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.
Only the most primitive fungi, chytrids, have flagella. Other eukaryotic cells Eukaryotes are a very diverse group, and their cell structures are equally diverse. Many have cell walls, many do not. Many have chloroplasts, derived from primary, secondary, or even tertiary endosymbiosis, and many do not.ther eukaryotic cells Eukaryotes are a very diverse group, and their cell structures are equally diverse. Many have cell walls, many do not. Many have chloroplasts, derived from primary, secondary, or even tertiary endosymbiosis, and many do not.