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Osmotic potential

Osmotic potential. Occurs in plant cells due to the cell wall (and fungi somewhat). The movement in and out of an animal cell is driven by the relative solute concentration gradient (after obeying the electrochemical gradient) Animal cells may swell, burst, or may crenate

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Osmotic potential

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  1. Osmotic potential

  2. Occurs in plant cells due to the cell wall (and fungi somewhat) • The movement in and out of an animal cell is driven by the relative solute concentration gradient (after obeying the electrochemical gradient) • Animal cells may swell, burst, or may crenate • Plant cells have a cell wall that prevents the cell from bursting • The cell wall contributes to osmotic potential and the flow of water in or out of the cell

  3. Water potential (osmotic potential) • Water potential predicts which way the water will flow: in or out of the cell • y represents osmotic potential • Osmotic potential is calculated by adding the solute potential (solute concentration) to the pressure potential (tension of the water) • Y = ys +yp • Water moves from an area of high water potential to an area of low water potential

  4. Solute potential • Ys = iCRT • Ionization constant = i • C is the molar concentration of the solute • R is the pressure constant (0.0831 l bars/ mole K) • T is temperature in K (273 +oC)

  5. Pure water has a water potential of 0 • Solute and pressure potentials are both 0

  6. If there is solute present • Lowers the solute potential and decreases the water potential • This will yield a negative pressure and the water will flow in the direction of the compartment with the solute

  7. Pressure potential is 0 at sea level • It is normally 0 at atmospheric pressure • 25oC is also considered standard temperature and the water potential is always calculated at STP

  8. Calculating osmotic potential of 2M sucrose • Y = ys +yp • Ys = -iCRT • Ys = -i2mol/L(0.0831 l bars/ mole K) (273 +25) • i=1 because sucrose doesn’t ionize • Ys =-49.52

  9. Turgor or Pressure Potential • Since the potential of pure water is 0, when the potato or other cell is placed in pure water, the % change in mass is the pressure potential • For example: if a potato cell is place in pure water and the difference is 3% then • Y= ys +yp • -3= (-3) +0 • 0= -3 + 3 consequently, the pressure potential is 3

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