Question

The enzyme, which can catalyse both carboxylation and oxygenation of RuBP in the chloroplast, is not found in which of the following cells?

• A. Mesophyll cells of $C_4$ plants
• B. Mesophyll cells of $C_3$ plants
• C. Mesophyll cells of CAM plants
• D. Bundle sheath cells of $C_4$ plants

Answer 1

The correct option is A Mesophyll cells of $C_4$ plants

• C4 plant is a plant that cycles carbon dioxide into four-carbon sugar compounds to enter into the Calvin cycle.
• Photorespiration occurs in C3 plants only, in mesophyll cells as the enzyme Rubisco catalysis both carboxylation and oxygenation reactions of the initial acceptor molecule that is RuBP.
• C4 pathway requires the presence of two types of photosynthetic cells, i.e., mesophyll cells and bundle sheath cells.
• Rubisco enzyme, which is present only in bundle-sheath cells, does not come into contact with O2, and thus, oxygenation of RuBP is completely avoided in the C4 cycle.
• Hence, The enzyme, which can catalyse both carboxylation and oxygenation of RuBP in the chloroplast, is not found in Mesophyll cells of C4 plants and is present in bundle-sheath cells.
• So, the correct answer is 'Mesophyll cells of C4 plants'.