RuBP oxygenase-carboxylase (rubisco) is a key enzyme in photosynthesis. This enzyme can use carbon dioxide and oxygen as substrates.
→ During photosynthesis, in the first stage of the Calvin cycle, this enzyme incorporates carbon dioxide into the organic molecule ribulose 1,5 diphosphate forming a sugar molecule.
→During photorespiration, the enzyme attaches oxygen to its oxygenase reaction and produces two molecules, one three-carbon compound called 3-PGA, and another two-carbon compound called phosphoglycolate.
3-PGA can enter the Calvin cycle but phosphoglycolate cannot enter it, and thus two carbons are eliminated from it which leads to a decrease in sugar synthesis, making photosynthesis less efficient.
So, the statement in option A indicates the normal function of the rubisco during photosynthesis.
The correct option is B.