Transcript Water Potential (Heavy Y)

Water Potential
(Heavy Y)
What is it?
• Water Potential is the tendency of water to
leave one place for another place.
• If it can, water will always move from an area
of higher water potential toward a region of
lower water potential.
• Symbolized as Y
Measuring Water Potential
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Measured in “bars” or megapascals (MPa)
1 bar is about 1 atm
1 bar is about 0.10 MPa
So, 10 bars is about 1 MPa
A car tire has about 0.2 MPa
House plumbing is about 0.25 MPa
Pure water in an open container @ STP has a
water potential of 0.00 bars or MPa
Two Factors Determine
Water Potential
1. Solute Potential (Ys): This is determined by the
solute concentration and it is inversely
proportional to solute concentration.
The formula for solute potential is Ys
where,
i = ionization constant
C = molar concentration
R = .0831 liter bars/mole K
T = temperature K
= -iCRT
Two Factors Determine
Water Potential
2. Pressure Potential (Yp) aka “fluid pressure” or
“hydrostatic pressure.”
This is the physical pressure inside the solution
which is directly proportional to water potential.
It can be >, =, or < 0
A positive Yp is called “pressure” (a “push”)
A negative Yp is called “tension” (a “pull”)
Together then, Y = Ys + Yp