What organisms did Cornelius van Niel study to demonstrate photosynthesis?

Step-by-step solution

A milestone contribution to the understanding of photosynthesis was that made by a microbiologist, Cornelius van Niel (1897-1985), who, based on his studies of purple and green bacteria, demonstrated that photosynthesis is essentially a light-dependent reaction in which hydrogen from a suitable oxidisable compound reduces carbon dioxide to carbohydrates. In green plants H2O is the hydrogen donor and is oxidised to O2 . Some organisms do not release O2 during photosynthesis. When H2 S, instead is the hydrogen donor