Biological classification NCERT biology chapter 2 notes.pdf

Biological Classification :- Class 11th biology
NCERT book chapter-2 notes
Science GyanMonday, September 05, 2022
BIOLOGICAL CLASSIFICATION
Biological classification is the scientific ordering of organism in a hierarchical
series of groups, on the basis of their relationship- morphological, evolutionary
and others.
Advantages of Biological classification:
· It makes their study convenient.
· It facilitates identification of organisms.
· It revels relationship among the various groups of organisms.
· It also enables the biologist to interpret the orderly visible structure of the fossil
organism.
· It gives information about the plants and animals which do not occur in one’s own
locality.

· It revels evolutionary trends by showing gradually increasing complexity of structure
in the various groups of organisms.
Aristotle was the earliest to attempts a more scientific basis for classification. He
used simple morphological (study of external structure of organism) characters
to classify plants into tress, shrub and herbs.
He also divided animals on the basis of presence of red blood cells into two
groups, those which had red blood (Enaima) and those that did not (Ananima).
TWO KINGDOM CLASSIFICCATION:
· Two kingdom classification is given by Swedist Naturalist Carolus Linnaeus.
· In this classification the organisms are classified into two kingdoms Plantae and
Animalia.
· In this classification bacteria and fungi were placed in the plant kingdom, Unicellular
eukaryotes (protistans) were placed among animals.
· Euglena is a unicellular eukaryotic organism placed into both plant and animal
kingdom, because euglena behaves like plant in presence of sun light
(photosynthetic) and in absence of sunlight they behave like animal (parasite).
THREE KINGDOM CLASSIFICATION:
· Three kingdom classification is proposed by Ernst Hackle.

· He introduced a new kingdom ‘Protista’.
· He classified organisms into Plantae, Animalia and Protista.
· He placed unicellular eukaryotes in a separate kingdom Protista.
· In this kingdom bacteria, fungi, diatoms and protozoans are placed into kingdom
Protista.
FOUR KINGDOM CLASSIFICATION:
· Four kingdom classification is proposed by Herbert F. Copeland.
· He introduced another new kingdom known as Monera.
· He classified organism into Plantae, Animalia, Protista and Monera.
· He placed bacteria and blue green algae in this kingdom.
· In this kingdom fungi are placed into kingdom Plantae, unicellular eukaryotes into
Protista and bacteria into kingdom Monera.
DRAWBACKS OF TWO KINGDOM CLASSIFICATION:
· This system does not distinguish between the eukaryotes and prokaryotes,
unicellular and multicellular organisms and photosynthetic (green algae) and
non-photosynthetic (fungi) organisms.

· Euglena has both animal and plant features. Euglena has dual mode of nutrition
called mixotrophic nutrition.
· Chlamydomonas is a unicellular motile (motile means- the organisms which can
move with the help of flagella) algae has fixed shape and possesses a
photosensitive organelle like the animals and is autotrophic like plants.
· This classification system included bacteria, blue-green algae, fungi, mosses, ferns,
gymnosperms and the angiosperms under plants. The character that unified this
whole kingdom was that all the organisms included had a cell wall in their cells.
· Fungi lack chlorophyll and are saprotrophic unlike the typical plants, yet they are
kept in plant kingdom.
● Therefore, the two-kingdom classification is inadequate and unjustified. It
does not indicate the gradual evolution of early organism into plants and
animals.
● A need was also felt for including, besides gross morphology, other
characteristics like cell structure, nature of cell wall, mode of nutrition,
habitat, method of reproduction, evolutionary relationship, etc.
FIVE KINGDOM CLASSIFICATION:
· Five kingdom classification was proposed by R.H Whittaker in 1969.
· He classified organisms into Plantae, Animalia, Protista, Fungi and Monera.
· He basically introduced another new separate kingdom ‘Fungi’.

· The main criteria for classification used by him includes cell structure, thallus
organisation, mode of nutrition, reproduction and phylogenetic relationship.
Representatives of five kingdoms:
● Plantae: Algae, Liverwort, Mosses, Ferns, Gymnosperms and Angiosperms.
● Animalia: Sponges, Cnidarians, Worms, Arthropods, Mollusca's, Echinodermata,
Hemicordate, and Chordate.
● Protista: Chrysophyta, Dinoflagellates, Euglenoids, Slime moulds and Protozoans.
● Fungi: Phycomycetes, Ascomycetes, Basidiomycetes and Deuteromycetes.
● Monera: Archaebacteria, Eubacteria and Cyanobacteria.
Drawbacks of five kingdom classification:
● The kingdoms Monera and Protista are still heterogenous group. Both photosynthetic
and non-photosynthetic forms and organisms with cell wall and without cell wall.
● Unicellular green algae, such as Chlamydomonas, Volvox, have not been included in
the kingdom protista.

● The slime moulds are quite different from the other protists with which they have
been combined.
KINGDOM MONERA:
● The kingdom monera includes the most ancient, the smallest, the simplest and
the most plentiful prokaryotes. (prokaryotes - without nuclear membrane)
● The nuclear material includes bacteria, cyanobacteria, archaebacteria and
some smallest group of organism like mycoplasma, rickets, actinomycetes,
etc.
● Bacteria are the sole members of the kingdom Monera.
● They are the most abundant micro-organisms, occur almost everywhere.
ABOUT BACTERIA:
● Bacteria are minute, unicellular, microscopic, simple, undifferentiated prokaryotic
organisms which are usually identified by their specific activities and not by their
general appearance.
● Bacteria were discovered by Antony Von Leeuwenhoek after inventing the
microscope.
● He gave the term animalcules to the bacteria sue to their small size and motility.
● Term Bacteria was given by Ehrenberg in 1838.
● In 1850, Louis Pasture laid the scientific foundation of Bacteriology (Branch of
biology that deals with study of Bacteria) by developing culture techniques
and method of sterilization.
● Father of Bacteriology :- Antony Von Leeuwenhoek.
● Father of modern microbiology :- Robert Koch.
● Louis pasture made a detailed study of bacteria and proposed germ theory of
disease.
● Pasteurization theory was proposed by Louis Pasture.
Pasteurization : It is the heat treatment process that destroys pathogenic (diseases
causing organisms) microorganisms in certain foods and beverages.

Germ theory : Proposed by Robert Koch and Louis Pasture.
'Every human disease is caused by a microbe or germ, which is specific for that
disease and one must be able to isolate the microbe from the diseased human being'.
OCCURENCE:
● Bacteria are ubiquitous, i.e., they occur everywhere, in water, in air, soil, in all living
organisms except the pits of volcanoes, deep strata of rocks, tops of high mountains
and blood of healthy animals.
● Thermophilic sulphur bacteria / marine archaebacteria can withstand the
temperature up to 100-150 degree Celsius.
● Psychrophilic bacteria occur up to the temperature of -190 degree Celsius.
SIZE:
● The average size of bacterial cell ranges from 1 micro meter to 10 micro meter in
length and 0.7 micro meter to 1.5 micrometer in width.
● Smallest known bacterium is Dialister Pneumonsintes (0.15 - 0.3 micro meter).
● Smallest bacterium without cell wall is Mycoplasma.
● Largest known bacterium is recently discovered bacterium Thiomargarita
namibiensis.
SHAPE:
● The bacteria possess the following forms:
1. Coccus: The coccus bacteria are spherical, ellipsoidal or oval is shape.
2. Bacillus: The bacillus bacteria are straight rod shaped or cylindrical. The ends may
be pointed, flat, concave or convex.
3. Spirillum: The spirillum bacteria are spiral ribbon like or coiled like a cork-screw.
The spirillum forms are usually rigid and bear two or more flagella at one end or both
the ends.

4. Vibrio: The bacteria are rod shaped with single curve, c-shaped or comma shaped.
They have one or more flagella at one pole.
5. Filament: The body of bacterium is filamentous like a fungal mycelia.
6. Stalked: The body of bacterium possess a stalk.
7. Budded: The body of bacterium is swollen at places.
● Types of flagellation in bacterial cell:
1. Atrichous: Flagella absent.
2. Monotrichous: Single flagellum attached to one end.
3. Cehalotrichous: Many flagella attached at each of the two ends.
4. Lophotrichous: A groups of flagella attached at each of the two ends.
5. Amphitrichous: Single flagellum attached at each of the two ends.
6. Peritrichous: Flagella are attached all over the body.
● Bacterial flagella are made up of flagellin protein.
● Bacterial flagella differ from the eukaryotic flagella. Bacterial flagella have not
9+2 arrangement.
● Bacterial flagella is a wavy helical or rope like structure.
● A cross section of the bacterial flagellum revels that there are 8 flagellum
molecule surrounding a central hollow cylinder.
● A bacterial flagellum is usually 4-5 micrometer long and 120-185 Angstrom in
diameter.
BACTERIAL CELL STRUCUTRE:
1. Surface Adnerents (Capsules and Slime layers):
2. Cell wall
3. Plasma membrane
4. Cytoplasm
5. Nucleoid
6. Plasmid
1. SURFACE ADERENTS (Capsule and slime layers):

● The bacterial cell may be covered by a polysaccharide coat.
● When this covering may is in the form of loose mass, it is called a slime or
slime layer.
● Slime is the gelatinous substance secreted by the protoplast and deposited over the
cell wall.
● In case of some virulent bacteria, the nitrogenous substances are also present
in addition to polysaccharides so that the slime layer becomes thick, called
Capsule.
● The capsule protects Bacterial cell from phagocytosis, drying and attack of
bacteriophages.
● The capsulated bacteria are usually non-flagellated.
2. CELL WALL:
● Bacterial cell wall is the outer rigid and tough covering of the cell, which provides
shape and protection to the protoplast and keeps the cell wall from bursting or
collapsing dur to osmotic change.
● The bacterial cell wall made up of peptidoglycan or glycopeptide or micro-peptide or
murine and mucopeptide.
● Mucopeptide is a polymer of two amino sugars: (i) N-acetyl Glucosamine & (ii)
N-acetyl muramic acid.
● One of the major components of cell wall of bacteria is peptidoglycan or
mucopeptide or murine.
On the basis of staining of bacteria, Christian Gram divided bacteria into two groups:
a) Gram Positive Bacteria: The bacteria which retain the purple stain during staining are
called Gram Positive Bacteria.
● The cell wall of gram positive bacteria is about 250 - 300 Angstrom.
● The cell wall of gram positive bacteria is homogenous, single layered, more rigid and
made up of mucopeptide (80%) and teichoic acid (5-10 %) .
● Spore producing forms included.

● Flagellum usually absent in gram positive bacteria.
● May produce exotoxins. Sensitive to penicillin.
b) Gram Negative Bacteria: Those bacteria which become decolourised are called as
Gram negative bacteria.
● The cell wall of gram negative bacteria is thin about 100 Angstrom, less rigid, three
layered and heterogeneous.
● Cell wall made up of lipoprotein, lipopolysaccharide and mucopeptide.
● Teichoic acid is absent in gram negative bacteria.
● No spore producing form. Flagella usually absent.
● Manny produce endotoxins, not sensitive to penicillin.
The enzyme lysozyme can dissolve the bacterial cell wall.
Teichoic acid present in cell wall of gram positive bacteria are acetic polymers
consisting of a carbohydrate, phosphate and an alcohol.
Teichoic acid have several function such as binding metals, acting as a receptor site
for some viruses and maintaining cell at low pH to prevent degradation of cell walls
by itself produced enzymes.
Function of outer cell envelope:
● Prevent the entry of harmful and toxic chemical that could damage the cell.
● Maintaining the permeability to nutrient by channels made up of porin proteins.
3. PLASMA MEMBRANE / CELL MEMBRANE:
● Each bacterial cell has plasma membrane situated just internal to the cell wall.
● The plasma membrane of a bacteria is trilayered membrane about 75 angstrom in
thickess.

● It is a thin, elastic and differentially or selectively permeable membrane that allows
passage of dissolved substances in and out of the cell wall.
● Plasma membrane is the principal osmotic and permeability barrier.
● The plasma membrane is a lipoprotein structure consisting large amount of
phospholipid, protein and some amounts of polysaccharides bur lacks sterols.
● The cell membrane maintains the cell turgor.
● The plasma membrane of bacteria provides site for most of the anabolic and
catabolic pathways.
STRUCTURE ASSOCIATED WITH PLASMA MEMBRANE :
a) Mesosomes b) Flagella c) Pilli d) Fimbrae
a) MESOSOMES:
● Fitz coined the term 'Mesosome'.
● Mesosome are the characteristic infolding of cell membrane invading the cytoplasm.
● These are finger like, spherical or villiform structure which may help in
compartmentalization of the cell.
● Mesosomes helps in the cell wall formation, DNA replication and distribution to
daughter cells. They also help in respiration, secretion process, to increase the
surface area of the plasma membrane and enzyme comtent.
Mesosomes are of two types:
i) Peripheral Mesosome:
● They show only little penetration in the cytoplasm.
● On the surface of the peripheral mesosome found enzymes associated with
respiration.
● Therefore they are supposed to be analogous to the mitochondria of eukaryotes.

ii) Central Mesosome:
● They penetrate deeply into the cytoplasm, are located near the middle of the cell wall
and seem to be attached to the cell's nuclear material.
● These are thought to be involved in DNA replication and septum formation during the
process of cell division.
In some prokaryotes like cyanobacteria, there are other membranous extensions into
the cytoplasm called chromatophores which contain pigments.
Another photosynthetic structure in bacteria are the photosynthetic lamellae and
chlorobium vesicles.
Photosynthetic lamellae possess all the essential pigments for light reaction but no
enzyme for dark reaction.
Complete notes visit: https://bioinfotec.blogspot.com

Biological classification NCERT biology chapter 2 notes.pdf

More Related Content

What's hot

Biological classification NCERT biology chapter 2 notes.pdf