chapter 39 - plant responses to internal and external signals
cytokinins
cell differentiation and division apical dominance anti-aging effects
flooding
plants destruct root cortex cells to create air tubes
Why might animal hormones function differently from plant hormones?
- Animals move rapidly away from negative stimuli, and most plants donʹt. - Plants are much more variable in their morphology and development than animals.
Which of the following has NOT been established as an aspect of auxinʹs role in cell elongation?
- Auxin increases the quantity of cytoplasm in the cell.
Which of the following has been established as an aspect of auxinʹs role in cell elongation?
- Auxin instigates a loosening of cell wall fibers. - Through auxin activity, vacuoles increase in size. - Auxin activity permits an increase in turgor pressure. - Auxin stimulates proton pumps.
Plants growing in a partially dark environment will grow toward light in a response called phototropism. Choose the correct statement regarding phototropism.
- It is caused by a chemical signal. - One chemical involved is auxin. - Auxin causes a growth increase on one side of the stem. - Removing the apical meristem prevents phototropism.
Regarding positive gravitropism exhibited by plant roots,
- it is mediated by auxin as for phototropism. - it depends on more rapid elongation of some cells than other cells. - gravity causes auxins to accumulate on the lower side of roots. - the phenomenon depends upon inhibition of cell elongation of certain root cells by auxins.
According to modern ideas about phototropism in plants,
- light causes auxin to accumulate on the shaded side of a plant stem. - auxin stimulates elongation of plant stem cells. - auxin is produced by the tip of the coleoptile and moves downward.
Auxins (IAA) in plants are known to affect all of the following phenomena except
- maintenance of dormancy.
Plant growth regulators can be characterized by all of the following
- may act by altering gene expression. - have a multiplicity of effects. - control plant growth and development. - affect division, elongation, and differentiation of cells.
Auxin is responsible for all of the following plant growth responses
- phototropism. - formation of adventitious roots. - apical dominance. - cell elongation.
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/8 hours dark/light flash/8 hours dark
Which of the following statements about plant hormones is false?
Abscisic acid generally promotes growth.
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.
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.
Why do coleoptiles grow toward light?
Auxin moves away from the light to the shady side.
Cells elongate in response to auxin. All of the following are part of the acid growth hypothesis
- Auxin stimulates proton pumps in cell membranes. - Lowered pH results in the breakage of cross-links between cellulose microfibrils. - The wall fabric becomes looser (more plastic). - The turgor pressure of the cell exceeds the restraining pressure of the loosened cell wall, and the cell takes up water and elongates.
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.
Which of the following is presently considered a major mechanism whereby hormones control plant development?
- affecting cell division via the cell cycle - affecting cell elongation through acid growth - affecting cell differentiation through altered gene activity - mediating short-term physiological responses to environmental stimuli
Plant hormones produce their effects by
- altering the expression of genes. - modifying the permeability of the plasma membrane.
Negative gravitropism of plant shoots
- depends upon auxin distribution. - depends upon the aggregation of statoliths. - results from relatively rapid elongation of some stem cells.
Auxins (IAA) in plants are known to affect all of the following phenomena
- geotropism of shoots. - phototropism of shoots. - inhibition of lateral buds. - fruit development.
phytochrome
- plant pigment responsible for photoperiodism - response depends on last flash of light - effects are reversible - lettuce seed: -- red light = increase germination -- far-red light = inhibits germination
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.
What does a short-day plant need in order to flower?
a night that is longer than a certain length
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
The hormone that helps plants respond to drought is
abscisic acid.
Auxin enhances cell elongation in all of these ways except
acidification of the cell wall, causing denaturation of growth-inhibiting cell wall proteins.
The biological clock controlling circadian rhythms must ultimately
affect gene transcription.
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
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.
One effect of gibberellins is to stimulate cereal seeds to produce
amylase
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
are more predictable than air temperature changes.
The apical bud of a pine tree inhibits the growth of lateral buds through the production of
auxin
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.
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.
Which of the following hormones would be most useful in promoting the rooting of plant cuttings?
auxins
Which plant hormones might be used to enhance stem elongation and fruit growth?
auxins and gibberellins
Most plants close their stomata at night. What color of light would be most effective in promoting stomatal opening in the middle of the night?
blue
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.
day-neutral plants
controlled by plant maturity, not photoperiod
All of the following are responses of plants to cold stress except
conversion of the fluid mosaic cell membrane to a solid mosaic one.
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?
cytokinin
Which plant hormone(s) is (are) most closely associated with cell division?
cytokinin
Buds and sprouts often form on tree stumps. Which of the following hormones would you expect to stimulate their formation?
cytokinins
Which hormone is incorrectly paired with its function?
cytokinins - initiate programmed cell death
heat
denatures plant enzymes plant sweats to cool and creates heat-shock proteins
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 plantsʹ environment?
ethylene
The ripening of fruit and the dropping of leaves and fruit are principally controlled by
ethylene
Which of the following does not reduce the level of the Pfr form of phytochrome?
exposure to red light
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.
We tend to think of plants as immobile when, in fact, they can move in many ways. All of the following are movements plants can accomplish except
folding and unfolding of leaves using muscle-like tissues.
Plant growth regulators can be characterized by all of the following except that they
function independently of other hormones.
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?
gibberellin
In attempting to make a seed break dormancy, one logically could treat it with
gibberellins
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
have no effect upon flowering
In extremely cold regions, woody species may survive freezing temperatures by
increasing cytoplasmic levels of specific solute concentrations, such as sugars.
According to the acid growth hypothesis, auxin works by
increasing wall plasticity and allowing the affected cell walls to elongate.
Which one of the following is not a direct function of either auxin or gibberellin?
inducing semescence and ripening
Charles and Francis Darwin discovered that
light is perceived by the tips of coleoptiles.
salt
lowers water potential plants produce solutes tolerated at high concentrations (water potential of the cell is more negative than in the soil)
A short-day plant will flower only when
nights are longer than a certain critical value.
abscicic acid
non-ideal environments seed dormancy drought tolerance
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?
photoperiodic response
Incandescent light bulbs, which have high output of red light, are least effective in promoting
phototropism.
cold
plant increases lipid coating to combat and makes anti-freeze proteins
drought
plant reduces transpiration by closing stoma, reduce surface area, no growth, deep roots grow, shallow roots do not
long-day plants
plants flower when light period is longer than certain length, more light
shot-day plants
plants flower when light period is shorter than certain length, more dark
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.
How does indoleacetic acid affect fruit development?
promoting rapid growth of the ovary
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
gravitropism
response to gravity down=positive up=negative plants detect gravity by the settling and denseness of statoliths
In legumes, it has been shown that ʺsleepʺ movements are correlated with
rhythmic opening and closing of K+ channels in motor cell membranes.
Plants that have their flowering inhibited by being exposed to bright lights at night are
short-day plants.
Both red and blue light are involved in
stem elongation
Gibberellins
stem elongation fruit growth seed germination
ethylene
stress mechanical/physical stress senescence leaf abscission ripens fruit
Auxin is responsible for all of the following plant growth responses EXCEPT
the detection of photoperiod.
A long-day plant will flower if
the duration of continuous darkness is less than a critical length.
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
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
If a scientist discovers an Arabidopsis mutant that does not store starch in plastids but has normal gravitropic bending, what aspect of our understanding would need to be reevaluated?
the role of statoliths in gravitropism
Plant cells begin synthesizing large quantities of heat-shock proteins
when the air around species from temperate regions is above 40°C.
Many plants flower in response to day-length cues. Which statement concerning flowering is false?
Long-day plants flower in response to long days, not short nights.
auxin (IAA)
Promotes plant growth by increasing H+ concentration activating enzymes that loosen cellulose fibers thereby expanding the cell wall also plays a role in phototropism and gravotropism
Roots exhibit negative geotropism whereas stems exhibit positive geotropism.
TRUE
The rapid leaf movements resulting from a response to touch (thigmotropism) involve transmission of electrical impulses called action potentials.
TRUE
What do results of research on gravitropic responses of roots and stems show?
The effect of a plant hormone can depend on the tissue.
