Deck 39: Plant Responses to Internal and External Signals

Question 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.

Answer 1

B

Question 2

The plant hormone involved in aging and ripening of fruit is

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

Answer 2

B

Question 3

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.

Answer 3

E

Question 4

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.

Question 5

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 6

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.

Question 7

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 8

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.

Question 9

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

Question 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

Question 11

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.

Question 12

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.

Question 13

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.

Question 14

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

Question 15

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 16

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 17

Which of the following conclusions is supported by the research of 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.
E)Light stimulates the synthesis of a plant hormone that responds to light.

Question 18

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

Question 19

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.

Question 20

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 21

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

Question 22

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.

Question 23

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

Question 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.

Question 25

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 26

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.

Question 27

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

Question 28

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 29

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 30

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.

Question 31

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

Question 32

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

Question 33

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.

Question 34

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.

Question 35

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.

Question 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

Question 37

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 38

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 39

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 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

Question 41

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 42

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

Question 43

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

Question 44

Ethylene differs from other plant hormones in that

A)it is produced in very small amounts.
B)it is a gas.
C)it has multiple effects.
D)it is only produced in seedlings.
E)it is transported in the xylem and phloem.

Question 45

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 46

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.

Question 47

Both red and blue light are involved in

A)stem elongation.
B)photoperiodism.
C)positive phototropism.
D)tracking seasons.
E)all of the above.

Question 48

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 49

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 50

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 51

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 52

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.

Question 53

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

Question 54

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.

Question 55

While ________ inhibit(s)early germination, ________ regulate(s)cell division in shoots and roots.

A)gibberellins; auxin
B)ethylene; cytokinins
C)auxin; ethylene
D)ABA; cytokinins
E)strigolactones; gibberellins

Question 56

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 57

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.

Question 58

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 59

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

Question 60

Most plants close their stomata at night. What colour 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

Question 61

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

A)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 62

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 63

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 64

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 65

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 66

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 67

Which of the following best describes positive gravitropism exhibited by plant roots?

A)It is mediated by auxin similar to the phototropism responses in shoots.
B)It depends on an inhibition of elongation of some cells.
C)Gravity causes gibberellins to accumulate on the lower side of roots.
D)The phenomenon depends upon inhibition of cell elongation of certain root cells by abscisic acid.
E)All of the above are correct.

Question 68

If you wanted to genetically engineer a plant to be more resistant to drought, increasing amounts of which of the following hormones might be a good first attempt?

A)abscisic acid
B)brassinosteroids
C)gibberellins
D)cytokinins
E)auxin

Question 69

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 70

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 71

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 72

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 and improve plant response and survival to 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 73

Which of the following watering regimens will be most effective at keeping a lawn green during the hot, dry summer months?

A)daily sprinkling to soak the soil to 0.5 inch
B)sprinkling every other day to soak the soil to 1.0 inch
C)sprinkling every third day to soak the soil to 2.0 inches
D)daily sprinkling to soak the soil to 0.5 inch or sprinkling every other day to soak the soil to 1.0 inch
E)sprinkling every other day to soak the soil to 1.0 inch or sprinkling every third day to soak the soil to 2.0 inches

Question 74

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 75

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 76

Plant cells begin synthesizing large quantities of heat-shock proteins

A)after the induction of chaperone proteins.
B)in response to the lack of CO₂ following the closing of stomata by ethylene.
C)when desert plants are quickly removed from high temperatures.
D)when they are subjected to moist heat (steam)followed by electric shock.
E)whenever the external temperature exceeds the threshold where photosynthesis is negatively impacted.

Question 77

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 78

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 79

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 80

Trees found at high elevations tend to be short with stocky tree trunks compared to trees growing in more sheltered areas. The term that describes plants' sensitivity to mechanical stress is

A)thigmomorphogenesis.
B)thigmotropism.
C)statolithogenesis.
D)florigenesis.
E)vernalization.