A structure made up of two or more tissues is called an organ.

Here's a breakdown:

* Cells are the basic unit of life.

* Tissues are groups of similar cells that work together to perform a specific function.

* Organs are made up of different tissues that work together to perform a more complex function.

For example, the stomach is an organ made up of epithelial tissue (lining), muscle tissue (for churning), connective tissue (for support), and nervous tissue (for regulation).