Practice important
Abscission inhibition
MCQ questions and answers.
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MCQ Questions
1. A leaf is treated with an auxin analogue on its petiole shortly before natural leaf fall. Which outcome most directly indicates successful inhibition of abscission?
A.
The leaf detaches earlier because the petiole becomes more sensitive to ethylene
B.
The formation and separation of cells in the abscission zone are delayed
C.
The leaf blade loses chlorophyll immediately but remains attached
D.
The petiole elongates rapidly because cell division increases in the abscission zone
Correct Answer:
The formation and separation of cells in the abscission zone are delayed
Explanation:
Auxin delays abscission by maintaining the tissues of the abscission zone and inhibiting the cellular separation that ultimately causes the organ to detach.
2. In an aging leaf, auxin production in the lamina declines while ethylene sensitivity of the abscission zone increases. What is the most likely consequence?
A.
The abscission zone becomes less responsive to ethylene and the leaf remains attached
B.
Auxin transport increases automatically and prevents separation of the petiole
C.
The decline in auxin protection permits abscission to proceed more readily
D.
The leaf undergoes stronger apical dominance because auxin is redistributed to the root
Correct Answer:
The decline in auxin protection permits abscission to proceed more readily
Explanation:
Auxin normally suppresses abscission. As its level or influence declines in an aging organ, the abscission zone becomes more capable of responding to ethylene and separating.
3. A researcher applies auxin only to the leaf blade of a detached experimental petiole, but the auxin is prevented from reaching the abscission zone. Why would inhibition of abscission be weak or absent?
A.
Auxin must act at or reach the abscission zone to maintain its resistance to separation
B.
Auxin can inhibit abscission only after being converted into starch in the leaf blade
C.
Auxin prevents abscission exclusively by increasing water absorption in roots
D.
Auxin is effective only when applied to the soil surrounding the plant
Correct Answer:
Auxin must act at or reach the abscission zone to maintain its resistance to separation
Explanation:
The inhibitory effect of auxin depends on its influence over the abscission zone. If auxin cannot reach or act there, the separation processes in that zone may continue.
4. Which treatment would most effectively reduce premature fruit drop caused by a decline in endogenous auxin near the fruit stalk?
A.
Apply a suitable auxin treatment to the fruit or pedicel before the abscission zone becomes fully active
B.
Remove all auxin from the fruit stalk so that the fruit matures rapidly
C.
Apply auxin only to the roots after the fruit has already separated
D.
Increase shading around the fruit to eliminate the abscission zone
Correct Answer:
Apply a suitable auxin treatment to the fruit or pedicel before the abscission zone becomes fully active
Explanation:
Exogenous auxin can delay premature fruit abscission when applied to the fruit or its stalk before separation is advanced, helping maintain the abscission zone in an attached state.
5. Two identical leaves receive equal auxin doses. In leaf P, auxin is applied before strong activation of the abscission zone; in leaf Q, it is applied after extensive cell separation has begun. Which result is most likely?
A.
Auxin prevents abscission more effectively in leaf P than in leaf Q
B.
Auxin prevents abscission more effectively in leaf Q because separated cells absorb more auxin
C.
Auxin has exactly the same effect because abscission is independent of timing
D.
Auxin accelerates abscission in leaf P but inhibits it in leaf Q
Correct Answer:
Auxin prevents abscission more effectively in leaf P than in leaf Q
Explanation:
Auxin is most effective when present before the separation process in the abscission zone is well established. Once cell separation has progressed, applying auxin is less likely to restore attachment.
6. Which observation best distinguishes auxin-mediated abscission inhibition from merely delaying visible leaf yellowing?
A.
The treated leaf remains attached because cells in its abscission zone do not separate readily
B.
The treated leaf remains green but detaches at the same time as the untreated leaf
C.
The treated leaf develops a larger lamina without any change in attachment
D.
The treated leaf absorbs more mineral ions through its roots
Correct Answer:
The treated leaf remains attached because cells in its abscission zone do not separate readily
Explanation:
Abscission inhibition specifically involves delayed separation in the abscission zone. Retention of green color alone does not demonstrate that auxin has inhibited organ detachment.
7. A fruit crop is sprayed with an auxin concentration that is too high. Why might this treatment fail to provide the intended control of fruit drop?
A.
Auxin effects are concentration-dependent, and an excessive dose may produce undesirable growth or injury rather than controlled retention
B.
High auxin concentrations always destroy the abscission zone before fruit development begins
C.
Excess auxin is unable to enter any plant tissue because it becomes chemically inert outside roots
D.
High auxin concentrations necessarily convert every fruit into a seedless fruit without affecting attachment
Correct Answer:
Auxin effects are concentration-dependent, and an excessive dose may produce undesirable growth or injury rather than controlled retention
Explanation:
Auxin must be used at an appropriate concentration for abscission control. Excessive doses can cause abnormal growth or injury, so they may not safely maintain fruit attachment.
8. A leaf petiole has an abscission zone, but the leaf remains attached after auxin treatment. Which cellular change is most consistent with the treatment?
A.
Reduced degradation of cell-wall components between cells in the abscission zone
B.
Complete destruction of vascular tissue throughout the petiole
C.
Conversion of all abscission-zone cells into root-hair cells
D.
Permanent inhibition of photosynthesis in the leaf blade
Correct Answer:
Reduced degradation of cell-wall components between cells in the abscission zone
Explanation:
Separation during abscission requires weakening and degradation of cell walls in the abscission zone. Auxin delays this process, helping keep the adjacent cells attached.
9. In an experiment, auxin is applied to one side of a fruit stalk and the untreated side later separates first. What does this result most strongly suggest?
A.
Local auxin application can maintain the treated portion of the abscission zone in a less separable condition
B.
Auxin acts only by increasing fruit respiration and cannot affect abscission tissues
C.
The untreated side separates first because auxin directly dissolves its cell walls
D.
Abscission occurs randomly and is unrelated to the distribution of auxin
Correct Answer:
Local auxin application can maintain the treated portion of the abscission zone in a less separable condition
Explanation:
The different responses on the two sides indicate a local effect: auxin can reduce the readiness of nearby abscission tissues to undergo cell separation.
10. Which experimental comparison would provide the strongest evidence that auxin delays abscission rather than simply delaying overall aging of a leaf?
A.
Compare treated and untreated leaves for attachment time while measuring separation specifically in their abscission zones
B.
Compare only the final heights of plants receiving different auxin treatments
C.
Measure root length without recording whether leaves remain attached
D.
Record flower color but exclude observations of the petiole and abscission zone
Correct Answer:
Compare treated and untreated leaves for attachment time while measuring separation specifically in their abscission zones
Explanation:
Direct evidence for abscission inhibition requires assessing whether auxin delays separation in the abscission zone and prolongs attachment, rather than relying on unrelated measures of plant aging or growth.
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