The tricarboxylic acid cycle (TCA cycle), also known as the Krebs cycle and citric acid cycle, is the second stage of cellular respiration, a three-step process by which living cells break down organic fuel molecules while being oxygenated in order to obtain the energy they require to grow and divide.
The TCA cycle does not require oxygen directly.
Carbon dioxide, ATPs, and reductants like NADH and FADH2 are all created throughout the process.
NADH and FADH2 are oxidized by the electron transport system in combination with ATP production.
The electron transport cycle requires oxygen, which serves as the last electron transporter and produces water.
Despite the fact that oxygen isn't directly involved in the TCA cycle, if it isn't available, the TCA cycle will come to a halt due to a lack of NAD+ and FAD.