The three boxes in this diagram represent the three major biosynthetic pathways in aerobic respiration. Arrows represent net reactants or products.

 

Arrows numbered 4, 8 and 12 can all be

 

Pathway A: Glycolysis; Pathway B: Krebs cycle; Pathway C: Terminal oxidation
Step 1: Any of the intermediate of glycolysis other than glucose
Step 2: Pyruvic acid
Step 3: NADH
Step 4: ATP
Step 5: Acetyl CoA from fatty acids or amino acids
Step 6: NADH/ FADH2 
Step 7: FADH2/ NADH
Step 8: ATP
Step 9: NADH/ FADH2 (other than Glycolysis and Krebs cycle)
Step 10: FADH2/ NADH (other than Glycolysis and Krebs cycle)

Step 11: ${\mathrm{H}}_2\mathrm{O}$
Step 12: ATP