Diffusion is defined by Hyperphysics as the process by which molecules intermingle with each other randomly as a result of their kinetic energy. In layman’s terms, it is the movement of particles in solution from a higher concentration to a lower concentration. There are two common types of diffusion: the facilitated and the passive.
This process requires the presence of energy for its occurrence. A good example is the application of heat to increase the movement of the particles in solution so they can move faster. An example also is when molecules move through cells in the body with the use of transport proteins. This is how essential nutrients are usually transported to different cells and tissues in the body.
Passive or simple diffusion
This process does not need applied energy to occur. An example is when water and its particles, from higher areas, diffuse into low lying areas until equilibrium is reached. The water seeks its own level. This is a simple but clear example of diffusion. The spread of a teaspoon of coffee in water demonstrates also passive or simple diffusion. The granules diffuse into the areas where it is less concentrated, thereby allowing the coffee granules to spread and make the solution homogeneous. Stirring the coffee and using warm water would make it facilitated diffusion, wherein the coffee spreads until equilibrium is achieved.
Diffusion in the human body
There is also a process called net diffusion in cells, in which particles or substances in solution pass through pores or tissue walls from a higher concentration gradient to a lower concentration gradient. As mentioned in facilitated diffusion, the human body uses this method to bring food and vital substances to cells and tissues.
Respiration is one good example of diffusion, as well. Carbon dioxide comes out when we exhale, instead of oxygen, because the concentration of carbon dioxide outside of the body is lower. On the other hand, oxygen enters the lungs because it diffuses into the area where it is less concentrated.
Diffusion in plants
Diffusion also occurs in plants in the same manner that it occurs in animals. This movement is from a higher concentration gradient to a lower one, too. This is how essential nutrients for plants, such as carbon dioxide, are transported from the stomata to the cells. Diffusion, specifically termed transpiration, is the manner by which oxygen is excreted by plants.
Hence, diffusion is a vital process that occurs in vivo (inside the body) and in vitro (outside the body) that is significant for the existence of man.