NMKRV PU COLLEGE, BENGALURU, KARNATAKA

BIOLOGY
For FIRST PUC
UNIT-1 Ashwini H.S

Chapter: 2 BIOLOGICAL CLASSIFICATION NCERT Syllabus

2 : INTRODUCTION:

 Biological Classification is the process of grouping of organisms into convenient categories on the basis of some
easily observable characters.
 Early human grouped the organisms on the basis of their use in food, shelter and clothing.
 Aristotle was the earliest to attempt a more scientific basis for classification.
o He used simple morphological characters to classify plants into herbs, shrubs and trees.
o He also divided animals into 2 groups, those which had red blood and those that did not.
 During Linnaeus time a two kingdom system of classification was developed.
o All the organisms were divided into two kingdoms, animalia and plantae.
o This system did not distinguish between the eukaryotes and prokaryotes, unicellular & multicellular organisms
and photosynthetic & non-photosynthetic organisms.
o Classification of organisms into plants and animals was easily done and was easy to understand, but a large
number of organisms did not fall into either category.
o The two kingdom classification used for a long time was found inadequate.
 Attempts were made to raise the number of kingdoms to three, four, & five.
 In such classifications along with gross morphology, cell, structure, nature of wall, mode of nutrition, habitat,
methods of reproduction and evolutionary relationships are taken into consideration.
 R.H Whittaker (1969) an American taxonomist proposed a five kingdom classification.
o Whittaker employed the following criteria for differentiating the five kingdoms – cell structure (cell type, cell wall
& nuclear membrane) body organization, mode of nutrition, reproduction and phylogenetic relationships.

Five kingdoms
Characters
Monera Protista Fungi Plantae Animalia
Cell type Prokaryotic Eukaryotic Eukaryotic Eukaryotic Eukaryotic
Non-Cellulosic present (without-
Present
Cell wall (Polysaccharide+ Present in some cellulose) Absent
(Cellulose)
aminoacid) Chitinaceous
Nuclear
Absent Present Present Present Present
membrane
Tissue/
Body Multicellular /
Cellular Cellular Tissue/ organ organ/organ
organisation loose tissue
system
Autotrophic
(Chemosynthetic
Autotrophic Heterotrophic Heterotrophic
Mode & Photosynthetic) Autotrophic
(Photosynthetic) (Saprophytic/ (holozoic/
of nutrition Heterotrophic (Photosynthetic)
& heterotrophic parasitic) saprophytic )
(Saprophytic/
parasitic)

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o Living beings are distributed into five kingdoms.
o The kingdoms defined by him were named Monera, Protista, Fungi, Plantae and animalia.
o Viruses, viroids and lichens are excluded.

2.1: KINGDOM: MONERA

 Kingdom Monera includes all prokaryotic organisms.
 Bacteria are the sole members of the kingdom Monera. They are the most abundant micro – organisms.
 Bacteria are cosmopolitan in distribution. They live in extreme habitats such as hot springs, deserts, snow and
deep oceans.
 Many bacteria are parasitic in nature.

Categories of bacteria:
 Bacteria are grouped into four categories, based upon the shape of the cell.
1) Coccus (pl.: cocci) : They are spherical (or) oval in outline
2) Bacillus (pl.: bacilli): The bacteria are rod like, straight & flat.
3) Vibrium (pl.: Vibrio): They are comma shaped.
4) Spirillum(pl.: Spirilla): A rigid helical form of 1-3 curves.

 The bacterial structure is very simple, but they show very complex behaviour.
 Some of the bacteria are autotrophic and heterotrophic.
 Autotrophic bacteria: Bacteria that synthesis their own food is called as autotrophic bacteria. They may be
photosynthetic and chemosynthetic bacteria.
 Photosynthetic autotrophic: Bacteria prepare their own organic food from inorganic raw material in presence
of sunlight.
 Chemosynthetic autotrophic: Bacteria oxidize various inorganic substances such as nitrates, nitrites and
ammonia and use the released energy for their ATP production.
o Chemosynthetic autotrophic bacteria play a great role in recycling the nutrients like nitrogen, phosphorous,
iron and sulphur.
 Heterotrophic bacteria: Bacteria that don’t synthesise their own food but depend on other organisms or on
dead organic matter for food.

Types: Bacteria have 2 major groups, archaebacteria & eubacteria.

2.1.1: Archaebacteria:

o Bacteria that live in most harsh habitats, such as salty areas. Hot springs, marshy areas.
o Bacteria living in the salty areas are called halophiles.
o Bacteria living in the hot spring are called thermoacidophiles.
o Bacteria living in the marshy areas are called methanogens.

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 Methanogens are present in the gut of several ruminant animals such as cows & buffaloes & they are
responsible for the production of methane (biogas) from the dung of these animals.
 Archaebacteria is having a different cell wall structure which is responsible for their survival in extreme
conditions.

2.1.2: Eubacteria:

 Eubacteria are true bacteria, characterized by the presence of a rigid cell wall.
 Eubacteria have subgroups like cyanobacteria, & mycoplasma.

Cyanobacteria / Blue green algae:

o Cyanobacteria are unicellular, colonial (or) filamentous forms.
o They are fresh or marine water forms or terrestrial algae.
o The colonies are surrounded by gelatinous sheath, often they form blooms in polluted water bodies.
o They have chlorophyll a and are photosynthetic autotrophs.
o Some of the cyanobacteria can fix atmospheric nitrogen in specialized cells
called heterocysts.
Ex: Nostoc & Anabaena.
 Majority of bacteria are Heterotrophs or heterotrophic bacteria.
 Heterotrophs or heterotrophic bacteria: Bacteria that don’t synthesise their
own food but depend on other organisms or on dead organic matter for food.
o Heterotrophic bacteria are abundant in nature, majority of them are decomposers.
o They have significant influence (effect) on human affairs.
o Some of them are useful i.e. they are helpful in making curd from milk, production of antibiotics, nitrogen fixing
in legume roots etc.,
o Some are pathogens causing damage to human beings, crops, farm animals and pets.
 Diseases caused by bacteria: Cholera, typhoid, tetanus, citrus canker etc.,
 Reproduction:
o Bacteria mainly reproduce by fission.
o Under unfavorable condition, they produce spores (endospores).
o Bacterial conjugation: It is a general type of sexual reproduction in which DNA is primitively transferred from
one bacterium to another.

Mycoplasma:
o They are the smallest living cells and can survive without oxygen (anaerobe).
o They completely lack a cell wall.
o Many Mycoplasma are pathogenic in animals and plants.

2.2: KINGDOM: PROTISTA

Salient features:
1. Unicellular eukaryotic organisms are placed under Protista but the boundaries of this kingdom are not well
defined.
2. Members of Protista are primarily aquatic. Living in both fresh water and sea. They commonly float on the
surface of water as plankton.
3. Protistan cell body contains a well defined nucleus and other membrane – bound organelles.
4. Protistans have flagella (or) cilia.

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5. This kingdom forms a link with the others dealing with plants, animals and fungi.
6. Protists reproduce asexually and sexually.
7. Asexual reproduction occurs by binary fission, budding sporulation.
8. Sexual reproduction occurs by formation of gametes of different types and fusion of the gametes and zygote
formation.
Classification:
Chrysophytes, Dinoflagellates, Euglenoids, Slime Moulds, Protozoans.

2.2.1: Chrysophytes:

 This group includes diatoms and golden algae (desmids).

 They are found in fresh water and in marine environments.
 They are microscopic and float passively in water currents (planktons). Most of them are photosynthetic.
Diatoms:
o Diatoms are microscopic, single celled forms.
o Diatoms have cell walls containing silica, constructed in two overlapping halves, which fit together like two parts
of a soap box.
o Diatomaceous earth: Accumulation of large amount of cell wall of diatoms in their habitat, over billions of years
is referred to as diatomaceous earth.
o Diatomaceous soil is gritty and used in polishing, filtration of oils and syrups.

2.2.2: Dinoflagellates:

 Most of dinoflagellates are marine and important photo-synthesizers in ocean.

 They appear yellow, green, brown, blue or red depending on the main pigments present in their cells.
 The cell wall has stiff cellulose plates of the outer surface.
 Some of them have two flagella one lies longitudinally and the other
transversely in a furrow between the wall plates.
 Red dinoflagellates undergo rapid multiplication that make the sea appear red
( red tides)
Ex: Gonyaulax
 Toxin released by rapid multiplying dinoflagellates may kill the other
marine animals such as fishes.

2.1.3: Euglenoids:

 They are fresh water organisms found in stagnant water.

 They are photosynthetic in the presence of sunlight, in the absence of
sunlight; they behave like heterotrophs by predating on other smaller
organisms.
 The pigments of euglenoids are identical to the pigment of higher plants.
 They are characterized by absence of cell wall but contain a protein rich
layer called pellicle, which makes their body flexible.
 They have 2 flagella a short and a long one. Ex: Euglena.

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2.1.4: Slime Moulds:
 Slime moulds are saprophytic protists.
 They occur in moist terrestrial habitats moving along decaying twigs and leaves, engulfing organic material.
 Under suitable conditions slime moulds form on aggregation called plasmodium.
 During unfavorable conditions, the plasmodium differentiates and forms fruiting bodies bearing spores at their
tips.
 The spores have true cell walls, extremely resistant and survive for many years.
 The spores are dispersed by air currents.

2.1.5: Protozoans:

 All Protozoans are heterotrophs, and live as predators (or) parasites.

 They are believed to be primitive relatives of animals.
Protozoans are four major groups
1. Amoeboid protozoans 2. Flagellated protozoans 3. Ciliated protozoans 4. Sporozoans
1. Amoeboid protozoans:
o These organisms live in fresh water, sea water or moist soil.
o They move and capture their prey by putting out pseudopodia (false feet). Ex: Amoeba.
o Marine forms have silica shells on their surface. Ex: Elphydium.
o Entamoeba is parasite, in human intestine and causes dysentery.

2. Flagellated protozoans:
o The members of this group are either free-living or parasitic.
o They have flagella.
o The parasitic forms cause diseases such as sleeping sickness.
Ex: Trypanosoma.
3. Ciliated protozoans:
o These are aquatic, actively moving organisms, because of the presence of
thousands of cilia.
o They have a cavity (gullet) that opens to the outside of the cell surface.
o The entry of food into gullet is by the movement of cilia.
Ex: Paramoecium.

4. Sporozoans:
o This includes diverse organisms that have an infectious spore-like stage in their life cycle.
Ex: Plasmodium – a malarial parasite.

2.3: KINGDOM FUNGI:

 Fungi are simple, non-chlorophyllous, heterotrophic organisms.
 Kingdom fungi also called mycota.
 Fungi show a great diversity in morphology and habitat.
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Occurrence:
o Fungi are cosmopolitan in distribution. They occur in all those places, where organic matter is available.
Ex: soil, water, air and inside plants and animals.
o They prefer to grow in warm and humid places.
Mycelium:
o With the exception of unicellular yeast, fungi are filamentous.
o The filaments are called hyphae (they are long, slender, tubular in shape).
o The network of hyphae of a fungus is called mycelium. Hyphae of some fungi are continuous tubes, filled with
multinucleated cytoplasm and aseptate they are called coenocytic hyphae.
o In others, the hyphae are multicellular and septate/ cross walls are found

Cell structure:
o Cells are eukaryotic; cell wall contains chitin and polysaccharides.
o Reserve food is glycogen and oil.
Nutrition:
 Fungi are heterotrophic in nutrition.
 Most of fungi are saprophytes. They obtain nourishment from the dead and decayed organic matters
 Some fungi that depend up on living plants and animals are called parasites.
 Some fungi live as symbionts, fungi is associated with algae to form lichens and it also associated with roots of
higher plants called mycorrhiza.
 Reproduction:
Reproduction in fungi takes place by
1. Vegetative reproduction
2. Asexual reproduction
3. Sexual reproduction
1. Vegetative reproduction: It takes place through fragmentation, fission and budding.
2. Asexual reproduction: Occurs through spores like conidia or sporangiospores or zoospores.
3. Sexual reproduction: Also leads to the formation of spores like oospores, ascospores, and basidiospores.
 The various spores are produced in distinct structures called fruiting bodies.

The sexual cycle involves the following 3 steps.

1. Plasmogamy: Fusion of protoplasms between two motile or non motile gametes or cells of hyphae of different
strains called plasmogamy.
2. Karyogamy: Fusion of two nuclei called karyogamy.
3. Meiosis in zygote resulting in formation of haploid spores.
Dikaryophase:
 In many fungi (ascomycetes, basidiomycetes) the two nucleate or dikaryotic stage (n+n) occurs, such a condition
is called as dikaryon, and the phase is called dikaryophase.

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 Later the parental nuclei fuse and the cells become diploid.
 In the fruiting bodies of fungi reduction division occurs, leading to the formation of haploid spores.

 Fungal Classification: It is based on morphology of mycelium, mode of spore formation, fruiting bodies and
 Presence or absence of sexual reproduction.
 Fungi are divided into 4 classes:
1. Phycomycetes. 2. Ascomycetes. 3. Basidiomycetes. 4. Deuteromycetes.

2.3.1: Phycomycetes:

Occurrence: Members of Phycomycetes are found in aquatic habitats and on decaying wood in moist and damp
places or as obligate parasites on plants.
Mycelium: The mycelium is aseptate and coenocytic.
Reproduction: Asexual reproduction:
 It is carried out by asexual spores. Spores are produced endogenously inside
the sporangia (sing: sporangium).
 Spores are motile in aquatic habitat (zoospores), and non motile
(aplanospores), in terrestrial habitats.
Sexual reproduction:
 Sexual reproduction occurs through fusion of similar (isogamous) or
dissimilar (anisogamous, oogamous) gametes.
 The fusion product is called zygospores.
 Ex: Mucor, Rhizopus(bread mould), Albugo (parasitic fungi on mustard)

2.3.2:. Ascomycetes (Commonly known as sac fungi):

Occurrence: They are terrestrial saprophytes, which grow on a variety of organic remains including dung
(coprophilous).
Mycelium:
o Yeasts are unicellular and penicillium are multicellular
o Mycelium is branched and septate.
Reproduction:
Asexual reproduction: Conidia are characteristic asexual spores of ascomycetes which develop exogenously over
the terminal ends of special hyphae called conidiophores.
Sexual reproduction:
o Sexual spores are called ascospores, which are produced endogenously in sac like
asci (singular: ascus).
o These asci are arranged in different types of fruiting bodies called ascocarps.
Ex: Aspergillus, Claviceps, Neurospora.
(Note: Neurospora is used extensively in biochemical and genetic work).

2.3.3:. Basidiomycetes: (Bracket fungi)

Occurrence:
 Basidiomycetes are terrestrial saprophytes and parasites.
 They are best decomposers growing on soil, logs and tree stumps.
 Rusts and smuts are diseases caused by parasitic forms.

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Mycelium: Mycelium is branched and septate.
Reproduction:
Asexual reproduction:
 Asexual spores are not found.
 Vegetative reproduction by fragmentation is common
Sexual reproduction:
 Sex organs are absent.
 Plasmogamy is brought about by fusion of two vegetative or somatic cells of
different strains or genotypes.
 The resultant structure is dikaryotic which ultimately gives rise to basidium.
 Karyogamy and meiosis takes place in the basidium producing four basidiospores.
 Basidiospores are exogenously produced on the basidium (pl.: basidia).
 The basidia are arranged in fruiting bodies called basidiocarps.
Ex: Puccinia (rust fungus), Ustilago (smut fungus), Mushroom, puff ball, bracket fungi.

2.3.4: Deuteromycetes: (Imperfect fungi)

 Commonly known as imperfect fungi, because sexual reproduction is absent and only the asexual or vegetative
phases of these fungi are known.
 The deuteromycetes reproduce only by asexual spores known as conidia.
 The mycelium is septate and branched.
 Some members are saprophytes or parasites while a large number of them are decomposers of litter and help in
mineral cycling.
Ex: Alternaria, Colletotrichum, Trichoderma.

2.6: Viruses, Viroids and Lichens:

Viruses:
Viruses are ultra microscopic nucleoprotein obligate parasitic entities which are active only inside living cells. They
are inert outside the host cell.
Historical accounts:
o The term virus (virus-poison) was coined by Pasteur (1880).
o D.J. Ivanowsky (1892) is credited with the discovery of virus, as he found that the disease, tobacco mosaic is
caused by a microbe smaller than bacteria.
o M. W. Beijerinek (1898) found that the extract of infected tobacco plants could cause infection in healthy plants.
He called the fluid extract as contagium vivum fluidum (Infectious living fluid)

o W. M. Stanly (1935) showed that viruses (TMV) could be crystallized and crystals consist largely of proteins.
Structure:
A virus is a nucleoprotein and the genetic material is infectious.
Capsid:
1. It is protein coat of virus.
2. It protects the genetic material of the virus.
3. Capsid is made of number of protein units called capsomeres.
Capsomeres are arranged in helical, polyhedral, or different geometrical forms.

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Nucleoid:
1) It is the genetic material of virus which either DNA or RNA but never both.
2) It is the infectious part of the virus.
3) It is single stranded RNA in many plant viruses.
4) Animal viruses have single /double stranded RNA or double stranded DNA (dsDNA).
5) Bacteriophages or bacterial viruses generally posses double stranded DNA (dsDNA).
Viral diseases of humans:
Mumps, chicken pox, small pox, Influenza, Herpes, common cold, AIDS, Polio
Viral diseases symptoms in plants:
Mosaics, leaf rolling and curling, yellow and vein clearing, dwarfing and stunted growth.

Viroids (T.O Diener, 1971)

o Viroids are smaller than viruses.
o Viroids are infectious agent with naked RNA.
o Viroids are lack of protein coat, that found in viruses.
o They have low molecular weight.
o It causes the potato spindle tuber disease.

Lichens:
Lichens are symbiotic associations (mutually useful associations) between algae and fungi.
 The algal component is called phycobiont. It is photosynthetic and forms food, not only for itself but also the
fungus.
 The fungal component is called mycobiont. The mycobiont absorbs water and mineral salts to its partner.
 Lichens occur in diverse habitats, over stones, rocks, walls, tree trunks, sand & soil.
 Lichens are very good pollution indicators- they don’t grow in polluted areas.

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