Van Niel in 1931 proposed the hypothesis that all photosynthetic organisms require a source of
hydrogen and in plants this source is water and the oxygen is evolved by the splitting of water.
(a) Van Niel observed that green sulphur photosynthetic bacteria fixed carbon dioxide in presence of hydrogen sulphide.
(b) Oxygen was not evolved instead globules of sulphur was formed.
(c) From this observation he concluded that during | above bacterial photosynthesis CO2 does not split,
instead hydrogen sulphide splits and acts as a 1 hydrogen donor to CO2 to form carbohydrates
and molecular sulphur is released as one of the products.
6C02 + 12H2S —-case ----> C6H1206 + 6H20 + 12S
This observation on photosynthetic bacteria led
Van Niel to propose above given hypothesis