Deck 31: Plant Responses to Internal and External Signals

Question 1

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.

Answer 1

D

Question 2

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.

Answer 2

B

Question 3

Auxins (IAA) in plants are known to affect all of the following processes except

A) geotropism of shoots.
B) maintenance of seed dormancy.
C) phototropism of shoots.
D) inhibition of lateral buds.
E) fruit development.

Answer 3

B

Question 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.
E) gibberellins produced at the stem tip cause phototropism.

Question 5

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.

Question 6

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

Question 7

Which of the following hormones would be most useful in promoting the rooting of plant cuttings?

A) strigolactones
B) abscisic acid
C) cytokinins
D) gibberellins
E) indolebutyric acid

Question 8

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.

Question 9

The plant hormone involved in aging and ripening of fruit is

A) auxin.
B) ethylene.
C) florigen.
D) abscisic acid.
E) gibberellin.

Question 10

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.

Question 11

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).

Question 12

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.

Question 13

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

Question 14

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.

Question 15

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.

Question 16

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

Question 17

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.

Question 18

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
E) RNAase

Question 19

All of the following can function in signal transduction in plants except

A) calcium ions.
B) nonrandom mutations.
C) receptor proteins.
D) phytochrome.
E) secondary messengers.

Question 20

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.

Question 21

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

Question 22

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+.

Question 23

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
E) a higher ratio of Pr to Pfr

Question 24

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.

Question 25

Which of the following statements is correct with regard 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.

Question 26

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.

Question 27

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.
E) only animal hormones may have either external or internal receptors.

Question 28

Which of the following plant growth responses is primarily due to the action of auxins?

A) leaf abscission
B) the triple response of shoots
C) cell division
D) the detection of photoperiod
E) cell elongation

Question 29

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.

Question 30

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.
E) Stem cells can overcome auxin inhibition with high levels of gibberellins.

Question 31

The detector of light during de-etiolation (greening) of a tomato plant is (are)

A) carotenoids.
B) xanthophylls.
C) phytochrome.
D) chlorophyll.
E) auxin.

Question 32

Which of the following best explains both the growth of a vine up the trunk of a tree as well as the directional growth of a houseplant toward a window?

A) nastic movement
B) taxic movement
C) tropism response
D) morphological response
E) acclimation

Question 33

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.

Question 34

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
E) ethylene

Question 35

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.

Question 36

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.

Question 37

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.

Question 38

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

Question 39

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

Question 40

Vines in tropical rain forests must grow toward large trees before being able to grow toward the sun. To reach a large tree, the most useful kind of growth movement for a tropical vine presumably would be the opposite of

A) positive thigmotropism.
B) positive phototropism.
C) positive gravitropism.
D) sleep movements.
E) circadian rhythms.

Question 41

The rapid leaf movements resulting from a response to touch (thigmotropism) primarily involve

A) rapid growth response.
B) potassium channels.
C) nervous tissue.
D) aquaporins.
E) stress proteins.

Question 42

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.

Question 43

The initial response of the root cells of a tomato plant watered with seawater would be to

A) rapidly produce organic solutes in the cytoplasm.
B) rapidly expand until the cells burst.
C) begin to plasmolyze as water is lost.
D) actively transport water from the cytoplasm into the vacuole.
E) actively absorb salts from the seawater.

Question 44

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

Question 45

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.

Question 46

What do the results of research on gravitropic responses of roots and stems show?

A) Different tissues have the same response to auxin.
B) The effect of a plant hormone can depend on the tissue.
C) Some responses of plants require no hormones at all.
D) Light is required for the gravitropic response.
E) Cytokinin can only function in the presence of auxin.

Question 47

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.

Question 48

Which of the following would only be activated or upregulated after a plant has already been infected by a pathogen?

A) phytochrome
B) salicylic acid
C) molecular chaperones
D) stress proteins
E) brassinosteroids

Question 49

A long-day plant will flower

A) in the late fall.
B) when the night is shorter than a critical value.
C) only under artificial light in the summer.
D) during short days with proper fertilization.
E) regardless of the photoperiod imposed.

Question 50

You are part of a desert plant research team trying to discover crops that will be productive in arid climates. You discover a plant that produces a hormone under water-deficit conditions that triggers a suite of drought responses. Most likely the hormone is

A) ABA.
B) GA.
C) IAA.
D) 2, 4-D.
E) salicylic acid.

Question 51

In order for a plant to initiate chemical responses to herbivory,

A) the plant must be directly attacked by an herbivore.
B) volatile "signal" compounds must be perceived.
C) gene-for-gene recognition must occur.
D) phytoalexins must be released.
E) it must be past a certain developmental age.

Question 52

A short-day plant exposed to nights longer than the minimum for flowering but interrupted by short flashes of light

A) will never flower.
B) might flower depending upon the duration of the light flash.
C) will not be affected and will flower.
D) might flower depending upon the wavelengths of the light flashes.
E) will still flower if ethylene is administered.

Question 53

What is the probable role of salicylic acid in the defense responses of plants?

A) to destroy pathogens directly
B) to activate the systemic acquired resistance of plants
C) to close stomata, thus preventing the entry of pathogens
D) to activate heat-shock proteins
E) to sacrifice infected tissues by hydrolyzing cells

Question 54

Which of the following is the most likely plant response to an attack by herbivores?

A) leaf abscission to prevent further loss
B) early flowering to try to reproduce before being eaten
C) production of chemical compounds for defense or to attract predators
D) production of physical defenses, such as thorns
E) production of thicker bark and cuticle to make it more difficult to eat

Question 55

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 plant's 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.

Question 56

A botanist discovers a plant that lacks the ability to form starch grains in root cells, yet the roots still grow downward. This evidence refutes the long-standing hypothesis that

A) falling statoliths trigger gravitropism.
B) starch accumulation triggers the negative phototropic response of roots.
C) starch grains block the acid growth response in roots.
D) starch is converted to auxin, which causes the downward bending in roots.
E) starch and downward movement are necessary for thigmotropism.

Question 57

Most scientists agree that global warming is under way; thus, it is important to know how plants respond to heat stress. Which of the following would be a useful line of inquiry to try to improve plant response to and survival of heat stress?

A) the production of heat-stable carbohydrates
B) increased production of heat-shock proteins
C) the opening of stomata to increase evaporational heat loss
D) protoplast fusion experiments with xerophytic plants
E) all of the above

Question 58

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, travels to the shoot apical meristems, 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.

Question 59

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 "heal" the wound.
D) block entry of pathogens through the wound.
E) induce the production of phytoalexins.

Question 60

In extremely cold regions, woody species may survive freezing temperatures by

A) emptying water from the vacuoles to prevent freezing.
B) decreasing the numbers of phospholipids in cell membranes.
C) decreasing the fluidity of all cellular membranes.
D) producing canavanine as a natural antifreeze.
E) increasing cytoplasmic levels of specific solute concentrations, such as sugars.

Question 61

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.

Question 62

The signaling molecule for flowering might be released earlier than usual 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.

Question 63

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 shoot phototropism.

Question 64

In cases where plants exhibit generalized defense responses in organs distant from the infection site, this is termed

A) a hyperactive response.
B) systemic acquired resistance.
C) pleiotropy.
D) hyperplasia.
E) a general systemic response.

Question 65

The hormone that helps plants respond to drought is

A) auxin.
B) gibberellin.
C) cytokinin.
D) ethylene.
E) abscisic acid.

Question 66

Auxin enhances cell elongation in all of these ways except

A) increased uptake of solutes.
B) gene activation.
C) acid-induced denaturation of cell wall proteins.
D) increased activity of plasma membrane proton pumps.
E) cell wall loosening.

Question 67

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 late spring.

Question 68

In nature, poinsettias bloom in early March. Research has shown that the flowering process is triggered 3 months before blooming occurs. In order to make poinsettias bloom in December, florists change the length of the light-dark cycle in September. Given this information and clues, which of the following is a correct statement about poinsettias?

A) They are short-day plants.
B) They require a light period longer than some set minimum.
C) They require a shorter 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 far-red illumination during the nighttime.

Question 69

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

Question 70

A plant mutant that showed normal gravitropic bending but did not store starch in its plastids would require a reevaluation of the role of ________ in gravitropism.

A) auxin
B) calcium
C) statoliths
D) light
E) differential growth

Question 71

Figure 31.1
The heavy line in Figure 31.1 illustrates the relationship between auxin concentration and cell growth in stem tissues. If the same range of concentrations were applied to lateral buds, what curve(s) would probably be produced?

A) I
B) II
C) III
D) II or III
E) I or III