Question

where did these electron - carrier molecules come from (what previous steps)?
oxidative phosphorylation
pyruvate oxidation
glycolysis
citric acid cycle
previous

Explanation:

NADH and FADH₂ are electron - carrier molecules. Glycolysis produces 2 NADH per glucose molecule. Pyruvate oxidation converts pyruvate to acetyl - CoA and generates NADH. The citric acid cycle produces NADH and FADH₂. Oxidative phosphorylation uses these electron carriers to produce ATP. So, NADH and FADH₂ come from glycolysis, pyruvate oxidation, and the citric acid cycle.

Answer:

Pyruvate oxidation, Glycolysis, Citric acid cycle