Question

Cycle photophosphorylation occurs when the wave length of light is :

• A. 480nm
• B. 660 nm
• C. 620 nM
• D. beyond 680

Answer 1

The correct option is D beyond 680

When non-cyclic photophosphorylation is stopped under certain conditions, cyclic photophosphorylation takes place. The non-cyclic photophosphorylation can be stopped by illuminating isolated chloroplast with a light wavelength greater than 680nm. By this way, photosystem II which has maximum absorption at wavelength 680nm remains inactivated and the process involves only photosystem I. It consists of a reaction center formed by a molecule of chlorophyll a called P-700 which has maximum absorption at a 700nm wavelength of light. Besides, it consists of molecules of essential pigments chlorophyll a and those of accessory pigments like chlorophyll b, carotene, and xanthophyll. All these molecules act as "antennae" to absorb and transfer the light energy to the reaction center i.e. P-700.

So the correct option is 'beyond 680nm'.