The three boxes in this diagram represent the three major...

Pathway $A$ is glycolysis, pathway $B$ is the krebs' cycle and pathway $C$ is oxidative phosphorylation Arrow 1 - ADP or $\mathrm{NAD}^{+}$ Arrow 2 - Pyrunate Arrow 3 - NADH Arrow 4 - ATP Arrow 5 - ADP, $\mathrm{NAD}^{+}$or $\mathrm{FAD}$ Arrow 6 and 7 - $\mathrm{FADH}_2$ and $\mathrm{NADH}$ (either one can be 6 or 7 ) Arrow 8 - ATP or $\mathrm{CO}_2$ Arrow 9 and $10-\mathrm{O}_2$ and ADP (either one can be 9 or 10 ) Arrow 11 and $12-\mathrm{H}_2 \mathrm{O}$ and ATP (either one can be 11 or 12)