ATP production is primarily achieved through oxidative respiration in mitochondria, which creates a hydrogen ion gradient to convert ADP to ATP.

“So a lot of metabolism is simply creating ATP, which the end of the line of that-- I'm going to work backwards-- is what's called oxidative respiration. So that happens in the mitochondria. Everybody's heard mitochondria, a powerhouse of the cell. And that is done through essentially creating a hydrogen ion gradient across the mitochondria, which powers the production of ATP by converting free phosphate plus ATP to ADP.”