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    Some questions: (though it probably wont come up in the exam!)

    Theory from TextBook: In the closing of stomata H+ is pumped out of the guard cells, and K+ follows due to electro-static pressure, H2O enters due to osmosis, therefore stoma beome turgid and opens

    Questions:
    1) Wouldnt water enter the cell if just H+ conc in the cell is too high? Maybe can K+ make solute potential made negative more effective than H+??
    2) Wouldnt Electro-static pressure differences apply in a) Na+/K+ pumps, b) Chemiosmosis? If it applies in Na+/K+ pumps wouldnt K+ diffuse IN, since cell is more negative, and it tries to maintain constant voltage. If it applies in Chemiosmosis, wouldnt K+/Na+ diffuse into intermembrane space and ruin everything?

    PS Maybe what I said doesnt make sense, if so pls say which part and I will try and clarify
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    I haven't done this, but just a quick note.
    Ion pumps only ever work one way - I don't know about this specific pump but one ion will move one way at the same time as the other moves the other.
    e.g. K+ will move in as Na+ moves out (this is just an example, not what actually happens)

    Hope that sheds some light on your second problem,
    skevvybritt x
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    Na+/K+ pumps works in 2 directions, 3 sodium ions out for every 2 potassium ions in
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    1)

    Solute potential effects water potential as if the solute potential more negative it would cause water potential to be more negative

    relative water potentials is what causes the movement of water

    since water always moves by osmosis.

    Osmosis occurs as water moves from a less negative water potential

    to a more negative water potential (via a partially permeable membrane)
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    (Original post by ecolier)
    2) Wouldnt Electro-static pressure differences apply in a) Na+/K+ pumps, b) Chemiosmosis? If it applies in Na+/K+ pumps wouldnt K+ diffuse IN, since cell is more negative, and it tries to maintain constant voltage. If it applies in Chemiosmosis, wouldnt K+/Na+ diffuse into intermembrane space and ruin everything?
    In an axon membrane

    the Na+/K+ pump works actively

    K+ will diffuse into the axon membrane down a electrochemical gradient and similarly Na+ ions will diffuse out of the axon membrane

    However, this is conteracted by the Na+/K+ pump that pumps 3 K+ out whilst pumping 2 Na+ in.

    The two effects cancel each out

    This means that a resting voltage of -70mV is maintained
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    Chemiosmosis... what is that?
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    (Original post by ecolier)
    Some questions: (though it probably wont come up in the exam!)

    Theory from TextBook: In the closing of stomata H+ is pumped out of the guard cells, and K+ follows due to electro-static pressure, H2O enters due to osmosis, therefore stoma beome turgid and opens

    Questions:
    1) Wouldnt water enter the cell if just H+ conc in the cell is too high? Maybe can K+ make solute potential made negative more effective than H+??
    Probably, but I think the problem is that the concentration is not higher inside the guard cells - so a H+ pump is needed to actively pump the protons out. [Subsequently, K+ diffuses down its electrochemical gradient, which the increases the solute potential inside the cell so water can diffuse in by osmosis]

    2) Wouldnt Electro-static pressure differences apply in a) Na+/K+ pumps, b) Chemiosmosis? If it applies in Na+/K+ pumps wouldnt K+ diffuse IN, since cell is more negative, and it tries to maintain constant voltage. If it applies in Chemiosmosis, wouldnt K+/Na+ diffuse into intermembrane space and ruin everything?
    a) If you're referring to say a neurone, then an electrochemical gradient is produced with as 3 Na+ are pumped out, and 2 K+ are simultaneously pumped in.
    I think what stops the ions moving in and out passively (down their electro / conc gradients) is the permeability of the membrane. i.e. in a resting neurone, the membrane is relatively impermeable to Na+, so this stops it from diffusing down its electrochemical gradient.


    This theory does seem pretty dodgy or "fudged", but that's pretty much the explanation given at A level I think. Maybe someone at a higher level can enlighten us further.
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    thanx endeavour, ur answer makes perfect sense, i hope someone would explain it better at uni level
 
 
 
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