BIOL 3070 Lecture Notes - Lecture 3: Facilitated Diffusion, Calcium Signaling, Membrane Transport Protein
Document Summary
Osmosis: passive transport of water across semi-permeable membrane. Osmotic pressure opposes hydrostatic pressure created by water flowing through membrane. Mass is not a useful measure for a solute in solution for physiologists, they use osmole instead. Solutes that can"t freely cross plasma membrane but can promote net movement of water across membrane as osmolically active solutes/particles. Osmolarity is simply the number of osmoles of solute per litre of solution (simple way to express overall concentration of a fluid because mass isn"t relevant in this situation) 1 molecule like glucose is generally equal to one osmole (things that dissociate further into its ion components like nacl or mgcl2 would have 2 and 3 osmoles, respectively) Most biological solutions are very dilute so use milli-osmoles instead (ie. human blood is 290-300 mosm. ) Osmolality is technically more correct because with osmolarity (number of solutes/l of solution) the volume of the solution may be affected due to pressure, etc.
