Question

The rate of photosynthesis decreases if the wavelength of visible light exceeds 680 nm. This was shown by which scientist and what is it's reason?

• A. Black man - Law of limiting factor
• B. Calvin and Benson - Photooxidation
• C. Emerson and Arnold - Red drop
• D. Ruben and Kamen - Photolysis

Answer 1

The correct option is C Emerson and Arnold - Red drop

While working with Chlorella, Emerson and Lewis, 1943, tried to calculate the quantum yield for different wavelengths. When they gave wavelengths longer than 680 nm, the quantum yield suddenly dropped. Since this wavelength belongs to the red region, they termed the phenomenon as a red drop. Later Emerson et al. 1957 showed that the light wavelengths beyond 680 nm, i.e., of the far red region, are not capable of performing photosynthesis efficiently.

However, if they combined with shorter wavelengths the photosynthetic activity increases. This photosynthetic enhancement with respect to yield or increased oxygen production is called Emerson effect. The discovery of Emerson effect confirms that in photosynthesis there are two distinct photochemical reactions.

So, the correct answer is option C.