Final answer:
The domain that includes unicellular organisms lacking membrane-bound organelles and involves parasitic and mutualistic relationships with humans is either Domain Archaea or Domain Bacteria, not Domain Eukarya, which consists of eukaryotic organisms.
Step-by-step explanation:
Members of Domain Archaea or Bacteria are unicellular organisms that lack membrane-bound organelles and have varying relationships with humans, ranging from parasitic to mutualistic. These two domains encompass prokaryotic organisms, meaning their cells do not contain a nucleus. In contrast, the Domain Eukarya, which includes kingdoms such as Animalia, Plantae, Fungi, and Protista, comprises organisms with eukaryotic cells that have a nucleus and membrane-bound organelles. Parasites such as Giardia or Plasmodium species fall under the domain Eukarya because they are classified as protozoans, which are eukaryotic.
It's important to note that while the domain Eukarya does contain unicellular eukaryotic parasites, the question is referencing cells that lack membrane-bound organelles, which are characteristic of the domains Archaea and Bacteria. Therefore, the domain that best fits the description given in the question is either Archaea or Bacteria, not Eukarya.