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History of classification
1. Aristotle, the Greek philosopher, classified animals based on whether they live on land, in water or in the air.
2. Charles Darwin put forward the idea of evolution in 1859, in his book, The Origin of Species.
3. Ernst Haeckel, Robert Whittaker and Carl Woese have tried to classify living organisms into broad categories, called kingdoms.
4. Carolus Linnaeus classified all the living organisms into two kingdoms namely, Plantae and Animalia.
5. Robert Whittaker, in 1969 proposed Five kingdom classification of living organisms.
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Five kingdom system of classifictaion
Robert H. Whittaker, in 1969 proposed a new five kingdom system of classification of organism. They are:
1. Monera includes unicellular, prokaryotic and autotrophic organism. For example – cyanobacteria.
2. Protista includes unicellular, eukaryotic organism. They are autotrophic as well as heterotrophic. For example – Euglena
3. Fungi are generally heterotrophic. They have a cell wall made up of chitin and have a symbiotic mode of nutrition. For example – Aspergillus.
4. Plantae includes eukaryotic and autotrophic organism. For example – ferns.
5. Animalia includes eukaryotic and heterotrophic. For example – sycon.
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Advantages and disadvantages of five kingdom classification
Advantages
1. It is largely the most accepted system of modern classification mainly because of the phylogenetic placing of different groups of living organisms.
2. Separation of prokaryotes into an independent kingdom is justifiable because they differ from all other organisms in their general organisation.
3. Grouping of all unicellular eukaryotes under the kingdom Protista has solved many problems, particularly related to the position of an organism like Euglena.
4. Classifying fungi in separate groups due to its distinguishing feature add a convenience for studying.
5. The kingdoms Metaphyta and Metazoa are now more homogenous groups than they were in the two kingdom classification as it shows the phylogeny of different lifestyles.
6. The five-kingdom classification gives a clear indication of cellular organization and modes of nutrition, the characters which appeared very early in the evolution of life.
Disadvantages
1. Slime moulds differ totally from other members of Protista in their general organisation.
2. Viruses have not been given proper place in this system of classification.
3. Unicellular green algae like Volvox and Chlamydomonas have not been included under Protista because of their resemblance to other green algae.
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Difference between various kingdoms
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Moneran characteristics of bacteria
1. Habitat – Monerans are found everywhere in hot springs, under ice, in deep ocean floor, in deserts and on or inside the body of plants and animals.
2. Nutrition – Autotrophs, heterotrophs, parasitic, symbiotic, commensalism, mutualism.
3. Respiration in these organisms vary, they may be obligate aerobes, obligate anaerobes and facultative anaerobes.
4. Circulation is through diffusion.
5. Movement is with the help of flagella.
6. Reproduction is mostly asexual, sexual reproduction is also seen. Asexual reproduction is by binary fission, sexual reproduction is by conjugation, transformation and transduction.
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Archaebacteria
1. Archaebacteria are ancient group of bacteria living in extreme environments.
2. They are characterized by possessing cell walls without peptidoglycan.
3. The lipids in their plasma membrane are branched differing from all other organisms.
4. They are categorized into methanogens, halophiles and thermoacidophiles.
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Characteristics of Mycoplasma
1. Mycoplasmas or PPLOs are a distinct group of prokaryotes.
2. Their occurrence was demonstrated by D. Iwanowsky in 1892.
3. They are characterized by the absence of cell wall.
4. Mycoplasma cell is delimited by a delicate cell membrane, of successive layers of protein, lipid, and proteins, and contains a long double-stranded molecule of DNA and RNA granules.
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General characteristics of kingdom protista
1. Unicellular, eukaryotic, autotrophic or heterotrophic organisms.
2. Most of the protists live in water, some in moist soil or even the body of humans and plants.
3. Movement is often by flagella or cilia.
4. For example, Amoeba, Euglena, Paramecium, etc.
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Photosynthetic protists
Dinoflagellates
1. Most of them are marine but some occur in fresh water.
2. Some show bioluminescence.
3. Nutrition is photosynthetic.
4. For example, Glenodinium.
Chrysophytes
1. They include diatoms and desmids.
2. For example, Spirogyra, Cymbella.
Euglenoids
1. Occur in fresh water and damp soils.
2. Nutrition is holophytic.
3. For example, Euglena, Phacus.
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Kingdom Fungi
1. Non-green, unicellular/multicellular, eukaryotic, heterotrophic and saprophytic organisms.
2. Has the presence of cell wall which is made up of chitin.
3. Most of them are made up of thread like hyphae rather than cells.
4. Reproduction in fungi is both by sexual and asexual means.
5. For example, yeast, moulds, mushrooms. Most common moulds (fungi) are Aspergillus and Penicillium.
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Viruses
Structure
1. A virus has a simple structure without cytoplasm or organelles.
2. It has a covering of proteins.
3. It contains DNA and RNA.
Characteristics:
1. They live inside host cell.
2. They can be cultured on living tissue.
3. They are highly specific.
Example
AIDS virus
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Viroids
- Viriods are small single-stranded circular RNA agents which infect plants.
- They differ from RNA viruses in three major aspects: their minute size (they are non-quarter of the size of the smallest RNA virus, i.e., 250-400 bases); the genome does not encode any proteins and they are not encapsidated.
- Viroid infections is mediated mechanically.
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Lichens
1. A lichen is not a single organism. Rather, it is a symbiosis between different organisms – a fungus and an alga or cyanobacterium.
2. The non-fungal partner contains chlorophyll and is called the photobiont.
3. The fungal partner is called mycobiont.
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