What is the difference between substrate-level and oxidative phosphorylation?

Substrate-level phosphorylation occurs in the cytoplasm, while oxidative phosphorylation occurs in the mitochondria.

Substrate-level phosphorylation is a process that occurs in the cytoplasm of cells during glycolysis and the Krebs cycle. It involves the transfer of a phosphate group from a substrate molecule to ADP, forming ATP. This process is catalysed by enzymes and does not require oxygen. For more details on this process, refer to the stages and locations of aerobic respiration.

Oxidative phosphorylation, on the other hand, occurs in the mitochondria and involves the transfer of electrons from NADH and FADH2 to the electron transport chain. This process generates a proton gradient across the inner mitochondrial membrane, which drives the synthesis of ATP by ATP synthase. This process requires oxygen and is the main source of ATP production in aerobic respiration. To understand why organisms need this energy, see the need for energy in organisms. For a detailed look at glycolysis, which is part of substrate-level phosphorylation, visit glycolysis and ATP production. Additionally, the broader context of these processes can be found under metabolic pathways.

A-Level Biology Tutor Summary: Substrate-level phosphorylation happens in the cytoplasm and produces ATP without oxygen. It's part of glycolysis and the Krebs cycle. Oxidative phosphorylation occurs in the mitochondria, uses oxygen, and produces most ATP during aerobic respiration by creating a proton gradient. While substrate-level is less efficient, it's crucial for generating ATP without oxygen.