Source of oxygen during photosynthesis:
This is an experiment that oxygen comes out during photosynthesis.
The source of oxygen evolved in photosynthesis: During photosynthesis green plants produce carbohydrate by the reactions; between the atmospheric carbon dioxide CO2 and the absorbed soil water and in this; process, oxygen is formed as a byproduct.
6 CO2 + 12 H2O → light/Chlorophyll → C6H12O6 + 6 H2O + 6 O2
It has been proved by the experiment that this oxygen comes out of water and not from carbon dioxide. This concept can be proved by following experiments.
1. Hill reactions: Robin Hill, an English Biochemist, in 1937 discovered that the oxygen during the photosynthesis comes from water and not from carbon dioxide. Hill demonstrate that isolated chloroplast in the presence of light, water and a suitable hydrogen acceptor envolve oxygen in absence of carbon dioxide. This experiment is known as Hill’s reaction.
A (Hydrogen Acceptor) H2O → light/Chlorophyll → A H2 + ½ O2
2. Van Niel’s concept: Van neil, in the field of photosynthetic sulphur, bacteria, showed that sulphur bacteria use H2S gas instead of H2O and thus sulphur is evoked in the reaction with CO2. Thus it is proved that oxygen evolved during photosynthesis in the higher plants must come from water and not from carbon dioxide.
2 H2S + CO2 → CH2O +2S + H2O
3. Ruben and Camen’s radio Active Experiment: In 1941, Samual Ruben and Camen marked oxygen and water by the radioactive Isotope 18O2 and put a few algal plants in the same water. They saw that the O2 evolved during the photosynthesis was 18O2. So it is proved that the O2 evolved during photosynthesis comes out from water and not from carbon dioxide.
6 CO2 + 12 H218O → light/Chlorophyll → C6H12O6 + 6 H2O + 6 18O2
They also demonstrated the same experiment by marking the oxygen or carbon dioxide with the radioactive isotope 18O2 and saw that the O2 evolved during this time was not marked with radioactive isotope. Thus it is proved that the oxygen evolved during the photosynthesis does not come from carbon dioxide.
6 CO218 + 12 H2O → light/Chlorophyll → C6H12O618 + 6 H2O18 + 6 O2