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 (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

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

Solute Potential The more negative the solute potential, the lower the water potential is, therefor movement of water out of that solution is lower You must know the solute concentration to calculate solute potential

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

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

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

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

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

4 Ψw=Ψp+Ψs -0.24= Ψs =Ψs Ψs=-0.7

5 Cell Ψs= 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

6 Ψw=Ψp+Ψs Ψw= Ψw= -0.24

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?

8 Hypertonic has a low water potential because?

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