Which is the role of the enzyme rubisco?
a. condensation of ribulose 1,5-bisphosphate with carbon dioxide.
b. regeneration of ribulose 1,5 bisphosphate molecules.
c. splitting of a six-carbon product during the calvin cycle.
d. condensation of ribulose 1,5 bisphosphate with carbon dioxide and splitting of a six-carbon product during the calvin cycle.

Option D, Condensation of ribulose 1,5 bisphosphate with carbon dioxide and splitting of a six-carbon product during the Calvin cycle.

Explanation:

The enzyme Ribulose 1,5- bisphosphate carboxylase/oxygenase act as a catalyst in the reaction where CO2 attaches to ribulose 1,5-bisphosphate. In the end of this process, an unstable six carbon compound is formed.

Ribulose 1,5- bisphosphate is a molecule containing 5 - carbon molecule an when it combines it with CO2 during the Calvin cycle it splits into two molecules of 3-phosphoglyceric acid (3-PGA) which contains three carbon. This reaction is catalysed by Ribulose 1,5- bisphosphate carboxylase/oxygenase enzyme.

Hence option D is correct.