Answer:
b. electron transport chain
Explanation:
Glycolysis and Kreb's cycle are first and second stages of cellular respiration respectively. Each of these stages produces 2 ATPs from substrate level phosphorylation. The NADH and FADH2 formed during redox reactions of glycolysis and Kreb's cycle are oxidized through the electron transport chain and drive the synthesis of up to 32 ATPs.
The proton motive force generated by oxidation of one NADH through electron transport chain drives the synthesis of around 3 ATPs. On the other hand, oxidation of FADH2 generates the proton motive force enough to drive the synthesis of around 2 ATPs.
