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I have a question about osmosis that goes a bit deeper than most basic textbooks so I cannot find the answer.Here's the problem:

Imagine an animal cell, say a red blood cell, in a slightly hypotonic solution. The water starts to flow in osmotically. The concentration of solute in the cell decreases. The cell slowly starts to swell but does not burst.

The question is: Does this water entering increases the pressure on the membrane (similar to turgor in plant cells only less, because the cell can increase in volume - comparable to elastic energy that must be overcome when blowing a baloon...) and does this cause osmosis to stop BEFORE the concentrations come to equilibrum (meaning that cytoplasm still has a bit more solute concentration than outside of cell) or do the concentrations perfectly match?

Thanx in advance.

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It doesn't

As long as liquid water is present osmosis will never stop, the closest you can get is a point at which it happens at equal rates in both directions, called equilibrium.

Plant cells will help you understand as osmosis will create immense internal pressure as water enters the cell even though the cell cannot expand thanks to the cell wall. the amount of water inside the cell will keep rising until it reaches equilibrium, this also makes the cell more rigid.

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If animal cells are incubated in pure (or v. Low solute conc.) water, they will swell until they burst.

So in that respect, I think osmosis doesn't stop for animal cells. At least not until either equilibrium has been reached, or the cell has burst.

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  • $\begingroup$ Equilibrium must be reached for osmosis to stop, but what equilibrium? Look at this example: canacopegdl.com/images/osmosis/osmosis-14.jpg Here, as water level rises in one side and falls in the other, hydrostatic pressure builds up. When hydrostatic pressure equals osmotic, net water flow into the STILL HYPERTONIC solution stops from the STILL HYPOTONIC one. My assumption is that something similar (just to a lesser extent) exists in the case of animal cell swelling so osmosis stops when the pressure buildup in the cell equals osmotic pressure. $\endgroup$
    – Liroj
    Feb 12, 2018 at 19:45
  • $\begingroup$ Hydrostatic pressure won't effect cells in the same way as that scenario. As the cells are surrounded by the solution, the pressure against the cell wall can lead to the cell bursting, if the osmotic potential of the solution is off. For mammalian cells, it's typically around 300 milliosmolar. Similar to tissue fluid. $\endgroup$
    – Oliver Houston
    Feb 17, 2018 at 18:37
  • $\begingroup$ Anyway, not really. Either the cell will swell and burst, or shrivel and die. In both scenarios the membrane disintegrates, so the cells contents mix with the solution. Now for an artificial membrane that cannot burst. That's a different question. $\endgroup$
    – Oliver Houston
    Feb 17, 2018 at 18:41
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I found this, which I think proves my point, but I cannot say I really understand all the math behind it.

https://i.stack.imgur.com/GgO01.jpg

http://www.princeton.edu/~akosmrlj/MAE545_S2017/lecture13-14_slides.pdf

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