Final answer:
The Domain Eukarya is distinctive due to its organisms having eukaryotic cells with a membrane-bound nucleus and organelles, and includes both unicellular and multicellular forms. It is divided into six supergroups that contain various kingdoms. The evolutionary history of these groups is studied through phylogenetic trees.
Step-by-step explanation:
The domain Eukarya is characterized by organisms that possess eukaryotic cells, which include a membrane-bound nucleus and various membrane-bound organelles. Members of this domain can be unicellular or multicellular, and they exhibit a high level of cellular complexity. Organisms within this domain are classified into several kingdoms, such as plants, animals, fungi, and protists.
The phylogenetic tree of life positions Eukarya as sharing a more recent common ancestor with Archaea than with Bacteria, suggesting a closer evolutionary relationship between these two domains.
Furthermore, modern classification systems have organized Eukarya into six supergroups, based on evolutionary relationships. These supergroups contain multiple kingdoms, linking a wide variety of life forms with similar eukaryotic cell structures. While the evolutionary relationships among these supergroups continue to be explored and debated, the presence of a nucleus and complex organelles remains the defining characteristic of the domain Eukarya.