Before You Begin
Question #46239
The Question
A plant physiologist applies a chemical uncoupler to a dicot leaf, rendering its thylakoid membranes freely permeable to protons. Despite the leaf possessing a highly efficient reticulate venation system, the mass flow of sugars from this source leaf to the sink completely ceases. Based on NCERT principles of transport and photosynthesis, which of the following best explains this physiological failure?
Options
- A.
The uncoupler prevents the reduction of NADP+, directly inhibiting the synthesis of sucrose in the mesophyll cells.
- B.
Dissipation of the proton gradient halts ATP synthesis, preventing the active loading of sucrose into companion cells.
- C.
The loss of the electrochemical gradient in the thylakoid lumen directly prevents the osmotic entry of water into the xylem.
- D.
The uncoupler destroys the plasmodesmata connections between mesophyll cells and bundle sheath cells, blocking symplastic transport.
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
Proton_Gradient_Directionality|Chemiosmotic_ATP_Synthesis|Leaf_Venation_Patterns
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Bridging Chapter 13 (Photosynthesis bioenergetics) with Chapter 11 (Transport in Plants).
Students often isolate these chapters and fail to connect that the structural advantage of leaf venation for translocation is entirely dependent on the biochemical generation of ATP via chemiosmosis to power the active loading of sucrose at the source.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Morphology of Flowering Plants - Class 11 |
| Concept | Leaf Venation Patterns |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |