Final answer:
A carboxyl group is removed from pyruvate, resulting in the release of carbon dioxide when it is converted into an acetyl group. This process is facilitated by the pyruvate dehydrogenase complex. The correct option is A.
Step-by-step explanation:
During the process of converting pyruvate into an acetyl group, a carboxyl group is removed from pyruvate, which releases a molecule of carbon dioxide. This reaction is catalyzed by the enzyme pyruvate dehydrogenase, which is part of the pyruvate dehydrogenase complex.
The removal of the carboxyl group transforms the pyruvate into a two-carbon hydroxyethyl group that is subsequently oxidized to an acetyl group. Ultimately, this acetyl group is attached to coenzyme A to form acetyl-CoA, which can then enter the citric acid cycle for further metabolism.
The correct answer to the question is: a) Carbon dioxide.