What substance is released during the light reactions of photosynthesis?

During the light reactions of photosynthesis, oxygen is released as a byproduct. This process occurs in the thylakoid membranes of chloroplasts, where light energy is captured by chlorophyll and used to split water molecules in a process known as photolysis. The splitting of water not only generates electrons needed for the electron transport chain but also releases oxygen as a waste product.

The absorption of light energy drives the formation of ATP and NADPH, which are then used in the Calvin cycle (the dark reactions) to synthesize glucose, a process that occurs later and does not take place during the light reactions. Therefore, while substances like carbon dioxide and glucose are integral to photosynthesis, only oxygen is produced and released during the initial light-dependent reactions.