Simple Diffusion vs Facilitated Diffusion
In cell biology, diffusion refers to passive transport and it is the net movement of particles from an area of high concentration to an area of low concentration. When molecules are evenly spread across a cell, it is called equilibrium. Simple diffusion is a type of passive transport where no energy is required for molecules to move out or into the cell. However, there are times when large molecules cannot, on their own cross the plasma membrane and are helped across the membrane by carrier proteins. This process is known as facilitated diffusion. There are differences in these two processes that will be described in this article.
In facilitated diffusion there are special carrier proteins having a central channel that provide a corridor which is selective in nature and allows some molecules to pass through the membrane. These carrier proteins allow only some molecules to bind with them such as some of amino acids or some sugar molecules. As soon as the molecule binds to this carrier protein, the protein changes its shape and helps the molecule to pass down its concentration gradient and releases it after passing it through the membrane. Thus it is clear that facilitated diffusion is similar to simple diffusion as no input of energy is required for the transport of molecules down their concentration gradient. The difference lies in the use of special carrier protein for the transport process. Another difference is that facilitated diffusion can take place in either direction that is the carrier protein can facilitate movement of the molecules in both directions depending upon the concentration gradient. So if the concentration of the molecule is too high inside the cell, the same carrier protein can help in moving these molecules out of the cell.
Simple Diffusion and Facilitated Diffusion
• Simple diffusion allows passage of non polar small molecules and does not require energy source while facilitated diffusion requires a source of ATP.
• Simple diffusion can move particles in the direction of concentration gradient whereas materials can move with or against concentration gradient in facilitated diffusion.
• The process of simple diffusion occurs only in prokaryotes while facilitated diffusion is seen only in eukaryotes.
• Facilitated diffusion requires specific facilitator for specific molecule which is not the case with simple diffusion