: Saturday, 24 November 2012, 8:58 AM