Here's a breakdown of why:

* Similar Cells: Tissues are made up of cells that share a common origin and structure. They are specialized to perform a particular function, but they all come from the same type of precursor cell.

* Specific Function: Each tissue type has a specific job to do. For example, muscle tissue contracts to produce movement, nervous tissue transmits signals, and epithelial tissue forms linings and coverings.

* Organism: Tissues are the fundamental building blocks of organs, which in turn make up the body of an organism.

So, tissues are essentially groups of cooperating cells working together to carry out a specific function within a larger organism.