45) 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
A) photosynthesis.
B) phloem loading.
C) xylem transport.
D) cellular respiration.
E) stomatal opening.
46) Which cells in a root form a protective barrier to the vascular system where all materials must move
through the symplast?
A) pericycle
B) cortex
C) epidermis
D) endodermis
E) exodermis
47) Guard cells do which of the following?
A) protect the endodermis
B) accumulate K+ and close the stomata
C) contain chloroplasts that import K+ directly into the cells
D) guard against mineral loss through the stomata
E) help balance the photosynthesis-transpiration compromise
48) All of the following normally enter the plant through the roots except
A) carbon dioxide.
B) nitrogen.
C) potassium.
D) water.
E) calcium.
49) Photosynthesis begins to decline when leaves wilt because
A) chloroplasts within wilted leaves are incapable of photosynthesis.
B) CO2 accumulates in the leaves and inhibits the enzymes needed for photosynthesis.
C) there is insufficient water for photolysis during the light reactions.
D) stomata close, restricting CO2 entry into the leaf.
E) wilted leaves cannot absorb the red and blue wavelengths of light.
50) The water lost during transpiration is a side effect of the plant’s exchange of gases. However, the
plant derives some benefit from this water loss in the form of
A) evaporative cooling.
B) mineral transport.
C) increased turgor.
D) increased growth,
E) only evaporative cooling and mineral transport.
51) Ignoring all other factors, what kind of day would result in the fastest delivery of water and minerals
to the leaves of a tree?
A) cool, dry day
B) warm, dry day
C) warm, humid day
D) cool, humid day
E) very hot, dry, windy day
52) If the guard cells and surrounding epidermal cells in a plant are deficient in potassium ions, all of the
following would occur except
A) photosynthesis would decrease.
B) roots would take up less water.
C) phloem transport rates would decrease.
D) leaf temperatures would decrease.
E) stomata would be closed.
53) The opening of stomata is thought to involve
A) an increase in the solute concentration of the guard cells.
B) a decrease in the solute concentration of the stoma.
C) active transport of water out of the guard cells.
D) decreased turgor pressure in guard cells.
E) movement of K+ from the guard cells.
54) Which of the following experimental procedures would most likely reduce transpiration while
allowing the normal growth of a plant?
A) subjecting the leaves of the plant to a partial vacuum
B) increasing the level of carbon dioxide around the plant
C) putting the plant in drier soil
D) decreasing the relative humidity around the plant
E) injecting potassium ions into the guard cells of the plant
55) Guard cells are the only cells in the epidermis that contain chloroplasts and can undergo
photosynthesis. This is important because
A) chloroplasts sense when light is available so that guard cells will open.
B) photosynthesis provides the energy necessary for contractile proteins to flex and open the guard cells.
C) guard cells will produce the O2 necessary to power active transport.
D) ATP is required to power proton pumps in the guard cell membranes.
E) chloroplasts sense when light is available so that guard cells will open and guard cells will produce
the O2 necessary to power active transport.
56) All of the following are adaptations that help reduce water loss from a plant except
A) transpiration.
B) sunken stomata.
C) C4 photosynthesis.
D) small, thick leaves.
E) crassulacean acid metabolism.
57) Which of the following best explains why very few CAM plants are tall?
A) They have difficulty moving water and minerals to the top of the plant during the day.
B) They would be unable to supply sufficient sucrose for active transport of minerals into the roots
during the day or night.
C) Transpiration occurs only at night, and this would cause a highly negative Ψ in the roots of a tall
plant during the day.
D) Since the stomata are closed in the leaves, the Casparian strip is closed in the endodermis of the root.
E) With the stomata open at night, the transpiration rate would limit plant height.
58) As a biologist, it is your job to look for plants that have evolved structures with a selective
advantage in dry, hot conditions. Which of the following adaptations would be least likely to meet your
objective?
A) CAM plants that grow rapidly
B) small, thick leaves with stomata on the lower surface
C) a thick cuticle on fleshy leaves
D) large, fleshy stems with the ability to carry out photosynthesis
E) plants that do not produce abscisic acid and have a short, thick taproot
59) A primary result for stomatal closure on a hot, dry day would be
A) release of K+ ions to the apoplast and subsidiary cells.
B) displacement of Ca++ ions from the thick inner walls of the guard cells.
C) disassembly of the microfibrils in the cell walls of the subsidiary cells.
D) upregulation of aquaporin synthesis.
E) downregulation of extension proteins.
60) What is the driving force for the movement of solutes in the phloem of plants?
A) gravity
B) a difference in water potential (Ψ) between the source and the sink
C) root pressure
D) transpiration of water through the stomata
E) adhesion of water to phloem sieve tubes
61) Phloem transport of sucrose is often described as going from source to sink. Which of the following
would not normally function as a sink?
A) growing leaf
B) growing root
C) storage organ in summer
D) mature leaf
E) shoot tip
62) Which of the following is a correct statement about sugar movement in phloem?
A) Diffusion can account for the observed rates of transport.
B) Movement can occur both upward and downward in the plant.
C) Sugar is translocated from sinks to sources.
D) Only phloem cells with nuclei can perform sugar movement.
E) Sugar transport does not require energy.
63) Phloem transport is described as being from source to sink. Which of the following would most
accurately complete this statement about phloem transport as applied to most plants in the late spring?
Phloem transports ________ from the ________ source to the ________ sink.
A) amino acids; root; mycorrhizae
B) sugars; leaf; apical meristem
C) nucleic acids; flower; root
D) proteins; root; leaf
E) sugars; stem; root
64) Arrange the following five events in an order that explains the mass flow of materials in the phloem.
1. Water diffuses into the sieve tubes.
2. Leaf cells produce sugar by photosynthesis.
3. Solutes are actively transported into sieve tubes.
4. Sugar is transported from cell to cell in the leaf.
5. Sugar moves down the stem.
A) 2, 1, 4, 3, 5
B) 1, 2, 3, 4, 5
C) 2, 4, 3, 1, 5
D) 4, 2, 1, 3, 5
E) 2, 4, 1, 3, 5
65) Water flows into the source end of a sieve tube because
A) sucrose has diffused into the sieve tube, making it hypertonic.
B) sucrose has been actively transported into the sieve tube, making it hypertonic.
C) water pressure outside the sieve tube forces in water.
D) the companion cell of a sieve tube actively pumps in water.
E) sucrose has been transported out of the sieve tube by active transport.
66) Which one of the following statements about transport of nutrients in phloem is false?
A) Solute particles can be actively transported into phloem at the source.
B) Companion cells control the rate and direction of movement of phloem sap.
C) Differences in osmotic concentration at the source and sink cause a hydrostatic pressure gradient to
be formed.
D) A sink is that part of the plant where a particular solute is consumed or stored.
E) A sink may be located anywhere in the plant.
67) According to the pressure flow hypothesis of phloem transport,
A) solute moves from a high concentration in the source to a lower concentration in the sink.
B) water is actively transported into the source region of the phloem to create the turgor pressure
needed.
C) the combination of a high turgor pressure in the source and transpiration water loss from the sink
moves solutes through phloem conduits.
D) the formation of starch from sugar in the sink increases the osmotic concentration.
E) the pressure in the phloem of a root is normally greater than the pressure in the phloem of a leaf.
68) Plants do not have a circulatory system like that of some animals. If a water molecule did “circulate”
(that is, go from one point in a plant to another and back in the same day), it would require the activity
of
A) only the xylem.
B) only the phloem.
C) only the endodermis.
D) both the xylem and the endodermis.
E) both the xylem and the phloem.
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69) Long-distance electrical signaling in the phloem has been shown to elicit a change in all of the
following except
A) rapid leaf movement.
B) gene transcription.
C) a switch from C4 to C3 photosynthesis.
D) gene transcription.
E) phloem unloading.
70) Plasmodesmata can change in number, and when dilated can provide a passageway for
A) macromolecules such as RNA and proteins.
B) ribosomes.
C) chloroplasts.
D) mitochondria.
E) cytoskeletal components.
Art Question
The following photo shows a strawberry leaf displaying guttation. Answer the following question
regarding guttation.
71) What is the main cause of guttation in plants?
A) root pressure
B) transpiration
C) pressure flow in phloem
D) plant injury
E) condensation of atmospheric water
Scenario Questions
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72) A fellow student brought in a leaf to be examined. The leaf was dark green, thin, had stoma on the
lower surface only, and had a total surface area of 10 square meters. Where is the most likely
environment where this leaf was growing?
A) a dry, sandy region
B) a large, still pond
C) a tropical rain forest
D) an oasis within a grassland
E) the floor of a deciduous forest
73) Several tomato plants are growing in a small garden plot. If soil water potential were to drop
significantly on a hot summer afternoon, which of the following would most likely occur?
A) Stomatal apertures would decrease.
B) Transpiration would increase.
C) The leaves would become more turgid.
D) The uptake of CO2 would be enhanced.
E) The proton gradient would dissipate.
End-of-Chapter Questions
The following questions are from the end-of–chapter “Test Your Understanding” section in Chapter 36
of the textbook.
74) The symplast transports all of the following except
A) sugars.
B) mRNA.
C) DNA.
D) proteins.
E) viruses.
75) Which of the following is an adaptation that enhances the uptake of water and minerals by roots?
A) mycorrhizae
B) cavitation
C) active uptake by vessel elements
D) rhythmic contractions by cortical cells
E) pumping through plasmodesmata
76) Which structure or compartment is part of the symplast?
A) the interior of a vessel element
B) the interior of a sieve tube
C) the cell wall of a mesophyll cell
D) an extracellular air space
E) the cell wall of a root hair
77) Movement of phloem sap from a source to a sink
A) occurs through the apoplast of sieve-tube elements.
B) depends ultimately on the activity of proton pumps.
C) depends on tension, or negative pressure potential.
D) depends on pumping water into sieve tubes at the source.
E) results mainly from diffusion.
78) Photosynthesis ceases when leaves wilt, mainly because
A) the chlorophyll in wilting leaves is degraded.
B) flaccid mesophyll cells are incapable of photosynthesis.
C) stomata close, preventing CO2 from entering the leaf.
D) photolysis, the water-splitting step of photosynthesis, cannot occur when there is a water deficiency.
E) accumulation of CO2 in the leaf inhibits enzymes.
79) What would enhance water uptake by a plant cell?
A) decreasing the Ψ of the surrounding solution
B) increasing the pressure exerted by the cell wall
C) the loss of solutes from the cell
D) increasing the Ψ of the cytoplasm
E) positive pressure on the surrounding solution
80) A plant cell with a ΨS of -0.65 MPa maintains a constant volume when bathed in a solution that has
a ΨS of -0.30 MPa and is in an open container. The cell has a
A) ΨP of +0.65 MPa.
B) Ψ of -0.65 MPa.
C) ΨP of +0.35 MPa.
D) ΨP of +0.30 MPa.
E) Ψ of 0 MPa.
81) Compared with a cell with few aquaporins in its membrane, a cell containing many aquaporins will
A) have a faster rate of osmosis.
B) have a lower water potential.
C) have a higher water potential.
D) have a faster rate of active transport.
E) accumulate water by active transport.
82) Which of the following would tend to increase transpiration?
A) a rainstorm
B) sunken stomata
C) a thicker cuticle
D) higher stomatal density
E) spiny leaves