A mitochondrion (pronounced my-toh-KON-dree-un) is a tiny structure inside most of your body's cells that acts like a power plant, converting the food you eat into energy your cells can use. Just as a power plant burns fuel to generate electricity for a city, mitochondria break down sugar and other nutrients to create a molecule called ATP, which powers everything your cells do.

These microscopic powerhouses are so important that most cells contain hundreds or even thousands of them. Cells that need lots of energy, like muscle cells in your heart or leg muscles, pack in extra mitochondria to keep up with demand. Brain cells also contain many mitochondria because thinking and learning require tremendous amounts of energy.

The plural of mitochondrion is mitochondria, which is the form you'll encounter more often since we usually talk about many of them at once. Scientists sometimes call mitochondria “the powerhouses of the cell,” a phrase that captures their essential role perfectly.

Interestingly, mitochondria have their own DNA, separate from the DNA in the cell's nucleus. This suggests that billions of years ago, mitochondria were independent bacteria that began living inside other cells in a partnership that benefited both. Today, neither can survive without the other. When you run, jump, think, or even breathe, you're relying on mitochondria working inside trillions of cells to keep you going.