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Tissue Culture Growth Promotion
MCQ questions and answers.
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MCQ Questions
1. In an in vitro culture of genetically identical dwarf shoot explants, which observation most directly indicates a gibberellin-mediated growth response?
A.
Increased shoot internode elongation without a corresponding increase in cell number
B.
Complete suppression of cell expansion with enhanced callus browning
C.
Exclusive formation of roots without any change in shoot length
D.
Permanent inhibition of meristematic cell division
Correct Answer:
Increased shoot internode elongation without a corresponding increase in cell number
Explanation:
Gibberellins primarily promote shoot elongation by stimulating cell expansion, especially in internodes. In tissue culture, this can produce longer shoots even when the main response is not increased cell-number production.
2. A tissue-culture protocol produces compact, genetically normal shoots that are difficult to separate and transfer. Which use of gibberellin is most appropriate?
A.
Adding a suitable low concentration during the shoot-elongation phase
B.
Adding a high concentration only during root initiation
C.
Replacing all mineral nutrients with gibberellin
D.
Applying gibberellin after complete plant senescence
Correct Answer:
Adding a suitable low concentration during the shoot-elongation phase
Explanation:
Gibberellin can promote internode elongation in cultured shoots, helping separate compact clusters before transfer. The concentration must be optimized because excessive gibberellin may cause abnormal, weak growth.
3. Why can gibberellin improve the handling of microshoots before their transfer from culture vessels to soil?
A.
It elongates short internodes, making individual shoots easier to excise
B.
It sterilizes the shoot surface and eliminates all microbial contamination
C.
It permanently replaces the need for root formation
D.
It converts every cultured cell directly into a mature seed
Correct Answer:
It elongates short internodes, making individual shoots easier to excise
Explanation:
In tissue culture, gibberellin is often useful during shoot elongation because longer internodes allow microshoots to be separated and handled more easily before rooting and acclimatization.
4. A researcher adds gibberellic acid to a culture medium intended specifically for rapid root induction. The rooting response decreases. Which interpretation is most consistent with gibberellin physiology?
A.
Gibberellin-induced shoot elongation can antagonize or reduce the effectiveness of root-induction conditions
B.
Gibberellin always converts roots into leaves in every culture system
C.
Gibberellin destroys the explant's chromosomes immediately after absorption
D.
Gibberellin prevents water uptake by all cultured plant cells
Correct Answer:
Gibberellin-induced shoot elongation can antagonize or reduce the effectiveness of root-induction conditions
Explanation:
Gibberellin promotes shoot elongation, but high or mistimed levels may interfere with rooting responses. Therefore, it is generally used cautiously and often separated from the root-induction phase.
5. Two otherwise identical shoot cultures receive different treatments. Culture X receives cytokinin alone, whereas culture Y receives cytokinin followed by a carefully optimized gibberellin treatment. What is the most likely purpose of the second treatment?
A.
To elongate newly formed shoots after cytokinin-supported shoot multiplication
B.
To prevent all cell division during shoot multiplication
C.
To replace the requirement for light in photosynthetic cultures
D.
To induce genetic recombination between unrelated explants
Correct Answer:
To elongate newly formed shoots after cytokinin-supported shoot multiplication
Explanation:
Cytokinin is commonly associated with shoot multiplication, while gibberellin can subsequently promote elongation of the compact shoots. This sequential use can improve the production of transferable microshoots.
6. In a tissue culture experiment, gibberellin increases the length of shoots but does not significantly increase the number of shoot primordia. Which conclusion is most justified?
A.
The principal response is elongation rather than multiplication of shoot initials
B.
Gibberellin has selectively destroyed all shoot meristems
C.
The culture has undergone complete root differentiation
D.
The hormone has acted only as a carbon source
Correct Answer:
The principal response is elongation rather than multiplication of shoot initials
Explanation:
Gibberellin is especially associated with cell expansion and internode elongation. An increase in shoot length without more shoot primordia indicates elongation rather than enhanced shoot multiplication.
7. A commercial micropropagation protocol uses gibberellin during shoot elongation, but excessive concentrations produce thin, weak shoots. What is the best explanation?
A.
Excessive gibberellin can cause over-elongation and reduce desirable shoot sturdiness
B.
Excessive gibberellin always increases lignification and makes shoots rigid
C.
Gibberellin at high concentration prevents every form of cell expansion
D.
The response proves that gibberellin functions only in root cultures
Correct Answer:
Excessive gibberellin can cause over-elongation and reduce desirable shoot sturdiness
Explanation:
Although gibberellin promotes elongation, an excessive dose may produce elongated, weak, or abnormal shoots. Tissue-culture protocols therefore require concentration and timing optimization.
8. A culture contains short shoot buds that remain compact despite adequate nutrients and light. Which change would most directly test whether gibberellin is limiting shoot elongation?
A.
Add a graded series of gibberellin concentrations and compare internode length
B.
Remove all water from the medium and measure root color
C.
Replace the explants with sterile glass pieces
D.
Measure only the pH before discarding the cultures
Correct Answer:
Add a graded series of gibberellin concentrations and compare internode length
Explanation:
A concentration-response experiment directly tests gibberellin involvement in shoot elongation. Internode length is an appropriate growth parameter because gibberellin commonly promotes extension of shoot regions.
9. Why might a tissue-culture scientist apply gibberellin after shoot formation rather than during the earliest stage of callus induction?
A.
Its main intended benefit may be elongation of formed shoots, not indiscriminate stimulation of undifferentiated callus
B.
Gibberellin is chemically active only after roots have completely died
C.
Gibberellin can function only in media lacking all plant nutrients
D.
Early exposure guarantees that every callus cell becomes a seed embryo
Correct Answer:
Its main intended benefit may be elongation of formed shoots, not indiscriminate stimulation of undifferentiated callus
Explanation:
Gibberellin is particularly useful when organized shoots need elongation. Applying it at the shoot-development stage allows the protocol to target shoot extension rather than using it indiscriminately during callus induction.
10. A micropropagated plantlet is transferred to soil immediately after a gibberellin treatment that produced very long shoots but weak roots. Which protocol adjustment is most logical?
A.
Use gibberellin only for shoot elongation, then provide a separate optimized rooting phase before acclimatization
B.
Increase gibberellin further during rooting to maximize shoot length
C.
Eliminate the rooting phase because elongated shoots root automatically
D.
Use gibberellin as the sole substitute for water during acclimatization
Correct Answer:
Use gibberellin only for shoot elongation, then provide a separate optimized rooting phase before acclimatization
Explanation:
Gibberellin can be valuable for elongating cultured shoots but is not a substitute for rooting conditions. Separating the elongation and rooting phases helps obtain shoots that are both manageable and capable of successful establishment.
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