Mao says that life exists due to contradictions and that once those contradictions cease, we die. But which are the contradictions which cause us to be alive? To me it is more cell cooperation than contradictions. I am not sure to which contradictions he is referring to.
Inhale/exhale, activity/rest
Oxidation/reduction
Edit: aww…I just saw someone else got there first.
Pretty much any biochemical reaction would fit though.