Final answer:
The correct option is B). Substrate-level phosphorylation occurs in both glycolysis and the citric acid cycle, contributing to ATP production in cellular respiration before oxidative phosphorylation.
Step-by-step explanation:
Substrate-level phosphorylation occurs in both glycolysis and the citric acid cycle. This process generates ATP by the direct transfer of a phosphate group to ADP from an intermediate substrate. While glycolysis occurs in the cytosol, the citric acid cycle takes place inside the mitochondria of eukaryotic cells and is part of the aerobic pathway that uses oxygen to help extract energy from glucose. Most of the ATP generated during the aerobic catabolism of glucose, however, comes not from these two cycles directly but from the process of oxidative phosphorylation, which includes electron transport and chemiosmosis. Oxidative phosphorylation is highly efficient and generates large amounts of ATP