An organized group of cells that work together is called a tissue.

Here's a breakdown:

* Cells: The basic building blocks of all living things.

* Tissue: A group of similar cells that work together to perform a specific function.

* Organ: A structure made up of different tissues that work together to perform a complex function.

* Organ System: A group of organs that work together to perform a major body function.

* Organism: A complete living being made up of multiple organ systems.