Which fundamental cellular structure is completely absent in the members of Kingdom Animalia?
Kingdom Animalia comprises heterotrophic, multicellular eukaryotic organisms. A major, defining structural characteristic that distinguishes animal cells from plant and fungal cells is the complete absence of a 'cell wall'. The NCERT textbook emphasizes this structural deficit, meaning animal cells are bound only by a flexible plasma membrane, which allows for highly varied cell shapes and the development of complex tissues like muscles and nerves.
Ref: NCERT Class 11 Biology > Chapter 2: Biological Classification > 2.5 Kingdom Animalia