What constitutes the fundamental building block of all living organisms?

The cell represents the most elementary structural and functional unit of life, capable of performing all essential biological processes independently. Cells exist in two primary categories: prokaryotic cells (lacking a defined nucleus) and eukaryotic cells (containing membrane-enclosed organelles). These microscopic units carry out vital functions including division, growth, and homeostasis maintenance. In multicellular organisms, specialized cells organize into tissues, which further combine to form organs with specific functions.