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Question #46825
The Question
The formation of heartwood in woody dicots requires the massive synthesis of secondary metabolites (such as tannins and resins) by ray parenchyma cells, which are then deposited into adjacent dead xylem vessels, often via tyloses. This process relies heavily on the amphibolic nature of cellular respiration. Which of the following statements correctly identifies the metabolic trade-off and its physiological consequence during this transition?
Options
- A.
Excessive diversion of Acetyl-CoA and Phosphoenolpyruvate (PEP) into secondary metabolic sinks can skew TCA cycle stoichiometry, depriving parenchyma cells of the ATP required for structural reinforcement and tyloses expansion.
- B.
The withdrawal of Succinyl-CoA for the synthesis of aromatic tannins increases the rate of substrate-level phosphorylation, providing the excess energy needed for tyloses formation.
- C.
Tannin and resin biosynthesis relies entirely on the continuous oxidative decarboxylation of Pyruvate, which upregulates the TCA cycle to produce excess ATP directly inside the dead xylem vessels.
- D.
The transition from sapwood to heartwood is a passive accumulation of metabolic wastes in dead vessels, meaning the amphibolic withdrawal of respiratory intermediates from the TCA cycle is not required.
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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
Heartwood|TCA Cycle Stoichiometry|Reducing vs Non-reducing Sugars
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often view respiration purely as a catabolic, ATP-generating process and fail to integrate its amphibolic role (providing carbon skeletons) with secondary growth (Anatomy of Flowering Plants).
The trap lies in balancing the dual roles of the TCA cycle: providing precursors for secondary metabolites versus generating the ATP required to actively transport and deposit them via tyloses.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Anatomy of Flowering Plants - Class 11 |
| Concept | Heartwood vs Sapwood |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |