The document discusses the historical classification of organisms, starting with Aristotle's division of plants and animals, and later Linnaeus' two-kingdom system which was further expanded by Whittaker into five kingdoms. It explores the characteristics of various groups including prokaryotes, eukaryotes, fungi, and their modes of reproduction, nutrition, and ecological roles. The document also highlights the relevance of viruses and viroids, their structure, and their relationship with plants and animals.

2. 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 which had red blood and
those that did not.
It is proposed by Linnaeus (1758).
This system classifies organisms into Two
Kingdoms- Plantae & Animalia.
Carl Linnaeus
Aristotle

3. Prokaryotes, {Bacteria & Cyanobacteria}, & eukaryotes {fungi, mosses, ferns, gymnosperms
& angiosperms} were included under “plants”. It is based on the presence of cell wall, but
prokaryotes & eukaryotes are widely different in other features
It included unicellular & multicellular organisms in the same group
Example: Chlamydomonas & spirogyra were placed under algae
It did not differentiate between heterotrophic Fungai & autotrophic green plants. Fungi have
chitinous cell wall while the green plants have cellulosic cell wall
It is proposed by R.H. Whittaker (1969).
It includes Monera, Protista, Fungi, Plantae & Animalia.
This classification is based on cell structure, thallus
organisation, mode of nutrition, reproduction & phylogenetic
relationships.
Characters Monera Protista Fungi Plantae Animalia
Cell type Prokaryotic Eukaryotic Eukaryotic Eukaryotic Eukaryotic
Cell wall
Non-cellular
(polysaccharide +
amino acid)
Present in some
Present
(without
cellulose)
Present
(cellulose)
Absent
Nuclear
membrane
Absent Present Present Present Present
Body
organization
Cellular Cellular
Multicellular,
loose tissue
Tissue/organ
Tissue/organ/
organ system
Mode of
nutrition
Autotrophic
(photosynthetic &
chemosynthetic)
and heterotrophic
(saprophyte/
parasite)
Autotrophic
(photosynthetic)
and
heterotrophic
Heterotrophic
(saprophytic
or parasitic)
Autotrophic
(photosynthetic)
Heterotrophic
(holozoic,
saprophytic etc)
R.H. Whittaker

4. Bacteria are the most abundant
microorganisms.
Hundreds of bacteria are present in a handful of
soil.
They also live in extreme habitats such as hot
springs, deserts, snow & deep oceans.
Many are parasites.
Bacterial structure is very simple but they
are complex in behaviour and show
metabolic diversity.
Some bacteria are autotrophic (synthesize
food from inorganic substrates).
Majority are heterotrophs (they do not
synthesize the food but depend on other
organisms or on dead organic matter for
food).

5. They live in harshest habitats such as extreme salty
areas (halophiles), hot springs (thermoacidophiles)
and marshy areas (methanogens).
Archaebacteria have a different cell wall structure for
their survival in extreme conditions.
Methanogens are present in the guts of ruminant
animals (cows, buffaloes etc). They produce methane
(biogas) from the dung of these animals.
They have a rigid cell wall and a
flagellum (if motile).
They include Autotrophs
(photosynthetic &
chemosynthetic) and
Heterotrophs.

6. They have chlorophyll a
similar to that of green
plants.
Cyanobacteria (blue-green
algae)
Unicellular, colonial or
filamentous, marine or
terrestrial algae.
The colonies are
generally surrounded by
gelatinous sheath.
They often form blooms in polluted water bodies.
Some of them fix atmospheric N2 in specialized cells called
heterocysts.
E.g. Nostoc & Anabaena.
They oxidize inorganic substances such as
nitrates, nitrites & ammonia and use the
released energy for their ATP production.
They play a great role in recycling nutrients
like nitrogen, phosphorous, iron & sulphur.
Most abundant in nature
Majority are important decomposers
They are used to make 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. E.g. Cholera, typhoid, tetanus,
and citrus canker.

7. Bacteria reproduce mainly by fission.
Under unfavourable conditions, they produce spores.
They also reproduce by a sort of sexual reproduction by adopting a primitive type of DNA
transfer from one bacterium to the other.
They are organisms without a cell wall.
They are the smallest living cells known.
They can survive without oxygen.
Many are pathogenic in animals and
plants.

8. It includes single-celled eukaryotes.
Protists are primarily aquatic.
It forms a link with plants, animals and fungi.
Cell contains well defined nucleus and other
membrane-bound organelles. Some have
flagella or cilia.
Reproduce asexually and sexually by a process
involving cell fusion & zygote formation.
They are found in fresh water and marine
environments.
They are microscopic and float passively in water
currents (plankton).
Most of them are photosynthetic.
It includes diatoms & golden algae (desmids).
Diatoms
They have siliceous cell walls forming two thin
overlapping shells, which fit together as in a soap
box.
The cell wall deposit of diatoms over billions of
years in their habitat is known as ‘diatomaceous
earth’. This is used in polishing, filtration of oils and
syrups.
Diatoms are the chief ‘producers’ in the oceans.
Mostly marine and photosynthetic.
They appear yellow, green, brown, blue or red
depending on the main pigments in cells.
Cell wall has stiff cellulose plates on the outer
surface.

9. Most of them have 2 flagella; one lies longitudinally and the
other transversely in a furrow between wall plates.
Red dianoflagellates (E.g. Gonyaulax) undergo rapid
multiplication so that the sea appears red (red tides). Toxins
released by such large numbers can kill other marine
animals such as fishes.
Mainly fresh water organisms found in stagnant water.
Instead of cell wall, they have a protein rich layer called pellicle. It makes their body flexible.
They have 2 flagella, a short and a long one.
They are photosynthetic in the presence of
sunlight. When deprived of sunlight they behave
like heterotrophs by predating on other smaller
organisms.
The pigments of euglenoids are identical to those
of higher plants. E.g. Euglena.
They are saprophytic protists.
The body moves along decaying twigs and leaves
engulfing organic material.
Under suitable conditions, they form an aggregation
called plasmodium which may grow and spread over
several feet.
During unfavourable conditions, the plasmodium
differentiates and forms fruiting bodies bearing spores
at their tips.
Spores possess true walls. They are extremely resistant
and survive for many years. The spores are dispersed by
air currents.

10. They are heterotrophs (predators or parasites).
They are believed to be primitive relatives of animals.
Amoeboid
Protozoans
Flagellated
Protozoans
Ciliated
Protozoans
Sporozoans
Live in fresh
water, sea water
or moist soil.
They move and
capture prey by
putting out
pseudopodia
(false feet).
E.g. Amoeba.
Marine forms
have silica shells
on their surface.
Some are
parasites. E.g.
Entamoeba.
Free-living or
parasitic.
They have
flagella.
Parasitic forms
cause diseases
like sleeping
sickness.
E.g.
Trypanosoma
Aquatic, actively
move using cilia.
They have a
cavity (gullet)
that opens to
outside.
Due to the
movement of
cilia, water with
food enters into
gullet.
E.g. Paramecium
infectious spore-
like stage in their
life cycle.
E.g. Plasmodium
(malarial
parasite) . It
causes malaria.

11. It is a unique kingdom of heterotrophic organisms.
Fungi are cosmopolitan and occur in air, water, soil and on animals and plants.
They prefer to grow in warm and humid places.
E.g. Bread Mould, Orange Rots, Mushroom, Toadstools etc.
White spots on mustard leaves are due to a parasitic fungus
Some fungi are the source of antibiotics, e.g., Penicillium.
Some unicellular fungi (e.g. Yeast) are used to make bread and beer.
Other fungi cause diseases in plants and animals. E.g. wheat rust-causing Puccinia.
Penicillium Yeast Puccinia
Except yeasts, fungi are filamentous. Their bodies consist of long, slender thread-like structures
called hyphae.
The network of hyphae is known as mycelium.
Some hyphae are continuous tubes filled with
multinucleated cytoplasm. These are called
coenocytic hyphae. Others have septae or
cross walls in hyphae.
Fungal cell wall is made of chitin &
polysaccharides

12. Most fungi are saprophytes (absorb soluble
organic matter from dead substrates).
Some are parasites.
Some live as symbionts – in association with
algae as lichens and with roots of higher plants
as mycorrhiza
The sexual cycle involves 3 steps:
Plasmogamy: Fusion of protoplasm between two motile or non-motile gametes.
Karyogamy: Fusion of two nuclei.
Meiosis: Occurs in zygote resulting in haploid spores.
Based on the morphology of mycelium, mode of spore formation and fruiting bodies, Fungi
are classified into various classes.

13. Asexual reproduction Takes place by zoospores
(motile) or by aplanospores (non-motile).
These are produced in sporangium.
Sexual reproduction :- Zygospores
are formed by fusion of two
gametes.
These gametes are isogamous
(similar) or anisogamous or
oogamous (dissimilar).
Unicellular (e.g. yeast, Sacharomyces) or multicellular (e.g. Penicillium).
They are saprophytic, decomposers, parasitic or coprophilous (growing on dung).
Mycelium is branched and septate.
Asexual reproduction
By conidia produced
exogenously on the
special mycelium
called conidiophores.
Conidia germinate to
produce mycelium.
Sexual reproduction
By ascospores produced endogenously in sac like asci (sing. ascus). Asci are arranged to form
ascocarps (fruiting bodies).
Examples
Aspergillus, Claviceps & Neurospora.
Neurospora is used in biochemical and genetic work.
Many members like morels & buffles are edible and are delicacies.

14. Includes mushrooms, bracket fungi or
puffballs.
They grow in soil, on logs and tree stumps
and in living plant bodies as parasites (e.g.
rusts & smuts).
Mycelium is branched & septate.
The asexual spores are generally not found,
but vegetative reproduction by fragmentation
is common.
Sex organs are absent, but plasmogamy occurs by fusion of two vegetative or somatic cells of
different strains or genotypes. The resultant structure is dikaryotic. It gives rise to basidium.
Karyogamy & meiosis occur in basidium producing 4 basidiospores exogenously.
Basidia are arranged in fruiting bodies called basidiocarps.
E.g. Agaricus (mushroom), Ustilago (smut) and Puccinia (rust fungus).
Sex organs are absent, but plasmogamy
occurs by fusion of two vegetative or somatic
cells of different strains or genotypes. The
resultant structure is dikaryotic. It gives rise
to basidium.
Karyogamy & meiosis occur in basidium
producing 4 basidiospores exogenously.
Basidia are arranged in fruiting bodies called
basidiocarps.
E.g. Agaricus (mushroom), Ustilago (smut)
and Puccinia (rust fungus).
Deuteromycetes reproduce only by asexual
spores (conidia).
Mycelium is septate and branched.
Some are saprophytes or parasites. Majority
are decomposers of litter and help in mineral
cycling.
E.g. Alternaria, Colletotrichum and
Trichoderma.

15. It includes all plants (eukaryotic chlorophyll-
containing organisms with cellulosic cell wall).
Some are partially heterotrophic such as the
insectivorous plants (e.g. Bladderwort and Venus
fly trap) or parasites (e.g. Cuscuta).
Plantae includes algae, bryophytes, pteridophytes,
gymnosperms & angiosperms.
Life cycle of plants has two distinct phases – the
diploid sporophytic & the haploid gametophytic –
that alternate with each other.
The lengths of the haploid and diploid phases, and
whether these phases are free living or dependent
on others, vary among different groups in plants.
This phenomenon is called alternation of
generation.
They are multicellular, heterotrophic,eukaryotic organisms without cell wall
They directrly or indirectly depend on plants for food. They digest food in an internal cavity
and store food reserves as glycogen or fat. Mode of nutrition is holozoic {ingestion of food}
They have a definite growth and pattern and grow into adults that have a definite shape and
size
Higher forms show sensory and neuromotor mechanism
Most of them are capablkeof locomotion
Sexual reproduction is by copulation of male and female followed by embryological
development

16. In five-kingdom classification, acellular organisms (viruses & viroids) and lichens are not
mentioned.
Viruses are non-cellular and not truly ‘living’. So they are not included in five-kingdom
classification.
Viruses have an inert crystalline structure outside the living cell.
Viruses are obligate parasites.
When they infect a cell they take over the machinery of host cell to replicate themselves,
killing the host.
Louis Pasteur : Gave the name ‘virus’ {means venom or
poisonous fluid}
D.J Ivanowsky : Discovered virus. He recognised certain microbes
that cause mosaic disease of tobacco. They were smaller than
bacteria because they passed through bacteria – proof filters
M.W. Beijernick : Demonstrated that the extract of the infected
plants of tobacco could cause infection in healthy plants and
called the fluid as ‘Contagium vivium fluidum’ {infectious living
fluid}
W.M. Stanley : Showed that viruses could be crystallized and
crystals consist largely of proteins

17. A virus is a nucleoprotein, i.e, it has a protein
coat (capsid) & genetic material (RNA or
DNA).
No virus contains both RNA & DNA.
The genetic material is infectious.
Generally, viruses that infect plants have
single stranded RNA.
Viruses that infect animals have either single
or double stranded RNA or double stranded
DNA.
Bacteriophages (viruses that infect bacteria)
usually have double stranded DNA. The protein coat (capsid) made of small
subunits (capsomeres) protects nucleic
acid.
Capsomeres are arranged in helical or
polyhedral geometric forms.
Helical
Polyhedral
geometric
Viruses cause diseases like mumps, small pox,
herpes, influenza & AIDS.
In plants, the symptoms can be mosaic formation,
leaf rolling & curling, yellowing & vein clearing,
dwarfing & stunted growth.

18. Viroid: It is an infectious agent with a free low molecular
weight RNA and no protein coat.
These are smaller than viruses.
It is discovered by T.O. Diener (1971). He found that it
caused potato spindle tuber disease.
Potato spindle tuber disease
Lichens: Lichens are
symbiotic associations
(mutually useful
associations) between algae
& fungi.
The algal component is
called phycobiont
(autotrophic) and fungal
component is mycobiont
(heterotrophic).
Algae prepare food for fungi and fungi provide
shelter and absorb mineral nutrients and water
for its partner.
Lichens are very good Pollution indicators.
They do not grow in polluted areas.
T.O. Diener