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Question #45930

Difficulty: 8/10 | 🟢 Free

The Question

Which of the following statements regarding the metabolic costs and spatial sequestration in $C_3$ and $C_4$ plants is INCORRECT?

Options

A.
In $C_4$ plants, the regeneration of PEP by Pyruvate Phosphate Dikinase (PPDK) in mesophyll cells consumes two ATP equivalents per $CO_2$ fixed.
B.
$C_3$ plants are universally less energy-efficient than $C_4$ plants because the inherent oxygenase activity of RuBisCO constantly drains ATP through the photorespiratory shuttle.
C.
The spatial sequestration of RuBisCO in the bundle sheath cells of $C_4$ plants creates a high $CO_2$ environment, effectively suppressing its oxygenase activity.
D.
Photorespiration in $C_3$ plants is a metabolic sink that involves a coordinated shuttle of intermediates between the chloroplast, peroxisome, and mitochondrion without synthesizing ATP or sugars.

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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

Shuttle System Impact|Photorespiration Metabolic Cost|C3 vs C4 Plants

Why This Question Is Tricky

Common Mistakes

Conceptual Pivot: Students often assume that because photorespiration is 'wasteful', $C_4$ plants are always more efficient.

They fail to account for the baseline metabolic cost (extra 12 ATP per glucose) of the $C_4$ shuttle.

The evolutionary advantage of $C_4$ plants is conditional, paying off only in hot, dry environments where photorespiration rates in $C_3$ plants would otherwise exceed the extra ATP cost of the $C_4$ pathway.

Quick Facts About This Question

Question Information

Subject	Biology
Chapter	Respiration in Plants - Class 11
Concept	Shuttle System Impact
Difficulty	8
Cognitive Load	5
Target Solve Time	120 sec
Access	Free