C₄ Plants & Photorespiration Advantage — NEET Biology

Correct answer: A — A-II-3, B-I-1, C-III-2, D-IV-4

The core concept tested is the advantages of the C₄ pathway and the underlying mechanisms. A. Kranz Anatomy is characterized by large, thick-walled bundle sheath cells (II) that lack intercellular spaces. This anatomy allows for the spatial separation of initial CO₂ fixation and the Calvin cycle, contributing to the greater productivity and biomass production (4) by efficiently concentrating CO₂. B. PEPcase activity involves the primary fixation of CO₂ by PEPcase, an enzyme with high CO₂ affinity (I) that does not bind O₂. This allows for increased CO₂ fixation even at low atmospheric CO₂ concentrations (1). C. CO₂ transport to bundle sheath involves the C₄ acids (malic/aspartic acid) being transported to bundle sheath cells where they undergo decarboxylation (III) to release CO₂. This CO₂ concentrating mechanism ensures that RuBisCO operates in a high CO₂ environment, minimizing its oxygenase activity (2) and thus photorespiration. D. RuBisCO location in bundle sheath cells, coupled with the efficient CO₂ concentrating mechanism (IV, representing spatial separation and CO2 pump), ensures that C₄ plants can tolerate higher temperatures and light intensities (3) by effectively suppressing photorespiration. Matching the columns: - A (Kranz Anatomy) matches with II (Thick-walled bundle sheath cells) and 4 (Greater productivity and biomass production). - B (PEPcase activity) matches with I (High CO₂ affinity) and 1 (Increased CO₂ fixation at low atmospheric CO₂). - C (CO₂ transport to bundle sheath) matches with III (C₄ acids decarboxylation in bundle sheath) and 2 (Minimised oxygenase activity of RuBisCO). - D (RuBisCO location in bundle sheath) matches with IV (Spatial separation of reactions) and 3 (Tolerance to higher temperatures and light intensities). Therefore, the correct option is A-II-4, B-I-1, C-III-2, D-IV-3. This question evaluates the student's understanding of how specific anatomical and biochemical features of C₄ plants contribute to their ecological and physiological advantages.