Biology

The Five Kingdom and Three Domain Classification System

Hard sciences like biology are especially dependent on proper division, i.e., classification. Due to the immense complexity and variety of biological organisms, including bacteria, classifying kingdoms of them based on similar properties is paramount to our understanding of the diversity and evolution of life. Therefore, we can assess organisms at the highest system-domain – kingdoms – right down to their cellular and molecular system domains.The Five Kingdom and Three Domain Classification System Essay explains how the classification system was corrected based on new relevant data.Much as classification in general, the classification of lifeforms is a matter of degree within a particular system. At the highest domains, encompassing all organisms, we have the Three Domains System telling us the grand story of life. Within it, biologists classified organisms based on the ribosomal RNA structure variations. Ribonucleic acid is one of the building blocks of all living cells across species. RNA is in charge of carrying messages from DNA to manage protein synthesis, except for viruses in which RNA is the carrier of genetic information.Based on the RNA differences, the Three Domain System of classification sorts all creatures into:EukaryotesArchaeaBacteriaGoing further into a more detailed and meaningful classification of the overall system regarding the nature of their cells, we can divide these three domains further into Six Kingdoms of organisms:Archaea bacteria – the domain of ancient (archaea) bacteria, discovered in the 1980s.Eubacteria – the kingdom of the so-called true bacteria, the common single-cell creatures we all know, from harmful like Streptococci to beneficial ones like Lactobacillus that aids digestion.Fungi – the domain of multi-cellular organisms with chitin-like cell membranes that don’t produce their own food like other plants. From mushrooms to molds, yeasts, and mildews. They reproduce via spores.Protista – the kingdom more complex than bacteria, but still single-celled organisms such as algae.Plants – the kingdom of multi-cellular flowering plants that are autotrophic – produce their own food via photosynthesis.Animals – the kingdom of multi-cellular organisms ranging from microscopic tardigrades to giant sperm whales and elephants. They do not have a cell membrane and need to feed on other organisms to survive.As you may surmise, the Archaea bacteria kingdom was added relatively recently, which means that the previous classification system consisted of Five Kingdoms, also known as the two-name naming system (binomial nomenclature). As we continue to acquire more detailed data of each kingdom, it is never an omission to add to the classification system. In point of fact, this makes the scientific endeavor simultaneously flexible and robust. Just because something is revised, it doesn’t mean that the scientific method is erroneous. On the contrary, it means that it has an internal updating mechanism that ensures our picture of reality is as closely aligned to objective reality.Accordingly, the Three Domain system was proposed in 1990 to account for our greater understanding of organisms at their molecular domain. It grouped organisms with nucleus cells within the Eukarya, which accounted for four kingdoms of the previous five. Accordingly, as organisms were revealed that were single-celled but without a nucleus, a further division was needed to clarify the domains. Hence, we now have to deal with archaea and bacteria – Archaea bacteria and Eubacteria – while the other groups from the Five Kingdoms remain as they were classified previously.The culprit for this more detailed division of the systems that prompted the creation of the Six Kingdoms was Dr. Carl Woese, from the University of Illinois. During the 1970s, alongside his fellow microbiologists, Dr. Woese discovered evidence for the existence of prokaryote organisms that lived in extremely hostile conditions. Something that was previously thought impossible – organisms with the kind of cells capable of living on top of hot springs, acid lakes, hydrothermal vents, salt-saturated waters – became a surprising reality. Although they are prokaryotic, further biochemical analysis revealed them to contain a number of key differences from other bacteria families.Interestingly, as the first round of DNA research was conducted on the newly discovered archaea bacteria, it suggested common ancestry. Only later, when more precise techniques were implemented, was the truth revealed. Eventually, through modern DNA sequencing, scientists determined that these Archaebacteria share a great deal more in common with eukaryotes than to bacteria they were previously lumped with. Unlike bacteria’s cells, eukaryotes cells have a nucleus embedded within a membrane. Hence, the delay from the first discovery in the 1970s to the new classification system submitted in the 1990s for the Six Kingdoms instead of five kingdoms.Although the current Six Kingdoms classification system is more accurate than the previous Five Kingdoms system, it builds upon the diligent and pioneering work of Swedish biologist Carolus Linnaeus, who developed it in the 18th century. His initial line of thinking that all organisms should be classified according to common physical properties still holds true. Without such a pioneering system, our scientific understanding of fauna and flora would have suffered greatly.

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