Final answer:
The claim about the immediate formation of a six-carbon sugar in the Calvin cycle is false; the initial six-carbon compound quickly splits into two three-carbon molecules.
Step-by-step explanation:
The statement "The first event in the Calvin cycle is the attachment of carbon dioxide to the five-carbon RuBP molecule, which immediately becomes a six-carbon sugar that is the base for starch, sucrose, cellulose, etc." is False.
In the Calvin cycle, carbon dioxide is first fixed to a five-carbon ribulose bisphosphate molecule (RuBP), which is aided by the enzyme RuBP carboxylase-oxygenase, or RuBisCO. This reaction initially creates an unstable six-carbon intermediate which immediately splits into two three-carbon molecules of 3-phosphoglycerate (3-PG). Each 3-PG is then reduced to form glyceraldehyde-3-phosphate (G3P). After the Calvin cycle turns six times, enough G3P is produced to form one molecule of glucose, which can then be used to synthesize complex carbohydrates such as starch, sucrose, and cellulose.