Question

In $C_4$ plants, the initial $C{O}_2$ fixation takes place in the chloroplasts of the

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

Answer 1

The correct option is B Spongy mesophyll.

In $C_4$ plants the carbon dioxide is initially fixed into four carbon atom containing organic acids, like malate and oxalo acetic acid. The carbon dioxide is fixed initially in the chloroplasts of spongy mesophyll tissue by the enzyme PEP carboxylase. The organic acids are then transported to bundle sheath cells, where the acids are decarboxylated to release carbon dioxide. The released carbon dioxide is now fixed by the enzyme RUBISCO via the Calvin cycle.