Under which of the following circumstances, will there be a temporary shift from noncyclic to cyclic e– flow during light reaction of photosynthesis?
(1) Absence of PS II
(2) Rise in level of ATP
(3) Rise in level of NADPH + H+
(4) Chl a < Chl b
Answer (3) Rise in level of NADPH+H+ Under these conditions the amount of acceptor of electrons, which is NADP, will be too low. Thus, the process of electrons transfer to it will occur at the lower rate. Thus, temporal blockage of non-cyclic pathway will take place. Electrons will move only via cyclic pathway.