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The typical equation 2H2S+Co2 ----------------->CH2O+H2O+2S represents the nutrition process of

One of the clues to the mechanism of photosynthesis came from the discovery that the O2 given off by plants comes from H2O, not CO2.
         Before the 1930s, the prevailing hypothesis was that photosynthesis split carbon dioxide and then added water to the carbon:
Step 1: CO2 --> C + O2
Step 2: C + H2O --> CH2O
        C. B. van Niel challenged this hypothesis.
  • In the bacteria that he was studying, hydrogen sulfide (H2S), not water, is used in photosynthesis.
  • These bacteria produce yellow globules of sulfur as a waste, rather than oxygen.
  • Van Niel proposed this chemical equation for photosynthesis in sulfur bacteria   

           CO2 + 2H2S --> [CH2O] + H2O + 2S

Thus, van Niel hypothesized that plants split water as a source of electrons from hydrogen atoms, releasing oxygen as a byproduct.
   Other scientists confirmed van Niel’s hypothesis twenty years later.


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