Sea_Guide7219 OP t1_jebavkc wrote on March 30, 2023 at 7:36 PM

Thank you all for your answers.

I have found this in a textbook, "fundamentals of biochemistry", Voet et al., 2016 :

"When a solution is separated from pure water by a semipermeable membrane that permits the passage of water molecules but not solutes, water moves into the solution due to its tendency to equalize its concentration on both sides of the membrane. Osmosis is the net movement of solvent across the membrane from a region of high concentration (here, pure water) to a region of relatively low concentration (water containing dissolved solute). The osmotic pressure of a solution is the pressure that must be applied to the solution to equalize the flow of water across the membrane in both directions."

So, I do not want to split hairs, but I gather (yet I might off course be totally wrong) that the "circulation" of ions following their concentration gradient is simply the net movement which tends to equilibrate the concentration gradients on both sides of the membrane, not because "a force" is acting on the particles, but simply because more particles go from A to B than from B to A.

What do you think about it ?

DudoVene t1_jedqphd wrote on March 31, 2023 at 7:41 AM

I think you get the point but the movment of ions IS a force, meaning you can calculate it or (better example in biochemistry ) translates it in another force. this way, the transfert of H+ ions throught the mitochondria membrane is converted in heat, and mostly in the regeneration of ADP to ATP. another example should be the transfert of seve in tree from roots to leaf : the osmotic pressure is able to elevate a volume of water versus the gravity force of the weight of the water. keep in mind if zero force is involved, any system should be considered at equilibrium. equilibrium in life means death.