If a mutation occurs such that photosystem i no longer functions as efficiently as it should, what might be most directly affected

it is a cluster of pigments, with a particular chlorophyl in the center. The energy is absorbed and is then passed to the Hugh energy electrons, NADP will then pick up the electrons and make NADPH.

if it is not working then NADPH will not be again resynthessized hence ATP synthesis will be inhibited

a community that experiences major changes undergoes progress