Answer:
There are two-phase of glycolysis preparatory phase and payoff phase. In the preparatory phase, ATP is used therefore it is called the energy investment phase and in the payoff phase, ATP is produced so it is called the energy generation phase.
In preparatory phase 2 ATP is used and it is converted into ADP and in pay off phase 4 ATP is produced from ADP. Therefore by subtracting 2 from 4, we get 2 ATP. Therefore in glycolysis, energy investing and energy harvesting step results into two ATP molecules.
