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Which pigment system becomes inactive in red drop?
Your answer:
Correct answer: (c)
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Explanation
Why (c) is correct
Red drop is the sharp fall in photosynthesis in far-red light (beyond 680 nm). PS II cannot absorb these wavelengths well, so PS II becomes inactive and water is not split. PS I (P700) can still work.
Why the other options are wrong
- (a) · your answer PS I still absorbs far-red light, so both systems do not stop.
- (b) · your answer PS I absorbs up to 700 nm and keeps working in far-red light.
- (d) · your answer Photosynthesis drops because one system (PS II) stops working.
NCERT point: PS II = P680 and PS I = P700. Far-red light drives cyclic flow through PS I only.
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