HESI A2 SCIENCE Practice Test

The correct stages of cellular respiration are glycolysis, the Krebs cycle, and the electron transport chain. This sequence accurately reflects the process by which cells convert glucose into usable energy in the form of ATP.

Glycolysis is the first step, occurring in the cytoplasm, where one molecule of glucose is broken down into two molecules of pyruvate, producing a small amount of ATP and NADH in the process.

Following glycolysis, if oxygen is present, the pyruvate enters the mitochondria and is converted into acetyl-CoA, which then enters the Krebs cycle (also known as the citric acid cycle). The Krebs cycle takes place in the mitochondrial matrix and generates additional ATP, NADH, and FADH2 while releasing carbon dioxide as a byproduct.

The final stage is the electron transport chain, which occurs in the inner mitochondrial membrane. Here, the high-energy electrons from NADH and FADH2 are passed through a series of proteins, leading to the production of a large amount of ATP by oxidative phosphorylation, using oxygen as the final electron acceptor.

This sequence of glycolysis, the Krebs cycle, and the electron transport chain is fundamental to cellular respiration and highlights how energy is harvested from glucose.