Campbell’s Biology, 9e (Reece et al.)
Chapter 39 Plant Responses to Internal and External Signals
Chapter 39 incorporates higher-level analytical and synthesis/evaluation skills through the discussion of
plant perception and response to environmental stimuli and stresses. Cell signaling, transduction of
signals to target cells, and molecular responses are presented within the context of a whole plant
response to abiotic and biotic environmental challenges.
Multiple-Choice Questions
1) All of the following may function in signal transduction in plants except
A) calcium ions.
B) nonrandom mutations.
C) receptor proteins.
D) phytochrome.
E) secondary messengers.
2) External stimuli would be received most quickly by a plant cell if the receptors for signal transduction
were located in the
A) plasma membrane.
B) cytoplasmic matrix.
C) endoplasmic reticulum.
D) nuclear membrane.
E) nucleoplasm.
3) What would happen if the secondary messenger cGMP was blocked in the de-etiolation pathway?
A) Specific protein kinase 1 would be activated, and greening would occur.
B) Ca2+ channels would not open, and no greening would occur.
C) Ca2+ channels could open, and specific protein kinase 2 could still be produced.
D) No transcription of genes that function in de-etiolation would occur.
E) Transcription of de-etiolation genes in the nucleus would not be affected.
4) If protein synthesis was blocked in etiolated cells, what would be necessary for the “greening” of
these cells?
A) reception of light by phytochrome
B) activation of protein kinase 1 by cAMP
C) activation of protein kinase 2 by Ca2+
D) post-translational modification of existing proteins
E) 100-fold decrease in cytosolic Ca2+ levels
5) The detector of light during de-etiolation (greening) of a tomato plant is (are)
A) carotenoids.
B) xanthophylls.
C) phytochrome.
D) chlorophyll.
E) auxin.
6) 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.
7) Plants growing in a partially dark environment will grow toward light in a response called
phototropism. Which of the following statements is true regarding phototropism?
A) It is caused by an electrical signal.
B) One chemical involved is ethylene.
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 enhances phototropism.
8) Which of the following 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.
9) 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.
10) Which of the following is a major mechanism whereby hormones control plant development?
A) cell respiration via regulation of the citric acid cycle
B) cell division via the cell cycle
C) cell elongation through production of cellulase
D) cell differentiation through altered spliceosome activity
E) cell synthesis of proteins via altered gene expression
11) Evidence for phototropism due to the asymmetric distribution of auxin moving down the stem
A) was first demonstrated in the coleoptiles of monocots.
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.
12) According to modern ideas about phototropism in plants,
A) light causes auxin to accumulate on the shaded side of a plant stem.
B) auxin indirectly inhibits elongation of plant stem cells.
C) auxin is produced by the apical meristem of the coleoptile and moves downward.
D) all hormones move downward via the xylem.
E) cytokinins are more directly involved than auxins.
13) 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.
14) The apical bud of a shoot produces ________, resulting in the inhibition of lateral bud growth.
A) abscisic acid
B) ethylene
C) cytokinin
D) gibberellin
E) auxin
15) After some time, the tip of a plant that has been forced into a horizontal position grows upward. This
phenomenon is related to
A) calcium release from the endoplasmic reticulum of shaded cells.
B) whether the plant is in the northern or southern hemisphere.
C) gibberellin production by stems.
D) auxin production in cells receiving red light.
E) auxin movement toward the lower side of the stem.
16) Gravitropism in plant shoots and roots differ in that
A) only shoots depend upon auxin distribution.
B) only shoots depend upon the aggregation of statoliths.
C) only roots exhibit rapid elongation of specific cells.
D) only roots sense gravity at the tips.
E) the threshold and response time is much less in shoots than in roots.
17) 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).
18) Which plant hormones would likely be found in high amounts in a sprouting vegetative stem?
A) auxins, gibberellins, cytokinins
B) gibberellins, brassinosteroids, cytokinins
C) auxins, abscisic acid, ethylene
D) auxins, phytochrome, brassinosteroids
E) gibberellins, cytokinins, abscisic acid
19) Which of the following plant hormones would be found in very low amounts in a mature, water-
stressed tomato plant?
A) auxins, abscisic acid, brassinosteroids
B) auxins, gibberellins, cytokinins
C) gibberellins, cytokinins, ethylene
D) phytochrome, cytokinins, abscisic acid
E) brassinosteroids, ethylene, phytochrome
20) The plant hormone involved in aging and ripening of fruit is
A) auxin.
B) ethylene.
C) florigen.
D) abscisic acid.
E) gibberellin.
21) 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
22) 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.
23) Which of the following statements applies to plant growth regulators?
A) They only act by altering gene expression.
B) They often have a multiplicity of effects.
C) They function independently of other hormones.
D) They directly control plant protein synthesis and assembly.
E) They affect the division and elongation, but not the differentiation, of cells.
24) 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) altering the expression of genes and modifying the permeability of the plasma membrane.
E) modifying the permeability of the plasma membrane and modifying the structure of the nuclear
envelope membrane.
25) Why might animal hormones function differently than plant hormones?
A) Animal receptors are very different than plant receptors.
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) Animal receptors are more hydrophobic than plant receptors.
26) Which of the following hormones would never be found in high concentrations in a dormant
overwintering flower bud?
A) auxin
B) cytokinins
C) abscisic acid
D) ethylene
E) gibberellins
27) 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) gibberellin concentration can both induce and break dormancy.
28) 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.
29) How does indoleacetic acid affect fruit development?
A) by preventing pollination
B) by inhibiting formation of the ovule
C) by promoting gene expression in cambial tissue
D) by promoting rapid growth of the ovary
E) by inducing the formation of brassinosteroids
30) 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.
31) Auxin triggers the acidification of cell walls, which 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 on the plasma membrane and certain
genes within the same cells.
D) The dual effects are due to two different types of auxins that are produced by different genes.
E) Other antagonistic hormones modify auxin’s effects.
32) If a farmer wanted more loosely packed clusters of grapes, he would most likely spray the immature
bunches with
A) auxin.
B) gibberellins.
C) cytokinins.
D) abscisic acid.
E) ethylene.
33) Which of the following plant hormones are most likely to act synergistically if expressed or applied
to a drought-stricken plant?
A) auxin and ethylene
B) phytochrome and gibberellins
C) gibberellins and abscisic acid
D) abscisic acid and ethylene
E) brassinosteroids and cytokinins
34) Which of the following statements best summarizes the acid growth hypothesis in an actively
growing shoot?
A) Auxin stimulates proton pumps in the plasma membrane and tonoplast.
B) Auxin-activated proton pumps lower the pH of the cell wall, which breaks bonds and makes the walls
more flexible
C) Auxins and gibberellins together act as a lubricant to help stretch cellulose microfibrils.
D) Auxins activate aquaporins that increase turgor pressure in the cells.
E) Auxins and gibberellins are transported to the vacuoles to build up turgor pressure.
35) 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.
36) 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
37) Which of the following plant hormones would most likely be found in high concentrations in a
mature, slightly overripe fruit?
A) auxins and cytokinins
B) auxins and abscisic acid
C) gibberellins and cytokinins
D) cytokinins and ethylene
E) abscisic acid and ethylene
38) The aleurone layer is stimulated to release ________ and ________ as a result of giberrellin release
from the embryo.
A) proteins; amino acids
B) carbohydrates; sugars
C) auxins; cytokinins
D) amylase; protease
E) RNAase; DNAase
39) Which of the following field treatments would be most likely to result in a wheat or corn field with
most of the plants of uniform height?
A) auxin spray early in the season
B) gibberellin spray early in the season
C) abscisic acid spray late in the season
D) auxin spray late in the season
E) auxin and gibberellin spray late in the season
40) 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 plants’ environment?
A) CO2
B) cytokinins
C) ethylene
D) auxin
E) gibberellic acids
41) Which of the following is currently the most powerful method of research on plant hormones?
A) comparing photoperiodic responses
B) comparing tropisms with turgor movements
C) subjecting plants to various abiotic stresses
D) studying plant/animal interactions
E) analyzing mutant plants
42) We tend to think of plants as immobile when, in fact, they can move in many ways. Which of the
following is a legitimate way in which plants move?
A) stretching or shrinking movements up or down in response to light
B) folding and unfolding of leaves using muscle-like tissues
C) growth movements toward or away from light
D) cessation of plant growth in response to wind or touch
E) rapid responses using action potentials from nervous tissue cells similar to those found in the nervous
tissue of animals
43) Which of the following plant growth responses is primarily due to the action of auxins?
A) leaf abscission
B) fruit development
C) cell division
D) the detection of photoperiod
E) cell elongation
44) Experiments on the positive phototropic response of plants indicate that
A) light destroys auxin.
B) auxin moves down the plant apoplastically.
C) auxin is synthesized in the area where the stem bends.
D) auxin can move to the shady side of the stem.
E) auxin is only of secondary importance in the process.
45) Why are lateral buds often inhibited from sprouting even though a stem may be actively elongating?
A) The cells of lateral buds are more sensitive to auxin than stem cells.
B) Lateral buds are high in abscisic acid that prevents elongation.
C) Lateral buds are low in gibberellins.
D) Stem cells lack receptors for auxin.
E) Stem cells can overcome auxin inhibition with high levels of gibberellins.
46) 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
47) 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.
48) Both red and blue light are involved in
A) stem elongation.
B) photoperiodism.
C) positive phototropism.
D) tracking seasons.
E) all of the above.
49) Seed packets give a recommended planting depth for the enclosed seeds. The most likely reason
some seeds are to be covered with only ¼ 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.
50) 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.
51) 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.
52) Many plants flower in response to day-length cues. Which of the following statements best
summarizes this phenomenon?
A) As a rule, short-day plants flower in the summer.
B) As a rule, long-day plants flower in the spring or fall.
C) Long-day plants flower in response to long days, not short nights.
D) Flowering in day-neutral plants is only influenced by day length if there is an exceptionally warm
spring.
E) Flowering in short-day and long-day plants is controlled by phytochrome.
53) Which of the following treatments would enhance the level of the Pfr form of phytochrome?
A) exposure to far-red light
B) exposure to red light
C) long dark period
D) inhibition of protein synthesis
E) synthesis of phosphorylating enzymes
54) 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
55) 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.
56) In legumes, it has been shown that “sleep” (nastic) 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+.
57) Which of the following statements is correct with regards to a “circadian rhythm” in plants?
A) It may have the same signal transduction pathway in all organisms.
B) Once set, it cannot be changed.
C) It works independently of photoperiodic responses.
D) Once set, it is independent of external signals.
E) It can be changed to a longer or shorter period by altering the light quality.
58) 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.
59) 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.