From which substance is oxygen produced during photosynthesis?

From which substance is oxygen produced during photosynthesis?

• A. Oxygen
• B. Water
• C. Glucose
• D. Carbon dioxide

Answer: (B)

Oxygen that is released during photosynthesis comes from water. In the light-dependent reactions, light energy powers the splitting of water in the thylakoid membranes (photolysis), producing electrons, protons, and O2 gas. The simplified reaction is 2 H2O → O2 + 4 H+ + 4 e−, with the oxygen atoms from water forming the O2 that leaves the plant. The electrons and protons from water drive the electron transport chain to generate ATP and NADPH, which then fuel sugar synthesis from carbon dioxide in the Calvin cycle. So, the oxygen gas observed is derived from water, not from carbon dioxide or glucose.

Oxygen that is released during photosynthesis comes from water. In the light-dependent reactions, light energy powers the splitting of water in the thylakoid membranes (photolysis), producing electrons, protons, and O2 gas. The simplified reaction is 2 H2O → O2 + 4 H+ + 4 e−, with the oxygen atoms from water forming the O2 that leaves the plant. The electrons and protons from water drive the electron transport chain to generate ATP and NADPH, which then fuel sugar synthesis from carbon dioxide in the Calvin cycle. So, the oxygen gas observed is derived from water, not from carbon dioxide or glucose.