Why are mitochondria called the “powerhouse of the cell?” What is this “power” used for and why is it important for staying alive?

Mitochondria are often called the “powerhouses” or “energy factories” of a cell because they are responsible for making adenosine triphosphate (ATP), the cell's main energy-carrying molecule. Mitochondria are tiny double membrane-bound organelles found in almost every cell of all organisms except bacteria. Known as the “powerhouse of the cell” they are primarily responsible for converting the air we breathe and the food we eat into energy that our cells can use to grow, divide and function. Mitochondria are tiny organelles inside cells that are involved in releasing energy from food. This process is known as cellular respiration. It is for this reason that mitochondria are often referred to as the powerhouses of the cell.

Alright, i'm gonna try to explain this as good as possible. the law of conservation is like a collection overtime. it never changes though. no matter how you change the constituent parts.