Cellular respiration overview.
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   During  glycolysis,  a  glucose molecule is broken into 2 molecules of
   pyruvate.
<P>
   The pyruvate enters the citric acid cycle.
<P>
   These  2  steps  produce  a  few  molecules  of ATP by substrate-level
   phosphorylation.
<P>
   Energy  stored  in electrons are moved to the ETC, where much more ATP
   are produced by oxidative phosphorylation.