Energy transfer from beta-carotene to chlorophyll in the photosystem (PS) I core complex and the CP43, CP47, and reaction center (RC) proteins of PSII was studied by the femtosecond fluorescence upconversion technique. The carotenoid S-2 lifetimes/transfer efficiencies, the latter obtained by comparison with beta-carotene in solution, are similar to97 fs/33% (CP43), similar to100 fs/31% (CP47), similar to106 fs/26% (PSII-RC), and similar to62 fs/57% (PSI). By combining previous steady-state fluorescence excitation measurements with our ultrafast results on the carotenoid S-2 lifetime and chlorophyll rise kinetics, we conclude that the beta-carotene S-1 state is insignificant for light harvesting in the PSII core proteins. Measurement of the steady-state fluorescence excitation spectrum of PSI at 77 K in this work yielded a beta-carotene to chlorophyll energy transfer efficiency of 62 +/- 3%, suggesting dominant transfer from the carotenoid S-2 state. Interestingly, while both PSI and PSII almost exclusively utilize the carotenoid S-2 state for light harvesting, we find that this pathway is nearly two times more efficient in PSI.