biology : class11 Late Embryogenesis Abundant Proteins : Functions, Stress Response, Dormancy : Abscisic Acid MCQ Questions and Answers
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Late Embryogenesis Abundant Proteins
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MCQ Questions
1. Which molecular property most directly explains how many Late Embryogenesis Abundant proteins protect plant cells during severe dehydration?
A.
They remain highly hydrophilic and can stabilize macromolecules without requiring a compact folded structure
B.
They hydrolyze membrane lipids to release osmoprotective sugars
C.
They function as membrane-spanning channels that import water into the cytoplasm
D.
They catalyze the synthesis of abscisic acid during embryo maturation
Correct Answer:
They remain highly hydrophilic and can stabilize macromolecules without requiring a compact folded structure
Explanation:
Many LEA proteins are intrinsically disordered and highly hydrophilic. This allows them to retain water, associate with cellular macromolecules, and reduce damage caused by dehydration without acting as enzymes.
2. A mutant plant produces normal amounts of abscisic acid during seed maturation but lacks a functional group of LEA proteins. Which phenotype is most directly expected?
A.
Seeds would be unable to synthesize storage lipids
B.
Seeds would show reduced tolerance to desiccation despite normal ABA accumulation
C.
Seeds would lose the ability to perceive light during germination
D.
Seeds would produce excessive chlorophyll during late embryogenesis
Correct Answer:
Seeds would show reduced tolerance to desiccation despite normal ABA accumulation
Explanation:
ABA can induce stress-responsive genes, including LEA genes, but LEA proteins act downstream as protective molecules. Their absence can therefore impair desiccation tolerance even when ABA production is normal.
3. Which observation would provide the strongest evidence that a newly identified seed protein belongs functionally to the LEA group?
A.
It accumulates during late embryogenesis, is highly hydrophilic, and improves survival after controlled drying
B.
It is restricted to chloroplast membranes and absorbs red light
C.
It is a protease that becomes active only in fully hydrated seeds
D.
It is a DNA polymerase expressed exclusively during cell division
Correct Answer:
It accumulates during late embryogenesis, is highly hydrophilic, and improves survival after controlled drying
Explanation:
LEA proteins characteristically accumulate during late seed development and are associated with protection against cellular dehydration. Hydrophilicity and improved survival after drying are especially informative functional clues.
4. Why can LEA proteins protect enzymes during cellular dehydration even though many LEA proteins lack a stable three-dimensional structure in solution?
A.
Their flexible chains can surround or associate with vulnerable proteins and limit dehydration-induced aggregation
B.
Their rigid active sites chemically replace damaged amino acids in enzymes
C.
Their instability causes them to release heat that prevents protein denaturation
D.
Their folded domains convert insoluble enzymes into membrane lipids
Correct Answer:
Their flexible chains can surround or associate with vulnerable proteins and limit dehydration-induced aggregation
Explanation:
Many LEA proteins are intrinsically disordered in hydrated conditions but can interact with target proteins during stress. These interactions help maintain protein solubility and reduce irreversible aggregation during water loss.
5. A seed line overexpresses a LEA protein and survives drying better than the wild type, but its total soluble sugar concentration is unchanged. Which conclusion is most justified?
A.
The LEA protein may provide protection independently of increasing soluble sugar accumulation
B.
The LEA protein must be functioning as a sugar-degrading enzyme
C.
The improved survival proves that ABA synthesis has been completely blocked
D.
The protein must have replaced all seed storage proteins
Correct Answer:
The LEA protein may provide protection independently of increasing soluble sugar accumulation
Explanation:
LEA proteins can stabilize proteins, membranes, and other cellular structures directly. Therefore, enhanced dehydration tolerance need not result from an increase in soluble sugars.
6. Which experiment most directly tests whether a candidate LEA protein protects membranes from dehydration-induced damage?
A.
Measure electrolyte leakage from liposomes containing the protein before and after controlled drying
B.
Measure the protein's ability to absorb ultraviolet light in a spectrophotometer
C.
Determine whether the protein increases DNA replication in hydrated cells
D.
Compare the number of chloroplasts in leaves expressing the protein
Correct Answer:
Measure electrolyte leakage from liposomes containing the protein before and after controlled drying
Explanation:
Membrane disruption caused by drying can be estimated by electrolyte leakage. Comparing dried liposomes with and without the candidate protein directly tests whether it reduces dehydration-induced membrane damage.
7. During maturation of a drought-tolerant seed, LEA transcripts rise before the corresponding proteins accumulate. Which explanation best accounts for this observation?
A.
Transcription and translation are separate stages, so protein accumulation can lag behind transcript accumulation
B.
LEA proteins are synthesized first and later converted into their own messenger RNAs
C.
The transcripts must be unrelated because stress proteins cannot be translated in seeds
D.
The delay proves that LEA proteins are produced only after seed germination
Correct Answer:
Transcription and translation are separate stages, so protein accumulation can lag behind transcript accumulation
Explanation:
LEA gene expression proceeds through transcription followed by translation. A rise in mRNA before protein accumulation is therefore consistent with regulated production of LEA proteins during seed maturation.
8. Which result would most strongly distinguish a protective LEA function from a merely correlated association with drought tolerance?
A.
Purified LEA protein increases the recovery of a dried enzyme's activity compared with a control protein
B.
The LEA gene is located near another drought-responsive gene on a chromosome
C.
LEA transcripts are detected in plants exposed to a nonstressful light cycle
D.
The protein has a molecular mass similar to that of another seed protein
Correct Answer:
Purified LEA protein increases the recovery of a dried enzyme's activity compared with a control protein
Explanation:
A direct in vitro protection assay demonstrates that the LEA protein itself can preserve enzyme function during dehydration. This is stronger evidence than simple co-expression with other stress-related genes.
9. A seed-specific LEA protein is experimentally redirected from the cytoplasm to a different cellular compartment. Its ability to protect cytoplasmic enzymes during drying is lost. What does this result suggest?
A.
LEA protection depends partly on localization near the cellular structures or macromolecules that require stabilization
B.
LEA proteins function only by increasing the rate of photosynthesis
C.
LEA proteins must be permanently secreted outside the seed to act
D.
LEA proteins protect cells exclusively by binding to nuclear DNA
Correct Answer:
LEA protection depends partly on localization near the cellular structures or macromolecules that require stabilization
Explanation:
LEA proteins act through physical and biochemical interactions with cellular components. Mislocalization can prevent them from reaching cytoplasmic enzymes and therefore eliminate their protective effect.
10. Which statement best describes the relationship between LEA proteins and seed desiccation tolerance?
A.
LEA proteins are one component of a coordinated protective system that helps cellular structures withstand severe water loss
B.
LEA proteins are the sole cause of seed dormancy and directly prevent all germination signals
C.
LEA proteins increase cellular water loss so that seeds mature more rapidly
D.
LEA proteins function only after seeds have completed germination and resumed active growth
Correct Answer:
LEA proteins are one component of a coordinated protective system that helps cellular structures withstand severe water loss
Explanation:
LEA proteins contribute to, but do not solely determine, desiccation tolerance. They help stabilize proteins, membranes, and other macromolecular structures during the dehydration associated with late embryogenesis.
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