The body is divided into four levels of organization, not four groups. They are:

1. Cells: The basic unit of life.

2. Tissues: Groups of similar cells that work together to perform a specific function.

3. Organs: Structures made up of different tissues that work together to perform a more complex function.

4. Organ Systems: Groups of organs that work together to perform major bodily functions.

You're missing tissues in your list.