What is the main force by which most of the water within xylem vessels moves toward the top of a tree?
c. evaporation of water through stoma
In which plant cell or tissue would the pressure component of water potential most often be negative?
b. stem xylem
Water potential is generally most negative in which of the following parts of a plant?
a. mesophyll cells of the leaf
Which of the following is responsible for the cohesion of water molecules?
c. hydrogen bonds between the oxygen atom of one water molecule and a hydrogen atom of another water molecule
Transpiration in plants requires all of the following except
d. active transport through xylem cells.
Which of the following statements about transport in plants is false?
e. Gymnosperms can sometimes develop especially high root pressure, which may account for the rise of water in tall pine trees without transpiration pull.
Active transport would be least important in the normal functioning of which of the following plant tissue types?
b. stem xylem
Which of the following statements is false concerning the xylem?
d. Movement of materials is by mass flow; materials move owing to a turgor pressure gradient from "source" to "sink."
Xylem vessels, found in angiosperms, have a much greater internal diameter than tracheids, the only xylem conducting cells found in gymnosperms. The tallest living trees, redwoods, are gymnosperms. Which of the following is an advantage of tracheids over vessels for long-distance transport to great heights?
d. Only A and C are correct.
Water rises in plants primarily by the cohesion-tension model. Which of the following is not true about this model?
b. The "tension" of this model represents the excitability of the xylem cells.
Assume that a particular chemical interferes with the establishment and maintenance of proton gradients across the membranes of plant cells. All of the following processes would be directly affected by this chemical except
c. xylem transport.
Photosynthesis begins to decline when leaves wilt because
d. stomata close, preventing CO2 entry into the leaf.
The water lost during transpiration is an unfortunate side effect of the plant's exchange of gases. However, the plant derives some benefit from this water loss in the form of
d. A and B only
Ignoring all other factors, what kind of day would result in the fastest delivery of water and minerals to the leaves of a tree?
b. warm, dry day
If the guard cells and surrounding epidermal cells in a plant are deficient in potassium ions, all of the following would occur except
d. leaf temperatures would decrease.
The opening of stomata is thought to involve
a. an increase in the osmotic concentration of the guard cells.