Which process directly produces oxygen as a byproduct during photosynthesis?

In photosynthesis, the process responsible for producing oxygen as a byproduct is the photolysis of water. This occurs during the light-dependent reactions, specifically in the thylakoid membranes of chloroplasts. When light energy is absorbed by chlorophyll, it initiates the splitting of water molecules (H2O) into oxygen (O2), protons (H+), and electrons. The oxygen is released into the atmosphere as a byproduct, which is crucial for life on Earth as it is used by many organisms for respiration.

The Calvin cycle, while important in synthesizing glucose, does not produce oxygen; instead, it utilizes CO2 and ATP generated from the light-dependent reactions. Photophosphorylation refers to the production of ATP from ADP and inorganic phosphate using energy derived from light, but again, this process does not produce oxygen. The purification of RuBP is not a recognized step in photosynthesis and does not play a role in the generation of oxygen. Thus, the photolysis of water is distinctly the process that facilitates oxygen liberation during photosynthesis.