Pronunciation: ' f ō -t ō - ˌ sis-t ə m
Function: noun
Date: 1964
: either of two photochemical reaction centers consisting chiefly of photosynthetic pigments complexed with protein and occurring in chloroplasts: a : one that absorbs light with a wavelength of about 700 nanometers ― called also photosystem I b : one that absorbs light with a wavelength of about 680 nanometers ― called also photosystem II