Introduction
In the earlier times, all living things were pooled together into two kingdoms. One was the plant kingdom, and the other was the animal kingdom. The animal kingdom was composed of every living thing that used to eat, move, grow to a specific size and then stop growing. On the other hand, the plant kingdom was about living things that did not move or eat but kept growing throughout their life.
Thus, it wasn’t easy to put other living things into either of these categories. As a result, we got a five-kingdom classification. It consists of Protista, Fungi, Plantae, Animalia, and Monera.
History of Five Kingdom Classification
In the early times, scientists began to group living organisms under distinct categories. Some classified them into plants and animals, while some, like Robert Whittaker, Ernst Haeckel and others tried to classify them under a broader system. The five-kingdom classification was the one that was widely used. The five-kingdom classification was proposed by R.H. Whittaker.
It was introduced in 1969, where he named them as Monera,Protista,Fungi, Plantae and Animalia. In the five-kingdom system, the main basis of classification is the complexity of the cell structure and organisms, body organisation, mode of nutrition, reproduction and interrelationships. It determines whether the organism is eukaryotic or prokaryotic, unicellular or multicellular, asexual or sexual, autotroph, heterotrophic, or more.
Features of the Five Kingdoms
The five kingdoms have been divided into different phylum(animals) and division (plants).Further there are other categories in which they are divided namely-Class, Order, Family, Genus, Species
Kingdom → Phylum → Class → Order → Family → Genus → Species
Now, let’s look at the different kingdoms and their features and examples.
Kingdom Monera
In this kingdom, the organisms are prokaryotic and unicellular. Further, these organisms do not have a well-defined nucleus. Similarly, it does not have cell organelles. In this kingdom, some organisms have a cell wall while some of them do not have it.
As a result, some organisms of this kingdom are autotrophic while the others are heterotrophic. For instance, bacteria, mycoplasma, cyanobacteria, etc., are all part of the Monera kingdom.
Kingdom Protista
Organisms that fall under the Protista kingdom are unicellular. However, they are eukaryotic organisms. Further, they are the simplest form of eukaryotes that display a mode of nutrition that is either autotrophic or heterotrophic.
Also, some of the organisms have appendages like cilia or pseudopodia or flagella that allows them to move around. For instance, Paramecium, diatoms, protozoans, etc., are all part of the Protista kingdom.
Kingdom Fungi
Under the kingdom of Fungi, we have multicellular, eukaryotic, and heterotrophic organisms. Further, when we observe their mode of nutrition, it is saprophytic. This is because this kingdom uses decaying organic matter as their food.
All organisms in this kingdom have cell walls composed of a substance called chitin. Moreover, Fungi have also created a symbiotic association with various blue-green algae. For instance, mushrooms, yeast, Aspergillus, etc., are all part of the Fungi kingdom.
Kingdom Plantae
Organisms that belong to the kingdom Plantae are all eukaryotic and multicellular. They have cell walls that are composed of cellulose. Further, they are known to be autotrophs. These organisms synthesise their food with the help of photosynthesis.
In this kingdom, all plants are included, like trees, bushes, ferns, herbs, and more. Moreover, this kingdom divides into different divisions based on their body differentiation and whether specialised vascular tissue is present or not.
The different divisions are, Thallophyta, Bryophyta,Pteridophyta, Gymnosperms and Angiosperms. For instance, pines, Spirogyra, mango plants, ferns, etc., are part of the Plantae Kingdom.
Kingdom Animalia
In the Animalia kingdom, we have organisms that are eukaryotic and multicellular. These organisms do not have a cell wall. Also, their mode of nutrition is heterotrophic. Similarly, they present huge diversity.
In this kingdom, some organisms are simple, whereas others come with a complex body with specialised tissue differentiation and body organs. The Animalia kingdom is divided into various classes and phyla. Coelenterata, Chordata, Porifera, Arthropoda, etc., are some of the phyla. For instance, monkeys, starfish, birds, Hydra, earthworms, etc., are all part of the Animalia kingdom.
Conclusion
In conclusion, a kingdom in biology is defined as the taxonomic rank. This is composed of small groups that we refer to as phyla. After that, we define a kingdom as the highest taxonomic rank for classifying organisms. The five-kingdom classification by Whittaker is the most popular one that includes Animalia, Monera, Protista, Fungi, and Plantae. The basis of this classification analysis is the structure of the cell, mode of nutrition, reproduction and organisation of the body, and the phylogenetic relationships.