Where do the excited electrons flowing through photosystem ii originally come from?

Photosystem II triggers chemiosmosis and ATP synthesis in the chloroplast. Electrons are passed from the reduced pheophytin to an electron transport chain in the thylakoid membrane. ... The capture of light energy by photosystem II to produce ATP is called photophosphorylation.

1. a tropical dry forest carries out more rapid nutrient cycling

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".