In the oxidation of pyruvate to acetyl CoA, one carbon atom is released as CO₂. However, the oxidation of the remaining two carbon atoms—in acetate—to CO₂ requires a complex, eight-step pathway—the citric acid cycle. Consider four possible explanations for why the last two carbons in acetate are converted to CO₂ in a complex cyclic pathway rather than through a simple, linear reaction. Use your knowledge of the first three stages of cellular respiration to determine which explanation is correct.
a. More ATP is produced per CO₂ released in cyclic processes than in linear processes.
b. It is easier to remove electrons and produce CO₂ from compounds with three or more carbon atoms than from a two-carbon compound such as acetyl COA.
c. Redox reactions that simultaneously produce CO₂ and NADH occur only in cyclic processes.
d. Cyclic processes, such as the citric acid cycle, require a different mechanism of ATP synthesis than linear processes, such as glycolysis.