The portion of respiration that yields the highest net ATP is the Electron Transport Chain.
Here's a brief overview of the ATP yield from each of the processes:
- Glycolysis: 2 ATP (net gain)
- Krebs Cycle: 2 ATP (through substrate-level phosphorylation)
- Electron Transport Chain: Approximately 26-28 ATP (depends on the cell type and conditions)
Fermentation typically yields 0 ATP (in terms of electron transport) and instead allows glycolysis to continue by regenerating NAD+.
Therefore, out of the options listed, the Electron Transport Chain produces the highest net ATP.