Final answer:
The domain Eukarya contains the most multicellular organisms, including the animal, plant, fungi, and protist kingdoms, whereas Archaea and Bacteria are domains primarily composed of unicellular prokaryotes.
Step-by-step explanation:
The domain that contains the most multicellular organisms is Eukarya. This domain is characterized by organisms having cells with membrane-bound nuclei. It is home to four major kingdoms: animals, plants, fungi, and protists, many of which are multicellular. In contrast, the domains Archaea and Bacteria consist of organisms that are unicellular and are known as prokaryotes due to the absence of a cell nucleus. In the context of multicellularity, prokaryotes like Archaea and bacteria do not exhibit multicellular forms. Hence, when comparing the three domains of life—Bacteria, Archaea, and Eukarya—it is the domain Eukarya that encompasses the diversity of multicellular life forms including the complex organisms found within animal and plant kingdoms.
While there is a diversity of life within the domains Archaea and Bacteria, these organisms are generally not multicellular. The organisms within the domain Eukarya can range from simple unicellular eukaryotes to complex multicellular organisms, demonstrating a greater range in terms of multicellularity.