Which group of organisms is characterized as the simplest eukaryotes?

The group of organisms known as Protista is characterized as the simplest eukaryotes because they represent a diverse array of predominantly unicellular organisms that possess a defined nucleus and membrane-bound organelles. This group includes organisms such as protozoa and some algae. Eukaryotes, by definition, are organisms whose cells have a nucleus enclosed within membranes, distinguishing them from prokaryotes, which include bacteria and archaea.

Protists exhibit a range of complexities in their cellular structures and functions, but they are generally less complex than multicellular eukaryotic groups like Plantae, which encompasses higher plants. The simplicity of protists is reflected in their varied life cycles and ecological roles, often functioning as primary producers or important components of food webs.

The other groups mentioned have distinct characteristics that differentiate them from Protista. Bacteria and archaea are prokaryotic and lack a defined nucleus, while Plantae includes more complex, multicellular organisms that perform photosynthesis and have specialized structures. Thus, Protista stands out as the simplest eukaryotic group.