Figure 3.10 Photosynthesis. The two-part process of photosynthesis begins with the light reactions that capture solar energy. When chlorophyll molecules absorb photons, they release electrons, which are passed along a chain of reactions that produces the high-energy molecules ATP and NADPH. In the process, H2O molecules split and produce O2 as a waste product. The second part of this process, known as the Calvin cycle, combines CO2 with RuBP, using the enzyme Rubisco, to form G3P, a three-carbon sugar that is later converted to glucose and other sugars.