Both NADH and FADH2 electron carriers give away electrons in the electron transport chain (ETC) of cellular respiration. NADH donates electrons to Complex I of the ETC, while FADH2 donates electrons to Complex II. This electron donation initiates a series of redox reactions that move electrons through the protein complexes in the inner mitochondrial membrane, ultimately leading to ATP production through oxidative phosphorylation. NADH transfers electrons at a higher energy level starting at Complex I, which pumps protons to create a proton gradient, while FADH2 donates electrons at a lower energy level starting at Complex II, which does not pump protons but passes electrons to ubiquinone for continuation down the chain.