In the second stage of aerobic respiration, what happens to the electrons that have been depleted of their energy during atp production?

You've gotten 2 different answers so far and both can be considered correct. It depends on the source. Some books/teachers give 5 steps: ... glycolysis - > transition reaction - > Krebs cycle - > electron transport system - > chemiosmosis Some books/teachers don't list the transition reaction as a separate step, considering it as a minor setup step for the "real" second step, the Krebs cycle ... glycolysis - > Krebs cycle - > electron transport system - > chemiosmosis Some books/teachers (wrongly) list only 3 steps as follows ... glycolysis - > Krebs cycle - > electron transport system That's wrong because the electron transport system doesn't make any ATP: it just sets up the proton gradient that chemiosmosis uses to create the ATP. If the steps are to be collapsed into just 3, then the correct formulation would be: ... glycolysis - > Krebs cycle - > oxidative phosphorylation