Five Kingdoms Classification

In biology, a kingdom is a taxonomic rank made up of smaller groupings known as phyla (or divisions, in plants).

Historically, the highest taxonomic rank, or the most broad taxon employed in classifying creatures, is kingdom. However, under Carl Woese’s new three-domain approach, announced in 1990, the domain is the most generic taxon, with the kingdom coming in second place.

The five-kingdom taxonomic categorization of the world’s biota, suggested by Robert Whittaker in 1969, into Kingdom Animalia, Plantae, Fungi, Protista, and Monera, has become a common standard for categorising species. It served as the foundation for future multi-kingdom systems, such as Carl Woese and colleagues’ 1977 six-kingdom system.

1. Monera Kingdom

These creatures are unicellular and prokaryotic. They lack a clearly-defined nucleus as well as cell organelles. Some species exhibit the presence of a cell wall, whereas others do not. As a result, certain species are autotrophic, while others are heterotrophic. Bacteria, Cyanobacteria, and Mycoplasma are a few examples.

Characteristics

• Aerobic or anaerobic respiration can occur.
• The mechanism of nourishment is either autotrophic (as in blue-green algae and certain bacteria) or heterotrophic (as in plants and animals) (Mycoplasma and most bacteria). They may be saprophytic as well as parasitic.
• Asexual reproduction is the most common way of reproduction.
• Some have cell walls, while others do not; 
• Some have an autotrophic form of nutrition, which means they can generate food on their own; and others have a heterotrophic style of nutrition.

2. Protista Kingdom

The species classified as Kingdom Protista are all unicellular, eukaryotic organisms. These are the most basic eukaryotes, with either an autotrophic or a heterotrophic mode of nutrition. To move throughout, some creatures have appendages such as cilia, flagella, or pseudopodia. Diatoms, Protozoans such as Amoeba, and Paramoecium are a few examples.

• They have both zygotic and gametic meiosis.
• For mobility, certain protists have hair-like cilia or whip-like flagella. Pseudopodia movement occurs in several protists, such as Amoeba (false feet).
• These creatures have characteristics of both plants and animals. This kingdom’s borders are not well defined.

3. Kingdom Fungi

Kingdom Fungi includes heterotrophic, multicellular, and eukaryotic creatures. Their diet is saprophytic, since they feed on decaying organic materials. They have cell walls formed of a material known as chitin. Fungi also have a symbiotic relationship with some blue-green algae. Fungi include yeast, mushrooms, and aspergillus.

Characteristics

• Glycogen is the reserve food resource.
• The body is made up of haploid and thalloid cells. The body is composed of thread-like elongated tubular hyphae.
• Many fungus cause illnesses in animals (such as ringworm) and plants (like black stem rust of wheat, white rust in mustard, late blight of potato).

4. Plantae Kingdom

These are Eukaryotic, multicellular creatures having cellulose-based cell walls. They are autotrophs, meaning they produce their own food through photosynthesis. All plants are included in this kingdom.

Kingdom Plantae is separated into five divisions based on body differentiation and the presence or lack of specialised vascular tissue: Thallophyta, Bryophyta, Pteridophyta, Gymnosperms, and Angiosperms. Spirogyra, Ferns, Pines, and Mango Plants are a few examples.

Characteristics

• Kingdom Plantae refers to all creatures that are multicellular, eukaryotic, and autotrophic in nature.
• The kingdom of green plants is further subdivided based on the differentiation of the plant body, whether it is well differentiated into separate components (such as root, stem, leaf, and so on) or not.

5. Kingdom Animalia

This Kingdom contains creatures that are multicellular, eukaryotic, and lack a cell wall. They feed in a heterotrophic manner. They are also quite diverse. Some species have basic bodies, whilst others have complex bodies with specialised tissue differentiation and bodily organs.

There are several phyla and classifications in the Animal Kingdom. Hydra, starfish, earthworms, monkeys, birds, and other organisms are examples.

Characteristics

• Most animals have highly differentiated tissues, and many have specialised bodily organs.
• The nervous system of most animals is employed to coordinate their body activities and reactions.
• Animal cells do not have cell walls.
• Animals have the ability to move around.

The Advantages of the Five Kingdom Classification

• Because prokaryotes vary from all other species in genetic, cellular, reproductive, and physi­ological structure, classifying them as a distinct kingdom of Monera was a reasonable approach.
• There are several transitional or intermediate species among the unicellular eukaryotes, which include both plants and animals. Because of the split of unicellular eukaryotes into the kingdom Protista, this anomaly has been resolved.
• Fungi have no resemblance to plants. They are biochemically, physiologically, and architecturally arranged in their unique way. Fungi had been separated into their own kingdom for a long time.
• The five kingdoms are classified based on early organisational and nutritional levels that got formed in subsequent groupings that exist today.
• The animal and plant kingdoms are more homogenous in this categorization than in the two-kingdom classification.
• It has sought to uncover evolutionary relationships between even the most primitive forms.

Limitations or objections to the Five Kingdom Classification System

• Some experts disagree that algae and protozoa belong in the same kingdom.
• Protozoa are classified as a subkingdom of the Animal Kingdom in certain categorization systems.

• In this categorization scheme, there is no distinction between unicellular and multicellular organisms in the case of algae.
• Each group is so diverse that it’s tough to keep them all together. Monera and Protista, for example, contain both walled and wall-less creatures. Organisms that are photosynthetic or non-photosynthetic, cellular or filamentous.
• This kingdom does not contain viruses.
• Archaebacteria are distinguished from other bacteria by their structure, composition, and physiology.
• Mycoplasma are distinct from bacteria and have been classified as prokaryotes.
• Symbiotic relationships are not taken into account in this categorization scheme. Lichens, for example, are creatures created by the symbiotic connection of fungus and algae.

Conclusion

The five-kingdom taxonomic categorization of the world’s biota, suggested by Robert Whittaker in 1969, into Kingdom Animalia, Plantae, Fungi, Protista, and Monera, has become a common standard for categorising species. The species classified as Kingdom Protista are all unicellular, eukaryotic organisms. Plantae refers to all creatures that are multicellular, eukaryotic, and autotrophic in nature. Animalia Kingdom contains creatures that are multicellular, eukaryotic, and lack a cell wall. There are several phyla and classifications in the Animal Kingdom. The animal and plant kingdoms are more homogenous in this categorization than in the two-kingdom classification. Protozoa are classified as a subkingdom of the Animal Kingdom in certain categorization systems.