What is the source of oxygen in photosynthesis?
GeneralClass 12AllAnswered 27 Mar 2026
Answer
The source of oxygen released during photosynthesis is water (H₂O), not carbon dioxide as commonly misunderstood. This was scientifically proven through experiments using isotope labeling techniques.
During the light-dependent reactions of photosynthesis, water molecules undergo photolysis (light-driven splitting) in the thylakoid membranes of chloroplasts. When water splits, it produces:
- Oxygen gas (O₂) – released into the atmosphere
- Hydrogen ions (H⁺) – used in ATP production
- Electrons (e⁻) – replenish chlorophyll in the photosystems
This oxygen production is vital for maintaining atmospheric oxygen levels, supporting respiration in most living organisms, and sustaining life on Earth. Plants, algae, and cyanobacteria collectively produce billions of tons of oxygen annually through this process, making photosynthesis one of the most important biochemical reactions for life.
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