I'm confused about the role of hydrostatic pressure compared to osmotic pressure.

Q1:If I have a U-tube with a membrane permeable only to water molecules and equal volumes of water on either side but only 1 side (side B) has NaCl, the osmotic pressure would cause water to move from side A to side B,correct ?

Q2.But then hydrostatic pressure would cause water to move back to side A. So, the water would move from side A to side B until the effect caused by the hydrostatic pressure = effect caused by osmotic pressure ?

Q3. The last statement wouldn't be correct If I said that "water moves until the hydrostatic pressure=osmotic pressure" would it ?

and lastly, My friend said the water would move until the hydrostatic pressure on both sides was equal Q4. If water is moving from side A to side B then the we have more water molecules at side B, how would side A ever reach the hydrostatic pressure at side B ? Do I have a misunderstanding in the concept of hydrostatic pressure ? In this context, I understand that it is the pressure exerted by the water molecules on the selectively permeable membrane.

The more I google hydrostatic pressure the more lost I get because all sources seem to explain in terms of equations and physics and I'm only taking this for an introductory course in physiology.

  • 1
    $\begingroup$ Do the answers at biology.stackexchange.com/questions/89609/osmotic-pressure help you? $\endgroup$
    – Bryan Krause
    Apr 5, 2020 at 21:14
  • 1
    $\begingroup$ I understand everything thats written in that page, I think of osmotic pressure as a vacuum too but I might have a misunderstanding in hydrostatic pressure and what equals what at equilibrium $\endgroup$
    – Alara
    Apr 6, 2020 at 3:20


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