Here's why:

* Cells: The basic building blocks of life.

* 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 for a common purpose.

For example, muscle tissue is made up of muscle cells, connective tissue is made up of various cells like fibroblasts and chondrocytes, and nervous tissue is made up of neurons and glial cells.