Since from the early civilization, many attempts were made to classify the living organisms based on the need of use.
Aristotle in 4th BC was the earliest, to attempt scientific basis of classification.
He classified plants into trees, shrubs, and herbs based on simple morphological features.
He also classified the animals into two groups, those which had red blood and those who did not.
Two Kingdom classification
In 18th century a Swedish Naturalist Carolus Linnaeus known as father of Taxonomy, gave two kingdom classification.
In two kingdom system of classification, organisms are grouped on the basis of presence and absence of cell wall.
Linnaeus named the groups as Plantae (Plants) and Animalia (Animals).
Kingdom Plantae includes all organism which are stationary, prepared their own food and has a cellulose cell wall. It includes all green plants, mosses, fungi, lichens and bacteria.
Kingdom Animalia includes all the organisms which could move, had heterotrophic nutrition and lack a rigid cell wall. It includes all multicellular and unicellular animals and protozoans.
This system of classification was used for a long time and later found that it was not sufficient to include all organisms. It does not differentiate unicellular and multicellular organisms, prokaryotes and eukaryotes.
Three kingdom Classification
Haeckel in 1866 proposed a new kingdom Protista, which includes all unicellular animals, algae and fungi.
Three Kingdoms are,
(i) Plantae- Multicellular plants
(ii) Animalia- Multicellular animals
(iii) Protista- Unicellular plants, fungi and animals.
Five Kingdom Classification
R H Whittaker in 1969 proposed five kingdom classification based on,
(i) The complexity of cell structure - prokaryotes or eukaryotes
(ii) The nature of body organization - unicellular or multicellular
(iii) The mode of nutrition - autotrophic or heterotrophic
(iv) Phylogenetic relationship
The five Kingdoms are Monera, Protista, Plantae, Fungi and Animalia.
In five kingdom classification, all the prokaryotes are separated from eukaryotes and unicellular eukaryotes grouped into separate kingdom.
Five kingdom classification is more phylogenetic.
Kingdom Monera
Kingdom monera includes all prokaryotes and hence it is also called as Prokaryota.
Only Bacteria are the members of this kingdom.
They are small and most abundant microorganisms on earth.
Bacteria found almost everywhere on earth even in extreme conditions like hot springs, deserts deep oceans.
Characteristics of Monera
(i) These organisms are most primitive and simplest forms of life with prokaryotic cells.
(ii) They are microscopic, Unicellular or colonial, motile or non- motile organisms.
(iii) Definite nucleus and membrane bound organelles are absent.
(iv) Cell wall is present and made up of peptidoglycan.
(v) Flagella, when present are made up of protein called Flagellin.
(vi) Nutrition is of various types- autotrophic, saprophytic or heterotrophic.
(vii) They are called natural scavengers because they decompose the dead matters.
(viii) They reproduce sexually by binary fission or spores of certain types.
Types depending on their shape
1. Coccus: Cells are spherical/oval. E.g. Staphylococcus
2. Bacillus: Cells are elongated, rod like and cylindrical. E.g. Lactobacillus
3. Spirillum: The cells are spirally coiled. E.g. Spirochaete
4. Vibrium: The cells are curved or comma shaped. E.g. Vibrio cholerae
Classification of Kingdom Monera
It is classified into Archaebacteria and Eubacteria (Cyanobateria and Bacteria).
Archaebacteria
Archaebacteria are the oldest and most primitive prokaryotes.
They lack peptidoglycan cell wall, instead cell wall is made up of proteins and non-cellulosic polysaccharides.
These bacteria live in some of the harsh habitats like extreme salty areas, hot springs and marshy areas.
Halophiles: Lives in highly saline conditions as aerobes or anaerobes. E.g. Halobactor, Halococcus.
Thermoacidophiles: They live in high temperature and high acidic conditions like hot springs. They possess enzymes that are thermostable. E.g. Thermus aquaticus.
Methanogens: These are anaerobes livin gin marshy areas. They produce methane gas. Some methanogens live in the rumen of herbivores. E.g. Methanobacterium.
Eubacteria
These are called true bacteria.
They are characterised by presence of a rigid cell wall and flagella (if motile).
They are grouped into, cyanobacteria and bacteria.
(i) Cyanobacteria
They are commonly called as blue green algae.
They have chlorophyll a, like green plants and are photosynthetic autotrophs.
They are unicellular, colonial or filamentous, marine or terrestrial algae.
The colonies are generally surrounded by a gelatinous sheath.
Some of the cyanobacteria are helpful in fixing atmospheric nitrogen with the special cells called Heterocysts.
Cyanobacteria generally form blooms in the polluted water bodies.
Chemosynthetic autotrophic bacteria oxidise various inorganic substances into nitrites, nitrates and ammonia.
Ex: Nostoc, Anabaena, Spirulina
(ii)Bacteria
They are the most abundant organisms in nature.
Majority are important decomposers.
They are microscopic, unicellular and small organisms.
Bacterial cells are generally surrounded by a slime layer.
Many bacteria have flagella as they are motile.
Some have hair like projections on the surface called Pilli or fimbriae.
Most of the bacteria have the saprophytic mode of nutrition. They helpful in recycling the nutrients in nature.
Several bacteria are beneficial to human beings as they are helpful in making curd from milk, production of antibiotics, nitrogen fixing etc.
Some of bacteria are pathogens, causing diseases in human beings and crops.
Bacteria mainly reproduce by binary fission. During unfavourable conditions they produce spores. They reproduce sexually by means of conjugation.
Mycoplasma
These are the smallest known prokaryotes.
They lack cell wall and can survive without oxygen.
Many mycoplasma are pathogenic and cause diseases in plants and animals.
Aristotle in 4th BC was the earliest, to attempt scientific basis of classification.
He classified plants into trees, shrubs, and herbs based on simple morphological features.
He also classified the animals into two groups, those which had red blood and those who did not.
Two Kingdom classification
In 18th century a Swedish Naturalist Carolus Linnaeus known as father of Taxonomy, gave two kingdom classification.
In two kingdom system of classification, organisms are grouped on the basis of presence and absence of cell wall.
Linnaeus named the groups as Plantae (Plants) and Animalia (Animals).
Kingdom Plantae includes all organism which are stationary, prepared their own food and has a cellulose cell wall. It includes all green plants, mosses, fungi, lichens and bacteria.
Kingdom Animalia includes all the organisms which could move, had heterotrophic nutrition and lack a rigid cell wall. It includes all multicellular and unicellular animals and protozoans.
This system of classification was used for a long time and later found that it was not sufficient to include all organisms. It does not differentiate unicellular and multicellular organisms, prokaryotes and eukaryotes.
Three kingdom Classification
Haeckel in 1866 proposed a new kingdom Protista, which includes all unicellular animals, algae and fungi.
Three Kingdoms are,
(i) Plantae- Multicellular plants
(ii) Animalia- Multicellular animals
(iii) Protista- Unicellular plants, fungi and animals.
Five Kingdom Classification
R H Whittaker in 1969 proposed five kingdom classification based on,
(i) The complexity of cell structure - prokaryotes or eukaryotes
(ii) The nature of body organization - unicellular or multicellular
(iii) The mode of nutrition - autotrophic or heterotrophic
(iv) Phylogenetic relationship
The five Kingdoms are Monera, Protista, Plantae, Fungi and Animalia.
In five kingdom classification, all the prokaryotes are separated from eukaryotes and unicellular eukaryotes grouped into separate kingdom.
Five kingdom classification is more phylogenetic.
Kingdom Monera
Kingdom monera includes all prokaryotes and hence it is also called as Prokaryota.
Only Bacteria are the members of this kingdom.
They are small and most abundant microorganisms on earth.
Bacteria found almost everywhere on earth even in extreme conditions like hot springs, deserts deep oceans.
Characteristics of Monera
(i) These organisms are most primitive and simplest forms of life with prokaryotic cells.
(ii) They are microscopic, Unicellular or colonial, motile or non- motile organisms.
(iii) Definite nucleus and membrane bound organelles are absent.
(iv) Cell wall is present and made up of peptidoglycan.
(v) Flagella, when present are made up of protein called Flagellin.
(vi) Nutrition is of various types- autotrophic, saprophytic or heterotrophic.
(vii) They are called natural scavengers because they decompose the dead matters.
(viii) They reproduce sexually by binary fission or spores of certain types.
Types depending on their shape
1. Coccus: Cells are spherical/oval. E.g. Staphylococcus
2. Bacillus: Cells are elongated, rod like and cylindrical. E.g. Lactobacillus
3. Spirillum: The cells are spirally coiled. E.g. Spirochaete
4. Vibrium: The cells are curved or comma shaped. E.g. Vibrio cholerae
Classification of Kingdom Monera
It is classified into Archaebacteria and Eubacteria (Cyanobateria and Bacteria).
Archaebacteria
Archaebacteria are the oldest and most primitive prokaryotes.
They lack peptidoglycan cell wall, instead cell wall is made up of proteins and non-cellulosic polysaccharides.
These bacteria live in some of the harsh habitats like extreme salty areas, hot springs and marshy areas.
Halophiles: Lives in highly saline conditions as aerobes or anaerobes. E.g. Halobactor, Halococcus.
Thermoacidophiles: They live in high temperature and high acidic conditions like hot springs. They possess enzymes that are thermostable. E.g. Thermus aquaticus.
Methanogens: These are anaerobes livin gin marshy areas. They produce methane gas. Some methanogens live in the rumen of herbivores. E.g. Methanobacterium.
Eubacteria
These are called true bacteria.
They are characterised by presence of a rigid cell wall and flagella (if motile).
They are grouped into, cyanobacteria and bacteria.
(i) Cyanobacteria
They are commonly called as blue green algae.They have chlorophyll a, like green plants and are photosynthetic autotrophs.
They are unicellular, colonial or filamentous, marine or terrestrial algae.
The colonies are generally surrounded by a gelatinous sheath.
Some of the cyanobacteria are helpful in fixing atmospheric nitrogen with the special cells called Heterocysts.
Cyanobacteria generally form blooms in the polluted water bodies.
Chemosynthetic autotrophic bacteria oxidise various inorganic substances into nitrites, nitrates and ammonia.
Ex: Nostoc, Anabaena, Spirulina
(ii)Bacteria
They are the most abundant organisms in nature.
Majority are important decomposers.
They are microscopic, unicellular and small organisms.
Bacterial cells are generally surrounded by a slime layer.
Many bacteria have flagella as they are motile.
Some have hair like projections on the surface called Pilli or fimbriae.
Most of the bacteria have the saprophytic mode of nutrition. They helpful in recycling the nutrients in nature.
Several bacteria are beneficial to human beings as they are helpful in making curd from milk, production of antibiotics, nitrogen fixing etc.
Some of bacteria are pathogens, causing diseases in human beings and crops.
Bacteria mainly reproduce by binary fission. During unfavourable conditions they produce spores. They reproduce sexually by means of conjugation.
Mycoplasma
These are the smallest known prokaryotes.
They lack cell wall and can survive without oxygen.
Many mycoplasma are pathogenic and cause diseases in plants and animals.
0 Comments