Hierarchy of Classification

Introduction 

The Hierarchy of classification refers to the grouping of organisms based on their similarities and dissimilarities. 

The hierarchical levels help in the categorization of the organisms which is essential to study the vast number of organisms in a defined manner. The hierarchy of classification groups aids in the identification of different species.

What Is Meant By Hierarchy of Classification?

We define a hierarchy of classification as a system where various categories of organisms are grouped based on their characteristics at different hierarchical levels. The levels in the hierarchy are either in descending or ascending order. 

The hierarchy of classification has different sequences of categories. 

The Hierarchy of Classification Groups

In the early days of civilization, many biologists, namely Ernst Haeckel, Carolus Linnaeus, Robert Whittaker, etc, have tried to put together various living organizations to explain the concept of the hierarchy of classification. 

Over time, the hierarchy of classification groups of living organisms has seen several changes and was named “kingdoms”.

In 1960, Robert Whittaker, an American plant ecologist recommended gathering all the living organisms present in the world and putting them together. 

Hence, five kingdoms in the system of hierarchy of classification led to the name “kingdom classification” and the five kingdoms that he recommended were Monera, Protista, Fungi, Plantae and Animalia. 

The biologists divided these kingdoms into the hierarchy of classification groups based on a few categories such as cellularity, body organization, mode of nutrition, reproduction and phylogenetic relationships.

At various levels, the hierarchy of classification groups was further sub-classified.

Sub- levels Explain The Hierarchy of Classification

Kingdom—It is the widespread level and has been further divided into different lower hierarchy levels. 

• The kingdoms are divided into Phylum or Division based on some other characteristics
• Phylum or division is separated into “Class” depending on specific qualities, and then the class is arranged into order
• The order is further divided into “Family,” then into “Genus,” and finally into “Species,” which is the smallest unit of classification

“This division of sublevels is known as the hierarchy of classification.”

The Hierarchy of Classification Table

Animals belonging to the same genus or species share the most similarities. Hence, similarity increases as we go down the hierarchy of classification groups.

Every organism that can breed and is similar belongs to the same species. 

These kinds of organisms have the same number of chromosomes, or they have a constant number of chromosomes.

Kingdom Hierarchy of Classification

Characteristics of The Five Kingdoms of Whittaker

• Kingdom Monera

Monera kingdom comprises small and simpler structured organisms but complex in behaviour. These organisms are unicellular. They do not possess any nuclear membrane around their chromosome. Hence because of undeveloped nucleus these are called “Prokaryotes” 

Cell walls may or may not be present in the Monera kingdom. 

The members of Monera Kingdom show two modes of nutrition namely autotrophic and heterotrophic. 

Some examples of the Monera kingdom are bacteria, blue-green algae, mycoplasma.

• Kingdom Protista

Protista groups are majorly unicellular organisms with undefined boundaries. The cells in Protista have a well-defined nucleus, and hence they are called eukaryotes. 

The cells in Protista do not have a cell wall, and their mode of nutrition can be anything from autotrophic to heterotrophic.

Like other eukaryotes, the Protista cell body has a clear nucleus and other membrane-bound organelles.

Some examples of Protista are diatoms, protozoans and unicellular algae.

• Kingdom Fungi

Fungi are very basic organisms. They are typically multicellular, except for yeast, which is a single-celled fungus. Fungi are classified as eukaryotes because they have a well-defined nucleus. Fungi have a proper cell wall formed of chitin, a complex chemical. 

Fungi are mainly divided into three nutrition modes to feed on. 

Saprophytes are a type of fungi that feed mostly on dead and decaying materials.

Fungi can also feed on living beings and this type of nutrition is named parasitic.

Fungi also have the unique ability to coexist with other species, such as blue-green algae. They benefit each other when they dwell together, and this is known as a symbiotic relationship, the third type of nutrition in fungi.

Lichen is the symbiotic connection between fungi and blue-green algae. 

Mucor, Penicillium, Mushroom, and other fungi are a few examples.

• Kingdom Plantae

Plantae is a kingdom of plants that contains multicellular organisms. These organisms are eukaryotic. Most of their cell wall is made of cellulose. The mode of nutrition is autotrophs.

The Plantae kingdom is further subdivided into many divisions that contain distinct plant types.

Mango, Rose, banana, and unicellular algae are all examples of plants.

• Kingdom Animalia

This kingdom’s organisms are multicellular. They are eukaryotes because they lack a cell wall and always feed in a hypertrophic manner.

Some common examples of Kingdom Animalia are dogs, cats, rats, insects, etc.

Conclusion 

1. The hierarchy of classification is organized from the Kingdom then proceeds with Phylum or Division, Class, Order, Family, Genus, and Species. 
2. Monera, Protista, Fungi, Plantae, and Animalia are the five-kingdom categories hypothesized by Whittaker.
3. Regarding cellularity Monera kingdom is the only prokaryote, the rest all the kingdoms are eukaryotes. 
4. In body organization, characteristics of the prokaryotes are unicellular in the bacteria of Monera and Protista, then from Fungi to Animalia, all the organisms are multicellular.
5. In cells, the bacteria Monera cell wall may or may not be present. In Protista, the cell wall is absent, in Fungi and Plantae the cell wall is present, and in Animalia, it is absent.
6. The mode of nutrition with Monera and Protista has both kinds of nutrition that are Autotrophic and Heterotrophic. 
7. In Fungi, they show only the heterotrophic mode of nutrition. Plants show only the autotrophic mode of nutrition. Animals show the heterotrophic mode of nutrition.