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

The primary function of the light reactions in photosynthesis is to produce NADPH and ATP. During these reactions, which take place in the thylakoid membranes of chloroplasts, sunlight is absorbed by chlorophyll and other pigments. This energy is then used to facilitate the transfer of electrons through a series of proteins in the electron transport chain.

As a result of this electron transport, a proton gradient is created across the thylakoid membrane, which drives the synthesis of ATP through a process called photophosphorylation. Additionally, the electrons that have moved through the chain reduce NADP+ to form NADPH. These two energy carriers, ATP and NADPH, are crucial as they provide the necessary energy and reducing power for the subsequent reactions in the Calvin cycle, where glucose is synthesized.

While releasing oxygen occurs during these light reactions as a by-product of water splitting, and carbon dioxide is utilized in later stages of photosynthesis, the main purpose of the light reactions is specifically the production of NADPH and ATP.