Five Kingdom Classification: Features, Examples

Five Kingdom Classification: The five-kingdom classification resulted after decades when scientists have tried to categorize living organisms in numerous ways. Even Aristotle categorized living things according to whether they were aquatic, terrestrial, or aerated. However, biologists want a more comprehensive system of classifying living things. Classification is a process that groups or sets of organisms based on similarities and differences. It very systematically simplifies the study of a large range of organisms. In 1969, R.H. Whittaker proposed the five-kingdom division.

Five Kingdom Classification

The taxonomy of living beings did not initially lead to the five-kingdom division that we see today. The earliest two-kingdom categorization devised by Carolus Linnaeus only contained kingdoms Plantae and Animalia. Due to the lack of consideration for many important factors while classifying, the two-kingdom classification persisted for a very long period but did not last forever. Eukaryotes and prokaryotes, monocellular and multicellular organisms, and photosynthetic and non-photosynthetic organisms were not distinguished from one another. There were many organisms that could not be classified as either plants or animals, thus simply placing all of the life in the plant or animal kingdom was insufficient. As a result of the misunderstanding, a new classification system was created that required taking into account factors such as cell wall existence, cell structure, reproduction process, and mode of nutrition. R. H. Whittaker developed the five-kingdom classification as a result. The following kingdoms were included in the classification of living things into five groups:

Kingdom Monera

The bacteria are classified under the Kingdom Monera. The Monera Kingdom includes Eubacteria, Cyanobacteria (blue-green algae), Mycoplasma, Spirochaetes, Actinomycetes, and other organisms.

Monerans have the following characteristics:

1. These creatures are prokaryotic, which means they lack a distinct nucleus and cell organelles.
2. They have only one cell. Some may be colonial or filamentous in nature. 
3. No cellular organelles are attached to membranes.
4. Some species have cell walls (such as bacteria and blue-green algae), whereas others have not (such as Mycoplasma).
5. Aerobic or anaerobic respiration can occur.
   1. Obligate aerobes are those that cannot survive in the absence of oxygen. Bacillus subtilis with Rhodospirillum.
   2. Obligate anaerobes are organisms that cannot thrive in an oxygen-rich environment, such as Clostridium botulinum.
6. Nutrition is either autotrophic (as in blue-green algae and some bacteria) or heterotrophic (as in Mycoplasma and the majority of bacteria). They may be both saprophytic and parasitic.
7. The most common way of reproduction is asexual.
   1. The most prevalent mechanism of multiplication is binary fission.
   2. Under some conditions, bacteria such as Clostridium and Bacillus create thick-walled endospores that are highly resistant.

Types of Monera

Based on how they look, bacteria can be divided into four groups:

1. These bacteria are spherical in shape and are known as coccus (plural: cocci).
2. The rod-shaped bacteria are called bacillus (plural: bacilli).
3. These bacteria have comma shapes and are known as vibrio (plural: vibrio).
4. Bacteria with a spiral shape are called spirillums (plural: spirilla).

There are three subkingdoms within the Kingdom of Monera:

1. Archaebacteria
2. Eubacteria
3. Cyanobacteria

Kingdom Protista

Protista has the following Characteristics:

1. The kingdom Protista contains unicellular algae, diatoms, fungi, and protozoans.
2. The organisms in this kingdom are unicellular, eukaryotic organisms (due to the presence of well-defined nuclei and other cell organelles).
3. They have cytoplasmic 80S ribosomes, Organelles include 70S ribosomes. 
4. They exhibit both zygotic and gametic meiosis.
5. The two main types of nutrition are autotrophic (found in algae and diatoms) and heterotrophic (found in protozoans). Some forms (for example, Euglena) exhibit mixotrophic feeding.
6. For mobility, some protists have hair-like cilia or whip-like flagella. Some protists, such as Amoeba, move by using pseudopodia (fake feet).
7. Flagella has a 9+2 microtubular organization pattern. 
8. These organisms exhibit plant and animal characteristics.
   1. Plant-like Protists include Diatoms, Dinoflagellates, and Euglenoids.
   2. There are protists that resemble fungi, such as slime Moulds.
   3. There are protists that resemble animals, including Sarcodina and Mastigophora members.

Protist Subgroups

1. Chrysophytes
2. Dinoflagellates
3. Euglenoids
4. Slime Moulds
5. Protozoans

Kingdom Fungi 

Fungi were classified as plants in the classic two-kingdom system due to the existence of a cell wall. Fungi have the following characteristics: 

1. Fungi are non-green (without chlorophyll) eukaryotic creatures. 
2. The body is made up of haploid and thalloid cells. The body is made up of elongated tubular hyphae that resemble threads.
3. Fungus bodies are built up of microscopic threads called hyphae (plural hypha). The mycelium (plural mycelia) is the mass of hyphae that forms an individual.
4. Fungi are heterotrophic in their diet, obtaining food either saprophytically (from dead organic matter) or parasitically (from the living tissues of other creatures). Saprophytes constitute the majority of fungi.
5. Chitin, a stiff complex sugar, makes up the cell wall.
6. Glycogen is the main component of reserve food material.
7. Some fungi, like lichens, have symbiotic relationships with green algae or blue-green algae.
8. Many fungi cause diseases in both animals (such as ringworm) and plants (such as wheat black stem rust, mustard white rust, and potato late blight).
9. Yeast, Rhizopus, mushrooms, Aspergillus, and Penicillium are other examples.
10. Fungi are categorized into four major classes based on reproduction:
    1. Phycomycetes
    2. Ascomycetes
    3. Basidiomycetes
    4. Deuteromycetes

Plantae Kingdom

Kingdom Plantae has the following characteristics:

1. The Kingdom Plantae encompasses all creatures that are multicellular, eukaryotic, and green autotrophs.
2. The kingdom of green plants is further subdivided based on whether the plant body is differentiated into its various sections (such as the root, stem, and leaf, ), or not.
3. The second level of classification is determined by whether or not the differentiated plant body has vascular tissues. Further classification is based on (i) whether or not seeds are present, and (ii) whether or not seeds are encased within fruits.
4. Aquatic thallophytes (green, brown, and red algae) and land plants (Bryophytes, Pteridophytes, Gymnosperms, and Angiosperms) are included in the Kingdom Plantae.
5. This kingdom's creatures are non-motile (in higher forms) and have hard cell walls and chlorophyll inside the plastids.
6. They are primarily photoautotrophic, which means they produce oxygen during photosynthesis.

Kingdom Animalia

Despite the fact that there are over a million different varieties of animals on the planet, the animal kingdom is distinguished by the following characteristics:

1. Animals are multicellular, eukaryotic creatures.
2. Most animals have highly differentiated tissues, and many have specialized bodily organs.
3. The nervous system is employed by most animals to coordinate their body activities and responses.
4. The nourishment of animals is heterotrophic. They are deficient in photosynthetic pigments.
5. Cell walls are absent from animal cells.
6. Animals have the ability to move.
7. Animals create haploid male gametes (sperms) and haploid female gametes (ova; singular ovum) during sexual reproduction. 
8. Following fertilization, the zygote divides and differentiates repeatedly to generate a new individual. 
9. Sponge, corals, flatworms, roundworms, earthworms, insects, snails, starfish, fishes, frogs, toads, birds, snakes, tigers, elephants, and humans are all members of the Animalia kingdom.

Benefits of the Five Kingdom Classification

• Kingdom Monera includes all prokaryotic creatures.
• Fungi were classified as a separate kingdom because they are heterotrophs with chitin cell walls.
• All unicellular eukaryotic species were classified as Protista.
• It looked at the evolutionary link between creatures.