Campbell Biology in Focus, 2e (Urry)
Chapter 31 Plant Responses to Internal and External Signals
31.1 Multiple-Choice Questions
1) Almost all plant cells have the ability to produce abscisic acid. One of the functions of
abscisic acid in plants is to
A) stimulate cell elongation.
B) regulate development of fruit.
C) promote stomatal closure during drought stress.
D) delay leaf senescence.
2) 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.
3) Which of the following conclusions is supported by the research of both Frits 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.
4) 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.
5) The apical bud of a shoot produces ________, resulting in the inhibition of lateral bud growth.
A) abscisic acid
B) ethylene
C) cytokinin
D) auxin
6) 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) auxin production in cells receiving red light.
D) auxin movement toward the lower side of the stem.
7) The ripening of fruit and the dropping of leaves and fruit are principally controlled by
A) auxins.
B) cytokinins.
C) indoleacetic acid (IAA).
D) ethylene.
8) The plant hormone involved in stimulation of stem elongation is
A) auxin.
B) ethylene.
C) florigen.
D) abscisic acid.
9) 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
10) 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.
11) 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 affect the division and elongation, but not the differentiation, of cells.
12) Plant hormones produce their effects by
A) altering the expression of genes.
B) modifying the structure of the hormones.
C) modifying the structure of the nuclear envelope membrane.
D) altering the expression of genes and modifying the permeability of the plasma membrane.
13) 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.
14) Which part of plant structure synthesizes cytokinins primarily?
A) shoot apical meristem
B) roots
C) ripened fruits
D) almost all plant parts
15) 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
16) 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) ethylene.
17) 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.
18) 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.
19) Which of the following hormones would be most useful in promoting the rooting of plant
cuttings?
A) strigolactones
B) cytokinins
C) gibberellins
D) indolebutyric acid
20) The aleurone layer is stimulated to release ________ as a result of gibberellin release from
the embryo.
A) amino acids
B) carbohydrates
C) cytokinins
D) amylase
21) 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
22) Which of the following plant responses is primarily due to the action of gibberellins?
A) cell division
B) sex determination
C) inhibits growth
D) promotes ripening of many types of fruit
23) 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.
24) Why are axillary buds often inhibited from growing even though a stem may be actively
elongating?
A) The cells of axillary buds respond differently to auxin than stem cells.
B) Axillary buds are high in abscisic acid that prevents elongation.
C) Axillary buds are low in gibberellins.
D) Stem cells lack receptors for auxin.
25) The application 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
26) Plant hormonal regulation differs from animal hormonal regulation in that
A) there are no dedicated hormone-producing organs in plants as there are in animals.
B) all production of hormones is local in plants with little long-distance transport.
C) plants do not exhibit feedback mechanisms like animals.
D) only animal hormone concentrations are developmentally regulated.
27) Young leaves and developing seeds are the prime sites for ________ synthesis.
A) auxin
B) gibberellin
C) cytokinin
D) ethylene
28) Which of the following best explains both the growth of a vine up the trunk of a tree and the
directional growth of a houseplant toward a window?
A) nastic movement
B) taxic movement
C) tropism response
D) morphological response
29) The detector of light during de-etiolation (greening) of a tomato plant is
A) carotenoids.
B) xanthophylls.
C) phytochrome.
D) chlorophyll.
30) 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.
31) 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.
32) 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.
33) 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 short-day and long-day plants is controlled by phytochrome.
34) 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
35) In legumes, it has been shown that “sleep” 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.
36) Statoliths are structures that are responsible for
A) phototropism.
B) gravitropism.
C) thigmotropism.
D) dormancy.
37) 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.
38) 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.
39) ________ promote(s) stomatal closure in plant leaves during drought stress.
A) Auxins
B) Cytokinins
C) Gibberellins
D) Abscisic acid
40) 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
41) What does a short-day plant require 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
42) 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
43) 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.