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Question #46888

Difficulty: 8/10 | 🟢 Free

The Question

A researcher applies a chemical uncoupler that specifically makes biological membranes highly permeable to protons ( $H^+$ ), thereby dissipating any established transmembrane electrochemical gradient without inhibiting primary pumps or electron carriers. Which of the following paired physiological failures will be observed if this uncoupler is applied to the thylakoid membrane of a $C_3$ plant and the Malpighian tubules of Periplaneta americana?

Options

A.
Thylakoid: Halting of $NADP^+$ reduction; Malpighian tubules: Failure to synthesize uric acid from ammonia.
B.
Thylakoid: Cessation of ATP synthesis; Malpighian tubules: Arrest of potassium and urate secretion into the lumen.
C.
Thylakoid: Inhibition of the cytochrome $b_6f$ complex; Malpighian tubules: Inability to reabsorb water in the rectum.
D.
Thylakoid: Continuous ATP synthesis without oxygen evolution; Malpighian tubules: Accumulation of sodium ions in the hemolymph.

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Regulatory_Failure

Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.

Concepts Behind This Question

Cockroach Excretory Malpighian Tubules|Chemiosmotic ATP Synthesis Logic|Proton Gradient Directionality

Why This Question Is Tricky

Common Mistakes

Conceptual Pivot: Students often restrict the concept of a 'proton gradient' solely to ATP synthesis in mitochondria and chloroplasts (Chemiosmosis).

This question tests the NCERT-Plus application that proton gradients act as a universal biological battery, also driving secondary active transport (like urate secretion in insects).

A common misconception is assuming uncouplers inhibit the entire electron transport chain or primary pumps, rather than specifically short-circuiting the electrochemical gradient.

Quick Facts About This Question

Question Information

Subject	Biology
Chapter	Structural Organisation in Animals - Class 11
Concept	Cockroach Excretory Malpighian Tubules
Difficulty	8
Cognitive Load	5
Target Solve Time	120 sec
Access	Free