Final answer:
The key enzyme for carbon dioxide fixation during the Calvin cycle is ribulose bisphosphate carboxylase (RuBisCO), which is the most abundant enzyme on Earth, essential for synthesizing organic molecules like glucose.the right answer is A
Step-by-step explanation:
The major enzyme responsible for 'fixing' carbon dioxide during the Calvin cycle is called ribulose bisphosphate carboxylase (RuBisCO). This enzyme catalyzes the crucial step of carbon fixation in the light-independent reactions - also known as the Calvin cycle - of photosynthesis. The process involves RuBisCO adding a CO₂ molecule to ribulose bisphosphate (RuBP), which then forms two molecules of 3-phosphoglycerate (3-PGA). Subsequently, these molecules are reduced to glyceraldehyde-3-phosphate (G3P) by utilizing ATP and NADPH produced in the light-dependent reactions. Some of this G3P is used to build glucose, while the rest is utilized to regenerate RuBP, thus enabling continuous fixation of CO₂. RuBisCO is not only vital for the Calvin cycle but also the most abundant enzyme on Earth. Other options mentioned, like G3P, PEP carboxylase (PEPcase), and lactate dehydrogenase, play different roles in various metabolic pathways but do not fix carbon dioxide in the way RuBisCO does during the Calvin cycle.