Q.Define and understand the following terms:

Each of these is a taxonomic category — a rank in the hierarchy — and each groups together members of the rank just below it, sharing progressively fewer common characters as we move up.

• (i) Phylum — the category just above class. Several related classes that resemble one another in a few basic features are grouped into a phylum. In animals the classes of fishes, amphibians, reptiles, birds and mammals are united in the phylum Chordata by shared features such as a notochord and a dorsal hollow neural system. (In plants the corresponding category is called Division.)
• (ii) Class — groups together related orders. For example, the orders Primata and Carnivora are both placed in the class Mammalia because they share the defining mammalian characters.
• (iii) Family — a group of related genera, sharing fewer similarities than are found within a single genus, e.g. Solanaceae (grouping Solanum, Petunia, Datura). …

Classification proceeds as a hierarchy of steps, each step a rank or taxonomic category. Understanding these five terms means seeing both what each groups together and how the shared characters thin out as we climb.

(v) Genus — Starting near the bottom, a genus is a group of closely related species that have more characters in common with one another than they share with the species of any other genus; in other words, it is an aggregate of closely related species. Potato and brinjal are different species yet both belong to the genus Solanum; the lion, leopard and tiger are all species of the genus Panthera, which is distinct from the genus Felis, the cats.

(iii) Family — The next category above genus, a family gathers a group of related genera. Because it spans several genera, its members share fewer similarities than are found within a single genus. In plants, families are recognised from both vegetative and reproductive features. The genera Solanum, Petunia and Datura fall together in the family Solanaceae; among animals, Panthera and Felis are grouped in the family Felidae, while the dog, differing enough, is placed in a separate family, Canidae.

(iv) Order — Higher still, an order is an assemblage of families that resemble one another in a small number of common features. As a higher category it is defined by the overall aggregate of characters rather than a long list of specific ones. The families Convolvulaceae and Solanaceae are placed together in the order Polymoniales on the basis of floral characters; in animals, the order Carnivora brings together Felidae and Canidae.

(ii) Class — A class groups together related orders. The orders Primata (monkeys, gorillas, gibbons) and Carnivora (tiger, cat, dog) are both placed in the class Mammalia, because despite their outward differences they all share the defining mammalian characters. A class sits above the order and below the phylum. …