This is a picture of a plant. Plants use photosynthesis to capture sunlight and turn it into energy. The Calvin cycle is the second stage of the photosynthetic process. The Calvin cycle takes place in the stroma of the chloroplast. It takes in CO2 and the energy by-products (ATP and NADPH) from the light reactions and makes glyceraldehyde-3-phosphate (G3P.) A glucose molecule consists of two G3P molecules.