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Calculating water potential

Calculating water potential. Ψ = Ψp + Ψs. The combined effects of these two factors: Solute concentration Pressure are incorporated into a single measurement called Water Potential or Ψ

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Calculating water potential

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  1. Calculating water potential Ψ= Ψp + Ψs

  2. The combined effects of these two factors: • Solute concentration • Pressure are incorporated into a single measurement called Water Potential or Ψ Water will move across a membrance from the solution with higher water potential to the solution with the lower water potential.

  3. Water Potential • Water potential is determined by solute potential and pressure potential. Ψ= Ψp + Ψs • Water moves from regions of high water potential to regions of low water potential.

  4. ΨsSolute (osmotic) potential Once you know the solute concentration, you can calculate solute potential using the following formula: • Solute potential (ΨS ) = –iCRT

  5. ΨsSolute (osmotic) potential • Pure water has a solute potential (Ψs) of zero. Solute potential can never be positive. • Adding more solute is a negative experience; the solute potential becomes negative. (-) in front of i

  6. Solute potentialΨs = − iCRT • i = The ionization constant • for NaCl this would be 2; • for sucrose or glucose, this number is 1 • C = Molar concentration (from your experimental data) • Iso-osmolar molarity (moles/L): would allow you to place a potato in the solution and get no movement of water. • Point at which the line crosses 0 on the graph. (x intercept) • R = Pressure constant = 0.0831 (liter bar/mole K) K is temperature in Kelvin) • T = Temperature in degrees Kelvin = 273 + °C of solution (room temperature is about 23 degrees C, thus in this case 296 K)

  7. Pressure Potential – the sum of all pressure on water. In units of pressure: MPa or Bars • Turgor pressure – forced caused by cell membrane pushing against cell wall. • Wall pressure – an equal and opposite force exerted by cell wall. Counteracts the movement of water due to osmosis. • Other pressures – tension, cohesion, atmospheric, root, etc.

  8. Calculating Water Potential • Water potential is calculated using the following formula: • Ψ = ΨP + ΨS • Pressure potential (ΨP ): In a plant cell, pressure exerted by the rigid cell wall that limits further water uptake. • Solute potential (ΨS ): The effect of solute concentration. • Pure water at atmospheric pressure has a solute potential of zero!!!!!!!!!!!!!!!!!!

  9. Water potential

  10. Chapter 32

  11. Practice Problem • The molar concentration of a sugar solution in an open beaker has been determined to be 0.3M. Calculate the solute potential at 27 degrees C. Round your answer to the nearest hundredth.

  12. -1 (0.3 M) x (0.0831L bars/mole K) x (300) • -7.479 bars of solute potential • Which means water will move • As molarity increase solute increase what will happen to water potential? What way will water move? Time to play! Osmosis lab

  13. The pressure potential of a solution open to the air is zero. Since you know the solute potential of the solution, you can now calculate the water potential. • What is the water potential for this example? Round your answer to the nearest hundredth.

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