Photosynthesis in green algae involves two key photosystems, PS I and PS II, which work together to convert light energy into chemical energy. These photosystems contain specific proteins and pigments that help in the process. A significant portion of chlorophyll is found in these complexes. Additionally, a protein complex called LHC II was thought to mainly interact with PS II, but new evidence suggests that phosphorylation of LHC can enhance energy transfer to PS I, shifting energy distribution between the two photosystems. This finding indicates that phosphorylation may play a crucial role in regulating the flow of excitation energy during photosynthesis.