Download Water potential 2.0

Water potential 2.0 The prediction of osmosis and how water is going to move!
Water potential = pressure potential + solute potential
Solute potential= If the concentration of “stuff” in a solution increases it binds up more water.
there is less water to move in/out of a cell because it is bound already. The water potential
decreases.
Formula for solute potential = -iCRT
I = the number of molecules the molecule will make in water
C = molar concentration
R= pressure constant 0.0831 liter per bar/ mole K
T= temperature in degrees K or 273 + Celsius temperature of the solution
Pressure potential is the physical pressure placed on the solution
Positive pressure is turgor pressure like in a plant cell
Negative pressure would be tension
Plants have the cell wall to exert pressure so that the cells won’t burst; so the pressure
potential is positive for a plant.
Animal cells don’t have a cell wall so the pressure inside the cell is the same as out of
the cell. It is the same as the water potential.
When a plant is turgid (stiff) the net movement of water is zero.
MORE SOLUTE =LOWER WATER POTENTIAL (expressed as a negative number)
WATER has the most potential when it is PURE because it isn’t bound to anything.
In a hypertonic solution: water leaves the cell because there is more water in the cell than in the
solution. The hypertonic solution has a negative/low water potential because it is bound up with
“stuff”.
In a hypotonic solution: water enters the cell because the concentration of water outside of the cell is
higher than the concentration in the cell. There was high water potential in the solution initially because
it only had a small amount of “stuff” for water to bind to, so there was a lot of free water to move
around.
In an isotonic solution: water potential is ZERO because the concentration inside and outside of the cell
is the same
Animal cells placed in a HYPOTONIC solution will burst. WHY?
Hypotonic means low “stuff” and high water; water moves into the cell (because the cell is
hypertonic inside)
Animal cells placed in a HYPERTONIC solution will shrink, or crenate. WHY?
Hypertonic solution has a lot of “Stuff” but little water; the inside of the cell is HYPOTONIC so it
has more water in the cell; water wants to leave the cell.