Water Potential Used to predict the movement of water in and out of plant cells. Water will move from areas of high water potential to areas of low water potential. Determined by solute concentration and pressure. Ψ= Ψs + Ψp Ψ=water potential Ψs=solute potential Ψp=pressure potential

Pressure Potential Pressure can come from the plant’s cell wall and roots. An increase in pressure raises water potential. At atmospheric pressure Ψp=zero

Solute Potential Solute concentration Addition of solute decreases the solute potential Pure water has a solute potential of zero. What is the highest possible solute potential (Ψs) value?

Sample Experiment (potato in distilled water) BEGINNING Water moves into the cell where the water potential is lower due to the solutes. END As water moves into the cells, the pressure begins to increase from the cell wall. What happens when the pressure potential from the cell wall balances the negative solute potential?

Consider…….. What would happen if you added solute to the distilled water in the beaker? Solute potential in the beaker would decrease making the water potential lower (water moves from high to low water potential). Water would flow out of the potato. Is it possible to add just enough solute to the water so that the water potential outside the cell is equal to that inside of the cell? Yes, there will be no net movement of water How can you use that information to determine the solute concentration inside the cell? Graph data! The solute concentration where there is no net movement of water is the concentration inside the potato.