During photosynthesis, from which molecule is the oxygen gas released in the light-dependent reactions?

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Multiple Choice

During photosynthesis, from which molecule is the oxygen gas released in the light-dependent reactions?

Explanation:
In the light-dependent reactions, the oxygen gas released comes from splitting water molecules. The oxygen-evolving complex at photosystem II uses light energy to break water into electrons, protons, and oxygen gas: 2 H2O -> 4 H+ + 4 e- + O2. The electrons travel through the electron transport chain to power ATP and NADPH formation, while the oxygen diffuses out as a byproduct. Carbon dioxide isn’t split in these reactions—it’s used later in the Calvin cycle to build sugars, not to release oxygen. Glucose is ultimately produced from CO2 through that cycle, not directly in the light-dependent stage.

In the light-dependent reactions, the oxygen gas released comes from splitting water molecules. The oxygen-evolving complex at photosystem II uses light energy to break water into electrons, protons, and oxygen gas: 2 H2O -> 4 H+ + 4 e- + O2. The electrons travel through the electron transport chain to power ATP and NADPH formation, while the oxygen diffuses out as a byproduct. Carbon dioxide isn’t split in these reactions—it’s used later in the Calvin cycle to build sugars, not to release oxygen. Glucose is ultimately produced from CO2 through that cycle, not directly in the light-dependent stage.

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