Question

Engelmann’s experiment with Spirogyra demonstrated that
A. The full spectrum of sunlight is needed for photosynthesis
B. Only red wavelengths are effective in causing photosynthesis
C. Only blue wavelengths are effective
D. Both blue and red wavelengths are effective

Answer 1

Hint: The experiment of effects of different colors of light on photosynthetic activity was performed by Theodor Wilhelm Engelmann who was a German botanist, physiologist, microbiologist, who observed that the conversion of light energy to chemical energy took place in the chloroplast.

Step by step answer:A classic experiment performed by Theodor Engmann showed which wavelengths are effective for photosynthesis in the green alga Spirogyra. The pigment molecules in photosynthetic organisms absorb specific wavelengths of light and oxygen-dependent bacteria produce a "living graph" as they accumulate near the parts of the alga that are illuminated with red and blue light and from this experiment it was concluded that Spirogyra can perform photosynthesis in both red and blue wavelength as it produced the highest oxygen in both the lights and the bacteria can move in the response to the oxygen produced by the photosynthetic algae.
Apart from the photosynthesis experiments, Theodor Engelmann had observed contraction in the striated muscle, with the finding that the volume of the anisotropic band increases during contraction and the volume of the isotropic band decreases. He also performed an action spectrum experiment with a modified microscope that had a prism which could produce a microscopic spectrum on a microscope slide and this device could also distinguish and measure different wavelengths of light making it a “micro-spectroscope” and using this instrument he illuminated a strand of Cladophora with light from the visible spectrum and exposed its different sections to different wavelengths of light and added the oxygen seeking bacteria and noted where they accumulated.
Hence, the correct answer is an option (D).

Note: The least efficient wavelength for photosynthesis is the green light because of the presence of a green pigment known as chlorophyll as the green light is transmitted and reflected instead of being absorbed by the chlorophyll.