How are cells with similar functions organized in multicellular organisms?

Cells can have similar functions, but the cooperation among cells of the same kind is important for their organization in multicellular organisms. Thus, a group of similar cells that work together to perform a specific job is called a tissue. The functional group of multiple tissues forms an organ. The functional group of organs forms an organ system. All organ systems together form the multicellular organism.
 

They are all in a iving organism.