Question

Which pigment system is inactivated in red drop?

• A. PS-I and PS -II
• B. PS-I
• C. PS-II
• D. None

Answer 1

The correct option is C PS-II

The sharp reduction in the rate of photosynthesis when monochromatic light of more than 680 nm wavelength (red region of spectra) is used is called as red drop.
PS-II which contains a P680 reaction centre is inactive at wavelengths greater that 680 nm.
Therefore, cyclic photophosphorylation takes place and as result a reduction in the rate of photosynthesis is observed.