iron and magnesium
First, notice where carbon is fixed by the enzyme Rubisco. In C-3, C-4, and CAM plants, CO 2 enters the cycle by joining with 5-carbon ribulose bisphosphate to form a 6-carbon intermediate, which splits so quickly that it isnt even shown into two 3-carbon 3-phosphoglycerate molecules. Now look for the points at which ATP and NADPH made in the light reactions add chemical energy Reduction in the diagram to the 3-carbon molecules. The resulting glyceraldehyde-3-phosphate half-sugars can enter several different metabolic pathways. One recreates the original 5-carbon precursor, completing the cycle. A second combines two of the 3-carbon molecules to form glucose, the universal fuel for life. The cycle begins and ends with the same 5-carbon RuBP molecule, but the process combines carbon and energy to build carbohydrates food for life.