Question

What happens to the free energy released as electrons are passed from photosystem ii to photosystem i through a series of electron carriers? it is used to establish and maintain a proton gradient. it is used to phosphorylate nad+ to nadph. it excites electrons of the reaction center in photosystem i. it is used to synthesize atp through substrate-level phosphorylation?

Answer 1

The correct answer is: It is used to synthesize ATP through substrate-level phosphorylation.  
The free energy released as electrons are passed from photosystem II to photosystem I drive pumping of H+ and building a gradient. H+ flow down their gradient and when they pass through ATP synthase, the ATP is produced by substrate-level phosphorylation (ADP+Pi).