Answer:
The carbon atoms used to build carbohydrate molecules come from carbon dioxide, the gas that we exhale with each breath.
Explanation:
Dark reactions are also referred as "light independent reactions" (since they can occur during day or night) or as "carbon-fixation" (since carbon dioxide is taken from the air and carbon is affixed to compounds in the plant) or as the Calvin Cycle (named for the person who discovered it).
