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A Handbook of Biology
The number of species that are known and described, ranges between
1.7-1.8 million.
Classification is the process by which anything is grouped into convenient
categories based on some easily observable characters.
ÅRÏSTØTLË’S ÇLÅSSÏFÏÇÅTÏØÑ
Aristotle was the earliest to attempt a more scientific basis for
classification of organisms. He classified plants into trees, shrubs & herbs
and animals into 2 groups; those with red blood (enaima) & without red
blood (anaima).
LÏÑÑÅËÜS TWØ-KÏÑGDØM ÇLÅSSÏFÏÇÅTÏØÑ
Linnaeus (1758) classified organisms into two kingdoms - Kingdom
Plantae & Kingdom Animalia.
THRËË- KÏÑGDØM ÇLÅSSÏFÏÇÅTÏØÑ
This system was proposed by Ernst Haeckel (1866).
He created a new kingdom Protista, having only unicellular eukaryotes.
FØÜR-KÏÑGDØM ÇLÅSSÏFÏÇÅTÏØÑ
Proposed by Copeland (1956).
Copeland created a separate kingdom 'Monera' (Mychota) for
prokaryotes.
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It included the unicellular and the multicellular organisms
in same group.
E.g.
Chlamydomonas
(unicellular)
and
Spirogyra
(multicellular) were placed under algae. It did not
differentiate between the heterotrophic fungi and the
autotrophic green algae and plants.
Drawbacks of 2-kingdom classification: Prokaryotes
(Bacteria, cyanobacteria) and eukaryotes (Fungi,
mosses, ferns, gymnosperms & angiosperms) were
included under ‘Plantae’ based on the presence of
cell wall but they widely differ in other characteristics.
Fungi have chitinous cell wall while the green plants
have cellulosic cell wall.
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