The five kingdom classification of organisms


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BACKGROUND (From 3-kingdom to 5-kingdom classification)……………………………… 1

KINGDOM ANIMALIA………………………………………………………………………………………....2

KINGDOM PLANTAE…………………………………………………………………………..2-3

KINGDOM PROTISTS………………………………………………………………………….3

KINGDOM FUNGI…………………………………………………………………………….4

KINGDOM PROKARYOTES (MONERA)…………………………………………….……4



People have always sought a better understanding of nature. Classification is one tool early scientists have used to gain that understanding.

Classification is the grouping of objects or information based on similarities. As time passed the science of taxonomy developed.

Taxonomy is the branch of biology concerned with the grouping and naming of organisms. The Greek philosopher and naturalistic Aristotle (384-322 B.C), developed the first method of classification. He classified all living things known at that time into two major groups- plants and animals.

It was not until 18th century that the Swedish botanist Colius Linnaeus (1707-1778), developed a method of classification based on close relationships of organisms. Linnaeus also inverted the two word system. The first word identifies genus in which the organism belong followed by a descriptive word of that organism.

During Linnaeus time, it was thought that there were three kingdoms namely animal, plant and mineral kingdoms. Every living thing was considered as either a plant or an animal. Animals were organisms that moved, ate things and breathed. There limbs and organs and bodies grew to a certain size and the stopped growing. Plants were organisms that did not move, eat or breath and grew indefinitely. Thus the fungi, algae and bacteria were grouped with the plants, and bacteria were grouped with the plants. The protozoans one- celled organisms that ate and moved were classified with the animals. From the above description it cannot escape our realization that this kind of classification was a fallacy and inaccurate especially at that both cellular, nuclear and biochemical level.

In the twentieth century new data began to emerge. This was to some extent because of the improvement in light microscopes and subsequently the development of the electronic microscopic development and also because of the application of biochemistry techniques in studies of differences and similarities among organisms. As a result, the number of groups recognized as constituting different kingdoms has increased as biological knowledge recommended five kingdom classification proposed by Whittker and this classification included, prokaryotes, Protista, fungi, Plantae, and animalia kingdoms.

This kind of classification, five- kingdom classification necessary and considered better than the three- kingdom classification with respect to many factors, among which was the fact that, all algae may not be plants necessary with appropriate plant structures as some algae may be animals. The other reason why the five kingdoms to three kingdom classification is that it is not logical and scientifically reasonable to place algae in plants and protozoa in animals, that create a lot of ambiguity. It was therefore imperatively accurate to create five kingdom classifications with the kingdom Protista to accounts for organism that have both plant and animal characteristics.

Furthermore the five - kingdom break down classification to basics which make it easier for new organisms to be accurately classified according to their features without assumptions ambiguity.

Unlike the three kingdom classification the five kingdom went deeper considering the organism entire form, structural, metabolic and biochemical characteristics. It was difficult to classify tiny and complex organisms in three kingdom classification which is not the case in five kingdom classification which take into account all microscopic characteristics and behavior of each organism discovered.


The animal kingdom has more than one million species. The main characteristics of members includes; multicellular, eukaryotic, heterotrophic, organisms nutrition mainly by ingestion, mostly have specialized diploid cell tissue, and many have complex organs and organ systems, no cell wall or chloroplasts; sexual reproduction predominates both aquatic and terrestrial forms. The cells contain chromosomes with DNA plus protein, a nucleus with nuclear envelope, the mean of genetic recombination is by fertilization and meiosis. The ability of animals to move more rapidly and in more complex ways than members of other kingdom is their most interesting characteristics. A remarkable form of movement unique to animals is flying, an ability that is well developed among insects and vertebrates, such as grasshopper and birds respectively. Most animals reproduce sexually. In animals, cells formed in meiosis function directly as gametes. The haploid cells do not divide by mitosis first as they do in plants and fungi but rather fuse directly with one another to form the zygote. The zygote then gradually develops into an adult by going through several development stages.

Almost all animals (99%) are invertebrates that is they have no backbones, of the more than one million living species, only 42,500 have back bones and are referred to as vertebrates. The animal kingdom includes about 35 phyla, most of which live in the sea. Far fewer phyla live in fresh water and fewer still live on land.


The plant kingdom has about 280,000 species. Their main characteristics include; multicellular, eukaryotic mostly autotrophic; mainly terrestrial organisms containing tissues and organs; cell wall with cellulose contain chlorophylls and is in plastids; life cycle is alternation of generalization. Plants are complex multicellular autotrophs, which mean they have specialized tissues, most plants have several different types of cells organized into many specialized cell tissues that transport water and dissolved nutrients. Plants cells are different from all other cells in that their cell walls are composed of cellulose, complex carbohydrates. The cells also contain the chromosomes with presence of DNA plus protein, a nucleus and mitochondria among others. Among other organism plants cannot move from one place to another. A few groups have mobile sperms, but most plants are rooted in the grounds. Portable structures, such as spores and seeds enable the dispersal of plants.

There are four kinds of plants namely non-vascular plants (Bryophytes) such as mosses; seedless Vascular plants such as fern; non-flowing seed plants (Gymnosperms) such as pines and spruce and flowing seed plants (angiosperms) such as roses, grasses and oak.

Plants are diversity in morphological structure. Individual moss plants, for example are usually not more than a few centimeters in height and most parts of the plant are only one cell thick. Giant redwoods on the other hand have a circumference of up to 30 meters and soar to the height of 90 meters or more.


This kingdom contains about 14 phyla and possesses the largest variety of organisms among the five kingdoms; there are about 43,000 species, which includes eukaryotes that are not plants, fungi or animals. It is the most structurally diverse kingdom. Both unicellular and multicellular, membrane-bound nucleus, nearly all have chromosomes, mitochondria and internal compartments, they may have chloroplasts and most have cell walls. Members reproduce sexually and asexually. They are aquatic or parasitic and many live in soil, contain DNA plus protein and cell wall. The means of Genetic recombination include fertilization (syngamy) and meiosis, conjugation or none. Mode of nutrition is photosynthetic and heterotrophic, or combination of these. Motility is by 9+2 cilia and flagella, amoeboid and contractile fibrils. Possess primitive mechanisms of nervous system for conducting stimuli in some forms. Protistis can also be found in lakes and oceans floating as planktons or anchored to rocks. They are common habitat of damp soil and sand; they thrive in most environments such as leaf litter.

Examples of Protists includes Amoebas member of the phylum Rhizopoda, and foraminifera members of the phylum. Foraminifera which are marine protistis feat live in sands and attach themselves to rock and other organisms.


In the fungi kingdom there about 3,900 species members of the kingdom have the following characteristics; eukaryotic heterotrophs with nutrition by absorption, all about yeasts are multicellular. Nearly all are terrestrials, body is typically composed of filaments called hyphae and is multinucleate, with incomplete divisions called septae between cells and the cell wall are made chitin, the rough polysaccharides and about 17,000 species (known as deuteromycetes) are without sexual stages.

Fungi happen to be the most unusual organisms that exists today, mushrooms and molds are common fungi that grow so rapidly, they sometimes appear overnight. Fungi are at least 400 million years old.

Fungi are classified by their sexual reproductive structures. Fungi in which sexual reproduction has not been observed are referred to as deuteromycetes. Whereas fungi in the phylum zygomycota produce spores in thick walled sexual structures called zygosporangia. The fungi in the phylum ascomyeota produce spores in a saclike structure called an ascus. Yeast are unicellular ascomycetes that reproduce by building fungi in the phylum basidiomycota produce spores in the shaped structure called a basiduim.


Monerans are the smallest and simplest of living things. In terms of complexity, they fall between the non-livings viruses and the living, eukaryotic, cellular organisms. Prokaryotic cells of monera have no membrane bound organelles such as a nucleus, mitochondria or chloroplasts. Their ribosomes are smaller than those of eukaryotes. Their inherited information is held in a single circular chromosomes rather than a pared chromosome, the cell wall is non cellulose (made of polysaccharides plus amino acids). The means of genetic information include conjugation transformation or none.

The mode of nutrition is autotrophic (chemosynthetic and photosynthetic in some members) and heterotrophic by saprobic and parasitic mode of feeding. The mode of mobility is bacteria flagella, gridding, or non-motile. They are completely unicellular with no nervous system. Example of members in monera kingdom include; archaebacteria less than100 species and eubacteria more than 4000 species. Bacteria are often classified by shapes of their cells. Three common shapes are spheres, rods and spirals. For instance a coccus is a round bacterium, Bacillus is a rod-shaped bacterium and a spirillum is a spiral-shaped bacterium.

With reference to the above discourse , it can be therefore, inferred that five- kingdom classification is the most accurate and scientific way of classifying organisms and that organism exhibit diverse characteristics that can be analyzed and used for grouping and naming of these organisms.


Kent, M (2000) Advanced Biology. Oxford university press, New York; USA.

Philip, W.D (1994) A-Level Biology. Oxford university press, New York; USA.

Rowland, M(1992) Applied Biology. University of Bath Science press; Philippians.

Taylor, D.T (1997) Biological science 3rd edition. Cambridge university press London; UK


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