NEETBotanyPhotosynthesis in Higher Plants
If a plant is exposed continuously to light of wavelengths strictly beyond 680 nm , which of the following describes the functional state and the product of the light reaction?
Options
- ABoth PS I and PS II are functional, resulting in the non-cyclic synthesis of both ATP and NADPH.
- BOnly PS II is functional, resulting in the splitting of water and synthesis of ATP.
- COnly PS I is functional, resulting in the cyclic flow of electrons and synthesis of both ATP and NADPH.
- DOnly PS I is functional, resulting in the cyclic flow of electrons and synthesis of ATP only.
Correct answer
D. Only PS I is functional, resulting in the cyclic flow of electrons and synthesis of ATP only.
Step-by-step solution
Photosystem II (PS II) has an absorption maximum at 680 nm , while Photosystem I (PS I) has an absorption maximum at 700 nm . When a plant is exposed to light of wavelengths beyond 680 nm , PS II cannot be excited. Therefore, only PS I remains functional. When only PS I is functional, the excited electron does not pass on to NADP+ but is cycled back to the PS I complex through the electron transport chain. This cyclic flow of electrons results only in the synthesis of ATP, but not of NADPH. Answer: Only PS I is fun