Question

The three boxes in this diagram represent the three major biosynthesis pathways in aerobic respiration. Arrows represent net reactants or products.
Arrow numbered $4$, $8$ and $12$ can all be?

• A. NADH
• B. ATP
• C. $H_{2}O$
• D. $FA{D}^{+}$ or $FAD{H}_2$

Answer 1

The correct option is A NADH

• During glycolysis, the carboxylic acid, nicotinamide adenine dinucleotide (NAD+), is reduced to NADH, but this must be regenerated for glycolysis to continue.
• In the presence of oxygen, the NADH is oxidized to NAD+ within the mitochondria, producing pyruvate.
• The eight steps of the citric acid cycle are a series of redox, dehydration, hydration, and decarboxylation reactions. Each turn of the cycle forms one GTP or ATP as well as three NADH molecules and one FADH2 molecule, which will be used in further steps of cellular respiration to produce ATP for the cell.
• Hence, Arrow numbered 4, 8 and 12 can all be NADH.
• So, the correct answer is 'NADH'.