The key difference between kingdom and domain is that the kingdom is one of the five major groups of living organisms while the domain is one of the three taxonomic categories of living organisms above the kingdom level.
There were many attempts of classification of organisms on earth. Till 1977, kingdom system was universally accepted across the world. Starting from the two kingdoms system called the Linnaean system way back in 1758 when the life forms were divided into plants and animals, the world has come to recognize the three-domain system as the most current and the most scientific system of classification of organisms. Though there are some similarities, the kingdom system of classification of organisms has now been relegated to having relatively little significance since the three-domain system popularized in all parts of the world. The aim of this article is to find out the difference between kingdom and domain system of classification of organisms.
CONTENTS
1. Overview and Key Difference
2. What is Kingdom
3. What is Domain
4. Similarities Between Kingdom and Domain
5. Side by Side Comparison – Kingdom vs Domain in Tabular Form
6. Summary
What is Kingdom?
The old two-kingdom system of classification comprised of two kingdoms; plant kingdom and animal kingdom. A Linnaean system called all organisms that moved with anima (with a soul), and fungi got classified as plants. The system went on adding kingdoms. However, the five-kingdom classification system was believed to be the complete system after the discovery of bacteria, algae and electron microscope.
Figure 01: Kingdom
Hence, the five-kingdom classification proposed in 1969, is the most updated system of classification today even though the six-kingdom classification is more accurate. Plantae, Archaebacteria, Eubacteria, Protista, Animalia, and Fungi are the six-kingdom included in the six-kingdom classification. In this classification system, the fifth kingdom; Monera has been divided into Archaebacteria and Eubacteria; thus, bringing the number of kingdoms to six. Five kingdom classification includes five kingdoms namely Monera, Protista, Fungi, Plantae and Animalia. In all classifications, whether 5 or 6 kingdoms, a kingdom has subdivision such as phyla or divisions. In fact, Kingdom Animalia consists of phyla while the Kingdom Plantae has divisions.
What is Domain?
Two scientists, Woese and Wolfe, in 1977, completely changed the system of classification of organisms in the world when they made use of 165 ribosomal RNA sequences. Till 1977, the world had come to accept the bifurcation of life forms into eukaryotes and prokaryotes. But it was the discovery of archaea; the microorganism that could live without oxygen, so reminded one of the ancient environment of earth that was devoid of oxygen, that forced scientists to conceive of a third category of organisms.
Figure 02: Domains
Therefore, Archaea was accepted as being different from the earlier two classifications, and thus the three-domain system came into existence. Accordingly, the three domains include Bacteria, Archaea and Eukarya.
What are the Similarities Between Kingdom and Domain?
- Kingdom and domain are two types of categories to classify living organisms.
- Kingdoms are coming under the domains.
- All living organisms belong to three domains as well as to five kingdoms.
What is the Difference Between Kingdom and Domain?
Three domains or five kingdoms are two types of classification systems to categorise living organisms. The key difference between kingdom and domain is that the kingdom is one of the five major groups of living organisms while the domain is one of the three taxonomic categories of living organisms above the kingdom level. Thus, domain is a category above the kingdom level. Accordingly, there are three domains namely bacteria, archaea and eukarya. On the other hand, the kingdom is a major category of living organisms below the domain level. There are five kingdoms namely monera, protista, fungi, plantae and animalia. Hence, this is another difference between kingdom and domain.
Summary – Kingdom vs Domain
Classification of living organisms is important to identify and study their characteristics and phylogenetic relationships. Classification systems include different hierarchical levels. Among the different hierarchical levels, domain and kingdom are two main levels. Accordingly, domain is a category above the kingdom level. There are five kingdoms; monera, protista, fungi, plantae and animalia. On the other hand, all living organisms belong to three domains namely, bacteria, archaea and eukarya. Similarly, domain Eukarya includes protista, fungi, plantae and animalia. Hence, this is the difference between kingdom and domain.