biology : class11 Bolting in Rosette Plants : Functions, Effects, Applications : Gibberellin MCQ Questions and Answers
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Bolting in Rosette Plants
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MCQ Questions
1. A genetically intact rosette plant remains compact under noninductive conditions but rapidly elongates its internodes after exogenous gibberellin treatment. Which interpretation most directly explains this response?
A.
Gibberellin induces bolting by stimulating internode elongation
B.
Gibberellin permanently converts vegetative meristems into roots
C.
Gibberellin suppresses stem growth while enlarging the rosette leaves
D.
Gibberellin prevents flowering by maintaining the rosette state
Correct Answer:
Gibberellin induces bolting by stimulating internode elongation
Explanation:
Bolting is the rapid elongation of the stem, especially the internodes, in a previously short-stemmed rosette plant. Gibberellin can promote this elongation and thereby produce the characteristic upright stem.
2. Which observation provides the strongest evidence that gibberellin treatment has caused bolting rather than merely increased leaf expansion in a rosette plant?
A.
The plant develops darker green leaves without any stem elongation
B.
The distances between successive stem nodes increase markedly
C.
The root system produces more lateral roots while the shoot remains compact
D.
The leaf blades become broader but remain attached to a shortened axis
Correct Answer:
The distances between successive stem nodes increase markedly
Explanation:
Bolting is identified primarily by rapid elongation of stem internodes. Increased leaf size alone does not demonstrate bolting.
3. A rosette species normally bolts only after exposure to a condition that promotes endogenous gibberellin activity. If a gibberellin-biosynthesis inhibitor is applied before this condition, what is the most likely result?
A.
Premature bolting because reduced gibberellin prevents rosette formation
B.
Suppressed stem elongation and delayed or reduced bolting
C.
Immediate bolting caused by accumulation of inactive gibberellin precursors
D.
Normal bolting because gibberellin has no role in internode elongation
Correct Answer:
Suppressed stem elongation and delayed or reduced bolting
Explanation:
Gibberellin promotes the internode elongation required for bolting. Inhibiting its biosynthesis generally reduces stem elongation and can delay or suppress the bolting response.
4. Why can exogenous gibberellin cause a compact rosette plant to bolt even when the environmental cue that normally precedes bolting is absent?
A.
It supplies a growth-promoting signal that can substitute for part of the endogenous gibberellin requirement
B.
It converts every leaf directly into a stem internode
C.
It eliminates the shoot apical meristem before elongation begins
D.
It prevents cell expansion, forcing the plant to grow vertically by compression
Correct Answer:
It supplies a growth-promoting signal that can substitute for part of the endogenous gibberellin requirement
Explanation:
In many rosette plants, environmental induction of bolting is associated with increased gibberellin action. Applied gibberellin can mimic or bypass part of this requirement by promoting stem internode elongation.
5. A rosette plant treated with gibberellin forms a tall elongated stem but does not yet produce flowers. Which conclusion is most scientifically justified?
A.
Bolting and flowering are identical processes and must always occur simultaneously
B.
Gibberellin has promoted bolting, but flowering may require additional regulatory conditions
C.
The treatment failed because bolting can occur only after seed formation
D.
The plant has undergone root bolting rather than shoot bolting
Correct Answer:
Gibberellin has promoted bolting, but flowering may require additional regulatory conditions
Explanation:
Bolting refers specifically to stem elongation. Although it often precedes flowering in rosette plants, gibberellin-induced bolting does not necessarily prove that all flowering requirements have been satisfied.
6. In an experiment, two genetically similar rosette plants receive equal gibberellin doses. Plant X elongates several internodes, whereas Plant Y remains compact. Which explanation is most consistent with the known basis of bolting?
A.
Plant Y may be less sensitive to gibberellin or defective in downstream gibberellin response
B.
Plant X must have absorbed no gibberellin because elongation indicates hormone absence
C.
Plant Y has necessarily completed bolting before treatment
D.
Plant X is responding only because gibberellin blocks all cell division in the stem
Correct Answer:
Plant Y may be less sensitive to gibberellin or defective in downstream gibberellin response
Explanation:
Bolting requires not only gibberellin availability but also the ability of stem tissues to respond to it. Reduced hormone sensitivity or defects in the response pathway can maintain the rosette habit despite treatment.
7. Which treatment would most directly be used to test whether gibberellin is sufficient to induce bolting in a rosette plant maintained under otherwise nonbolting conditions?
A.
Apply gibberellin to one group and compare internode elongation with an untreated control group
B.
Remove all roots from both groups and compare leaf color
C.
Apply only mineral nutrients and measure seed size after harvest
D.
Expose both groups to identical conditions without measuring stem length
Correct Answer:
Apply gibberellin to one group and compare internode elongation with an untreated control group
Explanation:
A treated-versus-control comparison under the same nonbolting conditions directly tests whether exogenous gibberellin can induce the stem elongation characteristic of bolting.
8. A rosette plant has extremely short internodes because of a mutation that reduces gibberellin production. Which result would most strongly support that interpretation?
A.
Application of gibberellin restores internode elongation and produces a bolting-like stem
B.
Application of gibberellin further shortens internodes in every tissue
C.
Application of gibberellin changes only root branching and never affects the shoot
D.
Application of gibberellin destroys the shoot apex while leaving internodes unchanged
Correct Answer:
Application of gibberellin restores internode elongation and produces a bolting-like stem
Explanation:
A gibberellin-deficient short-stem phenotype can often be rescued by supplying the hormone. Restoration of internode elongation is therefore evidence that inadequate gibberellin contributed to the failure to bolt.
9. Which anatomical change is most characteristic of gibberellin-promoted bolting in a rosette plant?
A.
Enhanced elongation of cells in stem internodes, producing rapid axis extension
B.
Complete replacement of the shoot apex by a root meristem
C.
Loss of all vascular tissues from the elongated stem
D.
Permanent inhibition of cell expansion in the stem with unchanged node spacing
Correct Answer:
Enhanced elongation of cells in stem internodes, producing rapid axis extension
Explanation:
Gibberellin promotes stem growth largely through enhanced elongation of cells in the internodes. The resulting rapid extension of the shoot axis is the defining feature of bolting.
10. A horticulturist wants to obtain elongated flowering stalks from a rosette crop before natural bolting occurs. Which application is most directly aligned with gibberellin's role?
A.
A carefully controlled gibberellin treatment aimed at stimulating stem internode elongation
B.
A treatment that blocks gibberellin synthesis to lengthen the flowering stalk
C.
A treatment that removes the shoot apex to induce internode elongation automatically
D.
A treatment that increases root compactness while preventing shoot growth
Correct Answer:
A carefully controlled gibberellin treatment aimed at stimulating stem internode elongation
Explanation:
Gibberellin is applied commercially and experimentally to promote bolting or elongation of flowering stalks in suitable rosette plants. Its relevant effect is stimulation of stem internode growth.
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