The first phase of cellular respiration is called glycolysis. Only 2.2% of the energy from cellular respiration is attained through glycolysis.
In general, gylcolysis can be divided into 2 phases: energy investment (Step#1-3) and energy payoff (Step#4-10). During the energy investment phase, 2 ATP molecules are used. In the energy payoff phase, 4 ATPs in addition to 2 NADHs are synthesized.
Reactants: glucose, 2ATP, 2NAD+, 4ADP, 2 phosphate groups
Products: 2 pyruvate, 4ATP, 2ADP, 2H+, 2NADH
Net ATP: 2
This video explores glycolysis with particular focus on the enzymes involved.