CBSENEETClass 10
Where does the oxygen liberated during photosynthesis come from?
Answer
The oxygen liberated during photosynthesis comes from water molecules, which are split during the light reaction.
The working
Source is water
The oxygen released is derived from water (H₂O), not from carbon dioxide.
Photolysis of water
During the light reaction, light energy splits water molecules in a process called photolysis, releasing oxygen, hydrogen ions, and electrons.
Equation clue
In 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O, tracing the atoms shows the evolved O₂ comes from the water used.
Proof
Experiments using water labelled with the heavy oxygen isotope (¹⁸O) confirmed that the released oxygen originates from water.
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