Classification of living organisms is made by different scientists in different times. Each organism is different from all other organisms by a lesser or greater extent. They are identified or categorized on the basis of their body design in form and function. Some characteristics can make more wide-ranging changes in body design than others. There are also roles of time as well. So, certain body design comes into existence, it will shape the effects of all other subsequent design changes.
Carolus Linnaeus, in his ‘Systema Naturae’ (1735), first distinguished living organisms into two different classifications – a) Plantae for plant kingdom and b) Animalia for the animal kingdom. He differentiates this on the basis of their nutrition and locomotion ( mobility)
Many other Scientists placed bacteria, microscopic algae and fungi under plant kingdom because –
Scientists were confused after the discovery of microorganisms which have characteristics of both plants and animals. So they decided to place it in a different classification or system.
Ernest Hackel, a German zoologist in 1866 proposed third kingdom ‘ Protista’ ( Gr. Protistos – first or primitive). He includes all microscopic, unicellular, motilenon-motile and non-motile, photosynthetic or non- photosynthetic, autonomously living organisms ( neither plant nor animal). Thus all unicellular microscopic organisms of algae, fungi, protozoa and also the bacteria are included under the kingdom protista.
Scientists gave this concept as – prokaryotic, eukaryotic and protista.
Copeland(1956) proposed the fourth kingdom classification. In this system, he gave lower protists into a different kingdom, Monera. While other protists remain in the same group Protista. Thus, Four kingdoms are – Monera, Protista, Metaphyta( green plants), Metazoa( animals).
Though the four kingdom system is highly developed it suffers from several deficiencies.
Important shortcomings are –
This division is based on what living things have in common and they differ. An American ecologist, Robert Whittaker in 1969 proposed the Five kingdom classification.
He used following criteria for classification of living organisms –
The kingdoms are –
Ex – Bacteria, blue-green algae,mycoplasma.
2.Protista – They are similar to monera in that they are unicellular but they are little complex having a nucleus. They have also moving parts which help them to move around the environment. Simply called they are unicellular eukaryotes.
Ex – Euglena, amoeba, paramecium.
Ex – Pogonatum, Dryopteris.
Ex – Yeast, Mukor, Penicillium.
For the above reasons, Five kingdom classification replaced the six kingdom system. Carl Woese first proposed the system in 1977. The kingdom Monera or Prokaryotes divided into two kingdoms – Archaebacteria and Eubacteria. Other kingdoms remain the same as proposed by Whittaker.
So, six kingdoms are Archaebacteria, Eubacteria, Protista, Plantae, Fungi, Animalia.
Cavalier-Smith proposed this eight kingdom classification of living organisms on the basis of cell structure and genetic organization. He considered ultra structural characteristics as well as rRNA sequence and other molecular characteristics. He divided the living organisms into 2 Empires i.e. Bacteria and Eukarya and 8 kingdoms.
The first empire Bacteria divided into two kingdoms –
The second empire Eukarya divided into six kingdom –
Ex – Giardia etc.
Ex – Diatoms etc.
Each organism is different from all other organisms by a lesser or greater extent. They are identified or categorized on the basis of their body design in form and function.
ধারণা (Concept) সাহিত্যের ক্ষেত্রে 1990 খ্রিস্টাব্দের শেষের দিকে অথবা 2000 খ্রীস্টাব্দের শুরুতে শিখণ নকশাটির ধারণার উল্লেখ পাওয়া যায়। শ্রেণীকক্ষে পাঠ…
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