Classification of Living Organisms (Monera, Protista, and Fungi)

Introduction

The Greek thinker Aristotle classified animals according to their habitat, namely land, water, or air. It is a very simple but misleading way of looking at life. Thus, it is required to decide characteristics that are to be made the basis for making the broadest divisions. Further, the next set of characteristics needs to be picked up for making sub-groups within these divisions.

Classification and Evolution:

• Earlier appearing traits are likely more fundamental than later appearing traits, which means that the classification of life forms is closely related to their evolution
• Most forms of life today have arisen from an accumulation of changes in body design that allow the organism that owns them to survive better. This idea of ​​evolution was first described by Charles Darwin in 1859 in his book “The Origin of Species”

The Hierarchy of Classification-Groups:

• Biologists such as Ernst Haeckel (1894), Robert Whittaker (1969) and Carl Woese (1977) have tried to divide all living organisms into large categories, so-called kingdoms
• Whittaker proposed the classification of the five kingdoms: Monera, Protista, Fungi, Plantae, and Animalia, and it is widely used
• The modification introduced by Woese divides the Monera into Archaebacteria (or Archaea) and Eubacteria (or Bacteria) is also in use
The following scheme represents the further classification, done by naming the sub-bunches at different levels:
• By separating organisms based on the hierarchy of characteristics into smaller and smaller groups, the basic unit of classification defined is ‘Species’
• A species includes all organisms that are similar to breed and perpetuate

Following are the important characteristics of the five kingdoms of Whittaker:

Monera:

• Cell Structure: These organisms do not have a defined nucleus or organelles. Some possess cell walls while some don’t
• Body Organization: None of them shows multicellular body designs
• Mode of nutrition: Either by synthesising their food (autotrophic) or getting it from the environment (heterotrophic)
• Examples: This group consists of bacteria, blue-green algae or cyanobacteria, and mycoplasma

Bacterial morphology

• Cocci: Cocci are spherical or oval
• Bacilli: Bacilli are rod-shaped bacteria. Flagella may or may not be present
• Vibrios: These are small and resemble a comma or kidney. They are motile and have a flagellum on one end. The cell of Vibrio bacteria has a curve
• Spirillum: They are spiral or corkscrew-shaped. Spirillum, Spirochaetes, and other spiral forms are rigid and have two or more flagella at one or both ends
• Filament: The bacterium’s body is filamentous, just like fungal mycelia. The filaments are extremely small. Beggiota, Thiothrix, and others are examples
• Stalked: A bacterium’s body, such as Caulobacter, has a stalk
• Budded: The bacterium’s body is swollen in places, such as Rhodomicrobium

Protista:

• Cell Structure: This group includes many kinds of unicellular eukaryotic organisms
• Body Organization: Some of these organisms use appendages, such as hair-like cilia or whip-like flagella for moving around
• Mode of nutrition: Autotrophic or heterotrophic
• Examples: Unicellular algae, diatoms, and protozoans

Major Groups of Protists:

Chrysophytes

The diatoms and golden algae make up this group (desmids). They can be found in both freshwater and marine environments. They are extremely small. These organisms float in water currents in a passive manner (plankton)

Dinoflagellates

These organisms are usually photosynthetic and marine. They come in a variety of colours, including yellow, green, brown, blue, and red. The main pigments present in their cells influence and determine their colour. On the outside of the cell wall are stiff cellulose plates. Flagella are usually found in a furrow between the wall plates, one longitudinally and the other transversely.

Euglenoids

These are mostly organisms that live in freshwater. They can be found in stagnant water. They are devoid of a cell wall.

Slime Moulds

Slime moulds are protists that feed on their surroundings. Their bodies can move through decaying twigs and leaves, consuming organic matter.

Protozoans

Protozoans are all heterotrophic, meaning they live as predators or parasites. Animal relatives are thought to be their ancestors.

Fungi

• Cell Structure: Eukaryotic organisms, cell walls made of a tough complex sugar called chitin
• Body Organization: A significant number of them can become multicellular living beings at specific stages in their lives

• Mode of nutrition: Heterotrophic

• Some feed on rotting natural material and are called saprotrophs
• Others require the living protoplasm of a host organism for food. They are called parasites
• Some fungal types live in permanent relationships that depend on each other with blue-green algae (or cyanobacteria). Such relationships are called symbiotic. In addition to this, the symbiotic life forms are called lichens

• Examples: Yeasts, moulds, and mushrooms

Conclusion

Monera, Protista and Fungi are the first three kingdoms given in the classification by Whittaker. His classification is based on the cell structure, mode, and source of nutrition, as well as the body’s structure. They are an important part of the classification of living organisms.