What is released as a by-product during the light-dependent reactions of photosynthesis?

During the light-dependent reactions of photosynthesis, oxygen is released as a by-product. This occurs when water molecules are split in a process known as photolysis, which is driven by the energy from sunlight. The splitting of water not only generates oxygen but also produces electrons and protons. The electrons are then used in the chain of reactions that leads to the formation of ATP and NADPH, which are essential for the subsequent light-independent reactions (Calvin cycle) where carbon dioxide is utilized to produce glucose. Thus, the release of oxygen is a key indicator of the photosynthetic process and is crucial for the maintenance of life on Earth, as it provides the oxygen necessary for respiration in many organisms.