NEETBotanyPhotosynthesis in Higher Plants
If a plant is illuminated exclusively with monochromatic light of wavelength greater than 680 nm, which of the following physiological events will occur in its chloroplasts?
Options
- ABoth PS I and PS II will be functional, resulting in the synthesis of ATP and NADPH.
- BOnly PS II will be functional, resulting in the synthesis of only ATP.
- COnly PS I will be functional, resulting in the synthesis of only ATP.
- DOnly PS I will be functional, but neither ATP nor NADPH will be synthesised.
Correct answer
C. Only PS I will be functional, resulting in the synthesis of only ATP.
Step-by-step solution
The reaction centre of Photosystem II (PS II) has an absorption peak at 680 nm, while the reaction centre of Photosystem I (PS I) has an absorption peak at 700 nm. When only light of wavelengths beyond 680 nm is available for excitation, PS II cannot be excited and becomes non-functional. Therefore, only PS I is functional. Under these conditions, the electron circulation is restricted within PS I, forcing the system into cyclic photophosphorylation. Cyclic photophosphorylation results in the synthesis of only ATP,