Q.47 Given below are two statements : One is labelled as Assertion (A) and the other is
labelled as Reason (R).
Assertion (A) :Phytochrome is most abundant in etiolated seedlings.
Reasons (R) :Most biochemical studies have been carried out on phytochrome
purified from non green tissues.
In the light of the above statements, choose the most appropriate answer from the
options given below :
(1)Both (A) and (R) are correct and (R) is the correct explanation of (A)
(2)Both (A) and (R) are correct but (R) is NOT the correct explanation of (A)
(3)(A) is correct but (R) is not correct
(4)(A) is not correct but (R) is correct
Both (A) and (R) are correct and (R) is the correct explanation of (A), making option (1) correct.
Question Breakdown
Phytochrome, a key photoreceptor regulating light responses, exists in highest concentrations in etiolated (dark-grown) seedlings. This abundance facilitates biochemical purification and study from non-green tissues where interfering chlorophyll/pigments are absent.
Option Analysis
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(1) Both correct, (R) explains (A): Correct; etiolated seedlings maximize phytochrome for light detection upon emergence, AND non-green tissues enable easier purification—directly linking abundance to research practicality.
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(2) Both correct, (R) not explanation: Incorrect; (R) causally explains why phytochrome studies target etiolated tissues (high yield, clean extraction).
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(3) (A) correct, (R) incorrect: Incorrect; both statements reflect established plant physiology facts.
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(4) (A) incorrect, (R) correct: Incorrect; phytochrome peaks in etiolated seedlings (phyA dominant form).
Phytochrome etiolated seedlings assertion reason tests plant photobiology critical for GATE Life Sciences. Dark-grown seedlings accumulate phytochrome (Pr form) for rapid light responses (de-etiolation), purified easily from non-green tissues lacking chlorophyll interference.
Phytochrome Biology
Pr (660 nm) ↔ Pfr (730 nm) photoconversion triggers germination, stem elongation inhibition, chlorophyll synthesis.
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Highest in etiolated: PhyA (90-95%) protects against far-red shade.
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Purification: Non-green = high yield, no pigment contamination.
AR Logic Table
| Statement | Fact | Causal Link |
|---|---|---|
| A: Abundant in etiolated | ✓ Highest phyA | N/A |
| R: Studies use non-green tissues | ✓ Biochemical reality | Explains A (research target) |
Exam Strategy
GATE links physiology to methodology. Key: Etiolation = phytochrome maximization for study. Trap: Option (2) ignores practical research connection. Memorize: Dark seedlings = phytochrome research gold standard.
