Which kingdom is known to contain no multicellular organisms?

The kingdom Protista is characterized by its diverse range of organisms, which predominantly include unicellular forms. While some Protista can form multicellular structures, they do not form true multicellular organisms with specialized tissues like those found in the kingdoms Fungi, Animalia, or Plantae. The majority of Protista are single-celled organisms, such as amoebas and paramecia, as well as simple multicellular forms like certain algae, which do not represent true multicellularity in the complex sense.

This distinguishes Protista from the other kingdoms mentioned. For example, Fungi includes multicellular organisms like mushrooms, yeast can exist as unicellular organisms but typically form multicellular mats, and Animalia exclusively comprises multicellular organisms. Bacteria, while primarily unicellular, belong to another domain of life entirely, further differentiating them from Protista. Thus, the defining characteristics of Protista lead to the conclusion that this kingdom contains no true multicellular organisms, making it the correct choice.