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Question #46754
The Question
While evaluating the bioenergetic efficiency of Crassulacean Acid Metabolism (CAM) compared to standard C3 photosynthesis, a unique metabolic bottleneck is observed. Which of the following statements correctly identifies the primary reason for the increased ATP demand in CAM plants?
Options
- A.
CAM plants require additional ATP during the day to actively transport malate out of the vacuole into the chloroplast stroma.
- B.
The nocturnal phase demands continuous ATP expenditure to actively sequester malic acid into the large central vacuole against a steep concentration gradient.
- C.
CAM plants bypass the ATP-consuming regeneration phase of the Calvin cycle by directly utilizing PEP carboxylase during the day.
- D.
The light reactions in CAM plants must generate extra NADPH to compensate for the nocturnal reduction of oxaloacetate to malate.
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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
Thylakoid Lumen Sequestration|Optimal Foraging Theory|PEP Carboxylase
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often assume that because CAM plants utilize the C3 cycle during the day, their overall energy budget is identical to C3 plants.
The trap lies in failing to account for the active transport costs of intracellular compartmentalization (vacuolar sequestration).
The misconception is applying standard C3 thylakoid energy budgets to CAM physiology, ignoring the nocturnal ATP starvation risk caused by the active pumping of malic acid.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Cell – The Unit of Life - Class 11 |
| Concept | Thylakoid Lumen Sequestration |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |