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Question #47589
The Question
A researcher applies exogenous Abscisic Acid (ABA) to the leaves of a well-watered plant to study stomatal dynamics. However, the plant is kept under continuous monochromatic light of 700 nm. The researcher observes that the stomata fail to close rapidly, remaining in a 'locked' non-responsive state. Based on plant bioenergetics, which of the following best explains this physiological failure?
Options
- A.
The lack of synergistic action between PSI and PSII prevents non-cyclic photophosphorylation, resulting in an ATP deficit that hinders the energy-dependent mechanisms of ABA signal transduction.
- B.
Monochromatic far-red light exclusively activates Photosystem II, causing an overproduction of NADPH that allosterically inhibits the guard cell H+-ATPase pumps.
- C.
ABA requires a direct photo-activation step by blue light receptors (phototropins) to initiate the efflux of potassium (K+) ions from the guard cells.
- D.
The Emerson effect blockade prevents cyclic electron flow in the stroma lamellae, completely stopping the synthesis of both ATP and O2 required for guard cell respiration.
Check Your Answer
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
Stomatal_Conductance|Photophosphorylation|ABA_Hormone
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize 'ABA closes stomata' as an absolute, passive rule, failing to realize that cellular signal transduction requires ATP.
The trap requires synthesizing three distinct NCERT concepts: the specific wavelength of PSI (700 nm), the Emerson enhancement effect (synergy of PSI and PSII for non-cyclic ATP production), and the bioenergetic dependency of guard cell dynamics.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Photosynthesis in Higher Plants - Class 11 |
| Concept | Red Drop and Emerson Enhancement Effect |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |