One substance strongly associated with mitochondria is ATP (adenosine triphosphate).

Here's why:

* Mitochondria are the powerhouses of the cell: They are responsible for producing ATP, the primary energy currency of cells.

* ATP synthesis occurs in the mitochondria: The process of cellular respiration, which generates ATP, takes place within the mitochondria.

Therefore, ATP is a crucial substance that directly relates to the function of mitochondria.