* The light reactions do not directly produce three-carbon sugars. They produce ATP and NADPH, which are energy carriers.
* The Calvin cycle does produce three-carbon sugars. Specifically, it produces glyceraldehyde-3-phosphate (G3P), a three-carbon sugar, as an intermediate.
* However, the Calvin cycle only produces one G3P molecule for every six CO2 molecules fixed. To make a complete glucose molecule (six-carbon sugar), the cycle needs to run six times.
So, while the Calvin cycle does produce three-carbon sugars, it's not the main product. Its primary goal is to produce glucose.
Therefore, the answer is: only the Calvin cycle directly produces three-carbon sugars, but both light reactions and the Calvin cycle are necessary to ultimately produce a six-carbon sugar like glucose.
