During photosynthesis, which process directly produces molecular oxygen as a byproduct?

During photosynthesis, which process directly produces molecular oxygen as a byproduct?

• A. Light-dependent reactions
• B. Calvin Cycle
• C. Krebs Cycle
• D. Glycolysis

Answer: (A)

The light-dependent reactions are where oxygen is produced. In these reactions, water is split by energy from light in the thylakoid membranes (photolysis), releasing electrons to power the electron transport chain and, as a byproduct, molecular oxygen is released. The ATP and NADPH made during this stage fuel the Calvin cycle, which uses those molecules to build sugars from CO2 and does not generate oxygen. The Krebs cycle and glycolysis belong to cellular respiration, not photosynthesis, and neither produces O2 as a byproduct.

The light-dependent reactions are where oxygen is produced. In these reactions, water is split by energy from light in the thylakoid membranes (photolysis), releasing electrons to power the electron transport chain and, as a byproduct, molecular oxygen is released. The ATP and NADPH made during this stage fuel the Calvin cycle, which uses those molecules to build sugars from CO2 and does not generate oxygen. The Krebs cycle and glycolysis belong to cellular respiration, not photosynthesis, and neither produces O2 as a byproduct.