Final answer:
Electrons are energized a second time in b) Photosystem I, where light energy is used to reduce NADP+ to NADPH, an important energy carrier for the Calvin cycle.
Step-by-step explanation:
The energization of electrons with a second input of light energy, so it can be used to reduce NADP+ to NADPH, occurs in b) Photosystem I (PSI).
When photons strike PSI, the pigments within transfer the light energy to chlorophyll a molecules, which in turn excite the electrons.
These energized electrons are then passed to the electron transport chain.
Through this process, which includes a cytochrome complex transferring protons across the thylakoid membrane, the electrons that were once excited in PSII are used to reduce NADP+ to NADPH in PSI.
This reduction is essential as NADPH serves as an energy carrier used later in the photosynthetic process, specifically in the Calvin cycle to produce glucose.