Here's a breakdown:

* Cells: The basic unit of life.

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

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

* Organ Systems: Groups of organs that work together to carry out major bodily functions.

For example, the stomach is an organ composed of:

* Epithelial tissue: Lining the stomach and protecting it from digestive juices.

* Muscle tissue: Responsible for contractions that churn food.

* Connective tissue: Providing support and structure.

* Nervous tissue: Regulating stomach function and communicating with the brain.