Final answer:
The three basic categories on a cellular level are called prokaryotes, eukaryotes, and viruses. Prokaryotic cells lack a nucleus and membrane-bound organelles, while eukaryotic cells have them. Viruses are not considered living since they're not made up of cells and need a host to replicate.
Step-by-step explanation:
The three basic categories at the cellular level are called prokaryotes, eukaryotes, and viruses. Prokaryotic and eukaryotic cells are the two broad categories into which all life forms are classified, while viruses are unique in that they are not made up of cells and require a host cell to replicate. Prokaryotic cells, which include the domains Bacteria and Archaea, lack a nucleus and membrane-bound organelles. Eukaryotic cells, found in animals, plants, fungi, and protists, have a nucleus and organelles enclosed within membranes. The basic components shared by all cells are: the plasma membrane, cytoplasm, DNA, and ribosomes; however, only eukaryotes have membrane-bound organelles.