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Gibberellin Synergism
MCQ questions and answers.
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MCQ Questions
1. In an experiment on stem elongation, gibberellin alone increases elongation by 20%, auxin alone by 10%, but their combined application increases elongation by 55%. Which interpretation best demonstrates gibberellin synergism?
A.
The combined response is less than the sum of the individual responses
B.
The combined response exceeds the expected additive response of the two hormones
C.
Auxin completely inhibits the action of gibberellin
D.
Gibberellin becomes inactive when applied with auxin
Correct Answer:
The combined response exceeds the expected additive response of the two hormones
Explanation:
Synergism occurs when two hormones produce a combined effect greater than the sum of their separate effects. Here, 55% is greater than the additive expectation of 30%.
2. A dwarf plant shows moderate internode elongation after gibberellin treatment and moderate elongation after auxin treatment. When both are supplied together, elongation becomes much greater than the sum of the two separate responses. What does this result most directly indicate?
A.
Antagonism between gibberellin and auxin
B.
Irreversible destruction of auxin by gibberellin
C.
Synergistic interaction between gibberellin and auxin
D.
Independent action of the two hormones without interaction
Correct Answer:
Synergistic interaction between gibberellin and auxin
Explanation:
A response substantially greater than the sum of individual responses indicates synergism, meaning the hormones enhance each other's effects.
3. Four treatments produce the following relative stem-growth responses: gibberellin alone, 30 units; auxin alone, 20 units; both hormones, 48 units; solvent control, 5 units. Which conclusion is most justified after correcting for the control response?
A.
The hormones act antagonistically because the combined response is below 50 units
B.
The combined response shows synergism because it exceeds the sum of their control-corrected individual effects
C.
Only auxin is biologically active because its individual response is lower
D.
Gibberellin and auxin have identical effects because both affect stem growth
Correct Answer:
The combined response shows synergism because it exceeds the sum of their control-corrected individual effects
Explanation:
Control-corrected effects are 25 units for gibberellin and 15 units for auxin, totaling 40 units. The combined treatment gives 43 control-corrected units, exceeding the additive prediction and indicating synergism.
4. Which experimental design would provide the strongest evidence for gibberellin synergism with another growth-promoting hormone?
A.
Compare only untreated plants with plants receiving both hormones
B.
Apply different hormones to different species under unrelated conditions
C.
Measure untreated, gibberellin-only, partner-hormone-only, and combined treatments under identical conditions
D.
Apply gibberellin at one concentration and the partner hormone at several concentrations without replication
Correct Answer:
Measure untreated, gibberellin-only, partner-hormone-only, and combined treatments under identical conditions
Explanation:
Synergism can be established only by comparing the combined response with both individual responses and an untreated control under controlled, comparable conditions.
5. If gibberellin and auxin act synergistically in promoting internode elongation, which prediction is most appropriate when the concentration of one hormone is gradually increased while the other is held at an effective level?
A.
The combined response may exceed the response predicted from either hormone acting independently
B.
The response must remain exactly equal to the response caused by gibberellin alone
C.
The combined treatment must always produce inhibition at every concentration
D.
The interaction cannot be detected unless both hormones are used at identical concentrations
Correct Answer:
The combined response may exceed the response predicted from either hormone acting independently
Explanation:
Synergism means enhancement of a biological response through interaction. Therefore, combined treatment may produce a response greater than that expected from independent action, although the magnitude can depend on concentration.
6. A researcher concludes that gibberellin synergizes with auxin merely because both hormones independently increase stem length. Why is this conclusion insufficient?
A.
Synergism requires evidence that the combined response exceeds the expected additive response
B.
Synergism can occur only when one hormone reduces stem length
C.
Independent activity proves that the hormones are antagonistic
D.
Gibberellin cannot influence stem elongation in the presence of auxin
Correct Answer:
Synergism requires evidence that the combined response exceeds the expected additive response
Explanation:
Two hormones producing the same response independently does not establish synergism. The combined treatment must be compared with the sum or expected combined effect of the separate treatments.
7. In a factorial experiment, gibberellin increases plant height by 12 cm, cytokinin increases it by 4 cm, and the combined treatment increases height by 17 cm relative to the control. Which interpretation is most accurate?
A.
The result is consistent with synergism because the combined increase exceeds the additive prediction
B.
The result proves complete antagonism because cytokinin contributes less than gibberellin
C.
The result shows no interaction because both hormones increase height
D.
The result proves that cytokinin is the primary hormone responsible for gibberellin action
Correct Answer:
The result is consistent with synergism because the combined increase exceeds the additive prediction
Explanation:
The additive prediction is 16 cm, obtained by adding the individual increases of 12 cm and 4 cm. The combined increase of 17 cm is slightly higher, consistent with a synergistic interaction.
8. Which observation would distinguish gibberellin synergism from simple additivity in seedling growth?
A.
Gibberellin and the second hormone each produce measurable growth separately
B.
The combined treatment produces growth equal to the sum of the separate hormone effects
C.
The combined treatment produces growth greater than the sum of the separate hormone effects
D.
The untreated seedlings show no growth during the experiment
Correct Answer:
The combined treatment produces growth greater than the sum of the separate hormone effects
Explanation:
Simple additivity gives a combined response equal to the sum of individual effects. A combined response greater than that sum is the defining experimental indication of synergism.
9. A plant response to gibberellin is weak in the absence of a second growth regulator but becomes disproportionately large when both regulators are supplied. Which statement best explains this observation?
A.
The second regulator may enhance the sensitivity or effectiveness of gibberellin in producing the response
B.
Gibberellin is necessarily degraded by the second regulator
C.
The two regulators must have exactly identical molecular functions
D.
The response demonstrates that the second regulator has no biological activity
Correct Answer:
The second regulator may enhance the sensitivity or effectiveness of gibberellin in producing the response
Explanation:
Synergism involves enhancement of one hormone's effect by another, so the partner regulator may increase the effectiveness or responsiveness associated with gibberellin action.
10. Two treatments produce these control-corrected values for leaf expansion: gibberellin alone, 8 units; a second hormone alone, 6 units; both together, 13 units. Which conclusion is most defensible?
A.
The interaction is synergistic because 13 units is greater than the additive prediction of 14 units
B.
The interaction is additive because the combined response is close to the individual gibberellin response
C.
The interaction is not synergistic; the combined response is slightly below the additive prediction
D.
The interaction is necessarily antagonistic because both hormones promote expansion
Correct Answer:
The interaction is not synergistic; the combined response is slightly below the additive prediction
Explanation:
The additive prediction is 8 + 6 = 14 units. Since the combined response is 13 units, it does not exceed the additive expectation and therefore does not demonstrate synergism.
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