The carriers that move energy from the light-dependent reactions to the Calvin cycle reactions can be thought of as “full” because they bring energy. After the energy is released, the “empty” energy carriers return to the light-dependent reactions to obtain more energy. You should be familiar with the energy carrier molecules used during cellular respiration: NADH and FADH2. Photosynthesis uses a different energy carrier, NADPH, but it functions in a comparable way. The lower energy form, NADP+, picks up a high energy electron and a proton and is converted to NADPH. When NADPH gives up its electron, it is converted back to NADP+.
