Question

The first carbon dioxide fixation product of\[{C_4}\] plants is
A. Oxaloacetic acid
B. Ribulose biphosphate
C. Phosphoenol pyruvate
D. Phosphoglyceric acid

Answer 1

Hint: A\[{C_4}\]plant is a plant that cycles carbon dioxide into four-carbon sugar compounds to enter into the Calvin cycle. These plants are very effective in hot, arid climates and make lots of energy.

Complete step-by-step answer:
 In\[{C_4}\] plants, the light-dependent reactions and the Calvin cycle are separated physically, with the light-dependent reactions that occur in mesophyll cells (spongy tissue in the centre of the leaf) and the Calvin cycle that occurs in special cells all over the leaf veins. Those cells are referred to as bundle-sheath cells. In\[{C_4}\] plants, the initial fixation of carbon dioxide takes place in mesophyll cells. The primary acceptor of \[C{o_2}\]i.e., \[C{o_2}\] mixes with phosphoenol pyruvate (PEP) in the presence of PEPcase or PEP carboxylase to form oxaloacetic acid, which is the first stable carbon dioxide fixation product in the\[{C_4}\] pathway. Then OAA is transformed into malic acid and transferred to bundle sheath cells. In the bundle sheath cells, \[C{o_2}\]is released and it goes into the Calvin cycle and is processed by RuBisCO. Because of the greater concentration of carbon dioxide in the bundle sheath cells, photorespiration is reduced.

Therefore the correct answer is option A.

Note: The \[{C_4}\]pathway is used in approximately \[3\% \] of all vascular plants. Some examples are sugarcane, crabgrass, and corn. \[{C_4}\]plants are common in environments that are hot but are less rich in regions that are cooler. In warm conditions, the advantages of decreased photorespiration likely go beyond the ATP cost of moving \[C{o_2}\]from the mesophyll cell to the bundle-sheath cell.