In 1882, Theodor Engelmann performed an important experiment in regards to photosynthetic activity.
What Engelmann did was to place oxygen seeking bacteria and algae (single celled photosynthetic organisms) on a microscope slide. He illuminated the slide through a glass prism. The prism splits white light into the various wavelengths of light so that each section of the slide was receiving a different wavelength/color of light. At the end of the experiment, he observed the following under a microscope, as demonstrated in the figure below.
a. What was Engelmann’s hypothesis about photosynthesis that formed the basis of the above experiment?
b. What are the various observations from the above experiment (based on the figure)?
c. What could be the possible conclusions from the above experiment?
d. What possible additional experiments would you suggest to exclude the possibility that the bacteria are attracted to the blue and red lights?
a. Engelmann’s hypothesis was that photosynthesis and oxygen production depend on the wavelength of the light.
b. It was observed that the density of bacteria was highest in red and blue light. Next, the illumination of the chloroplasts attracted bacteria, while the illumination of other cell components failed.
c. It can be concluded that the photosynthesis rate is higher at red and blue wavelengths, while that photosynthesis takes place in chloroplasts.
d. It could be possible to use a light filter of a certain wavelength.