BIOLOGICAL CLASSIFICATION

 BIOLOGICAL CLASSIFICATION 

What is the meaning of biological classification? 

Biological classification is a formal system of distinguishing, naming, and grouping of individual organisms. Whereas numerous systems have existed since antiquity, the modern system was initially developed by a binomial naming system after grouping of organisms based on traits. 

History of classification 

Aristotle was the earliest to attempt a more scientific basis for classification. 

• He used simple morphology characters to classify plants into trees,  herbs and shrubs. 

• He also divided animals into two groups, those which had red blood and those that did not. 

Types of classification of

system

Two kingdom classification 

This classification is given by Linnaeus 

• In Linnaeus' time a two kingdom classification with plantae and animalia  kingdom was developed that include all plant and animal respectively. 

Demerits of two kingdom classification 

• This system did not distinguish between the eukaryotes and prokaryotes. 

• It also grouped unicellular and multicellular organisms together. 

• Photosynthetic ( green algae)  and non photosynthetic (fungi)  organisms grouped together. 

Three kingdom classification system :

This classification system is given by hackel. 

He proposed a third kingdom protista to accommodate euglena-like organisms. He also included bacteria in kingdom protista. In this system, fungi were still included in the kingdom plantae.

Demetris of Three kingdom classification :-

• The kingdom did  not clear the difference between prokaryotes and eukaryotes.

• Some biologists disagree about the position of fungi in kingdom plantae. 

• Fungi resemble plants in many ways but are not autotrophs. 

Four kingdom classification :-

Copeland gave four kingdom classification and included Monera as the fourth kingdom.This kingdom include all the prokaryotic organisms.,  Eubacteria( including cyanobacteria or blue- green algae)  and archaebacteria

Demerits of four kingdom classification 

• Fungi continued to remain with the group plantae.

A need  was also felt for including, besides gross morphology, other characteristics like cell structure,  nature of wall, mode of nutrients,habitat,Method of reproduction, evolutionary relationship, etc. 

Five kingdom classification :-

R. H.   Whittaker (1969) proposed a Five Kingdom  Classification.

• The kingdom defined by him were named Monera, protests, fungi, plantae and animalia. 

• The main criteria for classification used by him include cell structure, thallus organisation, mode of nutrition, reproduction and phylogenetic relationship. 

• In five kingdom classification,bacteria are included in kingdom Monera. 

• Kingdom protista includes all single -celled eukaryotes such as chrysophytes, dinoflagellates, euglenoids, slime-moulds,  and protozoans. 

• Members of the kingdom fungi Show a great diversity in structure and  habitat. Most fungi are saprophytic in their mode of nutrition. 

• The heterotrophic eukaryotic chlorophyll-containing organisms. Algae, bryophytes, pteridophytes, gymnosperms,  and angiosperms are included in this group. 

• The heterotrophic eukaryotic, multicellular organisms lacking a cell wall are included in the kingdom Animalia.

KINGDOM MONERA

• Bacteria are the sole

• members of the kingdom Monera. They ate the most abundant microorganisms. 

• Bacteria occur almost everywhere. Hundreds of bacteria are present in a handful of soil. 

• They also live in extreme habitats such as hot springs, desert, Snow and deep oceans  where very few other life forms can Survive. Many of them live in other organisms as parasites. 

• Bacteria are grouped under four categories based on their shapes 

• The spherical Coccus (Cocci) 

• The rod shaped Bacillus(bacilli)

• The Comma-shaped Vibrium ( vibrio)

• The spiral shaped Spirillum ( spirilla) 

• The bacteria structure is very simple,They are very complex in behaviour. 

• Compared to many organisms, bacteria as a group show the most extensive metabolic diversity. 

• Some of the bacteria are autotrophic, they synthesis their own food from inorganic substances 

• They may be photosynthetic autotrophic  or chemosynthetic autotrophic. 

• The vast majority of bacteria are heterotrophs. They do not synthesise their own food but depend on other organisms or on dead organic matter for food. 

Archaebacteria

• These bacteria are special since they live in some of the most harsh habitats such extremely salty areas called as  halophiles, hot springs called thermoacidophiles, and marshy areas called as methanogens. 

• Archaebacteria differ from other bacteria in having a different cell wall structure and this feature is responsible for their survival in extreme conditions. 

• Methanogens are present in the gut of several ruminant animals such as cows and buffaloes and they are responsible for the production of methanes (Biogas) from the dung of these animals. 

Eubacteria

• There are thousands of different eubacteria of true bacteria. They are characterised by the presence of rigid cell walls, and if motile a flagellum. 

• The cyanobacteria (also referred to as blue-green algae) have chlorophyll "a"similar to green plants and are photosynthetic autotrophs. 

• The cyanobacteria are unicellular, colonial or filamentous.,freshwater/ marine or terrestrial algae.

• The colonies are generally surrounded by gelatinous sheaths. 

• They often form blooms in polluted water bodies. 

• Some of these organisms can fix atmospheric nitrogen in specialised cells called heterocysts, e.g.,Nostoc  and  anabaena.

• Chemosynthetic autotrophic bacteria oxidise various inorganic substances such as nitrates,nitrites and ammonia and use the released energy for their ATP production. 

• They play a great role in recycling nutrients like nitrogen, phosphorus,iron and sulphur. 

Heterotrophic bacteria 

• Heterotrophic bacteria are the most abundant in nature. The majority are important decomposers. 

• Many of them have a significant impact on human affairs.

• They are helpful in making curd from milk, production of antibiotics, fixing nitrogen in legume roots, etc. 

• Some are pathogens causing damage to human beings, crops,farm animals and pets.

• Cholera, typhoid, tetanus, and citrus canker are well known diseases caused by different bacteria.

• Bacteria reproduce mainly by fission. Sometimes, under unfavourable conditions, they produce spores. 

• They also reproduce by a sort of sexual reproduction by adopting a primitive type  of DNA  transefer from from one bacterium to other. 

Reproduction in Bacteria

• The mycoplasma are organisms that completely lack a cell wall. They are the smallest living cells known and can survive without oxygen. Many mycoplasma are pathogenic in animals and plants.

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