Diffusion is the flow of substance from higher concentration to lower concentration through the semipermeable membrane but it is the passive process there is no input of energy and without the involvement of proteins. Diffusion is described by Fick’s law. Where it is inversely proportional to the distance and directly proportional to the concentration.
Diffusion occurs at various parts of the body. In the lungs, there is the diffusion of gases, the carbon dioxide and oxygen diffuse into and out of the lungs and then they diffuse across the cells, the diffusion of gases occurs in the blood, and diffusion of water and waste products occurs in the kidneys.
Diffusion is of three types called. 1) simple diffusion. 2) facilitated diffusion. 3) osmosis. Simple diffusion is the process of transport of substances from higher concentration to the lower concentration and facilitated diffusion means the transport of molecules from high to low concentration with the help of proteins and osmosis means the transport of water molecules from low solute concentration to high solute concentration.
The process of transport of molecules through the plasma membrane across the hydrophobic part and takes place with the help of proteins called the carrier and channel proteins. The facilitated diffusion show saturation because of these proteins. But it doesn’t occur in the case of simple diffusion.