Here's a breakdown:

* Glycolysis is the first stage of cellular respiration, where glucose is broken down into pyruvate.

* Substrate-level phosphorylation is a process where a phosphate group is directly transferred from a high-energy molecule (a substrate) to ADP, forming ATP.

* In glycolysis, this occurs in two specific steps:

* Step 6: Glyceraldehyde-3-phosphate (G3P) is oxidized and a phosphate group is added, forming 1,3-bisphosphoglycerate.

* Step 7: The phosphate group is transferred from 1,3-bisphosphoglycerate to ADP, forming ATP. This happens twice per glucose molecule.

So, in summary:

* Glycolysis produces 2 ATP molecules per glucose molecule through substrate-level phosphorylation.

* This process is distinct from oxidative phosphorylation, which occurs in the mitochondria and produces significantly more ATP.