An organism is either multicellular or it is not.
An organism cannot have some parts of it being
multicellular and other parts of it not
Multicellular organisms include all animals,
all plants, most fungi (not yeasts), many types of
algae, a n Unicellular organisms include most
bacteria, many protists, and some yeasts. As far
as I know, all archaea are also unicellular, but
there may be exceptions that I do not know about.