Key Points

Defining features of living organisms include growth, reproduction, metabolism, cellular organization, and consciousness or the ability to respond to stimuli.

Biodiversity refers to the number and various kinds of organisms found on Earth. The number of species known and described is between 1.7 to 1.8 million.

Nomenclature is the process of standardizing the naming of organisms. It requires correct identification, which is the accurate description of an organism.

Proposed by Carolus Linnaeus, this system provides a scientific name with two components: the Generic name (genus) and the specific epithet (species).

Names are Latin, written in italics or underlined. The genus name starts with a capital letter, while the species name starts with a small letter, for example, Mangifera indica.

The naming of plants is governed by the International Code for Botanical Nomenclature (ICBN), and the naming of animals is governed by the International Code of Zoological Nomenclature (ICZN).

Classification is the process of grouping organisms into convenient categories (taxa) based on observable characters. Taxonomy is the science that deals with the principles and procedures of classification.

Systematics is the study of the diversity of organisms and their evolutionary relationships. It includes taxonomy along with the study of evolutionary history (phylogeny).

It is the framework by which taxonomic groups are arranged in a definite order, from higher to lower categories. All categories together constitute the taxonomic hierarchy.

The seven main categories in ascending order are: Species, Genus, Family, Order, Class, Phylum (for animals) or Division (for plants), and Kingdom.

Species is the basic unit of classification. It is a group of individual organisms with fundamental morphological similarities that are able to interbreed and produce fertile offspring.

A genus comprises a group of related species which has more characters in common in comparison to species of other genera. For example, Panthera is a genus that includes lion, tiger, and leopard.

A family is a group of related genera with a smaller number of similarities as compared to genus and species. For example, the family Felidae includes the genus Panthera and the genus Felis (cats).

An order is an assemblage of related families that exhibit a few similar characters. For example, the order Carnivora includes families like Felidae (cats) and Canidae (dogs).

A class is a major taxonomic rank that includes related orders. For example, Class Mammalia includes order Primata (monkeys) and order Carnivora (tigers).

A phylum consists of related classes of animals, such as Phylum Chordata. In plants, the equivalent category is called a Division, such as Angiospermae.

Kingdom is the highest category in the taxonomic hierarchy. The major kingdoms include Kingdom Animalia and Kingdom Plantae.

As we ascend the taxonomic hierarchy from species to kingdom, the number of common characteristics shared by organisms decreases, and their relationships become more distant.