Question: how many carbon atoms are present in one molecule of ribulose bisphosphate?
Answer: A CO2​start text, C, O, end text, start subscript, 2, end subscript molecule combines with a five-carbon acceptor molecule, ribulose-1,5-bisphosphate (RuBP). This step makes a six-carbon compound that splits into two molecules of a three-carbon compound, 3-phosphoglyceric acid (3-PGA).