In ‘regular’ C4 and CAM plants, the enzyme that first fixes CO 2 into an organic
ID: 205846 • Letter: I
Question
In ‘regular’ C4 and CAM plants, the enzyme that first fixes CO2 into an organic molecule is
a, Ribulose 1,5-bisphosphate carboxylase/oxygenase for both
b. Phosphoenolpyruvate carboxylase for both
c. NADP-malic enzyme for both
d. Rubisco in CAM, PEPCase in ‘regular’ C4
e. Rubisco in ‘regular’ C4, PEPCase in CAM
a, Ribulose 1,5-bisphosphate carboxylase/oxygenase for both
b. Phosphoenolpyruvate carboxylase for both
c. NADP-malic enzyme for both
d. Rubisco in CAM, PEPCase in ‘regular’ C4
e. Rubisco in ‘regular’ C4, PEPCase in CAM
Explanation / Answer
Answer -B. Phosphoenolpyruvate carboxylase for both
First, atmospheric CO2 is fixed in the mesophyll cells to form a carbon organic acid (oxaloacetate). This step is carried out by a non-rubisco enzyme, PEP carboxylase.
Inside the bundle sheath, malate breaks down, releasing a molecule of CO2. The CO2 is then fixed by rubisco and made into sugars via the Calvin cycle