Which process does NOT occur in the mitochondria?

The process that does not occur in the mitochondria is glycolysis. Glycolysis is the initial stage of cellular respiration and occurs in the cytoplasm of the cell, not within the mitochondria. During glycolysis, glucose is broken down into pyruvate, and a small amount of ATP is produced, alongside NADH. This process is critical as it prepares the products for subsequent reactions that take place in the mitochondria.

In contrast, the Krebs cycle, oxidative phosphorylation, and the electron transport chain all occur within the mitochondria. The Krebs cycle, also known as the citric acid cycle, takes place in the matrix of the mitochondria, where it processes the pyruvate generated by glycolysis. Oxidative phosphorylation and the electron transport chain occur across the inner mitochondrial membrane, where the high-energy electrons from NADH and FADH2 are used to create a proton gradient that leads to ATP production. Thus, glycolysis is distinct in its location and role within the broader context of cellular respiration.