Final answer:
The statement about the Calvin cycle's initial steps—where CO2 attaches to RuBP, forms a six-carbon intermediate, and immediately splits into two three-carbon PGA molecules—is True. The Calvin cycle must complete multiple turns to produce a single glucose molecule.the answer is true
Step-by-step explanation:
The first step in the Calvin cycle is the attachment of a carbon dioxide molecule to RuBP (ribulose bisphosphate). This process is facilitated by the enzyme RuBisCO. The six-carbon intermediate that is formed is unstable and so short-lived that it immediately breaks down into two molecules of 3-phosphoglycerate (3-PGA), each with three carbon atoms. Therefore, the statement that 'the first event in the Calvin cycle is the attachment of carbon dioxide to the five-carbon RuBP molecule, which forms a six-carbon molecule that immediately breaks down into two three-carbon PGA molecules' is True.
Each molecule of 3-PGA is then reduced to glyceraldehyde-3-phosphate (G3P). The Calvin cycle needs to turn three times to produce a single three-carbon G3P molecule and six times to produce a glucose molecule, which consists of six carbon atoms. While one G3P molecule exits the cycle to contribute to the formation of carbohydrates like glucose, the remaining G3P molecules help to regenerate RuBP, allowing the cycle to continue with the fixation of more carbon dioxide.