In animal cells where does the energy convert ADP TO ATP come from?

In animal cells, the energy to convert ADP to ATP primarily comes from the process of cellular respiration, which occurs in the mitochondria. During this process, glucose and oxygen are used to produce ATP, with the electron transport chain playing a crucial role in generating the proton gradient necessary for ATP synthesis via oxidative phosphorylation. Additionally, ATP can also be produced through substrate-level phosphorylation during glycolysis and the citric acid cycle.