The textbook the quantum efficiency for photosynthesis decreases abruptly when the wavelength of light being used becomes longer the 680 nm. which one of the following is the explanation for this "red drop"?

a. the reactions that extract electrons from water to make o2 take place in the photosystem that is activated by 680 nm light.
b. red light inhibits photosynthesis.
c. photosystem i requires 680 nm light
d. red light is absorbed co2 to initate the synthesis of carbohydrates.

The correct answer will be option- A

Explanation:

Red drop effect is the effect observed by the light present in the spectrum of the wavelength of red light. The effect is observed with the decrease in the quantum yield of the oxygen formed per quantum of light when the wavelength of light exceeds 680 nm.

The decrease of quantum yield is observed due to the fact that the oxygen is formed by the breakdown of the water molecule during light-dependent reaction which is initiated by the PS II which begins the chain at 680nm.

If light exceeds the 680 nm then, PS II will remain inactive and thus will abrupt the dissociation of the water molecule and thus the formation of oxygen during the light-dependent phase.

Thus, option-A is the correct answer.