Before You Begin
Question #45987
The Question
Phytochrome in its active Pfr form functions as a kinase to initiate photomorphogenesis (de-etiolation). A researcher applies a competitive inhibitor that specifically binds to the catalytic active site of the Pfr kinase domain in a germinating dicot seed, which is then exposed to continuous red light. Which of the following statements correctly describes the resulting physiological state of the seedling and the kinetic parameters of the Pfr kinase?
Options
- A.
The seedling undergoes etiolation; the apparent Km of the Pfr kinase increases, but Vmax remains unchanged.
- B.
The seedling undergoes de-etiolation; the apparent Km of the Pfr kinase increases, but Vmax remains unchanged.
- C.
The seedling undergoes etiolation; the Vmax of the Pfr kinase decreases, but Km remains unchanged.
- D.
The seedling undergoes de-etiolation; both the apparent Km and Vmax of the Pfr kinase decrease.
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
Pr_to_Pfr|Kinase_Cascades|Protein_Phosphorylation
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often rigidly memorize 'Red light = Pfr = Photomorphogenesis' without realizing that if the downstream enzymatic activity of Pfr is blocked, the physiological outcome reverts to the default dark state (etiolation).
This question requires synthesizing concepts from two distinct NCERT chapters: Plant Growth & Development (Phytochrome responses) and Biomolecules (Competitive Enzyme Inhibition Kinetics).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Plant Growth and Development - Class 11 |
| Concept | Phytochrome Interconversion |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |