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Question #45928

Difficulty: 8/10 | 🟢 Free

The Question

Eukaryotic aerobic respiration relies on shuttle systems (e.g., malate-aspartate) to transport cytosolic reducing equivalents into the mitochondria for the $O_2$ -dependent Electron Transport Chain (ETC). Methanogens (Archaea) thrive in strictly anaerobic niches and bypass this necessity. Which of the following statements INCORRECTLY describes the metabolic adaptations of methanogens?

Options

A.
They lack membrane-bound organelles, inherently eliminating the spatial barrier that necessitates eukaryotic NADH shuttle systems.
B.
They utilize $CO_2$ as a terminal electron acceptor, reducing it to $CH_4$ via specialized pathways, thereby decoupling ATP production from $O_2$ .
C.
Due to the absence of an $O_2$ -linked ETC, their energy homeostasis relies entirely on substrate-level phosphorylation in the cytoplasm.
D.
Their obligate anaerobic metabolism allows them to dominate extreme niches, such as the rumen of cattle, where standard oxidative phosphorylation is inhibited.

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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

Shuttle System Impact|Methanogens Metabolism|Electron Acceptors

Why This Question Is Tricky

Common Mistakes

Conceptual Pivot: Students frequently conflate 'anaerobic conditions' strictly with 'fermentation' (which relies solely on substrate-level phosphorylation).

They fail to recognize that true anaerobic respiration (like methanogenesis) still utilizes an electron transport chain and chemiosmosis across the plasma membrane, just with a different terminal electron acceptor (e.g., $CO_2$ instead of $O_2$ ).

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