Question

How many times ${\text{CO}}_2$ released in aerobic respiration-

• A. One or two
• B. Three
• C. Six
• D. Twelves

Answer 1

The correct option is B Three

Respiration proceeds in two stages. First stage is glycolysis, during which one molecule of hexose glucose is converted to two molecules of pyruvic acid. No oxygen is consumed nor any carbon dioxide is released during glycolysis.
Glycolysis is followed by oxidative decarboxylation of pyruvic acid, in which each molecule of three carbon atom containing pyruvic acid is converted to two carbon atom containing acetyl $\text{CoA}$ and a molecule of carbon dioxide is released. Next stage is the citric acid cycle, followed by the last stage the electron transport chain and oxidative phosphorylation.

In the course of the citric acid cycle, two molecules of ${\text{CO}}_2$ and the equivalent of eight hydrogen atoms ($8$ protons and $8$ electrons) are removed, forming three $\text{NADH}$and one ${\text{FADH}}_2$.

Thus, three times carbon dioxide is released during the course of aerobic respiration- once during oxidative decarboxylation of pyruvate and two during the Krebs or citric acid cycle.