The correct answer is A. Substrate-level phosphorylation
Explanation:
During the substrate-level phosphorylation, phosphoryl group is directly added to ADP or GDP to form ATP or GTP from phosphorylated intermediate rather than from inorganic phosphate like in case of oxidative phosphorylation.
So in glycolysis 4 ATP are produced by substrate-level phosphorylation. Apart from the 4 ATP, 2NADH are also produced during the glycolysis which is used during the oxidative phosphorylation and produce 4-6 ATP.
So ATP made during glycolysis is generated by substrate-level phosphorylation as ATP is produced by direct addition of phosphoryl group from intermediates.
