FRET allows the transfer of excitation energy in photosynthesis, by allowing neighbouring atoms to have electrons excited.
Electrons in chlorophyll molecules are excited by light energy, with blue photons exciting electrons to the S2 state, and red photons exciting electrons to the S1 state. As FRET is only able to occur at the S1 state, heat conversion is used to de-excite any electrons at the S2 state, converting the excess energy to thermal energy. The excitation energy (at the S1 level) is then able to transfer to a neighbouring electron, cascading down towards the reaction centre special-pair chlorophyll. As the excitation energy travels further through the light harvesting complex towards the reaction centre, it falls through the sub-levels of the S1 level, demonstrating the energy cascades through atoms towards the reaction centre.
By transferring this energy towards the reaction centre of the photosystem, the turnover rate increases, leading to a higher rate of H+ and e- transport. It also provides a greater surface area with which to capture light energy, further improving photosynthesis’ efficiency.