Prokaryotic cells and eukaryotic cells are the two fundamental types of cells that differ significantly in their structure, organization, and physiological functions. Prokaryotic cells are primitive, simple, and usually unicellular, whereas eukaryotic cells are more advanced, complex, and may be unicellular or multicellular. Understanding these differences is essential in applied physiology because cellular organization determines the efficiency of metabolic processes, growth, reproduction, and adaptation. The nucleus is one of the major distinguishing features. Prokaryotic cells lack a true, membrane-bound nucleus. Their genetic material is present in a nucleoid region without a nuclear envelope. In contrast, eukaryotic cells possess a well-defined nucleus enclosed by a double nuclear membrane, which protects DNA and regulates gene expression. The genetic material also differs. Prokaryotic cells contain a single, circular DNA molecule that is not associated with histone proteins, except in some archaea. They often possess plasmids, which are small circular DNA molecules carrying additional genes. Eukaryotic cells contain multiple linear chromosomes associated with histone proteins, allowing efficient DNA packaging and regulation. Membrane-bound organelles are absent in prokaryotic cells. Organelles such as mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and chloroplasts are not present. Therefore, metabolic reactions occur in the cytoplasm or across the plasma membrane. Eukaryotic cells possess numerous membrane-bound organelles