Lecture 19: Plant-Water Relations - 11/15

Question 1

What are 3 important physical properties of water?

Answer 1

Thermal capacity
Latent heat of fusion
Latent heat of vaporization
(high for all three)

Question 2

Why are water’s 3 important physical properties useful?

Answer 2

Water is useful at regulating temperature changes

Question 3

Why is water a universal solvent?

Answer 3

Because it is a polar molecule

Question 4

How does water diffuse through solute?

Answer 4

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

Question 5

Cohesion

Answer 5

The sticking together of particles of the same substance. This property results from hydrogen bonding between molecules

Question 6

Which is stronger: water-water cohesion or water-air attraction?

Answer 6

Water-water cohesion.

Thus, water tries to minimize the area of water-air contact, because it is the lowest energy configuration

Question 7

Adhesion

Answer 7

The attraction of water molecules to a different molecule

Question 8

How can you measure the degree to which water is attracted to a solid vs. to itself?

Answer 8

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˚.

Question 9

Capillarity

Answer 9

The tendency of a liquid in a capillary tube to rise or fall as a result of surface tension

Question 10

Ψw (water potential)

Answer 10

The potential of water to do work or move

Question 11

What water potential does pure water with no pressures acting on it have?

Answer 11

0

Question 12

Does pure water move from high to low or low to high Ψ?

Answer 12

From high to low Ψ

Question 13

Diffusion

Answer 13

The movement of molecules from regions of higher to lower concentration

Question 14

Osmosis

Answer 14

Movement of a solvent (for example, water) across a membrane from a less concentrated solution to a more concentrated one

Question 15

What does Ψs stand for?

Answer 15

Solute potential

Question 16

What does Ψp stand for?

Answer 16

Pressure potential (sometimes called turgor pressure)

Question 17

What is the relationship between Ψw, Ψs, and Ψp?

Answer 17

Ψw = Ψs + Ψp

Question 18

How does the addition of solute affect water potential?

Answer 18

It lowers water potential. Solute potential is always equal to or less than 0

Question 19

Is pressure potential positive or negative?

Answer 19

Always positive

Question 20

When will a cell with a cell wall stop taking up water?

Answer 20

When the turgor/pressure potential equals the solute potential, making the Ψw = 0

Question 21

What are the three ways plants move water?

Answer 21

Root pressure
Transpiration pull
Bulk flow

Question 22

Root pressure

Answer 22

A force that helps to drive fluids upwards from the soil into the xylem

Question 23

Transpiration pull

Answer 23

When water loss from the stomata creates a tension that is transmitted to the roots, facilitating water absorption from the soil

Question 24

What are the different parts the xylem is made out of?

Answer 24

Tracheids and vessels, which form long tubes through which water is drawn into leaves

Question 25

How do water’s properties enable it to be pulled up through a plant?

Answer 25

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

Question 26

What are the 4 types of cells that make up xylem?

Answer 26

Tracheids, vessel elements, fibers, and rays

Question 27

Why is transpiration important for leaves?

Answer 27

Because water vaporization cools leaves