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Agenda 9/27---Day 5

Agenda 9/27---Day 5. Take out water potential problems Take out enduring understanding work for check Notes if time. Calculating Water Potential. Things to remember! Water potential ( Ψ w) is the physical property predicting the direction in which water will flow

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Agenda 9/27---Day 5

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  1. Agenda9/27---Day 5 • Take out water potential problems • Take out enduring understanding work for check • Notes if time

  2. Calculating Water Potential • Things to remember! • Water potential (Ψw) is the physical property predicting the direction in which water will flow • This is governed by solute potential (Ψs)and pressure potential (Ψp) • Ψw= Ψs + Ψp

  3. What we know • Plant cells have a cell wall that will exert pressure =to the pressure entering the vacuole • Vacuole pressure is exerting pressure on the wall ONLY if the cell is taking in more water than it can hold • SO if the plant cell is flaccid (limp) there is 0 (zero) pressure inside the plant cell • To calculate you use the Ψw=Ψs+Ψp

  4. Solute Potential • The more negative the solute potential, the lower the water potential is, thereformovement of water out of that solution is lower • You must know the solute concentration to calculate solute potential

  5. Calculate using this formula • Ψs=-iCRT • Sugar molecules such as sucrose and glucose are 1 particle, they do not dissociate in water

  6. What is next • It’s a matter of thinking and working through the problems, each time trying to make sense of it. • This requires time and effort

  7. 1 • Calculate the water potential of a solution of 0.15 sucrose assuming the RT=2.478 • Ψs= -1(0.15)(2.478)= -0.37

  8. 2 • Cell is flaccid (pressure = 0), with Ψs=-0.65 Is placed in #1 solution with a Ψs = -0.37 At equilibrium, what is the pressure potential? At equilibrium, the water potential is zero SO 0= -0.37 + Ψp 0=-0.37 +0.37 0=0

  9. 3 • Put cell in 0.35 M solution • Calculate • Ψs = -1(0.35)(2.478)=-0.87 • Compared to the -0.65 inside cell • Which has MORE solute? • Which way will water move? • Therefore, what is the pressure inside the cell?

  10. 4 • Ψw=Ψp+Ψs • -0.24= 0.46 + Ψs -0.24-0.46=Ψs Ψs=-0.7

  11. 5 • Cell Ψs= -0.35 • In distilled water, the water will move into the cell until the pressure potential = that of the solute potential • BECAUSE, at equilibrium the water potential is zero • -0.35 + 0.35 = 0

  12. 6 • Ψw=Ψp+Ψs • Ψw=-0.67 + 0.43 • Ψw= -0.24

  13. 7 • The Water potential outside the cell goes from -1.0 to -0.2 • Does water continue to move in this case? • So what is the pressure potential inside the cell?

  14. 8 • Hypertonic has a low water potential because?

  15. 9. • The water will move out of cell, why?

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