What is the driving force behind osmosis in biology?

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    Biology Osmosis
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Discussion Overview

The discussion revolves around the driving force behind osmosis in biological systems, particularly focusing on the mechanisms involved when water moves across a semi-permeable membrane separating pure water and a solution. The scope includes theoretical explanations and conceptual clarifications related to the phenomenon of osmosis.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant describes a scenario involving pure water and a solution separated by a membrane, questioning the force that drives water to the solution side.
  • Another participant emphasizes the necessity of a semi-permeable membrane for osmosis and suggests that the desire for dilution is a topic for further explanation.
  • A participant proposes that the phenomenon may be explained through statistical mechanics, noting that mixed states are more probable than separated states.
  • It is suggested that a higher concentration of water molecules on one side leads to a greater likelihood of those molecules passing through the membrane.
  • A participant provides a link to additional resources on osmosis but expresses confusion about the movement of water across the membrane.
  • One participant explains that the movement of water molecules is influenced by pressure resulting from kinetic energy and random motion, indicating that more water on one side creates more pressure, which contributes to the movement.

Areas of Agreement / Disagreement

Participants express various viewpoints regarding the mechanisms of osmosis, with no consensus reached on a singular explanation for the driving force behind the process.

Contextual Notes

The discussion includes assumptions about the nature of the membrane and the conditions under which osmosis occurs, but these assumptions are not fully explored or resolved.

youknowme
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Let's say there are two parts in a container, one part is pure water and the other part is some solution. There is a membrane blocking the solution particles from moving to the other side. So eventually, water will be pulled to the solution side to make it less concentrated.

My question is, what is the force that pull the water to the other side?
 
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Welcome to PF, Youknowme.
Well, to start with, it has to be a semi-permeable membrane as opposed to a solid one. If the solution in question is saline, for instance, the membrane must have holes of a size that H20 can pass through but NaCl can't.
Unfortunately, I can't explain why the saline 'wants' to be diluted. Someone else here can, though.
 
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Isn't it purely statistical mechanics? There are vastly more 'mixed' states than totally separated states?
 
Yes. If there are "more" (higher concentration of) water molecules on one side, they are statistically more likely to pass through the membrane than water molecules on the other side.
 
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There are holes in the membrane that allow water to pass through. The water molecules move roughly, so two water molecules, one on each side, are each equally likely to happen to pass through the membrane.

And since there are more water molecules on one side than the other, overall there is more chance of water moving in that direction. The "force" is pressure and it comes from the kinetic energy and that random motion of the molecules. More water on one side than the other means more pressure.
 

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