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Question #47595
The Question
During severe drought stress in an ecotone, a C3 plant experiences a surge in Abscisic Acid (ABA). Which of the following best explains the sequential mechanism by which this hormonal response ultimately stalls the photolysis of water associated with Photosystem II?
Options
- A.
ABA induces stomatal closure, reducing intercellular CO2. This slows the Calvin cycle, halting the regeneration of NADP+, which creates an electron bottleneck in the Z-scheme and inhibits the Oxygen Evolving Complex.
- B.
ABA directly inhibits the efflux of K+ from guard cells, causing stomatal closure and a buildup of internal O2 that competitively inhibits the photolysis of water in the thylakoid lumen.
- C.
Stomatal closure depletes internal CO2, forcing the plant into photorespiration which rapidly consumes NADP+, leaving the non-cyclic electron transport chain without a primary electron donor.
- D.
The stress-induced ABA surge shifts the chloroplast entirely to cyclic photophosphorylation, which bypasses PSII and the Oxygen Evolving Complex, directly utilizing water to generate a proton gradient.
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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
Photolysis of Water Stoichiometry|Abscisic Acid (ABA) Antagonism|Ecotone and Edge Effect
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often treat the Light and Dark reactions as isolated events.
This question tests the critical biochemical link between them: the Dark reaction (Calvin cycle) provides the essential substrate (NADP+) required to keep the Light reaction (Z-scheme) running.
Failing to link ABA-induced stomatal closure to the biochemical bottleneck of NADP+ regeneration is the primary misconception.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Photosynthesis in Higher Plants - Class 11 |
| Concept | Photolysis of Water Stoichiometry |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |