In the early 1880s, German scientist Theodor Engelmann combined a photosynthetic filamentous alga with aerobic, oxygen-seeking bacteria in a tube of water. The alga was long and narrow and lined up in the same direction as the long tube, while the bacteria were much smaller and moved freely within the tube. When Engelmann exposed the tube to white light, the bacteria moved about randomly. When he placed a prism between the light and the tube, the bacteria gathered in two distinct regions along the length of the filamentous algae that correspond to different colors of light from the prism. What did Engelmann's experiment demonstrate

action spectrum of photosynthesis

Explanation:

The action spectrum of photosynthesis represents the regions of white light that are utilized during the process of photosynthesis by green plants.

According to studies, the action spectrum of photosynthesis corresponds to the blue and red regions of white light.

Hence, the two distinct regions of bacterial growth along the length of the filamentous algae observed by Engelmann represent the blue and red region of the white light.

As photosynthesis was taking place across the two regions, oxygen was being produced. Oxygen is necessary for the growth of aerobic bacteria and as such, they were able to grow across the regions where oxygen was being produced.