During the calvin cycle, carbon dioxide is to drive the formation of sugars. see section 10.4 ( page 224) .

During the Calvin cycle, carbon dioxide is reduced to drive the formation of sugars.
During the process of photosynthesis, a set of chemical reaction that occurs in the chloroplast is known as the Calvin cycle, which is light independent.
Photosynthesis reaction can be divided into two stages that are the light reaction and the Calvin cycle, in the first stage light energy converted to the chemical energy and the second stage use the products of light reaction to produce sugar.