Final answer:
FADH2 carries electrons into the electron transport chain of cellular respiration, where it enters at Complex II and helps establish a proton gradient for ATP synthesis.
Step-by-step explanation:
In the electron transport chain (ETC), the molecule that carries electrons into the system is FADH2. Other molecules such as NADH also play a crucial role in transporting electrons through the chain. These high-energy electrons are released from NADH and FADH2 and move along the ETC, which is situated on the inner membrane of the mitochondrion. The energy released during this transfer is used to pump protons across the membrane, thereby establishing a proton gradient that is essential for the synthesis of ATP. FADH2 specifically enters the ETC at Complex II, whereas NADH begins at Complex I.
FADH2 and NADH are the reduced forms of the carriers FAD and NAD+, respectively, and they are produced during the earlier stages of cellular respiration, such as the Krebs Cycle. The primary task of the electron transport chain is to transfer energy from these electron carriers to ATP, the energy currency of the cell.