Here's why:

* Structure: Mitochondria are physical, membrane-bound organelles found within cells. They have a distinctive double-membrane structure, with their own DNA and ribosomes.

* Function: Mitochondria are responsible for the crucial process of cellular respiration, where they convert energy from food into usable energy for the cell in the form of ATP. This is their primary function.

So, you can think of mitochondria as a specialized structure that performs a vital function for the cell.