The correct answer is:
b. Two photosystems operating simultaneously
Emerson's enhancement effect and Red drop were both instrumental in providing evidence for the existence of two photosystems operating simultaneously during photosynthesis. This discovery helped to elucidate the light-dependent reactions in plants and other photosynthetic organisms.
Emerson's enhancement effect refers to the observation that the rate of photosynthesis is higher when two different wavelengths of light are combined compared to the sum of the rates when each wavelength is applied separately. This effect suggested the presence of two separate photosystems, each absorbing a different range of wavelengths.
The Red drop phenomenon, on the other hand, refers to a decrease in the efficiency of photosynthesis at longer wavelengths of light. This reduction in efficiency was found to be a consequence of the absorption of light by a specific pigment molecule in the photosynthetic apparatus. The observation of the Red drop effect also supported the presence of two photosystems with distinct pigments.
Together, these observations provided strong evidence for the existence of two photosystems, known as Photosystem I and Photosystem II, which work in tandem during the light-dependent reactions of photosynthesis.
