The three domains of the classification system are Archaea, Bacteria, and Eukarya. Archaea are prokaryotic organisms that often inhabit extreme environments and have unique biochemical and genetic properties. Bacteria are also prokaryotic but are more commonly found in diverse environments and exhibit a wide range of metabolic activities. Eukarya includes all eukaryotic organisms, ranging from unicellular protists to multicellular plants, fungi, and animals. Each domain is characterized by distinct genetic, biochemical, and structural features.