Question

Photosynthesis cannot continue for long during light reaction, only cyclic photophosphorylation takes place. This is because

• A. There is unidirectional cyclic movement of the electrons.
• B. There is no evolution of .O2O2
• C. .Only ATP is formed NADPH++H+NADPH++H+ is not formed
• D. Photosystem I stops getting excited at a wavelength of light beyond 680 nm.

Answer 1

The correct option is D Photosystem I stops getting excited at a wavelength of light beyond 680 nm.

Cyclic photophosphorylation occurs occasionally only when synthesis of carbohydrates is curtailed due to limited supply of carbon di oxide and NADPH starts accumulating. At this time there is no need of additional NADPH. Moreover cyclic transport serves the purpose of more production of ATP when needed. If only cyclic photophosphorylation occurs, then only ATP will be formed and no NADPH. Due to the non production of NADPH, the process further will stop as both ATP and NADPH are required for dark reaction to take place.

Thus, the correct answer is option D.