Question

First carbon fixation in $C_4$ pathway occurs in chloroplasts of

• A. Pallisade tissue
• B. Spongy mesophyll
• C. Bundle sheath
• D. Guard cells

Answer 1

Answer: (B)

Spongy mesophyll

C carbon fixation is a metabolic pathway for carbon fixation in photosynthesis, along with C and CAM metabolic pathways. In C${}_4$ plants, for example maize, PEP carboxylase fixes bicarbonate in the mesophyll cells of the leaf and the resulting four-carbon compound, malate, is shuttled into the bundle sheath cells where it releases CO for fixation by RuBisCo. So, first carbon fixation in C${}_4$ plants occurs in spongy mesophyll cells. Thus, option B is correct and other options are incorrect.