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Question #45211
The Question
The evolutionary success of higher plants relies on the efficient fixation of carbon and its translocation as a chemically stable sugar. Considering the biochemical trade-offs between carbon assimilation and transport, which of the following statements is INCORRECT?
Options
- A.
Sucrose is the preferred carbohydrate for phloem translocation because the glycosidic linkage between the anomeric carbons of glucose and fructose renders it a non-reducing, unreactive sugar.
- B.
In C3 plants under high temperature and light stress, the oxygenase activity of RuBisCO initiates a pathway that releases CO2 in the mitochondrion at the expense of ATP.
- C.
The photorespiratory pathway acts as a highly efficient salvage mechanism that recovers all the carbon diverted by RuBisCO's oxygenase activity, thereby protecting the net yield of sucrose synthesis.
- D.
C4 plants bypass the metabolic penalty of photorespiration by utilizing PEP carboxylase in mesophyll cells, an enzyme that completely lacks oxygenase activity even at low intracellular CO2 concentrations.
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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
Reducing vs Non-reducing Sugars|Rubisco Dual Functionality|C3 Cycle Stoichiometry
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot & Quantitative Nuance Trap: Students often misinterpret the term 'salvage pathway' in photorespiration.
While it attempts to salvage carbon from toxic phosphoglycolate, it is inherently lossy (losing 1 CO2 for every 2 molecules of phosphoglycolate processed) and consumes ATP.
The trap lies in the absolute phrase 'recovers all the carbon', which contradicts the NCERT fact that photorespiration is a wasteful process that heavily penalizes the energy budget required for synthesizing stable transport sugars like sucrose.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Biomolecules - Class 11 |
| Concept | Reducing vs Non-reducing Sugars |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |