QUESTION 1 Which of the following best describes the forces acting on water in t

Question

QUESTION 1

Which of the following best describes the forces acting on water in the xylem of a tall tree that is transpiring?

A-Positive pressure

B-Diffusion and osmosis

C- Capillary action

D-Cohesion and tension

QUESTION 2


In which plant cell or tissue of a transpiring tree would the pressure component of water potential most often be positive?

a- leaf mesophyll cell

b- stem xylem

c- sapwood

d- vessel element

QUESTION 3

In which plant cell or tissue would the solute component of water potential be clearly (ie substantially) negative?

A- leaf mesophyll cell

B- stem xylem

C- trachied

D- vessel element

QUESTION 4

Which of the following is an advantage of tracheids over vessels for long-distance transport to great heights (eg in tall conifers)?

A-Tracheids can transport water at higher rates than vessels.

B-Tracheids protect the tree against cavitation because the cohesive and adhesive properties of water are greater in narrow tubes than in wide tubes.

C-Tracheids protect the tree against cavitation because the cohesive and adhesive properties of water are greater in wide tubes than in narrow tubes.

D-Trachieds are living cells while vessel elements are not

QUESTION 5

You measure xylem pressure in two plants using the pressure chamber. In one, you apply 10 bars of pressure before you notice water coming from the xylem of your sample. In the other you apply 15 bars of pressure. Which plant is more water stressed? What is the pressure potential of the water stressed plant in MPa?

QUESTION 6

If (water potentional)P = 0.3 MPa and (water potentional)S = -0.45 MPa, the resulting (water potentional)W is ...

QUESTION 7

Solute and pressure potential is measured in two different places in the same plant. Fill in the table below with plausible numbers (based on physiological principles). (Note: the plant is healthy and well-watered).

Solute (osmotic) Potential

(water potentional)s
(MPa)

Pressure Potential

(water potentional)p

(MPa)

Total water potential

(water potentional)w

(MPa)

Xylem in the stem

0.0

Root cell

- 1.4

QUESTION 8

A researcher measures a carbon isotopic ratio (?13C) of -28 in a needle near the bottom or the tree. Which value would you expect from a needle near the top of the tree?

A- +28

B- -22

C- -34

D- 0

QUESTION 9

Briefly describe what happens in the xylem when cavitation due to water stress occurs. Mention one structural feature of xylem in conifers that protects against cavitation. (3 - 5 sentences).   

A-Positive pressure

B-Diffusion and osmosis

C- Capillary action

D-Cohesion and tension

Explanation / Answer

1). d

2). c

3). d

4). a

9).

Soil water enters the root through its epidermis. It appears that water then travels in both

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