Five Kingdom Classification

Segregating living organisms into different hierarchical groups depending upon their similarities in their structure, functions, physiology, etc. is Biological Classification. Aristotle first, classified living organisms on the basis of their habitat (living on water, land, or air). The systematic classification of organisms is needed to study them properly. As evolution is a continuous process with a standard classification system in place it is easier to place the organisms according to their groups and identify their characteristics.

What is the Five Kingdom Classification

The basic two-kingdom classification that divides plants and animals into two groups was not efficient enough to help study other organisms that did not fall in either of the categories. There are organisms, with no similarities with plants or animals. Hence, to classify and study all organisms, a broader system was needed to first classify and put all of them into different groups. 

The Five Kingdom System Differentiates Organisms on the Basis of:

  • Cell Structure

  • Body organization

  • Mode of Nutrition

  • Mode of Reproduction

  • Phylogenetic Relationship (Evolutionary development and diversification)

Robert H Whittaker introduced the Five Kingdom Classification in 1969 for the study of organisms.

The Five Kingdom System

The Five major groups as per this system are: 

  • Animalia

  • Plantae

  • Fungi

  • Protista

  • Monera

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Kingdom Animalia

Eukaryotic and multicellular organisms with no cell wall or photosynthetic pigments come under this group. Organisms in this group are heterotrophs and feed on external food (plants or animals). Their mode of nutrition is holozoic. So, with such a mode of nutrition, they have to ingest, digest, absorb, and assimilate the food in order to utilize it. Organisms of this group reproduce sexually or asexually. The most distinguishing feature of this group of organisms is the presence of sensory organs and a nervous system.

Examples- Porifera- Sponges, Cnidaria- Jellyfishes, Echinodermata- Starfishes, Arthropoda- insects, Mammals, Birds, Amphibians.

Kingdom Animalia has a further sub-classification: 

  • Vertebrates- Those who have backbones.

  • Invertebrates- Those who do not possess backbones.

Kingdom Plantae

As the name suggests, plants come under the kingdom Plantae. Organisms in this group are Eukaryotes and multicellular with the presence of a cell wall made of cellulose. They also have photosynthetic pigments present so that they can prepare their own food. Thus, they show the autotrophic mode of nutrition mostly. Organisms in this group reproduce sexually or asexually. Plants are further divided into two types: 

  • Flowering plants

  • Non-Flowering plants

Plants with flowers reproduce sexually by pollination and the non-flowering plants reproduce asexually by vegetative propagation.

Examples- Ferns, Mosses, Flowering plants, etc.

Kingdom Fungi

Fungi are Eukaryotes, can be unicellular, multicellular, or filamentous. They have a cell wall made of chitin and polysaccharides. Their mode of nutrition is heterotrophic, which means they cannot make their own food and rely on external sources. If you have noticed, most often, long decomposing food or stale bread develops a furry growth on them, this growing organism is nothing but fungi. Some fungi also survive as parasites and most of them are saprophytes, that is, they survive on a dead or decaying matter. Some fungi are also found to be surviving in symbiotic associations with other organisms, like plants or viruses. Fungi are an important class of organisms for the ecosystem as they facilitate the decaying process. We also see commercial uses of fungi in our day to day lives. Fungi can reproduce sexually or asexually by spore formation.

Examples- Mushrooms, yeasts, etc.

 Kingdom Protista

Eukaryotic and single-celled, also called unicellular organisms to come under this group. Protists are both heterotrophs or autotrophs. The pant protists are autotrophs. Example: Algae- Spirogyra, Euglena, etc. Animal and fungus-like protists are heterotrophs. Example- Amoeba, Paramecium. Some Protists also possess flagella or cilia for locomotion. Protists can reproduce asexually by Binary Fission, Nucleus division, budding, etc. Or sexually by gametes formation. 

Protists are further divided into three major groups:

Photosynthetic Protists

The protists which are capable of doing photosynthesis come under this group.

There are three types of photosynthetic protists: 

  • Chrysophytes are diatomic and desmids.

  • Dinoflagellates are mostly marine planktons but are also found in freshwater bodies.

  • Euglenoids have a protein layer called pellicle in place of the cell walls and are found in freshwater bodies.

Saprophytic Protists

Are slime molds. They gain energy from dead and decaying organic matter, mostly twigs, leaves, etc. 

Parasitic Protists

Single-celled eukaryotic protozoans are under this group.

Kingdom Monera

Single-celled prokaryotic organisms with a cell wall are categorized under Kingdom Monera. Their cell wall is made up of a polysaccharide and protein compound instead of cellulose like other organisms. They lack many cell organelles like a cell membrane, Golgi apparatus, mitochondria, endoplasmic reticulum, etc. Bacteria is the only organism in this group. They are microscopic and are found in abundance. Life originated and evolved from bacteria. 

Kingdom Monera is further divided into a) Archaebacteria- The most simple and primitive form of bacteria that can survive in extreme conditions. b) Eubacteria- Organisms lacking membrane-bound nucleus often found in the intestines of the vertebrates and in soil.

Types of bacteria

Depending upon their shape, bacteria are divided into four groups

  • Micrococcus- Are generally round or sphere-shaped. They are commonly found on the skin, soil, meat, etc. These bacteria are harmless and are generally saprophytic in nature. They need oxygen to grow and reproduce.

  • Staphylococcus- Are also sphere-shaped bacteria but in some cases, they are infectious and cause some major health problems like food poisoning, diarrhea, skin infection, etc. They are also found on skin, hair, and other surfaces. They can thrive and grow even in the absence of oxygen.

  • Bacillus- Are rod-shaped bacteria. They produce endospores as a result of which they are very tough. These are also saprophytes, found in soil water, dust.

  • Pseudomonas- They are also rod-shaped bacteria. Pseudomonas can produce exotoxins, which is why they infect individuals who have suppressed immunity or less immunity. They hardly attack healthy individuals. They are found in soil, over the skin, etc.

FAQ (Frequently Asked Questions)

1. What are the advantages of Five Kingdom Classification over Two Kingdom Classification?

Two kingdom classification only divided the organisms into plants and animals. It did not give an idea of the character of a particular set of organisms and there are many organisms that do not fall under either of the categories. On the other hand, the five-kingdom classification is diverse, and divides single cellular and multicellular organisms into different groups. It eases the study of organisms on the basis of their characteristics.

2. What is the basis of the five-kingdom classification?

Five kingdom classification is done on the basis of 5 factors- cell structure, body organization, mode of nutrition, mode of reproduction, and phylogenetic relationship. It also puts unicellular and multicellular organisms into different groups.

3. What is the kingdom Monera further divided into?

It is further divided into two groups- Archaebacteria and Eubacteria.