An account of the structure of plants naturally begins with the cell which is the proximate unit of organic structure. The elementary unit of plant structure, as of animal structure, is the cell. Faunistically, although not geographically, the Nearctic and Palaearctic areas must form the two subdivisions of one great unit, for which the  Holarctic region  is now the generally accepted term.
Definition: a subclass considered a phylum of the kingdom Protista in some classifications; includes holozoic or saprozoic flagellates.
For bacterial flagella and their differences, see Flagellum. A flagellate is a cell or organism with one or more whip-like organelles called flagella. The word flagellate also describes a particular construction (or level of organization) characteristic of many protists (eukaryotic organisms) and their means of motion.