) Charles and Francis Darwin concluded from their experiments on phototropism by grass
seedlings that the part of the seedling that detects the direction of light is the
A) tip of the coleoptile.
B) part of the coleoptile that bends during the response.
C) base of the coleoptile.
D) cotyledon.
E) phytochrome in the leaves.

A

Plants growing in a partially dark environment will grow toward light in a response called
phototropism. Choose the incorrect statement regarding phototropism.
A) It is caused by a chemical signal.
B) One chemical involved is auxin.
C) Auxin causes a growth increase on one side of the stem.
D) Auxin causes a decrease in growth on the side of the stem exposed to light.
E) Removing the apical meristem prevents phototropism.

D

Which of these conclusions is supported by the research of both Went and Charles and
Francis Darwin on shoot responses to light?
A) When shoots are exposed to light, a chemical substance migrates toward the light.
B) Agar contains a chemical substance that mimics a plant hormone.
C) A chemical substance involved in shoot bending is produced in shoot tips.
D) Once shoot tips have been cut, normal growth cannot be induced.
E) Light stimulates the synthesis of a plant hormone that responds to light.

C

We know from the experiments of the past that plants bend toward light because
A) they need sunlight energy for photosynthesis.
B) the sun stimulates stem growth.
C) cell expansion is greater on the dark side of the stem.
D) auxin is inactive on the dark side of the stem.
E) phytochrome stimulates florigen production.

C

Which of the following is not presently considered a major mechanism whereby hormones
control plant development?
A) affecting cell respiration via regulation of the citric acid cycle
B) affecting cell division via the cell cycle
C) affecting cell elongation through acid growth
D) affecting cell differentiation through altered gene activity
E) mediating short-term physiological responses to environmental stimuli

A

Evidence for phototropism due to the asymmetric distribution of auxin moving down the
stem
A) has not been found in eudicots such as sunflower and radish.
B) has been found in all monocots and most eudicots.
C) has been shown to involve only IAA stimulation of cell elongation on the dark side of
the stem.
D) can be demonstrated with unilateral red light, but not blue light.
E) is now thought by most plant scientists not to involve the shoot tip

A

According to modern ideas about phototropism in plants,
A) light causes auxin to accumulate on the shaded side of a plant stem.
B) auxin stimulates elongation of plant stem cells.
C) auxin is produced by the tip of the coleoptile and moves downward.
D) A and B only
E) A, B and C

E

A plant seedling bends toward sunlight because
A) auxin migrates to the lower part of the stem due to gravity.
B) there is more auxin on the light side of the stem.
C) auxin is destroyed more quickly on the dark side of the stem.
D) auxin is found in greatest abundance on the dark side of the stem.
E) gibberellins produced at the stem tip cause phototropism.

D

The apical bud of a pine tree inhibits the growth of lateral buds through the production of
A) abscisic acid.
B) ethylene.
C) cytokinin.
D) gibberellin.
E) auxin

E

After some time, the tip of a plant that has been forced into a horizontal position grows
upward. This phenomenon is related to
A) light.
B) whether the plant is in the northern or southern hemisphere.
C) gibberellin production by stems.
D) auxin production in roots.
E) auxin movement toward the lower side of the stem.

E

) Negative gravitropism of plant shoots
A) depends upon auxin distribution.
B) depends upon the aggregation of statoliths.
C) results from relatively rapid elongation of some stem cells.
D) A and B only
E) A, B and C

E

The ripening of fruit and the dropping of leaves and fruit are principally controlled by
A) auxins
B) cytokinins
C) indole acetic acid
D) ethylene
E) carbon dioxide concentration (in air)

D

) Which one of the following is not a direct function of either auxin or gibberellin?
A) inducing semescence and ripening
B) producing apical dominance
C) producing positive geotropism of shoots
D) stimulating cell elongation
E) breaking dormancy in seeds

A

Which of the following statements about plant hormones is false?
A) The growth of plants in nature is probably regulated by a combination of
growth-stimulating and growth-inhibiting hormones.
B) Abscisic acid generally promotes growth.
C) Gibberellins stimulate cell enlargement.
D) Cytokinins promote cell division.
E) Ethylene contributes to the aging of plants.

B

The plant hormone involved in aging and ripening of fruit is
A) auxin.
B) ethylene.
C) florigen.
D) abscisic acid.
E) gibberellin.

B

When growing plants in culture, IAA is used to stimulate cell enlargement. Which plant
growth regulator has to now be added to stimulate cell division?
A) ethylene
B) indoleacetic acid
C) gibberellin
D) cytokinin
E) abscisic acid

D

Why do coleoptiles grow toward light?
A) Auxin is destroyed by light.
B) Gibberellins are destroyed by light.
C) Auxin synthesis is stimulated in the dark.
D) Auxin moves away from the light to the shady side.
E) Gibberellins move away from the light to the shady side.

D

Plant growth regulators can be characterized by all of the following except that they
A) may act by altering gene expression.
B) have a multiplicity of effects.
C) function independently of other hormones.
D) control plant growth and development.
E) affect division, elongation, and differentiation of cells.

C

) Plant hormones produce their effects by
A) altering the expression of genes.
B) modifying the permeability of the plasma membrane.
C) modifying the structure of the nuclear envelope membrane.
D) both A and B
E) B and C only

D

Why might animal hormones function differently from plant hormones?
A) Animals move rapidly away from negative stimuli, and most plants donʹt.
B) Plant cells have a cell wall that blocks passage of many hormones.
C) Plants must have more precise timing of their reproductive activities.
D) Plants are much more variable in their morphology and development than animals.
E) Both A and D are correct.

E

Buds and sprouts often form on tree stumps. Which of the following hormones would you
expect to stimulate their formation?
A) auxin
B) cytokinins
C) abscisic acid
D) ethylene
E) gibberellins

B

Plant hormones can have different effects at different concentrations. This explains how
A) some plants are long-day plants and others are short-day plants.
B) signal transduction pathways in plants are different from those in animals.
C) plant genes recognize pathogen genes.
D) auxin can stimulate cell elongation in apical meristems, yet will inhibit the growth of
axillary buds.
E) they really donʹt fit the definition of ʺhormone.ʺ

D

Auxins (IAA) in plants are known to affect all of the following phenomena except
A) geotropism of shoots.
B) maintenance of dormancy.
C) phototropism of shoots.
D) inhibition of lateral buds.
E) fruit development.

B

How does indoleacetic acid affect fruit development?
A) preventing pollination
B) inhibiting formation of the ovule
C) promoting gene expression in cambial tissue
D) promoting rapid growth of the ovary
E) inducing the formation of brassinosteroids

D

) Oat seedlings are sometimes used to study auxins because
A) they are a readily accessible monocot, and auxins affect only monocots.
B) they have a stiff coleoptile.
C) they green rapidly in the light.
D) their coleoptile exhibits a strong positive phototropism.
E) monocots inactivate synthetic auxins.

D

Auxin triggers the acidification of cell walls that results in rapid growth, but also stimulates
sustained, long-term cell elongation. What best explains how auxin brings about this dual
growth response?
A) Auxin binds to different receptors in different cells.
B) Different concentrations of auxin have different effects.
C) Auxin causes second messengers to activate both proton pumps and certain genes.
D) The dual effects are due to two different auxins.
E) Other antagonistic hormones modify auxinʹs effectS

C

Which plant hormones might be used to enhance stem elongation and fruit growth?
A) brassinosteroids and oligosaccharides
B) auxins and gibberellins
C) abscisic acid and phytochrome
D) ethylene and cytokinins
E) phytochrome and flowering hormone

B

Which of the following has not been established as an aspect of auxinʹs role in cell
elongation?
A) Auxin instigates a loosening of cell wall fibers.
B) Auxin increases the quantity of cytoplasm in the cell.
C) Through auxin activity, vacuoles increase in size.
D) Auxin activity permits an increase in turgor pressure.
E) Auxin stimulates proton pumps.

B

Cells elongate in response to auxin. All of the following are part of the acid growth
hypothesis except
A) Auxin stimulates proton pumps in cell membranes.
B) Lowered pH results in the breakage of cross-links between cellulose microfibrils.
C) The wall fabric becomes looser (more plastic).
D) Auxin-activated proton pumps stimulate cell division in meristems.
E) The turgor pressure of the cell exceeds the restraining pressure of the loosened cell
wall, and the cell takes up water and elongates.

D

According to the acid growth hypothesis, auxin works by
A) dissolving sieve plates, permitting more rapid transport of nutrients.
B) dissolving the cell membranes temporarily, permitting cells that were on the verge of
dividing to divide more rapidly.
C) changing the pH within the cell, which would permit the electron transport chain to
operate more efficiently.
D) increasing wall plasticity and allowing the affected cell walls to elongate.
E) greatly increasing the rate of deposition of cell wall material.

D

Which of the following hormones would be most useful in promoting the rooting of plant
cuttings?
A) oligosaccharins
B) abscisic acid
C) cytokinins
D) gibberellins
E) auxins

E

Which plant hormone(s) is (are) most closely associated with cell division?
A) ethylene
B) cytokinin
C) abscisic acid
D) phytochrome
E) brassinosteroids

B

A

The synthesis of which of the following hormones would be a logical first choice in an
attempt to produce normal growth in mutant dwarf plants?
A) indoleacetic acid
B) cytokinin
C) gibberellin
D) abscisic acid
E) ethylene

C

The results of this experiment, shown on the left of the graph (area A), may be used to
A) show that these plants can live without gibberellin.
B) show that gibberellin is necessary in positive gravitropism.
C) show that taller plants with more gibberellin produce fruit (pods).
D) show a correlation between plant height and gibberellin concentration.
E) study phytoalexins in plants.

D

This experiment suggests that the unknown amount of gibberellin in the experimental plant
(B) is approximately
A) zero.
B) 0.01 μg/mL.
C) 0.1 μg/mL.
D) 1.0 μg/mL.
E) equal to the amount of gibberellin in the shortest plant.

C

One effect of gibberellins is to stimulate cereal seeds to produce
A) RuBP carboxylase.
B) lipids.
C) abscisic acid.
D) starch.
E) amylase

E

In attempting to make a seed break dormancy, one logically could treat it with
A) IAA.
B) 2, 4-D.
C) CO2.
D) gibberellins.
E) abscisic acid.

D

Ethylene, as an example of a plant hormone, may have multiple effects on a plant,
depending on all of the following except the
A) site of action within the plant.
B) developmental stage of the plant.
C) concentration of ethylene.
D) altered chemical structure of ethylene from a gas to a liquid.
E) readiness of cell membrane receptors for the ethylene.

D

If you were shipping green bananas to a supermarket thousands of miles away, which of
the following chemicals would you want to eliminate from the plantsʹ environment?
A) CO2
B) cytokinins
C) ethylene
D) auxin
E) gibberellic acids

C

Which of the following is currently the most powerful method of research on plant
hormones?
A) comparing of photoperiodic responses
B) comparing tropisms with turgor movements
C) subjecting plants to unusual stresses
D) studying phytochromes
E) analyzing mutant plants

E

We tend to think of plants as immobile when, in fact, they can move in many ways. All of
the following are movements plants can accomplish except
A) growth movements up or down in response to gravity.
B) folding and unfolding of leaves using muscle-like tissues.
C) growth movements toward or away from light.
D) changes in plant growth form in response to wind or touch.
E) rapid responses using action potentials similar to those found in the nervous tissue of
animals.

B

Auxin is responsible for all of the following plant growth responses except
A) phototropism.
B) formation of adventitious roots.
C) apical dominance.
D) the detection of photoperiod.
E) cell elongation

D

Incandescent light bulbs, which have high output of red light, are least effective in
promoting
A) photosynthesis.
B) seed germination.
C) phototropism.
D) flowering.
E) entrainment of circadian rhythms.

C

) Both red and blue light are involved in
A) stem elongation.
B) photoperiodism.
C) positive phototropism.
D) tracking seasons.
E) all of the above

A

) Seed packets give a recommended planting depth for the enclosed seeds. The most likely
reason some seeds are to be covered with only 1/4 inch of soil is that the
A) seedlings do not produce a hypocotyl.
B) seedlings do not have an etiolation response.
C) seeds require light to germinate.
D) seeds require a higher temperature to germinate.
E) seeds are very sensitive to waterlogging

C

A short-day plant will flower only when
A) days are shorter than nights.
B) days are shorter than a certain critical value.
C) nights are shorter than a certain critical value.
D) nights are longer than a certain critical value.
E) days and nights are of equal length.

D

A flash of red light followed by a flash of far-red light given during the middle of the night
to a short-day plant will likely
A) cause increased flower production.
B) have no effect upon flowering.
C) inhibit flowering.
D) stimulate flowering.
E) convert florigen to the active form

B

Many plants flower in response to day-length cues. Which statement concerning flowering
is false?
A) As a rule, short-day plants flower in the spring or fall.
B) As a rule, long-day plants flower in the summer.
C) Long-day plants flower in response to long days, not short nights.
D) Flowering in day-neutral plants is not influenced by day length.
E) Flowering in short-day plants is controlled by photochrome.

C

Which of the following does not reduce the level of the Pfr form of phytochrome?
A) exposure to far-red light
B) exposure to red light
C) long dark period
D) destruction of phytochrome
E) synthesis of phosphorylating enzymes

B

) Most plants close their stomata at night. What color of light would be most effective in
promoting stomatal opening in the middle of the night?
A) red
B) far-red
C) blue
D) red followed by far-red
E) far-red followed by blue

C

The houseplants in a windowless room with only fluorescent lights begin to grow tall and
leggy. Which of the following treatments would promote more normal growth?
A) Leave the lights on at night as well as during the day.
B) Add additional fluorescent tubes to increase the light output.
C) Add some incandescent bulbs to increase the amount of red light.
D) Set a timer to turn on the lights for 5 minutes during the night.
E) Turn off the lights for 5 minutes during the day.

C

) In legumes, it has been shown that ʺsleepʺ movements are correlated with
A) positive thigmotropisms.
B) rhythmic opening and closing of K+ channels in motor cell membranes.
C) senescence (the aging process in plants).
D) flowering and fruit development.
E) ABA-stimulated closing of guard cells caused by loss of K+.

B

Biological clocks cause organisms to perform daily activities on a regular basis. Which of
the following is a false statement about this kind of ʺcircadian rhythmʺ?
A) It may have the same signal transduction pathway in all organisms.
B) It must be reset on a daily basis.
C) It may help to cause photoperiodic responses.
D) Once set, it is independent of external signals.
E) The exact mechanism of biological clocks remains unknown

D

The biological clock controlling circadian rhythms must ultimately
A) depend on environmental cues.
B) affect gene transcription.
C) stabilize on a 24-hour cycle.
D) speed up or slow down with increasing or decreasing temperature.
E) do all of the above.

B

Plants often use changes in day length (photoperiod) to trigger events such as dormancy
and flowering. It is logical that plants have evolved this mechanism because photoperiod
changes
A) are more predictable than air temperature changes.
B) alter the amount of energy available to the plant.
C) are modified by soil temperature changes.
D) can reset the biological clock.
E) are correlated with moisture availability

A

If the range of a species of plants expands to a higher latitude, which of the following
processes is the most likely to be modified by natural selection?
A) circadian rhythm
B) photoperiodic response
C) phototropic response
D) biological clock
E) thigmomorphogenesis

B

In nature, poinsettias bloom in early March. Research has shown that the flowering process
is triggered three months before blooming occurs. In order to make poinsettias bloom in
December, florists change the length of the light-dark cycle in September. Given the
information and clues above, which of the following is a false statement about poinsettias?
A) They are short-day plants.
B) They require a light period shorter than some set maximum.
C) They require a longer dark period than is available in September.
D) The dark period can be interrupted without affecting flowering.
E) They will flower even if there are brief periods of dark during the daytime.

D

A botanist exposed two groups of the same plant species to two photoperiods–one with 14
hours of light and 10 hours of dark and the other with 10 hours of light and 14 hours of
dark. Under the first set of conditions, the plants flowered, but they failed to flower under
the second set of conditions. Which of the following conclusions would be consistent with
these results?
A) The critical night length is 14 hours.
B) The plants are short-day plants.
C) The critical day length is 10 hours.
D) The plants can convert phytochrome to florigen.
E) The plants flower in the spring

E

What does a short-day plant need in order to flower?
A) a burst of red light in the middle of the night
B) a burst of far-red light in the middle of the night
C) a day that is longer than a certain length
D) a night that is longer than a certain length
E) a higher ratio of Pr to Pfr.

D

If a short-day plant has a critical night length of 15 hours, then which of the following
24-hour cycles will prevent flowering?
A) 8 hours light/16 hours dark
B) 4 hours light/20 hours dark
C) 6 hours light/2 hours dark/light flash/16 hours dark
D) 8 hours light/8 hours dark/light flash/8 hours dark
E) 2 hours light/20 hours dark/2 hours light

D

A long-day plant will flower if
A) the duration of continuous light exceeds a critical length.
B) the duration of continuous light is less than a critical length.
C) the duration of continuous darkness exceeds a critical length.
D) the duration of continuous darkness is less than a critical length.
E) it is kept in continuous far-red light.

D

Plants that have their flowering inhibited by being exposed to bright lights at night are
A) day-neutral plants.
B) short-night plants.
C) devoid of phytochrome.
D) short-day plants.
E) long-day plants.

D

) Plants that have their flowering inhibited by being exposed to bright lights at night are
A) day-neutral plants.
B) short-night plants.
C) devoid of phytochrome.
D) short-day plants.
E) long-day plants.

D

Classic experiments suggested that a floral stimulusFlorigencould move across a graft
from an induced plant to a noninduced plant and trigger flowering. Recent evidence using
Arabidopsis has recently shown that florigen is probably
A) a phytochrome molecule that is activated by red light.
B) a protein that is synthesized in leaves and travels to the shoot apical meristem and
initiates flowering.
C) a membrane signal that travels through the symplast from leaves to buds.
D) a second messenger that induces Ca++ ions to change membrane potential.
E) a transcription factor that controls the activation of florigen specific genes.

B

In general, which of the following is not a plant response to herbivores?
A) domestication, so that humans can protect the plant
B) attracting predatory animals, such as parasitoid wasps
C) chemical defenses, such as toxic compounds
D) physical defenses, such as thorns
E) production of volatile molecules

A

) In order for a plant to initiate chemical responses to herbivory,
A) the plant must be directly attacked by an herbivore.
B) volatile ʺsignalʺ compounds must be perceived.
C) gene-for-gene recognition must occur.
D) phytoalexins must be released.
E) all of the above must happen.

B

Plants are affected by an array of pathogens. Which of the following is not a plant defense
against disease?
A) cells near the point of infection destroying themselves to prevent the spread of the
infection
B) production of chemicals that kill pathogens
C) acquiring gene-for-gene recognition that allows specific proteins to interact so that
the plant can produce defenses against the pathogen
D) a waxy cuticle that pathogens have trouble penetrating
E) All of the above are plant defenses against disease.

E

A pathogenic fungus invades a plant. What does the infected plant produce in response to
the attack?
A) antisense RNA
B) phytoalexins
C) phytochrome
D) statoliths
E) thickened cellulose microfibrils in the cell wall

B

) Which of the following are defenses that some plants use against herbivory?
A) production of the unusual amino acid canavanine
B) release of volatile compounds that attract parasitoid wasps
C) association of plant tissues with mycorrhizae
D) A and B only
E) A, B, and C

D

The transduction pathway that activates systemic acquired resistance in plants is initially
signaled by
A) antisense RNA.
B) Pfr phytochrome.
C) salicylic acid.
D) abscisic acid.
E) red, but not far-red, light.

C

Which of the following are examples or parts of plantsʹ systemic acquired resistance against
infection?
A) phytoalexins
B) salicylic acid
C) alarm hormones
D) A and B only
E) A, B, and C

E

A plant will recognize a pathogenic invader
A) if it has many specific plant disease resistance (R) genes.
B) when the pathogen has an R gene complementary to the plantʹs antivirulence (Avr)
gene.
C) only if the pathogen and the plant have the same R genes.
D) if it has the specific R gene that corresponds to the pathogen molecule encoded by an
Avr gene.
E) when the pathogen secretes Avr protein.

D

What is the probable role of salicylic acid in the defense responses of plants?
A) destroy pathogens directly
B) activate systemic acquired resistance of plants
C) close stomata, thus preventing the entry of pathogens
D) activate heat-shock proteins
E) sacrifice infected tissues by hydrolyzing cells

B

When an arborist prunes a limb off a valuable tree, he or she usually paints the cut surface.
The primary purpose of the paint is to
A) minimize water loss by evaporation from the cut surface.
B) improve the appearance of the cut surface.
C) stimulate growth of the cork cambium to ʺhealʺ the wound.
D) block entry of pathogens through the wound.
E) induce the production of phytoalexins.

D

Which of the following is not a typical component of a signal transduction pathway?
A) production of more signal
B) production of second messengers such as cGMP
C) expression of specific proteins
D) activation of protein kinases
E) phosphorylation of transcription factors

A

Auxin enhances cell elongation in all of these ways except
A) increased uptake of solutes.
B) gene activation.
C) acidification of the cell wall, causing denaturation of growth-inhibiting cell wall
proteins.
D) increased activity of plasma membrane proton pumps.
E) cell wall loosening.

C

Charles and Francis Darwin discovered that
A) auxin is responsible for phototropic curvature.
B) auxin can pass through agar.
C) light destroys auxin.
D) light is perceived by the tips of coleoptiles.
E) red light is most effective in causing phototropic curvatures.

D

Which hormone is incorrectly paired with its function?
A) auxinpromotes stem growth through cell elongation
B) cytokininsinitiate programmed cell death
C) gibberellinsstimulate seed germination
D) abscisic acidpromotes seed dormancy
E) ethyleneinhibits cell elongation

B

) The hormone that helps plants respond to drought is
A) auxin.
B) gibberellin.
C) cytokinin.
D) ethylene.
E) abscisic acid.

E

) The chemical signal for flowering could be released earlier than normal in a long-day plant
exposed to flashes of
A) far-red light during the night.
B) red light during the night.
C) red light followed by far-red light during the night.
D) far-red light during the day.
E) red light during the day.

B

If a long-day plant has a critical night length of 9 hours, which 24-hour cycle would
prevent flowering?
A) 16 hours light/8 hours dark
B) 14 hours light/10 hours dark
C) 15.5 hours light/8.5 hours dark
D) 4 hours light/8 hours dark/4 hours light/8 hours dark
E) 8 hours light/8 hours dark/light flash/8 hours dark

B

If a scientist discovers an Arabidopsis mutant that does not store starch in plastids but has
normal gravitropic bending, what aspect of our understanding would need to be
reevaluated?
A) the role of auxin in gravitropism
B) the role of calcium in gravitropism
C) the role of statoliths in gravitropism
D) the role of light in gravitropism
E) the role of differential growth in gravitropic bending

C

How may a plant respond to severe heat stress?
A) by orienting leaves toward the sun, increases evaporative cooling
B) by producing ethylene, which kills some cortex cells and creates air tubes for
ventilation
C) by producing salicylic acid, which initiates a systemic acquired resistance response
D) by increasing the proportion of unsaturated fatty acids in cell membranes reducing
their fluidity
E) by producing heat-shock proteins, which may protect the plantʹs proteins from
denaturing

E

In systemic acquired resistance, salicylic acid probably
A) destroys pathogens directly.
B) activates defenses throughout the plant before infection spreads.
C) closes stomata, thus preventing the entry of pathogens.
D) activates heat-shock proteins.
E) sacrifices infected tissues by hydrolyzing cells.

B