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Question #47618
The Question
Read the following statements regarding the evolutionary and physiological constraints of the enzyme RuBisCO. Which of the following statements is INCORRECT?
Options
- A.
RuBisCO has a significantly higher affinity for CO2 than for O2, and the relative concentration of these gases determines which substrate binds to the active site.
- B.
The oxygenase activity of RuBisCO is considered an evolutionary relic from an ancestral era when the atmosphere was rich in CO2 and lacked O2, presenting no selective pressure to discriminate against O2.
- C.
In C4 plants, evolutionary pressure has successfully mutated the active site of RuBisCO in the bundle sheath cells to completely abolish its oxygenase binding capacity.
- D.
Despite the metabolic cost of photorespiration, C3 plants persist because structural modifications to completely exclude O2 from RuBisCO would drastically reduce its overall catalytic rate for CO2 fixation.
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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
C3_vs_C4_Plants|Evolution|Environment
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often confuse 'avoiding a process' with 'eliminating the capacity for a process'.
Because C4 plants do not exhibit photorespiration, a common misconception is that their RuBisCO enzyme is structurally superior or mutated to ignore O2.
In reality, the enzyme remains fundamentally flawed; the evolutionary adaptation is anatomical and biochemical (the PEPcase pump), not a redesign of RuBisCO's active site.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Photosynthesis in Higher Plants - Class 11 |
| Concept | Photorespiration Metabolic Cost |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |