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Diversity in living organisms
The planet Earth is rich in biodiversity of organisms – plants, animals, and microorganisms. In order to identify them with ease, they are classified into groups and sub-groups at various levels.
Some organisms differ from each other but have similar characteristics; these organisms are known to have evolved over a period of time
The basis of classification:
All living creatures on our planet are classified by grouping them into the same kind so as to identify them with ease. All organisms have certain common characteristics so that they can be categorized into major groups. Then, some organisms may have certain characteristics which are different from others and hence they are further classified into sub-groups and so on.
This is how organisms are classified. For example, we have learned in previous grades that prokaryotic cells differ from eukaryotic cells, birds differ from fishes, cactus differs from rose plant, etc. Thus all living things are classified majorly based on their body design and shape.
It is well-understood that some organisms may differ in habitat but may have the same characteristics. This indicates that the organisms evolve over a period of several thousand years.
This process is known as evolution and was first discovered and termed by Charles Darwin. Evolution has resulted in vast biodiversity over the entire planet in all organisms – plants, animals, and microorganisms.
The hierarchy of classification:
Ernst Haeckel, Robert Whittaker, and Carl Woese were 3 biologists, who tried to classify all living organisms into groups based on cell shape, mode of nutrition, and body organization.
They proposed the Whitaker model which had 5 major groups namely, Monera, Protista, Fungi, Plantae, and Animalia. Further then, Monera was modified into 2 groups namely – archaebacteria and eubacteria.
Further classification is done by naming and grouping organisms under sub-groups at various levels of hierarchy as follows
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
Thus, each organism is classified and named at various levels in order to be identified. Species is the lowest unit of classification.
Group 1 – Monera:
- Unicellular
- The absence of a well-defined nucleus or organelles
- Presence or absence of cell wall
- Mode of nutrition – some are autotrophic, while some are heterotrophic
- Organisms belonging to this group – Bacteria, blue-green algae and mycoplasma
Group 2 – Protista:
- Unicellular
- Eukaryotic cell
- Characteristic feature – Appendages like flagella used for the locomotion of the organism
- Mode of nutrition – autotrophic or heterotrophic
- Examples of organisms belonging to this group – are unicellular algae, diatoms, and protozoans