During aerobic respiration, the total number of ATP formed from one glucose molecule through substrate level phosphorylation is ----------------------.

SIn aerobic respiration, ATP is synthesized from a single molecule of glucose through two distinct pathways: substrate-level phosphorylation and oxidative phosphorylation.

In the classical balance sheet of aerobic respiration, the complete oxidation of one glucose molecule yields a net total of $38$ ATP molecules. This total consists of $34$ ATP molecules produced via oxidative phosphorylation in the electron transport chain and $4$ ATP molecules produced via substrate-level phosphorylation.

The breakdown of ATP formed directly by substrate-level phosphorylation is as follows:

In glycolysis, which takes place in the cytoplasm, a gross total of $4$ ATP molecules are synthesized during the payoff phase. However, $2$ ATP molecules are consumed during the initial preparatory phase, leaving a net gain of $2$ ATP molecules.

In the Krebs cycle, which takes place in the mitochondrial matrix, $1$ GTP molecule (equivalent to $1$ ATP) is generated directly per turn during the conversion of succinyl-CoA to succinate. Since one molecule of glucose gives rise to two molecules of acetyl-CoA, the Krebs cycle operates twice per glucose molecule, resulting in the production of $2$ ATP molecules.

Summing up the net contributions from both stages, the total number of net ATP molecules formed through substrate-level phosphorylation is:
$2\text{ (from glycolysis)} + 2\text{ (from Krebs cycle)} = 4\text{ ATP}$

Answer: $4$