Here's why:

* Cells: The basic building blocks of life.

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

* Organs: Structures made of different tissues working together for a common purpose.

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

For example:

* Muscle tissue is made of cells that contract, allowing movement.

* Nervous tissue is made of cells that transmit signals, enabling communication throughout the body.

* Epithelial tissue forms linings and coverings, protecting and regulating what enters and leaves the body.