11th Class Biology Photosynthesis And Translocation Of Organic Solute Mechanism Of Photosynthesis

Mechanism Of Photosynthesis

Category : 11th Class

On the basis of discovery of Nicolas de Saussure that "The amount of \[{{O}_{2}}\] released from plants is equal to the amount of \[C{{O}_{2}}\] absorbed by plants", it was considered that \[{{O}_{2}}\] released in photosynthesis comes from \[C{{O}_{2}},\] but Ruben proved that this concept is wrong.

In 1930, C.B. Van Niel proved that, sulphur bacteria use \[{{H}_{2}}S\](in place of water) and \[C{{O}_{2}}\] to synthesize carbohydrates as follows:


This led Van Niel to the postulation that in green plants, water \[({{H}_{2}}O)\] is utilized in place of \[{{H}_{2}}S\] and \[{{O}_{2}}\] is evolved in place of sulphur (S). He indicated that water is electron donar in photosynthesis.


This was confirmed by Ruben and Kamen in 1941 using Chlorella a green alga.

They used isotopes of oxygen in water, i.e., \[{{H}_{2}}^{18}O\] instead of \[{{H}_{2}}O\] (normal) and noticed that liberated oxygen contains \[^{18}O\] of water and not of \[C{{O}_{2}}.\] The overall reaction can be given as under :


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