There have been many scientists who have attempted to classify the various living organisms in the past. Two significant classification systems that are useful to you are:

• • Two Kingdom Classification by Carolus Linnaeus: In this classification system, Carolus Linnaeus classified all living organisms into two broad kingdoms, i.e., Plants and Animals.
  • Five Kingdom Classification by Robert Whittaker: According to Robert Whittaker, the diversity of living organisms was way more and so, he divided all living organisms into five kingdoms, namely:
    • Kingdom Monera
    • Kingdom Protista
    • Kingdom Fungi
    • Kingdom Plantae
    • Kingdom Animalia

The main criteria used by Whittaker for classification of all living organisms into these five kingdoms are–

• • Cell structure
  • Thallus organisation
  • Mode of nutrition
  • Reproduction method
  • Phylogenetic relationships

After classifying living organisms into five kingdoms, Whittaker also gave the taxonomy that these organisms can be further segregated under each kingdom. According to Whittaker, the diversity of living organisms was so varied and complex that there needed to be more classifying levels. Based on this, the hierarchy of Whittaker’s Five Kingdom Classification include:-

• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species

Each kingdom is phylogenetically linked to the kingdom before it and here are some typical characteristics of each of the five kingdoms.

Kingdom Monera

• Includes all unicellular prokaryotes. 
• They lack a true nucleus. 
• May have or may not have a cell wall.
• Maybe autotrophic or heterotrophic in nature.
• A large number of monerans live inside other organisms like parasites.
• Can survive in a variety of habitats, even extreme ones.

Examples: Bacteria, cyanobacteria, etc.

Kingdom Protista

• Comprises unicellular eukaryotic organisms but there are no clear boundaries for this kingdom.
• Many scientists often argue over whether a particular organism is an autotrophic protestant or a plant.
• Have a well-defined nucleus and other membrane-bound organelles.
• Reproduce asexually as well as sexually.
• Can be autotrophic or heterotrophic in nutrition.
• Have special organs for locomotion like flagella, cilia, etc.

Examples: Chrysophytes, Dinoflagellates, Euglenoids, slime moulds

Kingdom Fungi

• Organisms in Kingdom Fungi are majorly heterotrophic in their mode of nutrition with a large number of fungi being saprophytic in nature.
• They are multicellular and eukaryotic.
• Have a cell wall filled with chitin.
• Some fungi have a symbiotic relationship with other organisms like blue-green algae.
• Show sexual as well as asexual modes of reproduction.

Examples: Yeast, Aspergillus, Mycorrhiza, etc.

Kingdom Plantae

• Are eukaryotic and multicellular.
• Have a cell wall that is made of cellulose.
• Are mostly autotrophic and prepare their own food by photosynthesis. However, some heterotrophs do exist.
• Kingdom Plantae can be further divided into– Thallophytes, Bryophytes, Pteridophytes, Gymnosperms(non-flowering plants with uncovered seeds), and Angiosperms(Flowering plants with covered seeds).

Examples: Mango tree, apple tree, ferns, pine trees, etc.

Kingdom Animalia

• It can be characterised by heterotrophic, multicellular eukaryotes.
• Cells lack a cell wall.
• Show holozoic nutrition and internal digestion.
• Store their food in the form of fat or glycogen.
• Have an organ-system organisation.
• Show growth and the young ones look different from the adults.
• Exhibit advanced, elaborate sensory and motor mechanisms.
• Show locomotion and sexual reproduction is the main way of continuing their species.
• Kingdom Animalia is further divided into different phylums such as Porifera, Coelenterata, Echinodermata, Chordata, and so on.

Examples: Hydra, Earthworms, reptiles, man, etc.

1. Why is diversity in living organisms important?

The diversity of living organisms helps us understand how organisms have developed, how they are interlinked, and the kind of phylogenetic relationship between closely linked organisms.

2. What is the basis of classification in diversity in living organisms?

Living organisms have been classified based on cell structure, thallus organisation, their mode of nutrition, reproduction, habitats and adaptations, and phylogenetic relationships.

3. What causes diversity in organisms?

Each organism has a different genetic make-up. Their genes undergo mutation when they are subjected to different habitats and environments. It is these genetic and environmental adaptations that bring about diversity in living organisms.

4. What are the advantages of classifying organisms?
There are many advantages of classifying living organisms. These include:

• Gives us a better understanding of the evolution of different organisms.
• Makes it easy to study the different organisms.
• Sheds light on the inter-relations between organisms.
• Helps scientists, researchers and environmentalists find ways to conserve the diversity of living organisms.
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5. What are the disadvantages of classifying organisms?

Few disadvantages of classifying organisms are

• Each classification system is subjective and is based on the judgements of different scientists who have developed them. They may not appeal to everyone at large
• There can be a bias in the minds of those classifying
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