Final answer:
Pyruvate is the key intermediate that bridges the gap between glycolysis and the citric acid cycle in glucose catabolism. It undergoes oxidation to form acetyl CoA, which enters the citric acid cycle, yielding ATP, NADH, and FADH2, critical components of cellular respiration.
Step-by-step explanation:
The key intermediate of glucose catabolism leading to the citric acid cycle is B) pyruvate. During glycolysis, glucose is broken down into two molecules of pyruvate. This pyruvate is then further oxidized in the presence of oxygen to form an acetyl group that combines with coenzyme A, resulting in the formation of acetyl CoA. Acetyl CoA then enters the citric acid cycle, where it undergoes further oxidation to produce ATP, NADH, and FADH2. These electron carriers, especially NADH and FADH2, play an essential role in oxidative phosphorylation, which significantly contributes to ATP production. Additionally, an end product of glucose metabolism in the citric acid cycle is carbon dioxide.