Cells couple the free energy available in organic molecules, like sugars and fats, with non-spontaneous biochemical reactions in order to maintain homeostasis. The energy in organic molecules is not instantaneously used, rather it is converted into high-energy compounds like ATP.
The hydrolysis of ATP into ADP and inorganic phosphate releases the free energy needed to drive certain biochemical pathways. The figures below illustrate endergonic and exergonic reaction pathways.
Which of the following is the BEST explanation for the energetics of ATP hydrolysis?