Individual cells in biology rely on diffusion for transport of molecules across
ID: 165166 • Letter: I
Question
Individual cells in biology rely on diffusion for transport of molecules across them. How long does it take for a molecule to get across a typical cell? Organisms starting at a certain size require organs (e.g. a heart) to facilitate the transport of nutrients etc. through them. Correlate this to diffusive transport. The objective of this homework question is not any precise number. Rather, please discuss how fundamental laws of physical chemistry have far-reaching consequences by utilizing what you learned about transport.
Explanation / Answer
Molecules pass through a membrane which is located below their concentration gradient and the process is called simple diffusion. Increase in entropy would power the transport of the molecules across the membrane. According to the Second Law of Thermodynamics, molecules spontaneously move from a region of higher concentration to one of lower concentration, which doesn't happen in this case.
Sodium ions will have to pass through particular channels that has developed a hydrophobic barrier formed by membrane proteins. This membrane crossing would be called as facilitated diffusion, because the would be facilitated by ion specific channels. At times, it is also called passive transport, because the energy that drives the ion movement would develop from the ion gradient, with no contribution by the transport system. There are certain channels that show substrate specificity, such as enzymes.