Why are H2 and O2 functionally the outside points on the electron tower?
because there's so much water in cells
if any molecule is a better electron donor than H2, it can reduce the hydrogen in water to create H2 gas
if any molecule is a better electron acceptor than oxygen, it can oxidize the oxygen in water to create O2
electron transport chains in cells have to use redox compounds with reduction potentials between H2 and O2