Hierarchy of Classification in Biological Taxonomy

The categorising of organisms according to their similarities and differences is referred to as the hierarchy of classification. The categorisation of organisms at the hierarchical stages facilitates the systematic study of the numerous species in a specified way.

Different species can be identified more easily thanks to the hierarchy of classification categories. The process of categorising various living organisms falls under the umbrella of the biological field known as taxonomy. An organised group of organisms is referred to as a taxon.

What is the Hierarchy of Plants and Animals?

Over several millions of years, a huge variety of species have evolved on earth and time immemorial many attempts of classification of things have been made. The life forms that surround us range from small ants to big trees, colourless insects to brightly coloured flowers or birds. For ease in studying and identifying, the idea of biological classification was put forth but for the applicable classification, a fundamental basis of classification became a necessity.

Initially, things around us were segmented into living and nonliving things and later, when the variety of living things started to grow, there came the necessity for the biological classification. The classification of living organisms based on similarities and dissimilarities is known as biological classification. Each of the biologists who classified organisms, have done it by separating them into different groups according to various criteria. It took years for researchers to decide the most basic characteristics for the process of classification.

What is the Hierarchy for Classification of Living Organisms?

The following are the important hierarchies in which different organisms are classified:

Kingdom

The kingdom is the highest level of classification, which is divided into subgroups at various levels. There are 5 kingdoms in which the living organisms are classified, namely, Animalia, Plantae, Fungi, Protista, and Monera.

Phylum

This is the next level of classification and is more specific than the kingdom. There are 35 phyla in the kingdom Animalia. For example – Porifera, Chordata, Arthropoda, etc.

Class

Class was the most general rank in the taxonomic hierarchy until phyla were not introduced. Kingdom Animalia includes 108 classes including class mammalia, reptilia, aves, etc. However, the classes used today are different from those proposed by Linnaeus and are not used frequently.

Order

Order is a more specific rank than class. The order constitutes one or more than one similar family. There are around 26 orders in class mammalia such as primates, carnivora, etc.

Family

This category of taxonomic hierarchy includes various genera that share a few similarities. For eg., the families in the order Carnivora include Canidae, Felidae, Ursidae, etc.

Genus

A group of similar species forms a genus. Some genera have only one species and are known as monotypic, whereas some have more than one species and are known as polytypic. For eg., lion and tiger are placed under the genus Panthera.

Species

It is the lowest level of taxonomic hierarchy. There are about 8.7 million different species on earth. It refers to a group of organisms that are similar in shape, form, reproductive features. Species can be further divided into subspecies.

What is the Hierarchy of Classification?

Hierarchical classification is a system of classifying organisms in different hierarchical levels. It includes the sequence of categories in a decreasing or increasing order from kingdom to species and vice versa. The domain is the highest rank in the hierarchy followed by division or kingdom, phylum, class, order, family, genus, and species.

Interesting Facts

• The word Hierarchy dates back to ancient Greece. It seems to have been coined by Pseudo-Dionysius the Areopagite in the 6th Century AD.

• In 1758, Carolus Linnaeus, the Swedish naturalist and founder of biological classification, published his 10th edition of the Systema Naturae. This book of names is the commencement date for classification.

Practice Questions

1. Which group has the widest variety of nutrients?

1. Monera

2. Plantae

3. Fungi

4. Animalia

Ans: The correct answer is (a).

2. What function does taxonomy serve?

1. Explains the origin of life

2. Identifies of unknown species

3. Searches the history of evolution

4. Identifies medicinal plants

Ans: The correct answer is (b).

Summary

The kingdom is first in the hierarchy of categorisation, which is followed by Phylum or Division, Class, Order, Family, Genus, and Species. Whittaker proposed five kingdom classifications: Monera, Protista, Fungi, Plantae, and Animalia. Prokaryotes have traits that are unicellular in Monera and Protista bacteria, followed by multicellular creatures in Fungi and Animalia. The bacterial Monera cell wall may or may not be found in cells.

The cell wall is absent in Protista, present in Fungi and Plantae, but present in Animalia and Plantae. Both autotrophic and heterotrophic forms of nutrition are present in the nutrition mode with monera and protozoa. Only the heterotrophic form of nutrition is displayed in fungi. Only the autotrophic form of nutrition is displayed by plants. The heterotrophic way of nutrition is evident in animals.