What is the net gain of $\text{ATP}$ molecules produced via substrate-level phosphorylation during the complete oxidation of one glucose molecule in aerobic respiration?

Solution

1. Glycolysis yields $2$ $\text{ATP}$ molecules via substrate-level phosphorylation.
2. The Krebs cycle yields $1$ $\text{GTP}$ (equivalent to $\text{ATP}$) per acetyl-CoA.
3. Since one glucose produces two acetyl-CoA molecules, the Krebs cycle yields $2$ $\text{ATP}$ equivalents.
4. Total substrate-level phosphorylation is $2 + 2 = 4$ $\text{ATP}$.
5. Hence the answer is (B).