Chapter 39: Practice Test Flashcards

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Which of the following statements about plant hormones is false?

abscisic acid generally promotes growth


Negative gravitropism of plant shoots

results from relatively rapid elongation of some stem cells, depends upon the aggregation of statoliths, and depends auxin distribution


Many plants flower in response to day-length cues. Which statement concerning flowering false?

long-day plants flower in response to long days, not short nights


How may a plant respond to severe heat stress?

by producing heat-shock proteins, which may protect the plant's proteins from denaturing


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

maintenance of dormancy


Plants growing in a partially dark environment will grow toward light in a response called phototropism. Choose the incorrect statement regarding phototropism.

auxin causes a decrease in growth on the side of the stem exposed to light


A plant will recognize a pathogenic invader

if it has the specific R gene that corresponds to the pathogen molecule encoded by an Avr gene


Seed packets give a recommended planting depth for the enclosed seeds. The most likely reason some seeds are to be covered with only 1/4 inch of soil is that the

seeds require light to germinate


We tend to think of plants as immobile when, in fact, they can move in many ways. All of the following are movements plants are accomplish except

folding and unfolding of leaves using muscle-like tissues


Ethylene, as an example of a plant hormone, may have multiple effects on a plant, depending on all of the following except the

altered chemical structure of ethylene from a gas to a liquid


If a long-day plant has a critical night length of 9 hours, which 24-hour cycle would prevent flowering?

14 hours light/10 hours dark


If a scientist discovers an Arabidopsis mutant that does not store starch in plastids has normal gravitropic bending, what aspect of our understanding would need to be reevaluated?

the role of statoliths in gravitropism


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

increasing cytoplasmic levels of specific solute concentrations, such as sugars


Most plants close their stomata at night. What color of light would be effective in promoting stomatal opening in the middle of the night?



Regarding positive gravitropism exhibited by plant roots

it depends on more rapid elongation of some cells


Plants often use changes in day length (photoperiod) to trigger events such as dormancy and flowering. It is logical that plants have this mechanism because photoperiod changes

are more predictable than air temperature changes


What would happen if the secondary messenger cGMP was clocked in the de-etiolation pathway?

Ca2+ channels could open, and specific protein kinase 2 could still be produced


After some time, the tip of a plant that has been forced into a horizontal position grows upward. This phenomenon is related to

auxin movement toward the lower side of the stem


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 guard cell hormone under water-deficit conditions. Most likely the hormone is



In attempting to make a seed break dormancy, one logically could treat it



What is the probable role of salicylic acid in the defense response of plants

activate systemic acquired resistance of plants


Both red and blue light are involved in

stem elongation


Which of the following is not presently considered a major mechanism whereby hormones control plant development?

affecting cell respiration via regulation of the citric acid cycle


Charles and Francis Darwin concluded from their experiments on phototropism by grass seedlings that the part of the seedling the detects the direction of light is the

tip of the coleoptile


In general, which of the following is not a plant response to herbivores?

domestication, so that humans can protect the plant


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

sprinkling every third day to soak the soil to 2.0 inches


When an arborist prunes a limb a valuable tree, he or she usually paints the cut surface. The primary purpose of the paint is to

block entry of pathogens through the wound


Which plant hormones might be used to enhance stem elongation and fruit growth?

auxins and gibberellins


Incandescent light bulbs, which have high output of red light, are least effective in promoting



According to modern ideas about phototropism in plants

auxin is produced by the tip of the coleoptile and moves downward, auxin stimulates elongation of plant stem cells, and light causes auxin to accumlate on the shaded area of a plant stem


A pathogenic fungus invades a plant. What does the infected produce in response to the attack?



The results of this experiment, shown on the left of the graph (area A) may be used to

show a correlation between plant height and gibberellin concentration


Plant growth regulators can be characterized by all of the following except that they

function independently of other hormones


All of the following are responses of plants to cold stress except

conversion of the fluid mosaic cell membrane to a solid mosaic one


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?



According to the acid growth hypothesis, auxin works by

increasing wall plasticity and allowing the affected cell walls to elongate


Bald cypress and Loblolly pine are both gymnosperm trees native to the southern United States. The cypress grows in swamps; the pine grows in sandy soil. How do you think their anatomies differ?

there are larger intercellular spaces in the roots of the cypress than in the roots of the pine


The hormone that helps plants respond to drought is

abscisic acid


Which one of the following is not a direct function of either auxin or gibberellin?

inducing semescence and ripening


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?



Auxin enhances cell elongation in all of these ways except

acidification of the cell wall, causing denaturation of growth-inhibiting cell wall proteins


Plants that have their flowering inhibited by being exposed to bright lights at night are

short-day plants


Plant cells begin synthesizing large quantities of heat-shock proetins

when the air around species from temperate regions is above 40 C


Which of the following does not reduce the level of the Pfr form of phytochrome?

exposure to red light


The apical bud of a pine tree inhibits the growth of lateral buds through the production of



This experiment suggests that the unknown amount of gibberellin in experimental plant (B) is approximately

0.1 ug/mL


External stimuli would be received most quickly by a plant cell if the receptors for signal transduction were located in the

cell membrane


Which of the following is not a typical component of a signal transduction pathway?

production of more signal


Biological clocks cause organisms to perform daily activities on a regular basis. Which of the following is a false statement about this kind of "circadian rhythm?"

once set, it is independent of external signals


The biological clock controlling circadian rhythms must ultimately

affect gene transcription


The ripening of fruit and the dropping of leaves and fruit are principally controlled by



A long-day plant will flower if

the duration of continuous darkness is less than a critical length


Why might animal hormones function differently from plant hormones?

animals move rapidly away from negative stimuli, and most plants don't, and plants are much more variable in their morphology and development than animals


Cells elongate in response to auxin. All of the following are part of the acid growth hypothesis except

auxin-activated proton pumps stimulate cell division in meristems


If the range of species of plants expands to a higher latitude, which of the following processes is the most likely to be modified by natural selection?

photoperiodic response


Which of the following is currently the most powerful method of research on plant hormones?

analyzing mutant plants


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?

the plants flower in the spring


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

the effect of a plant hormone can depend on the tissue


Why do coleoptiles grow toward light?

auxin moves away from the light to the shady side


In systemic acquired resistance, salicylic acid probably

activates defenses throughout the plant before infection spreads


If a short-day plant has a critical night length of 15 hours, then which of the following 24-hour cycles will prevent flowering?

8 hours light/light flash/8 hours dark


Plant hormones produce their effects

modifying the permeability of the plasma membrane and altering the expression of genes


Which of the following has not been established as an aspect of auxin's role in cell elongation?

auxin increases the quantity of cytoplasm in the cell


We know from the experiments of the past that plants bend toward light because

cell expansion is greater on the dark side of the stem


Auxin is responsible for all of the following plant growth responses except

the detection of photoperiod


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



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

nonrandom mutations


Oat seedlings are sometimes used to study auxins because

their coleoptile exhibits a strong phototropism


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 likely

have no effect upon flowering


The plant hormone involved in aging and ripening of fruit is



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 protein that is synthesized in leaves and travels to the shoot apical meristem and initiates flowering


Which hormone is incorrectly paired with its function?

cytokinins - initiate programmed cell death


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?

add some incandescent bulbs to increase the amount of red light


The chemical signal for flowering could be released earlier than normal in a long-day plant exposed to flashes of

red light during the night


The heavy line in Figure 39.1 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 would probably be produced?



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

positive phototropism


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

The dark period can be interrupted without affecting flowering.


Auxin triggers the acidification of cell walls that results in rapid growth, but also stimulates sustained, long-term cell elongation. What best explains how auxin brings about this dual growth response?

auxin causes second messengers to activate both proton pumps and certain genes


A plant seedling bends toward sunlight because

auxin is found in greatest abundance on the dark side of the stem


Which of the following are defenses that some plants use against herbivory?

release of volatile compounds that attract parasitoid wasps and production of the unusual amino acid canavanine


Most scientists agree that global warming is underway; thus it is important to know how plants respond to heat stress. Which of the following is an immediate short-term response of plants to heat stress?

the production of heat-shock proteins like those of other organisms


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?



Which of the following are examples or parts of plants' systemic acquired resistance against infection?

salicylic acid, alarm hormones and phytoalexins


Buds and sprouts often form on tree stumps. Which of the following hormones would you expect to stimulate their formation?



Evidence for phototropism due to the asymmetric distribution of auxin moving down the stem

has not been found in eudicots such as sunflower and radish


One effect of gibberellins is to stimulate cereal seeds to produce



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

auxin can stimulate cell elongation in apical meristems, yet will inhibit the growth of axillary buds


Plants are affected by an array of pathogens. Which of the following is not a plant defense against disease?

production of chemicals that kill pathogens, a waxy cuticle that pathogens have trouble penetrating, cells near the point of infection destroying themselves to prevent the spread of the infection, and acquiring gene-for-gene recognition that allows specific proteins to interact so that the plant can produce defenses against the pathogen


Which of these conclusions is supported by the research of both Went and Charles and Francis Darwin on shoot responses to light?

a chemical substance involved in shoot bending is produced in shoot tips


Which plant hormone(s) is (are) most closely associated with cell division?



If protein synthesis was blocked in etiolated cells, what would be necessary for the "greening" of these cells?

post-translational modification of existing proteins


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?

abscisic acid


Charles and Francis Darwin discovered that

light is perceived by the tips of coleoptiles


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

salicylic acid


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

volatile "signal" compounds must be perceived


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

begin to plasmolyze as water is lost


How does indoleacetic acid affect fruit development?

promoting rapid growth of the ovary


A short-day plant will flower only when

nights are longer than a certain critical value


In legumes, it has been shown that "sleep" movements are correlated with

rhythmic opening and closing of K+ channels in motor cell membranes


What does a short-day plant need in order to flower?

a night that is longer than a certain length


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

falling statoliths trigger gravitropism