If a mitochondrion ran out of molecular oxygen (O2), predict which of the following situations would occur in its electron transport chain. If a mitochondrion ran out of molecular oxygen (O2), predict which of the following situations would occur in its electron transport chain. H2O would be made instead of O2 at the end of the chain. Cyt a 3 prosthetic groups would remain oxidized and Cyt a would have nowhere to donate electrons. FMN prosthetic groups would remain reduced and NADH would have nowhere to donate electrons. FADH2 would be the main electron donor to the electron transport chain instead of NADH. Electrons would start to flow in the opposite direction, converting water into O2 and H+.