How would you explain the role of oxygen in aerobic respiration?
O2 is the final electron acceptor (from outside the cell, so it's an exogenous acceptor).
Remember that aerobic respiration is a three-stage process for glucose...
Glycolysis: Initial oxidation and degradation of glucose to pyruvate (produces some ATP, as well as NADH, FADH2, or both)
Tricarboxylic acid cycle (TCA cycle) or Krebs or Citric acid cycle: Oxidation and degradation of pyruvate
to CO2 (produces some ATP or GTP, as well as NADH, and FADH2)
ETC: NADH and FADH2 formed by glycolysis and TCA cycle are oxidized by an ETC, using O2 as the terminal electron acceptor (produces LOTS of ATP)