Who proposed that  comes from water instead from  during photosynthesis?
a)	Von Neil	b)	Engelmann	c)	Blackman	d)	Warburg

(a)

Cornelius van Niel (1897-1985) who based on his studies on 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 carbohydrate. This can be expressed by

In green plants,  is the hydrogen donor and is oxidised to  photosynthesis. Some organism do not release  during photosynthesis. When  instead is the hydrogen donor for purple and sulphur bacteria, the oxidation product is sulphur or sulphate depending on the organism and not . Hence, he inferred that  evolved by green plant comes from , not  from carbon dioxide