Which of the following steps is NOT part of cellular respiration?

Fermentation is indeed not considered a part of cellular respiration in the context used for aerobic processes. Cellular respiration primarily refers to the series of metabolic processes that convert biochemical energy from nutrients into adenosine triphosphate (ATP), utilizing oxygen in the process.

The primary steps of cellular respiration include glycolysis, the citric acid (or Krebs) cycle, and the electron transport chain. In glycolysis, glucose is broken down into pyruvate, producing a small amount of ATP and NADH. This pyruvate then enters the mitochondria where it is further processed in the citric acid cycle, generating additional ATP, NADH, and FADH2 as it fully oxidizes. Finally, the electron transport chain takes place in the mitochondria's inner membrane, where the electrons from NADH and FADH2 are transferred through a series of proteins, ultimately leading to the production of a significant amount of ATP through oxidative phosphorylation.

Fermentation, on the other hand, occurs in the absence of oxygen and is a different metabolic pathway used mainly by anaerobic organisms or in situations where oxygen is depleted. It allows for the regeneration of NAD+ from NADH, enabling glycolysis to continue producing ATP, but does not involve the Krebs