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Eukaryotic cells keep a sodium-potassium gradient across their external membrane. The concentration of potassium ions is about 5mM outside the cell. Although the potential gradient keeps most of these ions close to the membrane, won't some of these ions diffuse away from the cell/organism? Over long periods of time, wouldn't cells 'dry' out of potassium? I guess the same sort of question can be asked about phosphate.

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  • $\begingroup$ Might help to focus your question: which organism (unicellular, multi-celluarl) and water kind of water (sea water vs. fresh water)? $\endgroup$
    – Minnow
    Commented Aug 22, 2016 at 17:21
  • $\begingroup$ If I understand correctly, all organisms in water would be continuously losing potassium by diffusion. Unicellulars in fresh water more so than thick-skinned multicellulars in sea water. $\endgroup$ Commented Aug 23, 2016 at 12:48
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    $\begingroup$ If cells are in a condition where there is low potassium outside, and some of the inside potassium leaches out via diffusion, then they use mechanisms like the Na-K pump to restore the cellular levels. $\endgroup$
    – MattDMo
    Commented Aug 23, 2016 at 21:19
  • $\begingroup$ I think that answers the question. It follows that cells require a certain minimum concentration of potassium in the surrounding water to survive, or at least must replenish it via roots or food. $\endgroup$ Commented Aug 24, 2016 at 12:46

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