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In sugarcane plant $^{14}CO_2$ is fixed in malic acid, in which the enzyme that fixes $CO_2$ is :-
A
Ribulose biphosphate carboxylase
B
Phosphoenol pyruvic acid carboxylase
C
Ribulose phosphate kinase
D
Fructose phosphatase
Detailed Solution
Sugarcane is a $C_4$ plant (Hatch and Slack pathway).
In the mesophyll cells, $CO_2$ (as bicarbonate) combines with phosphoenolpyruvate (PEP), catalysed by PEP carboxylase, to form the 4-carbon oxaloacetic acid (OAA).
OAA is then reduced to malic acid, which carries the fixed carbon to the bundle sheath cells.
There malic acid is decarboxylated, and the released $CO_2$ is fixed again by RuBisCO in the Calvin cycle.
So the enzyme that first fixes $CO_2$ (into OAA and then malic acid) is phosphoenol pyruvic acid carboxylase.
In the mesophyll cells, $CO_2$ (as bicarbonate) combines with phosphoenolpyruvate (PEP), catalysed by PEP carboxylase, to form the 4-carbon oxaloacetic acid (OAA).
OAA is then reduced to malic acid, which carries the fixed carbon to the bundle sheath cells.
There malic acid is decarboxylated, and the released $CO_2$ is fixed again by RuBisCO in the Calvin cycle.
So the enzyme that first fixes $CO_2$ (into OAA and then malic acid) is phosphoenol pyruvic acid carboxylase.