Which kingdom includes unicellular eukaryotes with a nucleus and organelles?

The kingdom that includes unicellular eukaryotes with a nucleus and organelles is Protista. This kingdom is characterized by its diverse array of organisms, which can be both unicellular and multicellular, but it primarily includes protists that are unicellular. Protists possess a true nucleus that houses their genetic material and various organelles that perform specific functions, similar to those found in more complex eukaryotic cells.

Many members of the Protista kingdom, such as amoebas and paramecia, exhibit complex behaviors and life cycles despite their unicellularity. They are essential in various ecological roles, from being primary producers in aquatic environments (like algae) to acting as consumers in food chains.

In contrast, Monera consists primarily of prokaryotic organisms like bacteria, which do not have a nucleus or membrane-bound organelles. Fungi, while eukaryotic and including both multicellular and unicellular forms like yeast, do not primarily include unicellular organisms as a defining characteristic. Animalia, on the other hand, primarily includes multicellular, heterotrophic organisms without cell walls, ruling them out as a kingdom for unicellular eukaryotes.