Practice important
Dormancy Release
MCQ questions and answers.
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MCQ Questions
1. A batch of viable seeds remains dormant even when supplied with water, oxygen, and a favorable temperature. Exogenous gibberellin releases germination, whereas exogenous abscisic acid maintains dormancy. Which interpretation best explains this result?
A.
Gibberellin promotes dormancy by suppressing embryo growth
B.
Abscisic acid and gibberellin act antagonistically in regulating dormancy release
C.
Abscisic acid directly increases water uptake during germination
D.
Gibberellin prevents the mobilization of stored food reserves
Correct Answer:
Abscisic acid and gibberellin act antagonistically in regulating dormancy release
Explanation:
ABA maintains seed dormancy, while gibberellin promotes embryo growth and germination. Their opposing effects are central to dormancy release.
2. Which change most directly favors the release of physiological seed dormancy in a mature, viable seed?
A.
An increase in the ABA-to-gibberellin ratio
B.
A decrease in embryo sensitivity to gibberellin
C.
A decline in ABA concentration accompanied by increased gibberellin action
D.
Continued accumulation of ABA in the embryo
Correct Answer:
A decline in ABA concentration accompanied by increased gibberellin action
Explanation:
Dormancy release generally involves reduced ABA influence and enhanced gibberellin-mediated growth, allowing the embryo to resume development.
3. A seed fails to germinate because its seed coat restricts oxygen diffusion and prevents water entry, although the embryo is physiologically capable of growth. Which treatment most specifically releases this type of dormancy?
A.
Scarification of the seed coat
B.
Application of additional ABA
C.
Removal of oxygen from the environment
D.
Increasing the ABA concentration inside the embryo
Correct Answer:
Scarification of the seed coat
Explanation:
Scarification physically weakens or removes part of a hard seed coat, improving water and oxygen access and thereby releasing physical dormancy.
4. Some temperate plant seeds germinate only after exposure to a prolonged period of moist chilling. This treatment releases dormancy primarily by:
A.
Increasing ABA synthesis during chilling
B.
Replacing the embryo with a vegetative bud
C.
Inducing physiological changes that reduce dormancy and permit subsequent germination
D.
Desiccating the seed coat and blocking water uptake
Correct Answer:
Inducing physiological changes that reduce dormancy and permit subsequent germination
Explanation:
Cold, moist stratification releases physiological dormancy through internal biochemical changes, including reduced ABA influence and improved responsiveness to germination-promoting signals.
5. A dormant seed is exposed to favorable water and temperature conditions, but germination begins only after a period of dry storage. Which process most plausibly accounts for this dormancy release?
A.
After-ripening that gradually decreases the seed's dormancy state
B.
Permanent inhibition of embryo metabolism
C.
Accumulation of ABA until the embryo becomes dormant
D.
Conversion of the embryo into non-living storage tissue
Correct Answer:
After-ripening that gradually decreases the seed's dormancy state
Explanation:
After-ripening is a post-maturation period during which dry storage can reduce physiological dormancy, allowing the seed to germinate when favorable conditions return.
6. A mutant seed produces normal levels of ABA but shows reduced sensitivity to ABA in the embryo. Compared with the wild type, what is the most likely phenotype?
A.
Enhanced dormancy and delayed germination
B.
Premature germination and reduced dormancy
C.
Complete inability to absorb water
D.
Failure to respond to gibberellin because ABA sensitivity is reduced
Correct Answer:
Premature germination and reduced dormancy
Explanation:
ABA sensitivity is required to maintain dormancy. If embryo tissues cannot respond effectively to normal ABA levels, dormancy may be weakened and premature germination may occur.
7. A developing seed germinates prematurely while still attached to the parent plant. Which defect most directly explains this failure to maintain dormancy?
A.
Excessive gibberellin breakdown in the embryo
B.
Insufficient ABA production or signaling during seed maturation
C.
Complete absence of water in the maternal tissue
D.
Overproduction of dormancy-maintaining proteins by the embryo
Correct Answer:
Insufficient ABA production or signaling during seed maturation
Explanation:
ABA normally establishes and maintains dormancy during seed maturation. Reduced ABA synthesis or signaling can cause vivipary, or premature germination on the parent plant.
8. A researcher applies gibberellin to intact dormant seeds, but germination remains poor. After the seed coat is mechanically weakened, the same gibberellin treatment produces rapid germination. What does this demonstrate?
A.
Gibberellin can always overcome every type of dormancy without external modification
B.
Physical seed-coat constraints can prevent a hormonal germination signal from being effective
C.
ABA is synthesized only after scarification
D.
Scarification increases dormancy by reducing oxygen entry
Correct Answer:
Physical seed-coat constraints can prevent a hormonal germination signal from being effective
Explanation:
Gibberellin promotes embryo growth, but a restrictive seed coat may block water or oxygen entry and mechanically resist radicle emergence. Scarification removes this barrier.
9. Which experimental result would provide the strongest evidence that a treatment has released ABA-maintained physiological dormancy rather than merely softened the seed coat?
A.
The treated seed coat becomes visibly thinner, but the embryo remains inactive
B.
Germination occurs only when the seed is physically opened
C.
The isolated embryo resumes growth after treatment, even without mechanical damage to the seed coat
D.
Water uptake increases while radicle emergence remains absent
Correct Answer:
The isolated embryo resumes growth after treatment, even without mechanical damage to the seed coat
Explanation:
If an isolated embryo resumes growth, the treatment has acted on internal physiological dormancy rather than simply removing a mechanical or permeability barrier imposed by the seed coat.
10. In a dormant seed, which sequence most accurately represents the hormonal changes associated with release of dormancy and initiation of germination?
A.
ABA increases, gibberellin decreases, and embryo growth is suppressed
B.
ABA influence decreases, gibberellin action increases, and embryo growth resumes
C.
Both ABA and gibberellin increase equally, producing permanent dormancy
D.
Gibberellin influence decreases first, followed by increased ABA sensitivity and radicle emergence
Correct Answer:
ABA influence decreases, gibberellin action increases, and embryo growth resumes
Explanation:
Dormancy release involves weakening of ABA-mediated inhibition and strengthening of gibberellin-promoted embryo growth, ultimately permitting radicle emergence and germination.
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