Practice important
Stem Internode Elongation
MCQ questions and answers.
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MCQ Questions
1. A genetically dwarf pea plant has short internodes because it produces insufficient active gibberellin. Which treatment would most directly restore internode elongation?
A.
Application of gibberellic acid to the shoot
B.
Application of abscisic acid to the shoot
C.
Removal of the shoot apex
D.
Application of a cytokinin that promotes cell division only
Correct Answer:
Application of gibberellic acid to the shoot
Explanation:
Gibberellic acid promotes elongation of stem internodes, so supplying it externally can restore elongation in a dwarf plant deficient in active gibberellin.
2. In an experiment, two plants have identical shoot apices and leaf numbers, but one receives a gibberellin-biosynthesis inhibitor. Compared with the untreated plant, the treated plant would most likely show:
A.
Longer internodes with unchanged stem thickness
B.
Shorter internodes and a more compact stem
C.
Normal internodes but complete loss of root hairs
D.
Increased internode length caused by reduced gibberellin activity
Correct Answer:
Shorter internodes and a more compact stem
Explanation:
Inhibiting gibberellin synthesis reduces the hormone available for stem internode elongation, producing shorter internodes and a compact growth habit.
3. A tall plant is treated with gibberellin only on one side of a single elongated internode. Which result most directly indicates a local effect on internode growth?
A.
The treated side elongates more, causing bending toward the untreated side
B.
The entire root system becomes shorter without stem changes
C.
All internodes elongate equally regardless of treatment position
D.
The treated internode becomes shorter because gibberellin inhibits elongation
Correct Answer:
The treated side elongates more, causing bending toward the untreated side
Explanation:
Localized gibberellin application can stimulate cell elongation in the treated stem region, creating unequal growth across the internode and resulting in curvature.
4. Which observation would provide the strongest evidence that gibberellin promotes stem internode elongation mainly by stimulating cell elongation rather than merely increasing cell number?
A.
Treated internodes contain fewer cells, each substantially longer than cells in controls
B.
Treated internodes contain more cells of the same length as control cells
C.
Treated internodes have reduced cell length and increased lignification
D.
Treated internodes show no change in either cell number or cell length
Correct Answer:
Treated internodes contain fewer cells, each substantially longer than cells in controls
Explanation:
A greater internode length associated chiefly with longer cells indicates that gibberellin is promoting longitudinal cell elongation rather than primarily increasing cell number.
5. A dwarf mutant fails to elongate after gibberellin application, whereas a second dwarf mutant elongates normally after the same treatment. Which interpretation is most appropriate for stem internode growth?
A.
The first mutant may be defective in gibberellin response, while the second may be deficient in gibberellin production
B.
The first mutant produces excess gibberellin, while the second cannot perceive light
C.
Both mutants must be defective only in cytokinin synthesis
D.
The second mutant is gibberellin-insensitive because it elongates after treatment
Correct Answer:
The first mutant may be defective in gibberellin response, while the second may be deficient in gibberellin production
Explanation:
An applied gibberellin rescues a biosynthetic deficiency but not a defect in hormone perception or downstream response, allowing the two dwarf phenotypes to be distinguished.
6. A plant has five stem internodes. Gibberellin is applied specifically to the third internode, and only that internode becomes markedly longer. What does this result most directly demonstrate?
A.
Gibberellin can act directly on developing internode tissues to enhance elongation
B.
Gibberellin always inhibits elongation in untreated internodes
C.
Internode elongation occurs only in roots after hormone application
D.
Gibberellin causes permanent shortening of mature internodes
Correct Answer:
Gibberellin can act directly on developing internode tissues to enhance elongation
Explanation:
The selective response of the treated internode shows that developing stem internode tissue can respond locally to gibberellin by increasing elongation.
7. Two plants receive equal amounts of gibberellic acid, but only the plant with actively growing internodes shows substantial stem elongation. Which explanation best accounts for this result?
A.
Gibberellin is most effective in tissues that retain the capacity for internode cell expansion
B.
Gibberellin promotes elongation only after all internode cells have stopped growing
C.
Mature internodes elongate more rapidly because their cells are fully lignified
D.
Gibberellin acts exclusively by increasing the number of mature, non-growing cells
Correct Answer:
Gibberellin is most effective in tissues that retain the capacity for internode cell expansion
Explanation:
Gibberellin strongly affects developing internodes because their cells can still expand; fully mature internode tissues have much less capacity for hormone-induced elongation.
8. In a cereal seedling, the internode between the seed and the shoot apex elongates rapidly after gibberellin treatment. Which conclusion is most directly supported?
A.
Gibberellin can promote elongation of a stem region located below the shoot apex
B.
Gibberellin promotes elongation only in the shoot apex itself
C.
The observed elongation must result from increased root growth
D.
Gibberellin prevents elongation of subapical stem regions
Correct Answer:
Gibberellin can promote elongation of a stem region located below the shoot apex
Explanation:
Rapid elongation of the subapical internode demonstrates that gibberellin acts on stem internode tissues and is not restricted to the shoot apex.
9. A plant growth regulator causes elongated stems only when applied during the phase in which internode cells are expanding. When cell expansion has ceased, the same treatment has little effect. Which regulator best fits this pattern?
A.
Gibberellin
B.
Abscisic acid
C.
Ethylene
D.
A cell-division inhibitor
Correct Answer:
Gibberellin
Explanation:
Gibberellin is closely associated with stem internode elongation through promotion of cell expansion, so its effect is greatest while internode cells are still elongating.
10. A mutation causes a plant to accumulate a precursor of gibberellin but produce little biologically active gibberellin. Which phenotype is most consistent with this biochemical defect?
A.
Short internodes that can be lengthened by applying active gibberellic acid
B.
Long internodes that become shorter after applying active gibberellic acid
C.
Normal internodes because inactive precursors directly stimulate elongation
D.
Short internodes that cannot respond to any external gibberellin
Correct Answer:
Short internodes that can be lengthened by applying active gibberellic acid
Explanation:
Accumulation of an inactive precursor indicates a defect in gibberellin activation or synthesis. Supplying active gibberellic acid bypasses that defect and promotes internode elongation.
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Stem Internode Elongation
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