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Question #47653

Difficulty: 8/10 | 🟢 Free

The Question

When a $C_3$ plant is exposed exclusively to monochromatic light of 700 nm, the 'Red Drop' phenomenon occurs. Under this specific environmental constraint, which of the following accurately describes the metabolic state of the chloroplast?

Options

A.
ATP synthesis occurs via cyclic photophosphorylation, but $CO_2$ assimilation halts due to the unavailability of NADPH for the reduction of 3-PGA.
B.
Stroma lamellae facilitate non-cyclic electron transport, generating sufficient ATP and NADPH to maintain a basal rate of the Calvin cycle.
C.
Photolysis of water continues at a reduced rate, allowing minimal $O_2$ evolution and sustained RuBP regeneration.
D.
The plant shifts entirely to photorespiration because the high internal $O_2$ concentration outcompetes $CO_2$ for the active site of RuBisCO.

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Evolutionary_Exception

Tackle problems where standard rules evolve or change based on specific environmental constraints.

Concepts Behind This Question

Respiratory Quotient (RQ) Constants|Red Drop and Emerson Enhancement Effect|Cyclic Photophosphorylation Pathways

Why This Question Is Tricky

Common Mistakes

Conceptual Pivot: Students often memorize that 'Dark reactions depend on Light reactions' but fail to dissect the exact biochemical dependencies.

The trap tests the decoupling of ATP production from NADPH production during cyclic photophosphorylation and its precise consequence on the reduction phase of the Calvin cycle.

It also tests the NCERT fact that stroma lamellae lack both PSII and NADP reductase.

Quick Facts About This Question

Question Information

Subject	Biology
Chapter	Respiration in Plants - Class 11
Concept	Respiratory Quotient (RQ) Constants
Difficulty	8
Cognitive Load	5
Target Solve Time	120 sec
Access	Free