Question

In $C - 4$ plants, the primary $C{O_2}$ acceptor is ?

Answer 1

$C - 4$ photosynthesis is a carbon concentration mechanism used by some plants to increase photosynthetic carbon fixation ability. Most $C - 4$ plants' leaves have a Kranz Type anatomy composed of bundle sheath and mesophyll cells. Rubisco is only found in internalised bundle sheath cells or internalised chloroplasts in $C - 4$ leaves, where it protects against atmospheric ${O_2}$ and limits the oxygenase function of this enzyme.

Complete explanation:
The $3$-carbon molecule phosphonyl pyruvate is the main $C{O_2}$ acceptor in $C - 4$plants (PEP). The first step in the $C - 4$ pathway is the carboxylation of PEP, which results in the formation of oxaloacetic acid. It is eventually converted into malic acid, a $4 - C$compound. They are later moved from mesophyll to bundle sheath cells. In this step, OAA is broken down to produce carbon dioxide and a $3 - C$ molecule. The $C{O_2}$generated is used in the Calvin cycle, while the $3 - C$ molecule is transferred back to mesophyll cells for PEP regeneration.

Note:
Thus, it is stated that the $C - 4$ pathway begins with a three-carbon molecule known as phosphoenolpyruvate (PEP). This is the main $C{O_2}$ acceptor, and carboxylation occurs with the aid of an enzyme known as PEP carboxylase. They produce oxaloacetic acid, a $4 - C$ molecule (OAA).

Additional knowledge:
Just about $3\%$ of all vascular plants use the $C4$ pathway. The plants get their name from the $4$-carbon compound oxaloacetate, which is formed during the pathway.
$C4$ plants are extremely active in hot and dry climates, producing a large amount of energy. $C4$ plants that we commonly eat include pineapple, corn, sugar cane, and so on.