Each cell does a specific job in the body, for instance a red blood cell carries oxygen around to places that need it, and a nerve cell carries signals to and from the brain.
Every cell is like a bag of chemicals.
It does an obvious job of stopping the inside of the cell from leaking out and unwanted things from getting in. A very special chemical called DNA is kept in the nucleus. The DNA is a chemical blueprint that tells the cell what other chemicals to make, and so what job the cell will do in the body. The mitochondria are the powerhouses of the cell. The chemical reactions that release energy from food go on inside them.