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.
Flagellum is the one on the left, cilia are on the right. A flagellum (plural: flagella) is a long, whip-like projection of a cell composed of microtubules.They help propel cells and organisms in a whip-like motion. The flagellum of eukaryotes usually moves with an âSâ motion, and is surrounded by cell membrane.Flagella are structurally almost identical with the much smaller Cilia.lagellum is the one on the left, cilia are on the right. A flagellum (plural: flagella) is a long, whip-like projection of a cell composed of microtubules.