Final answer:
The physical transfer of a phosphate group from a high-energy donor molecule to ADP is known as substrate-level phosphorylation, a process distinct from oxidative phosphorylation and one that does not involve the electron transport chain.
Step-by-step explanation:
When a high-energy "donor" molecule physically transfers a phosphate group to ADP, this process is called substrate-level phosphorylation. This is a type of phosphorylation where a phosphate group is directly transferred from an intermediate substrate in a metabolic pathway to ADP, forming ATP.
For example, during glycolysis, a molecule such as 1,3-bisphosphoglycerate donates a high-energy phosphate to ADP, resulting in ATP formation, thanks to the catalytic action of the enzyme phosphoglycerate kinase. This process does not require an electron transport chain or the presence of oxygen, differentiating it from oxidative phosphorylation.
The generation of ATP via substrate-level phosphorylation is a very direct method occurring within catabolic pathways like glycolysis, where the high-energy phosphate from intermediate molecules is transferred to ADP, thus creating ATP.