What did van Niel hypothesize?

Answer 1

C.B. van Niel's hypothesized that the oxygen released by plants during photosynthesis comes from carbon dioxide. In the 1930s, he studied photosynthesis in bacteria that make their carbohydrate from carbon dioxide but do not release oxygen. One such group used hydrogen sulfide, rather than water for photosynthesis, as illustrated by its chemical equation:

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

Since no oxygen was released in these experiments despite the presence of carbon dioxide, he concluded that carbon dioxide is not split into carbon and oxygen, at least in these bacteria, which helped to disprove the prevailing hypothesis of his day.

From his experiment results shown below, he also conjectured that all photosynthetic organisms require a hydrogen source although the source varies.

Sulfur bacteria: CO2 + 2 H2s-->[CH2O] + H2O + 2S

Plants: CO2 + 2 H2O--> [CH2O] + H2O + O2

General: CO2 + 2 H2X--> [CH2O] + H2O + 2X

Van Niel also used his inductive reasoning to hypothesize that the oxygen given off by photosynthetic plants is derived from water as plants split water as a source of electrons from hydrogen atoms, releasing oxygen as a byproduct, which later proven true two decades later as his hypothesis was tested using an isotope of oxygen that acts as a radioactive tracer to follow the oxygen atoms during photosynthesis.