Deck 37: Plant Sensory Systems, Signals, and Responses

Question 1

Mammalian eyes sense light because the photoreceptor cells have molecules called opsins, which change structure when exposed to light. Which of the following plant molecules would be analogous to mammalian opsins in their light-sensing ability?

A) auxin and phytochrome
B) auxin and Pfr
C) Pfr and phytochrome
D) cytokinins and phototropins
E) abscisic acid (ABA) and Pfr

Answer 1

C

Question 2

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) Cells on the shaded side of the coleoptile elongate in response to auxin.

Answer 2

C

Question 3

Which of the following treatments would increase the level of the Pfr form of phytochrome?

A) exposure to far-red light
B) exposure to red light
C) a long dark period
D) inhibition of protein synthesis
E) synthesis of phosphorylating enzymes

Answer 3

B

Question 4

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 5

Plant hormones ________.

A) naturally exist in very large amounts in plants
B) change their shape in response to stimulus
C) are unable to move from one cell to another
D) affect only cells with the appropriate receptor

Question 6

To find the gene that encodes for the blue-light receptor, researchers inserted the gene for the PHOT1 protein into insect cells growing in culture. When they exposed the transgenic cells to blue light, they found that the PHOT1 protein became phosphorylated. No other plant proteins were present in the insect cells. Which of the following is a reasonable conclusion from this result? The PHOT1 protein ________.

A) enabled the insect cells to photosynthesize
B) phosphorylated itself in the presence of blue light
C) is not responsive to blue light
D) is photoreversible
E) is not functional in insect cells

Question 7

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 8

You observe a houseplant on your window sill bending toward the bright afternoon sunlight. Being knowledgeable, you wish to explain the molecular events of the phototropic response to your friend. What is the correct sequence that you would describe?
I) PHOT1 attains a phosphate group and changes shape.
II) Cell elongation occurs on the shady side of the plant.
III) Auxin binds its receptor at target tissues.
IV) Light strikes PHOT1.
V) PHOT1 stimulates downward auxin transport on the shady side of the plant.
VI) Light strikes stomata, which close to minimize water loss.
VII) Cells on the illuminated side of the plant become shorter.

A) VI, VII, II
B) VII, II, III, I
C) IV, I, V, III, II
D) IV, VI, III, VII
E) Any of these sequences can initiate phototropism.

Question 9

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

A) carotenoid
B) xanthophyll
C) phytochrome
D) chlorophyll
E) auxin

Question 10

Which of the following can be sensed by plants?
I) gravity
II) pathogens
III) wind
IV) light

A) only I and III
B) only III and IV
C) only I, II, and IV
D) only II, III, and IV
E) I, II, III, and IV

Question 11

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) elongating cells in the coleoptile
C) base of the coleoptile
D) cotyledon
E) phytochrome in the coleoptile

Question 12

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) predict moisture availability
C) are modified by soil temperature changes
D) can reset the biological clock

Question 13

Which of the following can function in signal transduction in plants?
I) calcium ions
II) nonrandom mutations
III) receptor proteins
IV) red light
V) second messengers

A) only I, III, and IV
B) only I, II, and V
C) only I, III, and V
D) only II and IV
E) only II, III, and V

Question 14

According to the acid-growth hypothesis, auxin works by ________.

A) dissolving sieve plates, permitting more rapid transport of nutrients
B) dissolving cell membranes temporarily, permitting cells that were on the verge of dividing to divide more rapidly
C) changing the pH within the cell, permitting the electron transport chain to operate more efficiently
D) increasing the activity of proton pumps that lower the pH of cell walls, allowing cells to elongate
E) greatly increasing the rate of deposition of cell wall material

Question 15

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 will not emerge from soil if buried slightly deeper than this
B) seedlings do not have an etiolation response
C) seeds require light to germinate
D) seeds require a higher temperature to germinate
E) seeds cannot germinate in waterlogged soils

Question 16

Recent research on Arabidopsis has 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 Ca2+ ions to change membrane potential
E) a transcription factor that controls the activation of florigen-specific genes

Question 17

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 18

Before plowing a field, a farmer thought the bare field looked weed-free. Three days after plowing and turning over the soil, he was amazed to see thousands of tiny seedlings. What is the most likely reason for the mass germination of seeds?

A) large seeds that needed soil disturbance to germinate
B) small seeds that needed light to germinate
C) small seeds that were scarified by exposure to the plow
D) large seeds that needed exposure to higher levels of oxygen to germinate

Question 19

You have discovered a previously unidentified plant, and you cultivate it in your lab. You notice that its flowers close when people are talking yet are open when the lab is relatively quiet. You suspect that this plant may have the ability to hear! Which of the following hypotheses is (are) the most reasonable to explain this phenomenon?
I) There is a cell-surface protein on the epidermal cells that becomes phosphorylated in response to vibration by sound waves.
II) There are tiny hairs on epidermal cells that bend in response to the vibration of sound waves, triggering an action potential in epidermal cells.
III) There is a cell-surface receptor on root cells that becomes phosphorylated when the soil vibrates in response to sound waves.

A) only I
B) only II
C) only III
D) only II and III
E) I, II, and III

Question 20

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 days
D) days and nights are of equal length

Question 21

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

A) ethylene
B) abscisic acid
C) cytokinins
D) gibberellins
E) auxins

Question 22

Many plants are capable of responding very rapidly to mechanical stimuli. For instance, Venus Flytraps respond more quickly than their insect prey can escape. A very mild touch or a light breeze can cause the leaves of the Sensitive Plant to close tightly. This rapid transmission of touch is accomplished by ________.

A) rapid changes in phloem pressure
B) efficient, rapid transport of auxin
C) self-propagating changes in membrane potential
D) release of volatile airborne signals
E) All of the above are employed by these plants.

Question 23

Plant hormones can have different effects at different concentrations. This explains how ________.

A) some plants are long-day plants, while others are short-day plants
B) signal transduction pathways in plants differ from those in animals
C) plant genes recognize pathogen genes, although plants lack an immune system
D) auxin can stimulate cell elongation in apical meristems yet inhibit the growth of axillary buds
E) gibberellin concentration can both induce and break seed dormancy

Question 24

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 ________.

A) negative thigmotropism
B) negative phototropism
C) negative gravitropism
D) positive thigmomorphogenesis
E) the opposite of circadian rhythms

Question 25

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) Amyloplasts are required for the gravitropic response.
E) Cytokinin can only function in the presence of auxin.

Question 26

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

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

Question 27

A researcher found a beautiful plant while traveling in Alaska and collected its seeds. When she came back to Florida, she soaked some seeds in pure water and some in water with a hormone. When she put the seeds in soil to grow, only the seeds that had been soaked with the hormone germinated. The hormone most likely was ________.

A) gibberellin
B) abscisic acid (ABA)
C) auxin
D) ethylene

Question 28

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, under water-deficit conditions, produces a hormone that triggers a suite of drought responses. Most likely the hormone is ________.

A) abscisic acid
B) gibberellin
C) auxin
D) florigen
E) methyl salicylate

Question 29

What do thigmomorphogenesis, thigmotropism, and thigmonastic movements have in common?

A) All three plant responses are mediated by auxins.
B) All three plant responses are plant responses to touch.
C) All three plant responses alter the direction of stem growth.
D) In all three plant responses, gene transcription is altered in response to touch.

Question 30

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

A) falling amyloplasts 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 31

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 responses
D) morphological responses
E) acclimation

Question 32

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) accumulation of amyloplasts on the lower side of the stem
C) gibberellin production by stems
D) exposure of phytochrome in the stem to red light
E) auxin movement toward the lower side of the stem

Question 33

Which of the following is the strongest evidence that cytokinins regulate cell divisions? There is ________.

A) an increase of cyclin gene expression in tissues exposed to cytokinin
B) a decrease of cyclin gene expression in tissues exposed to cytokinin
C) induction of shoot growths in tissues exposed to cytokinin
D) induction of root growths in tissues exposed to cytokinin
E) an ability of cytokinin to interact with auxin at the molecular level and change auxin biosynthesis and transport

Question 34

Which of the following is NOT an effect observed in the guard cells of stomata?

A) guard cell shrinkage
B) K+ exiting guard cells
C) changes in membrane potential
D) cell expansion driven by proton ATPases
E) water exiting guard cells

Question 35

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 36

If cells in the ________ are removed, roots will no longer respond to gravity.

A) root hairs
B) zone of elongation
C) root cap
D) secondary meristem

Question 37

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 38

Which of the following signals indicates shade to a plant?

A) light quantity
B) blue light
C) far-red light
D) red light

Question 39

Plant growth regulators ________.

A) only act by altering gene expression
B) may have a multiplicity of effects
C) function independently of hormones
D) directly control plant protein synthesis and assembly
E) affect the division and elongation, but not the differentiation, of cells

Question 40

The dropping of leaves and fruit are principally controlled by ________.

A) gibberellins
B) cytokinins
C) auxins
D) ethylene
E) carbon dioxide concentration

Question 41

The transduction pathway that activates systemic acquired resistance in plants is initially signaled by ________.

A) herbivory
B) phytochrome production
C) methyl salicylate
D) systemin release
E) proteinase inhibitors

Question 42

Use the following information to answer the question below.
Some plants continually produce secondary defense compounds. Other plants are induced to form secondary defense compounds when they are injured. Corn seedling leaves that are chewed on by the caterpillars of a type of cutworm moth emit immediate volatile chemicals

Question 43

You have a small tree in your yard that is the height that you want it, but it does not have as many branches as you want. How can you prune it to trigger it to increase the number of branches?

A) Cut off the leaves at the ends of several branches.
B) Cut off the tips of the main shoots.
C) Cut off lower branches.
D) Cut some of the higher branches off at the stem.
E) Cut off the leaves at the base of most of the branches.

Question 44

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) carbon dioxide
B) cytokinins
C) ethylene
D) auxin
E) gibberellic acids

Question 45

The heavy line in the accompanying figure 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

Question 46

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

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

Question 47

For a plant to initiate chemical responses to herbivory before it is directly attacked by herbivores, ________.

A) a plant must have already flowered at least once
B) volatile "signal" compounds must be perceived
C) systemin must be produced
D) the hypersensitive response must be induced

Question 48

When an arborist prunes a limb off a valuable tree, he or she may paint the cut surface with a nontoxic sealant. 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 proteinase inhibitors