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.
A whip-like organelle specialized for locomotion. Flagella are found among all three domains of life-bacteria, archaea, and eukaryotes-but the structure of the appendage i â¦ s different in each of these domains.n example of a flagellated bacterium is the ulcer-causing Heliobacter pylori, which uses multiple flagella to propel itself through the mucus lining to reach the stomach epithelium.