Download Answers to End-of-Chapter Questions – Brooker et al ARIS site

Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 38
Test Yourself Questions
1. An aquaporin is?
a. a channel protein that allows the influx of K+ into cells, causing water to also flow in
between the phospholipids of a plasma membrane.
b. a type of blue-colored pore in the epidermal surfaces of plants.
c. a protein channel in plasma membranes that facilitate the diffusion of water.
d. a protein transporter in plasma membranes that use protons to cotransport water.
e. none of the above.
Answer: c. Aquaporins are protein channels in cell membranes that facilitate the diffusion of water.
2. Why is turgor pressure a property of plant cells?
a. Plant cells possess the necessary chloroplasts.
b. Plant cells possess a cell wall, necessary for formation of turgor.
c. Plant cells possess mitochondria, which provide the ATP needed for turgor.
d. All of the above.
e. None of the above.
Answer: b. The relatively rigid and strong plant cell wall is necessary for the buildup of turgor pressure.
3. How might plant cells avoid losing too much water in very cold, dry, or saline habitats?
a. They may balance the osmotic condition of their cytosol with that of the environment.
b. They may drop their leaves.
c. They may stabilize their membranes with sugars or dehydrin proteins.
d. They may produce more aquaporin water channels to take maximum advantage of
available moisture.
e. All of the above are possible.
Answer: e. Balancing osmotic conditions of the cytosol, leaf drop, membrane stabilization, and
producing more aquaporins are all examples of plant adaptations that help avoid water loss in very cold,
dry, or saline conditions.
4. What are ways in which plants accomplish tissue-level transport?
a. transmembrane transport of solutes from one cell to another
b. symplastic transport of materials from one cell to another via plasmodesmata
c. apoplastic transport of water and dissolved solutes through cell walls and intercellular
spaces
d. all of the above
e. none of the above
Answer: d. Plants accomplish tissue-level transport by means of transmembrane, symplastic, and
apoplastic transport.
5. A root endodermis is
a. an innermost layer of cortex cells that each display characteristic Casparian strips.
b. a layer of cells just inside the epidermis of a root.
c. a layer of cells just above the epidermis of a root.
d. a group of cells that occur within the root epidermis.
e. none of the above.
Answer: a. A root endodermis is the innermost layer of cortex cells, which each display a ribbon of waxy
material (the Casparian strip) in their cell walls.
6. Xylem loading is?
a. the process by which water from the air enters vascular tissues of the leaf.
b. the process by which sugar is transported via plasmodesmata directly into vessel elements.
c. the process by which sugar is transported directly into sieve-tube elements.
d. the process in which ions are transported across the membranes of root xylem parenchyma
into the xylem apoplast, followed by water.
e. none of the above.
Answer: d. Xylem loading is the process by which root xylem parenchyma cells transport ions and water
across their membranes into the xylem apoplast, which includes the vessel elements and tracheids.
7. What features of water explain how it can be drawn up a tall tree from roots to leaves?
a. cohesion, the result of extensive hydrogen-bonding
b. adhesion, water’s tendency to stick to surfaces such as the inner walls of tracheid and
vessels
c. high surface tension that develops when water evaporates from intercellular leaf spaces
d. all of the above
e. none of the above
Answer: d. Cohesion, adhesion, and surface tension are all important features of water than allow it to
be drawn up a tall tree.
8. What feature of terrestrial plants contributes to their ability to maintain relatively stable internal water
content?
a. a waxy surface cuticle
b. an extensive root system that mines water from soil
c. specialized water-conducting tissues composed of dead cells
d. epidermal pores that open and close
e. all of the above
Answer: e. Waxy cuticle, extensive root system, specialized conducting cells, and stomata all foster
stability of terrestrial plants’ water content.
9. What structural features of stomatal guard cells foster their ability to form an open pore in plant
epidermal surfaces?
a. thickened inner cell walls and radially oriented microfibrils
b. thickened outer cell walls and radially oriented microfibrils
c. thickened inner cell walls and longitudinal microfibrils
d. thickened outer cell walls and longitudinal microfibrils
e. uniform thickness of cell walls and randomly arranged microfibrils
Answer: a. Thickened inner cell walls and radially oriented cellulose microfibrils both foster the ability of
guard cells to form an open pore in plant epidermal surfaces when these cells are turgid.
10. What substances plug wounded sieve-tube elements, thereby preventing the leakage of phloem
sap?
a. X protein and callose
b. C protein and callose
c. P protein and callose
d. P protein and sucrose
e. None of the above
Answer: c. P protein plugs wounded sieve-tube elements in the short term, while callose forms a longerterm seal.
Conceptual Questions
1. Why is it a bad idea to overfertilize your houseplants? If the amount recommended on the package
is good, wouldn’t more be better?
Answer: In the case of plant fertilizers, more is not better, because the ion concentration of overfertilized
soil may become so high as to draw water from plant cells. In this case, the cells would be bathed in a
hypertonic solution and would likely lose water to the solution. If plant cells lose too much water, they
will die.
2. Why is it a bad idea for subsistence farmers (those barely able to grow enough crops to feed
themselves) to allow livestock to graze natural vegetation to the point that it disappears?
Answer: When the natural vegetation is removed, transpiration stops, so water is not transported from
the ground to the atmosphere, where it may be an important contributor to local rainfall. Extensive
removal of plants actually changes local climates in ways that reduce agricultural productivity and
human survival.
3. In the desert southwestern U.S., the ocotillo plant is often used as a landscaping plant, thanks to its
interesting shape and beautiful floral displays. Imagine that you are responsible for property
landscaped with ocotillo, but find the plants bare of leaves. Can you assume that the plants are
dead and need to be replaced?
Answer: No, you cannot assume that an ocotillo plant lacking leaves is dead, because this plant
responds to drought by shedding its leaves, and living plants can produce new leaves when the drought
stress is relieved. However, if the ocotillo plants do not produce new leaves after normal rainstorms, you
might suspect that they have died.
Experimental Questions
1. Why did the Holbrook team use the same plant to examine the effect of a pure water control and an
experimental, artificial xylem sap?
Answer: This design allowed them to compensate for variation among plants, which might have
influenced the results had they used separate plants for experiments and controls.
2. What caused water to flow from the source of artificial sap (or water) into the xylem of the plants
used in the experiment conducted by Holbrook and associates?
Answer: Transpiration! Water evaporating from the surfaces of leaves exerted a tension on the water
column of the xylem, pulling sap and water through it.
3. Why were sap flow rates the same in living and dead plants in the experiment conducted by the
Holbrook team?
Answer: The effects of ions on sap flow rates did not directly depend on a biological process, so xylem
sap of the same ionic concentration moved through dead plants at the same rate as in living plants.
Collaborative Questions
1. Imagine that you are part of a team that is assigned to determine what environmental conditions
best suit a new crop, so that the crop can be recommended to farmers in appropriate climate
regions. What features of the crop plants might you investigate?
Answer: You could experimentally determine how effectively your crop plants obtain water and soil
nutrient ions, and resistant your plant is to water loss under different simulated climate regimes. You
could measure the relative water content of plants grown under different conditions of soil moisture.
You might want to examine the extent of the root system, how thick the cuticle is, how responsive the
stomata are to drought conditions, and whether or not your crop can use root pressure to refill xylem
that has become embolized as the result of cold or drought. You might want to examine your crop for
its ability to balance cytoplasmic osmotic conditions with solutes and protect membranes from
plasmolysis damage.
2. Take a look outside or imagine a forest or grassland. What can you deduce about the availability of
soil water from the types of plants that occur?
Answer: If you see or imagine tall trees growing closely together, you can assume that soil moisture is
high on average, because trees transpire huge quantities of water obtained from the soil. If you see or
imagine abundant or low-growing plants, such as might occur in a grassland, you can deduce that soil
water is relatively low, but constant enough to prevent plant death. If you see or imagine a desert, with
relatively few plants visible, you can deduce that soil water is very low or sporadically available and that
the plants present likely have specific adaptations allowing them to cope with water stress.