Final answer:
FADH2 is an electron carrier used in cellular respiration to transport electrons. It is reduced from FAD during the citric acid cycle and plays a key role in the electron transport chain, leading to ATP synthesis.
Step-by-step explanation:
An electron carrier is a molecule that transports electrons during cellular respiration. The correct option from the given choices is FADH2, which along with NADH, plays a crucial role as an electron shuttle in biological systems. Electron carriers are derived from the B vitamin group and are nucleotide derivatives. They can be easily reduced by accepting electrons or oxidized by losing electrons. NAD+ is an oxidized form that becomes NADH once reduced after accepting electrons and a proton. FADH2 results from the reduction of FAD (flavin adenine dinucleotide) in the citric acid cycle, another key step in cellular energy production. During the electron transport chain in the inner mitochondrial membrane, electrons from NADH and FADH2 are transferred through a series of reactions, ultimately aiding in the synthesis of ATP.