What is the primary purpose of the light reactions in photosynthesis?

The primary purpose of the light reactions in photosynthesis is to produce ATP and NADPH. During these reactions, which occur in the thylakoid membranes of chloroplasts, chlorophyll absorbs sunlight. This light energy is then converted into chemical energy in the forms of ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate). These energy-rich molecules are crucial for powering the subsequent steps of photosynthesis, particularly the Calvin cycle, where carbon fixation and the synthesis of organic molecules occur. The generation of ATP and NADPH from the light reactions is essential as they provide the energy and reducing power necessary for the synthesis of glucose and other organic compounds in the plant.

The other options relate to different aspects of photosynthesis: storing energy as starch occurs later in the process when plants convert glucose into starch for storage, the production of organic molecules happens in the Calvin cycle using ATP and NADPH generated in the light reactions, and the absorption of carbon dioxide is part of the process that occurs mainly during the Calvin cycle, not directly during the light reactions.