AP BIOLOGY

Detailed explanation-1: -The tricarboxylic acid (TCA) cycle, also known as the Krebs or citric acid cycle, is the main source of energy for cells and an important part of aerobic respiration. The cycle harnesses the available chemical energy of acetyl coenzyme A (acetyl CoA) into the reducing power of nicotinamide adenine dinucleotide (NADH).

Detailed explanation-2: -Nonavailability of these reducing powers results in entry of pyruvate in anaerobic respiration pathway. So, to maintain continuity of Kreb cycle, oxidation of NADH and FADH2 by oxygen is prerequisite and the cycle is considered aerobic.

Detailed explanation-3: -The Krebs cycle is used by organisms that respire (as opposed to organisms that ferment) to generate energy, either by anaerobic respiration or aerobic respiration.