What gas is released during the water splitting at PSII?

What gas is released during the water splitting at PSII?

• A. Hydrogen
• B. Oxygen
• C. Carbon dioxide
• D. Nitrogen

Answer: (B)

The key idea is that the oxygen-evolving complex at PSII uses light energy to split water into electrons, protons, and oxygen. The gas released in this water-splitting step is molecular oxygen, O2. The overall reaction is 2 H2O → O2 + 4 H+ + 4 e−, so oxygen gas is produced and exits the plant cells. The other outcomes aren’t released here: hydrogen isn’t emitted as H2 in this process (the protons go into a gradient for ATP synthesis rather than as a separate gas), carbon dioxide is fixed later in the Calvin cycle, and nitrogen isn’t involved in this reaction.

The key idea is that the oxygen-evolving complex at PSII uses light energy to split water into electrons, protons, and oxygen. The gas released in this water-splitting step is molecular oxygen, O2. The overall reaction is 2 H2O → O2 + 4 H+ + 4 e−, so oxygen gas is produced and exits the plant cells. The other outcomes aren’t released here: hydrogen isn’t emitted as H2 in this process (the protons go into a gradient for ATP synthesis rather than as a separate gas), carbon dioxide is fixed later in the Calvin cycle, and nitrogen isn’t involved in this reaction.