Water PotentialPotential energy of water per unit area compared to pure

water

Water Potential =

• Allows us to determine where water is going to flow due to osmosis, gravity, pressure surface tension

• Into or out of cell?so cruel!

Out

side

of ce

llIn

side

of ce

ll

• Na+ and Cl- ionize and are surrounded by hydration shells

• Opens up all these excess spaces

• Decreases water potential

Out

side

of ce

llIn

side

of ce

ll• Water leaves

the cells of the slug

• Pure water = 0

• Water moves from greater water potential to less

Wat

er p

oten

tial

gr

adie

nt

Distilled H2O = 0 bars

Roots = -2 bars

Stems = -6 bars

Leaves = -15 bars

Atmosphere = -1000 bars

• More solute drops potential– Because it opens up spaces for

water to flow in• Physical pressure– Plant’s cell walls put pressure

back on water (+ because it is pushing water out)

-5 bars

2 bars = -3 bars

ψs = -iCRT • i = ionization constant (for sucrose, this is 1

because sucrose does NOT ionize in water• C = molar sucrose concentration at

equilibrium (determined from your graph…the point at which your line (of best fit) crosses the x-axis.• R = pressure constant (0.0831 liter

bar/mole °K)• T = temperature in Kelvins (273 + °C)

The molar concentration of a sugar solution in an OPEN beaker has

been determined to b 0.2 M. Calculate the solute potential at

22C.• i = 1 (sugar does not ionize)• C = 0.2 moles/liter (M)• R = 0.0831 liter bar/mole K• T = 22+ 273 KWhat is the OVERALL water

potential?Pressure potential = 0 in open container…

0.0

M

0.2

M

0.4

M

0.6

M

0.8

M

1.0

M

% c

hang

e in

m

ass

0

% change in mass of simulated animal cells containing various sucrose

molarities.

Molarity =

moles/liter

16

% CHANGE IN MASS OF POTATOES (1st period)Solution Solutio

n Color% ∆ in Mass

Molarity

Type of Solutio

n

Temp(K)

A Purple -13% 0.6 Hypertonic 294

B Green +24%

0.0 VERYHypotoni

c294

C Red -23% 1.0 VERYHyperto

nic294

D Yellow +4% 0.2 Hypotonic 294

E Pink -8% 0.4 Hypertonic 294

F Blue -13% 0.8 Hypertonic 294

% CHANGE IN MASS OF POTATOES (4th period)Solution Solutio

n Color% ∆ in Mass

Molarity

Type of Solutio

n

Temp(K)

A Purple -18% 0.6 Hypertonic 294

B Green +16%

0.0 VERYHypotoni

c294

C Red -33% 1.0 VERYHyperto

nic294

D Yellow +6% 0.2 Hypotonic 294

E Pink -14% 0.4 Hypertonic 294

F Blue -24% 0.8 Hypertonic 294

0.0

M

0.2

M

0.4

M

0.6

M

0.8

M

1.0

M

% c

hang

e in

m

ass

0

Molarity =

moles/liter

% change in mass of potato cells submerged in solutions of different

sucrose molarities.

10

20

-10

-20

0.0

M

0.2

M

0.4

M

0.6

M

0.8

M

1.0

M

% c

hang

e in

m

ass

0

Molarity =

moles/liter

% change in mass of potato cells submerged in solutions of different

sucrose molarities.

10

20

-10

-20

Sucrose molarity inside potato cells?Isotonic solution!C for equation!