Question

What conclusion was drawn from the red drop and enhancement experiments in the light reaction of photosynthesis

• A. Two photosystems are present
• B. One photosystem is present
• C. Two photosystems are present which work at different wavelengths
• D. Two photosystems are present which work at some wavelength

Answer 1

The correct option is C

Two photosystems are present which work at different wavelengths

The correct option is C.

Explanation of correct option:

1. Photosynthesis is a physiochemical process in which light energy is converted into chemical energy by photosynthetic organisms in the form of NADPH and ATP.
2. Photosynthesis happens in two stages: light reaction and dark reaction.
3. Light reactions require direct light energy to make NADPH and ATP that are used in dark reactions. Takes place in the grana of the chloroplast.
4. The red drop experiment was demonstrated by Robert Emerson and Charlton Lewis in 1943.
5. The scientists set an experiment for oxygen evolution in the green algae Chlorella pyrenoidosa and examined the action spectrum in the visible region.
6. They observed the fairly constant quantum yield up to 680nm but beyond which it declined sharply.
7. This drop-in quantum yield in the far-red region of the spectrum was called the red drop phenomenon.
8. The conclusion of this experiment is light with a wavelength greater than 680nm is much less efficient than the light of shorter wavelengths.
9. Emerson and his colleagues conducted an experiment in which two beams of light were used- one in the red region(wavelengths less than 680nm) and the other one in the far red region(wavelengths greater than 680nm).
10. When the two beams were applied simultaneously, the rate of photosynthesis was 2-3 times greater than the sum of the rates obtained with each beam separately. This phenomenon is called as Emerson Enhancement effect.
11. This also suggested that photosynthesis involves two photosystems- one involves the light of long-wavelength(greater than 680nm) and the other is driven by the light of short wavelength(less than or equal to 680nm).

Final answer: The conclusion drawn from the red drop and enhancement experiments in the light reaction of photosynthesis was that Two photosystems are present which work at different wavelengths