Water Relations
 How water and minerals flow through the
plant.
Water Relations
 How water and minerals flow through the
plant.
 Why does the plant need water?
Water Relations
 How water and minerals flow through the
plant.
 Why does the plant need water?
•
•
•
•
•
Turgidity
growth
photosynthesis
cooling (evaporative)
solvent/metabolic medium
Movement of Water?
Movement of Water

Leaves ->

stem->

roots ->
Leaf Structure
Purpose of Stomata (?)
Purpose of Stomata (?)
 Gas Exchange
Purpose of Stomata (?)
 Gas Exchange
• C02 and H20
• Transpiration
• Trade Off (?)
Purpose of Stomata (?)
 Gas Exchange
• C02 and H20
• Transpiration
• Trade Off:
– How can a plant take in adequate carbon dioxide
without losing too much water???
– Natural adaptations
– Synthetic solutions - antitranspirants
Leaf Structure
Leaf Structure
Diffusion?
 (Much of what happens during water
transport depends on physical laws and
the physical characteristics of water.)
Diffusion
Diffusion
 The movement of molecules from an area
of greater concentration to an area of
lesser concentration.
 TKE Translocational Kenetic Energy
 Solute
& Solvent
Laws of Thermodynamics
 First
 Second
Laws of Thermodynamics
 First
• the total amount of energy in the universe is
constant. Can change from one form to
another.
 Second
Laws of Thermodynamics
 First
• The total amount of energy in the universe is
constant. Can change from one form to
another.
 Second
• The total amount of free (usable) energy is
declining.
• Some energy lost as heat of every transfer.
Osmosis?
Osmosis
Osmosis
The movement of water through a
differentially permeable
membrane.
Solutions
 Hypotonic - lesser concentration of solute
on the outside of the cell. (Turgor
Pressure)
Solutions
 Hypotonic - Lesser concentration of solute
on the outside of the cell. (Turgor
Pressure)
 Hypertonic - Greater concentration of
solute on the outside of the cell.
(Plasmolysis)
Solutions
 Hypotonic - Lesser concentration of solute
on the outside of the cell. (Turgor
Pressure)
 Hypertonic - Greater concentration of
solute on the outside of the cell.
(Plasmolysis)
 Isotonic - Equal concentrations of solutes
on the inside and outsides of the cell.
Plasmolysis & Turgor Pressure
Properties of Water

1. Dipolar -
Properties of Water
Properties of Water
1. Dipolar  2. Universal solvent


Properties of Water

Hydrated shells -
Properties of Water
Properties of Water
1. Dipolar  2. Universal solvent
 3. As solutes are added to pure water the boiling
point increases and the freezing point depression
decreases.

Properties of Water

3. As solutes are added to pure water the boiling
point increases and the freezing point depression
decreases. Freezing Point Determination for
osmotic pressure (O)
Properties of Water
Osmotic
pressure
 (O)

Properties of Water

Plasmolytic Method for (O)
• series of sugar solutions:
• 0.2M 0.3M 0.4M 0.5M ………
Incipient Plasmolysis
Properties of Water

Plasmolytic Method for (O)
• series of sugar solutions:
• 0.2M 0.3M 0.4M 0.5M ………
• use plant cells - epidermal tissue
• check for incipient plasmolysis O solution = O cells
Osmotic Potential (O) of a Plant

Gravimetric Method for O determination:
• 1. Series of Known sucrose solutions:
• 2. Cylinders of plant tissue in each solution
– 0.5M -14.3 Bars
– 0.55 -16.0 Bars
– 0.60 - 17.7 Bars
• 3. Determine wt. Loss or gain - (No change in wt. = O of
plant cells.)
Osmotic Potential (O) of a Plant
 Chardakoff Falling Drop Method for W
determination:
• 1. Series of Known sucrose solutions:
• 2. Cylinders of plant tissue in a series of each
solution and MB in another series
– 0.5M -14.3 Bars tissue … MB
– 0.55 -16.0 Bars tissue … MB
– 0.60 - 17.7 Bars tissue … MB
• 3. If tissue absorbs water (O > sol) = drop rises
• If tissue emits water (O < sol) = drop falls
Overall Water Status of a Plant
 Water Potential (W) =

Osmolarity (O) + Wall Pressure (P)
W=O+P
Overall Water Status of a Plant
• Pressure Bomb Method for determining W:
• (direct measurement - most accurate)
– 1. Place plant part in pressure chamber with cut
stem on the outside. (Cut stem usually shows water
under tension.)
– 2. Increase pressure inside of chamber until water
droplets pushed out of cut stem. Pressure reading
at this point = W
Overall Water Status of a Plant
• Water Potential ( W)
• Water tends to move from cells that have
relatively high (less negative!) water
potentials to cells that have lower (more
negative) water potentials!!
Overall Water Status of a Plant
• Water Potential ( W)
• …………………………..
Overall Water Status of a Plant
• Water Potential ( W)
• Water tends to move from cells that have
relatively high (less negative!) water
potentials to cells that have lower (more
negative) water potentials!!
• Soil --> Root --> Stem --> Leaves --> Atmosphere