Answer: photosystems

AnswerCrossword Clue
photosystemsA biochemical mechanism in plants by which chlorophyll absorbs light energy for photosynthesis. There are two such mechanisms (photosystems I and II) involving different chlorophyllûprotein complexes
photosystemsPHOTOSYSTEM, either of two photochemical reaction centers consisting chiefly of photosynthetic pigments complexed with protein and occurring in chloroplasts