Lecture 19: Plant-Water Relations - 11/15 Flashcards
What are 3 important physical properties of water?
Thermal capacity
Latent heat of fusion
Latent heat of vaporization
(high for all three)
Why are water’s 3 important physical properties useful?
Water is useful at regulating temperature changes
Why is water a universal solvent?
Because it is a polar molecule
How does water diffuse through solute?
When water (the solvent) is diluted with solute, it moves along the concentration gradient to establish equilibrium.
The solute does the same, producing a solution with equal concentrations of water and solute throughout
Cohesion
The sticking together of particles of the same substance. This property results from hydrogen bonding between molecules
Which is stronger: water-water cohesion or water-air attraction?
Water-water cohesion.
Thus, water tries to minimize the area of water-air contact, because it is the lowest energy configuration
Adhesion
The attraction of water molecules to a different molecule
How can you measure the degree to which water is attracted to a solid vs. to itself?
By measuring the contact angle of water with the solid.
On a hydrophilic substrate that water is more attracted to, it will have an angle < 90˚. On a hydrophobic substrate it isn’t attracted to, it will have an angle of > 90˚.
Capillarity
The tendency of a liquid in a capillary tube to rise or fall as a result of surface tension
Ψw (water potential)
The potential of water to do work or move
What water potential does pure water with no pressures acting on it have?
0
Does pure water move from high to low or low to high Ψ?
From high to low Ψ
Diffusion
The movement of molecules from regions of higher to lower concentration
Osmosis
Movement of a solvent (for example, water) across a membrane from a less concentrated solution to a more concentrated one
What does Ψs stand for?
Solute potential
What does Ψp stand for?
Pressure potential (sometimes called turgor pressure)
What is the relationship between Ψw, Ψs, and Ψp?
Ψw = Ψs + Ψp
How does the addition of solute affect water potential?
It lowers water potential. Solute potential is always equal to or less than 0
Is pressure potential positive or negative?
Always positive
When will a cell with a cell wall stop taking up water?
When the turgor/pressure potential equals the solute potential, making the Ψw = 0
What are the three ways plants move water?
Root pressure
Transpiration pull
Bulk flow
Root pressure
A force that helps to drive fluids upwards from the soil into the xylem
Transpiration pull
When water loss from the stomata creates a tension that is transmitted to the roots, facilitating water absorption from the soil
What are the different parts the xylem is made out of?
Tracheids and vessels, which form long tubes through which water is drawn into leaves
How do water’s properties enable it to be pulled up through a plant?
Due to water’s adhesive and cohesive properties.
Water adheres to the cellulose in the surrounding cell walls, while coheres with other water molecules through hydrogen bonding
What are the 4 types of cells that make up xylem?
Tracheids, vessel elements, fibers, and rays
Why is transpiration important for leaves?
Because water vaporization cools leaves
