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Biological Classification – Introduction
Aristotle’s system
Aristotle used simple morphological characters to classify plants into trees, shrubs and herbs. He also
divided animals into two groups, those which had red blood and those that did not.
Two kingdom system of classification
In Linnaeus time there were two kingdoms
a. Plantae-organism with cell wall
b. Animalia-organism without cell wall
This system was used till very recently.
Drawbacks of 2 kingdom system
 This system did not distinguish between
o The eukaryotes and prokaryotes
o Unicellular and multicellular organisms
o Photosynthetic (green algae). And non-photosynthetic (fungi) organisms.
 Two kingdom classification systems included bacteria, blue green algae, fungi, mosses, ferns,
gymnosperms and the angiosperms under ‘plant’ because of cell wall
 It brought together the prokaryotic bacteria and the blue algae with other groups which were
eukaryotic
 It also grouped together the unicellular organism and the multicellular organisms like,
Chlamydomonas and spirogyra were placed together heterotrophic group-fungi and he
autotrophic green plants, even though their cell wall composition was different- the fungi had
chitin in their walls while the green plants had a cellulosic cell wall
Five kingdom system of classification by R.H. Whittaker (1969)
This is the most accepted system of classification. The five kingdoms are as follows:
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Monera: Included all prokaryotic organism including cyanobacteria.
Protista: Included all unicellular eukaryotic organism
Fungi: Included all multicellular, eukaryotic, walled hetrotrophs with absorptive nutrition
Plantae: Included all multicellular photosynthetic org
Animalia: Included all multicellular without walled, showing holozoic nutrition.
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SUNSHIELD CLASSES
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The main criteria for classification used by Whittaker
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Cell Structure
Thallus Organization
Mode of Nutrition
Reproduction and
Phylogenetic Relationships
Kingdom monera
Kingdom Monera - All the organisms of this kingdom are prokaryotes. Complex structure was the basis
of classification of organisms, many centuries ago.
According to R.H. Whittaker's five kingdom classification all the bacteria were placed under the
Kingdom Monera.
Monera are considered as the most primitive group of organisms. They include various types of bacteria
and blue-green algae.
Monerans are most abundant of all organisms, due to their versatility of their habitat.It is estimated that
a single drop of water contains 50 billion bacteria.
Kingdom Monera - All the organisms of this kingdom are prokaryotes. Complex structure was the basis
of classification of organisms, many centuries ago. According to R.H. Whittaker's five kingdom
classification all the bacteria were placed under the Kingdom Monera.
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Monera are considered as the most primitive group of organisms. They include various types of bacteria
and blue-green algae.
Monerans are most abundant of all organisms, due to their versatility of their habitat.It is estimated that
a single drop of water contains 50 billion bacteria.
The Kingdom Monera includes organisms that are single-celled known as bacteria. The microorganisms
in Kingdom Monera are considered as the most ancient living forms on earth. The kingdom is divided
into two groups Archaebacteria and Eubacteria. All the organisms of this kingdom are prokaryotes.
These cells do not have nuclear membrane, the chromosome is a single and circular, they also lack
membrane bound cellular organelles. This kingdom includes bacteria, cyanobacteria, mycoplasma etc.
They are unicellular organisms and do not have specific mode of nutrition. They can be either aerobic or
anaerobic.These organisms have cell wall which is made up of peptidoglycans. The cell organelles are
not membrane bound. Cell organelles like endoplasmic reticulum, mitochondria are
absent. Reproduction is by spore formation and binary fission.
General characteristics of the kingdom Monera are as follows:
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They are primitive organisms.
All organisms of the kingdom are prokaryotes.
They are present in both living and non-living environment.
They can survive in harsh and extreme climatic conditions like in hot springs, acidic soils etc.
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They are unicellular organisms.
Membrane bound nucleus is absent.
DNA is in double stranded form, suspended in the cytoplasm of the organism,referred as
nucleoid.
A rigid cell wall is present.
Membrane bound cellular organelles like mitochondria are absent.
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.
Nutrition - autotrophs - can prepare their own food, heterotrophs - depend on others for
food, saprophytes - feed on dead and decaying matter, parasitic - live on other host cells for
survival and cause, symbiotic - in mutual relation with other organisms, commensalism - it is
where one organism is benefited and the other is not affected, mutualism - where both the
organisms are benefited.
Respiration - respiration in these organisms vary, they may be obligate aerobes - the organisms
must have organisms for survival; obligate anaerobes - the organisms cannot survive in the
presence of oxygen; facultative anaerobes - these organisms can survive with or without
oxygen.
Circulation - is through diffusion.
Movement - is with the help of flagella.
Reproduction is mostly asexual, sexual reproduction is also seen. Asexual reproduction is by
binary fission, sexual reproduction is by conjugation, transformation and transduction.
Classification of Kingdom Monera
Kingdom Monera has been classified into two groups - Archaebacteria and Eubacteria.
Archaebacteria are microbes that live in extreme and harsh conditions, they are known as
extremophiles. These bacteria lack cell wall, their cell membrane is made up of different lipids, and their
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ribosomes are similar to that of eukaryotes.
Archaebacteria are of three major groups of bacteria based on their habitat i.e., thermophiles,
halophiles and methanogens.
Some extremophiles live in boiling water like geysers of Yellowstone National Park and and in volcanoes.
These are known as 'thermophiles'.
Some extremophiles live in extremely salty water, the salt loving bacteria are known as 'halophiles'.
Some bacteria are present in the guts of ruminants and are responsible for production of methane gas
from their dung. These bacteria are known as 'methanogens'.
Eubacteria are true bacteria. The characteristic feature is the presence of rigid cell wall and if present a
motile flagelllum that aids in locomotion.These organisms are characterized based on their nutrition and
their shapes.
Classification based on Shape
Bacteria can be classified in four groups based on shape : Spherical or round shaped bacteria are called
cocci, Rod-shaped are bacilli, Comma-shaped bacteria are vibrio and spiral shaped bacteria are spirilla.
Classification Based on Mode of Nutrition
Based on the mode of nutrition bacteria are broadly classified into Autotrophic and Heterotrophic.
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Autotrophic bacteria - Bacteria which prepare their own food are autotrophic. (Example Cyanobacteria)
Heterotrophic bacteria - Bacteria which are dependent on other organisms for their food are
heterotrophic.(Example Escherichia coli)
Autotrophic bacteria can be Chemosynthetic or Photosynthetic.
Chemosynthetic bateria are those which prepare their food with the help of inorganic substrates.
Photosynthetic bacteria are autotrophic bacteria which prepare their own food by the process of
photosynthesis.
Cyanobacteria (Blue-green algae) - They have chlorophyll similar to plants and hence they are
photosynthetic autotrophs. The marine and terrestrial and they may be unicellular, colonial or
filamentous. The colonies are surrounded by gelatinous sheath. They can also fix atmospheric nitrogen.
Example: Nostoc and Anaebena.
Chemosynthetic autotrophs - these organisms oxidise substances like nitrites, nitrates, ammonia etc. The
help in recycling substances like nitrogen, sulphur, iron etc.
Heterotrophic bacteria are those which are dependent on other organism either directly or indirectly
for their nutrition. They are most abundant and are important decomposers. Some are helpful in
curdling milk, production of antibiotics, in nitrogen fixation and some are pathogens.
Heterotrophic bacteria can be parasitic and saprophytic. Parasitic bacteria are those which depend on
the host for nutrition and cause harm to the host. Saprophytic bacteria feed on dead and
decaying matter.
Symbiotic - it is a type where the bacteria are in mutual relation with other organisms. Symbiosis is of
two types mutualism and commensalism. Mutualism is where the bacteria and the other organism
are benefited due to the relationship. Commensalism is a relationship where the bacteria is benefited
while the other organism is not affected by the relationship.
Reproduction in Bacteria
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Reproduction in bacteria is mainly by fission.Under unfavourable conditions they reproduce by spores.
Sexually bacteria reproduce by a primitive mode of DNA transfer from one bacterium to another i.e., by
conjugation, transduction or transformation.
Mycoplasma
Mycoplasma are the known to be the smallest living cells. They completely lack cell wall and can survive
without oxygen. Most of the mycoplasma are pathogenic in nature in animals and plants.
Economic Importance of Bacteria
Lactic acid bacteria like Lactobacillus and Lactococcus have been used in fermentation process for
thousands of years.
The ability of the bacteria to degrade variety of organic compounds has been used in waste
management processing and biorememdiation.
In pest control, bacteria can be used in the place of pesticides as these pesticides are regarded
environmentally friendly.
Example: Bacillus thuringenesis.
The ability of the bacteria in dividing rapidly and by studies on the bacterial genome, these bacteria can
be bio-engineered for the production of therapeutic proteins like insulin, growth factors
and antibodies, etc.
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Kingdom Monera Examples
The Monerans comprises of mostly bacteria. Following are a few well known examples.
Blue-green algae - Cyanobacteria, Cocci shaped bacteria - Streptococcus, Bacilli shaped bacteria E.coli, Vibrio shaped - Vibrio cholerae (cholera), Spiral shaped bacteria- Treponema pallidum (syphilis).
Gram positive bacteria - Mycobacterium; Gram negative bacteria - E.coli (coliforms)
Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris, Streptococcus pyogens, Clostridium
botulinum, Listeria monocytogenes, Salmonella enterica, Vibrio cholerae, Bacillus anthracis, Bacillus
cereus.
Shapes of bacteria
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Kingdom Protista
All single celled eukaryotes are placed under protista, but the boundares of this kingdom are not well
defined.
Here we include following under protita
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Chrysophytes
Dianoflagellates
Euglenoids
Slime moulds
Protozoans
Also include Chlamydomonas and Chlorella
Habitat : members of protista are primarily aquatic
Cell body of protista:
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Being eukaryotes, the protistan cell body cell conatins a well defined nucleus and other
membrane-bound organelles.
Some have flagella or cilia.
Reproduction
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Protists reproduce asexually by spores
Also sexually by a process involving cell fusion and zygote formation.
Chrysophytes
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This group includes diatoms and golden algae (desminds).
It also includes Xanthophyceae-Yellow green algae (Vaucheria – synnzoospores)
Diatoms
Habitat
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They are found in fresh water as well as in marine environments.
They are microscopic and float passively (non motile) in water currents (plankton). Most of them
are photosynthetic.(diatoms are the chief ‘producers’ in the oceans ).
They have have oil drops which helps in floating, after death they sink to bottom.
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Cell all of diatoms
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In diatoms the cell walls / frustules form two thin overlapping shells, which fit together as in a
soap box.
 The walls are embedded with silica, cellulose, pectin and thus the walls are indestructible
a. Diatomaceous earth
Diatoms have left behind large amount of cell wall deposits in their habitat;this accumulation
over billions of years is referred to as ‘diatomaecous earth’.
b.
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Uses of diatomaceous earth
Being gritty this soil is used in
Polishing.
Filtration of oils and syrups.
Pigments: Chl a + Chl c + diatomin (golden brown colour) + Fucoxanthin (Brown) and 𝛽 carotene
Reserved food: Chrysolaminarin / Leucosin (CH) + oil
The oil reserve of diatos have contributed to petroleum
Reproduction : By binary fission, and semiconservative wall formation, Zygote becomes Auxospores
Dinoflagelates / whirling whips / pyrrophyceae
Habitat
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These organism are mostly marine and photosynthetic
Colours of dianoflagellates
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They appear red, brown, yellow, blue, green, or depending on the main pigment present
present in their cells
Show bioluminescence, in response to snmall predatory fishes.
Cell wall
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The cell wall has stiff cellulose plates on the outer surface.
Most of them have two flagella; one lies logtidunally and the other transversely in a furrow
between the wall plates.
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Red tides
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Very often, red dinoflagellates (examples: Gonyaulax)undergo such rapid multiplication that
they make the sea appear red (red tides).
Toxins (saxitoxins) released by such large numbers may even kill other marine animals such as
fishes.
Pigments : Chl a + Chl c + peridinin (Brown colour) and 𝛽carotene
Reserve food : Oil and Starch.
Reproduction is mostly asexual
Euglenoid
Habitat
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Mostly of them are fresh water organism found in stagnant water. (some marine)
Pellicle
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Instead of a cell wall, they have a protein rich layer called pellicle which makes their body
flexible.
They have two flagella a short and long one.
Mode of nutrition
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Though they are photosynthetic in the presence of sunlight, when deprived of sunlight they
behave like heterotrophs b predating on other smaller organism.- MIxotrophic nutrition
Pigments
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Interestingly, the pigments of euglenoids are indentical to those present in higher plants.
Example : Euglena
 Pigments smilar to higher pants : Chl a + Chl b + 𝛽 carotene
 Reserve food is paramylon (CH)
 The eye spot / stigma is a light sensitive area contining pigment Astaxanthin eye spot
Slime moulds
Consumer decomposer protest / Mycetozoa (Fungal animals) / Gymnomycota / Myxomycetes
Slime moulds are saprophytic protists
Plasmodial SM / Acellular slime mould / Myxomycota / True SM:
Eg. Physarum and Fuligo (Dog vomit)
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1. They exist as well less mass of multinucleated protoplasm (thallus has diploid nucleus), Free
nuclear condition is formed by karyokensis without cytokensis in zygote nucleus. It slowly
streams or glides over decaying twigs, logs, leaves and engulfs organic material – phagocytosis /
holozoic. This network of moving a strand of protoplasm is called plasmodium-this may grow /
soread over several feet
2. In favorable conditions-dryness or food scarcity, the plasmodium of a cellular slime mould
transforms itself into fruiting bodies having sporangia. Spores are produced by meiosis. Spores
have true cell wall and are extremely resistant which survive for many years and are dispersed
by air currents. Spores germinate to form motile or non motile gametes.
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