Plant water relations involve the absorption of water, ascent of sap, loss of water by transpiration, and the internal water balance of the tree.
Water Properties
1. Polar molecule
2. Cohesion and adhesion
3. High specific heat
4. Density-greatest at 40C
5. Universal solvent of life
1. Polarity of Water
In water molecule, 2 hydrogen atoms form single polar covalent bonds with an oxygen atoms. because oxygen is more electronegative.
- the region around oxygen has a partial negative charge.
- the region near the two hydrogen atoms has a partial positive charge.
A water molecule is a polar molecule with opposite ends of the molecule with opposite charge.
Water has a variety of unusual properties because of attractions between these polar molecules.
- The slightly negative regions of one molecule are attracted to the slightly positive regions, forming a hydrogen bond.
The oxygen end "acts" negative while the hydrogen end "acts" positive. It causes the water to be POLAR.
2. Cohesion and Adhesion
Hydrogen bonding makes water cohesive and adhesive. Water is sticky because of H bonding.
Cohesion = water molecules are attracted to other water molecules.
Adhesion = water molecules are attracted to other substances.
Water molecules stick the walls of the xylem on the inside of the plant.
3. Specific Heat
Water has high specific heat. The amount of heat that must be absorbed or lost for 1.0 gram of a substance to change its temperature by 1 Celsius.
This is because water molecules are constrained by hydrogen bonding.
Moderates temperatures on Earth
- Water stabilizes air temperatures by absorbing heat from warmer air and releasing heat to cooler air.
- Water can absorb or release relatively large amounts of heat with only a slight change in its own temperature.
4. Density of Water
Water is less dense as a solid than as a liquid.
- At temperature above 4 Celsius, water expanding when it warm and contracting as it cools.
- At temperature 0 Celsius, water freezes and it forms a crystalline lattice because each water molecules has H bonding locked to four neighbors.
- The H bonds keep the molecules for enough apart.
5. Universal solvent of life
Water potential
Water potential is a useful measurements to determine water-deficit stress in plants. Water potential can affects plants in many ways.
a) Atmospheric water potential
- one of the factors that influences the rate of transpiration or water loss in plants.
b) Soil water potential
- influences the water available for uptake by plant roots.
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