Who used a prism, green alga Cladophora, and aerobic bacteria and plotted the first action spectrum for photosynthesis?
(a) Sachs
(b) Arnon
(c) Arnold
(d) Engelmann

Hint: Action spectra is a graph to relate light absorption with photosynthesis. The scientist experimented with different wavelengths of light and its effect on photosynthesis. He is also the first one to discover that chloroplast is the site of photosynthesis.

Complete answer:
In 1883, Theodor W. Engelmann determined the first action spectra by measuring oxygen evolution at different wavelengths of light. A white light was passed through a prism that split into the light of different wavelengths. The green alga Cladophora, mixed with a suspension of aerobic bacteria, was then exposed to these different wavelengths. Aerobic oxygen-seeking bacteria concentrate near an oxygen source and thus were helpful in determining which segments of the alga were releasing the most oxygen or photosynthetically the most active. He observed that bacteria congregated in incredible amounts around the parts of the alga illuminated with a blue or red light.

Additional Information: -Julius von Sachs was a German botanist who is a pioneer in the field of plant physiology. He was the first scientist in 1854 to find out that starch is the first fixed product of photosynthesis that occurs in the green parts of the plants.
-Emerson and Arnold performed a range of experiments in 1932 where the plants were exposed to flashes of light at different temperatures. Their results found out the existence of light and dark reactions of photosynthesis.
-Arnon et al discovered photophosphorylation in the year of 1954. They used the radioactive isotope of carbon to trace the fixation pathways of carbon dioxide from illuminated isolated chloroplasts.
So, the correct answer is ‘Engelmann.’

Note: -Photosynthesis is a two-stage process where one stage is dependent on light or the light reaction and the other is independent of light or the dark reaction.
-In the light reaction, using the direct energy of light, photophosphorylation occurs. It is the process of formation of ATP from ADP and inorganic phosphate in the presence of solar energy.
-In dark reaction, the products of the light reactions are used to reduce carbon dioxide into sugars.