The Calvin cycle is the second stage of photosynthesis where carbon dioxide (CO2) is transformed to sugar (glucose) by a plant. The Calvin cycle occurs in the chloroplast of a plant cell and specifically in the stroma of the chloroplast. Unlike the first stage of photosynthesis, the Calvin cycle is a part of photosynthesis that is not directly dependent on light from the sun to occur. ATP energy produced by the first stage of photosynthesis powers the Calvin cycle. The first stage of photosynthesis and the Calvin cycle are linked by ATP and NADPH and rely on the products of each other to occur.