During the light reactions of photosynthesis, which process directly produces molecular oxygen ($O_2$)?

• A. Reduction of $N{+}^3$ to $NADPH$ at Photosystem I
• B. ATP synthesis by ATP synthase via chemiosmosis
• C. Photolysis of water at Photosystem II (splitting $H_{2}O$ to release $O_2$)
• D. Carbon fixation by Rubisco in the Calvin cycle

Answer: (C)

Verified step by step guidance

1. Understand that the light reactions of photosynthesis occur in the thylakoid membranes of chloroplasts and involve capturing light energy to produce ATP and NADPH.
2. Recall that molecular oxygen (O\_2) is produced as a byproduct during the splitting of water molecules, a process known as photolysis.
3. Identify that photolysis occurs specifically at Photosystem II, where water (H\_2O) is split into oxygen, protons, and electrons.
4. Recognize that the electrons released from water replace those lost by Photosystem II when it absorbs light energy.
5. Conclude that the direct production of molecular oxygen (O\_2) during the light reactions is due to the photolysis of water at Photosystem II.