While there are many variations in cell structure across kingdoms, all living organisms are made up of one or more cells. This is a fundamental principle of the cell theory.

Here's a breakdown:

* Eubacteria and Archaebacteria (Monera): These are single-celled organisms with simple cell structures, lacking a nucleus and membrane-bound organelles.

* Protista: This kingdom includes a diverse range of single-celled and multicellular organisms. Some have simple cell structures, while others are more complex.

* Fungi: Mostly multicellular organisms (except yeasts) with cells containing nuclei and other organelles.

* Plantae: Multicellular organisms with complex cell structures, including chloroplasts for photosynthesis.

* Animalia: Multicellular organisms with complex cell structures, specialized for various functions.

So, while the specific details of cells vary greatly between kingdoms, the fundamental building block of life is the cell.