During photosynthesis, what is released as a byproduct in the light-dependent reactions?

• A. Carbon dioxide.
• B. Oxygen.
• C. Water.
• D. Glucose.

Answer: (B)

In the light-dependent reactions, water is split to provide electrons for the photosynthetic electron transport chain. This splitting releases oxygen gas as a byproduct, which is the oxygen we breathe. The light-driven transfer of electrons also pumps protons to create a gradient that powers ATP production and reduces NADP+ to NADPH, both of which fuel the later Calvin cycle that builds sugars. So, oxygen is produced and released during these light-driven steps, while carbon dioxide is fixed in the later stage to make glucose, and water serves as the electron source rather than a byproduct.