In the early 20th century, scientists believed that carbon dioxide was the source of O2 released during photosynthesis. It has now been proved that water is the source of O2 released in the process of photosynthesis.
1. Van Niel test
Scientist Van Niel (1935) observed the photosynthesis of sulfur bacteria. Sulfur bacteria use hydrogen sulfide (H2S) instead of H2O in photosynthesis. That is, sulfur bacteria produce sugars using CO2 and H2S. O2 is not produced as H2O is not used.
2. Hill reaction
British biochemist Robin Hill (1937) took chloroplasts, water (H2O) and hydrogen acceptors (2A) in a container. Then put the test in the light for some time. Observe that H2 and O2 are produced. Not using H2O produced no sugars, but using CO2 produced O2.
2H2O + 2A → 2AH2 + O2
3. Ruben Kamen’s radioactive oxygen experiment
In 1941, Reuben, Camen and Randall of the University of California in the United States used radioactive oxygen (18O2) in photosynthesis to prove that the source of O2 released in the photosynthesis process is water. They observed the photosynthesis of Chlorella algae by identifying the radioactive isotope 18O2 in water. See the released oxygen has a radioactive isotope (H218O).
6CO2+12H218O→ C6H12O6+6H2O+618O2
Again, he observed the photosynthesis of Chlorella algae by labeling the oxygen of CO2 with the radioactive isotope 18O2. They found that sugar has a radioactive isotope of oxygen (C6H1218O6). Emitted oxygen does not contain radioactive isotopes.
6C18O2 +12H2O→ C6H1218O6+6H2O+6O2
It is clear from the experiments that water is the source of O2 released in the photosynthesis process.