Who described the first action spectrum of photosynthesis?
a)	Sachs	b)	Engelmann	c)	Arnold	d)	Von Helmont

(b)

TW Engelmann (1843-1909) performed an interesting experiment using a prism. He split light into its spectral components and then illuminated a green alga, Cladophora, placed in a suspension of aerobic bacteria.

The bacteria were used to detect the sites of  evolution. He observed that the bacteria accumulated mainly in the region of blue and red light of the split spectrum. A first action spectrum of photosynthesis was thus described