Biologicalclassification

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Biological classification

Biological Classification is the scientific

study of arranging organisms into group and subgroup on the basis of their similarities and

dissimilarities and placing the group in a hierarchy of categories.

The purpose of biological classification is to organise the vast number of known plants into

categories that could be named, remembered and studied.

Objectives of classification

To identity and describe all the possible types of species.

To arrange the species in various categories on the basis of their similarities and

dissimilarities.

To evolve a truly natural or phylogenetic system which should indicate origin and evolution

of the species.

Helping in easy identification of organisms.

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Types of Biological Classification

There are three main types of classificationartifical, natural and phylogenetic:

Artificial system of classification

It is a system of classification which uses one or two morphological character for grouping of

organisms. Some artificial system have used habot and habitat for this purpose. Aristotle (c

350 BC) divided animals into two categories, enaima (with red blood) and anaima (without red

blood). Aristotle also classified animals on the basis of their habitat aquatic (e.g, fish, whale),

terrestrial (e.g, reptiles, cattle) and aerial (e.g. birds, bat). Pliny the Elder (2379 A.D.) used

artificial system of classification for both plants and animals dividing them into land, air and

water. Pliny distinguished animals into flight band nonflight ones. Flight animals included bats,

birds and insects.

Natural system of classification

It is a system ofclassification which takes into consideration comparable study of a number of

characters so as to bring out nature similarities and dissimilarities and hence nature

relationship among the organisms. The system employs those characters which are relatively

constant. They include morphological characters, anatomical characters, cytological

characters, physiology, ontogeny or development, reproduction, cytochemistry and

biochemistry, experimental taxonomy, etc. the characteristics are helpful in bringing out

maximum numberof similarities in a group and comparable differences with other group of

organisms. For example, mammals are charactriesed by the presence of mammae, birds

possess wings, feathers, pneumatic bones, ovipary, 4 chambered. They are coldblooded.

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Homology is the relationship of comparable structures having been derived from a

common form. For example, the fore arm of different land vertebrates has the

same pentadactyl constition.

Molecular homology is the finding of relationship of comparable molecules like

DNA, RNA and proteins by studying their similarities and dissimilarities. Even

certain biochemicals occur in specific group, e,g. betacyanin is found in beet root

and related plantes. The branch of biology that utilizes the study of chemicals in

classification is called chemotaxonomy. Chromosomes or karyotypes are also

important for knowing natural relationships.

Phylogenetic System Of Classification

Classification based on evolutionary relationship of organisms is called phylogenetic system

of classification. It is based on the evolutionary concept from darwin’s book on the origin of

species by means of natural selection. The preservation of favoured races in the struggle for

life (1859). It reflects the true relationships among the organisms. First phylogenetic system

was proposed by Engler and Prantl (188799). Zoologists believe that since similarity in

structure represents close evolutionary relationship, their natural classification represents

evolutionary and phylogenetic classification.

History of Classification:

1. Aristotle: Father of biology & father of zoology.

2. Theophrastus:

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He is known as father of ancient plant taxonomy

and father of botany.

Theophrastus wrote many books on 'plants.

Few of them are as follows:

(a) Historia plantarum

(b) Causes of plants

(c) Enquiry into plants

Theophrastus gave names and descriptions of 480 plants in his book Historia

plantarum.

Theophrastus proposes the first classification of plant kingdom. He classified plant

kingdom in to four groups on the basis of growth habit. (a) Trees (b) Shrubs (c)

Under shrubs (d) Herbs

3. Carolus Linnaeus: [1707 – 1778]

He is known as father of taxonomy, father of plant taxonomy and father of animal

taxonomy.

Linnaeus gave the two kingdom system classification. He grouped plants and

animals into kingdom plantae and kingdom Anirnalia respectively.

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Linnaeus wrote many books. Some important books are:

(1) Hortus uplandicus First book

(2) Flora lapponica

(3) Philosophia botanica

(4) Critica botanica

(5) Systema naturae (1737)

(6) Genera plantarum

(7) Species plantarum last book (1753)

4. A.P. De Candolle:

He wrote the book "Theories

Elementaire de la botanique”

He was the first to propose the significance of vascular tissue in taxonomy. On this

basis of vascular tissue he classified plants into two groups

(a) Cellular plants (Non vascular plants) This group includes Thallophyta and Bryophyta

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(b) Vascular plants This group includes Pteridophyta, Gymnosperm and Angiosperms.

5. George Bentham (1800 1884) and Joseph Dalton Hooker (1817 1911):

Both Bentham and Hooker were related to Royal botanical garden.

They wrote the book "Genera plantarum" (1862 1883).

In this book, Bentham and Hooker gave the biggest and natural classification of

spermatophyta i.e. plants with seeds

In Genera plantarum, there is description of 202 families. In it, basically the

description of plants with seeds is present.

6. A. W. Eichler:

Syllabus de vorlesungen uber phanerogamen kunde Book written by Eichler.

In this book, Eichler gave the first phylogenetic classification of plant kingdom.

The classification of Eichler is very little phylogenetic.

In this way Eichler classified plant kingdom into five divisions and arranged them in

the order of evolution (Phylogeny).

7. Engler (1844 1930) & Pranti (1849 1893):

Book "Die Naturlichen Pflanzen Familien".

He gave the phylogenetic classification of plant kingdom. This classification was

more phylogenetic as compared to Eichler's classification.

8. Oswald Tippo:

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Proposed the biggest phylogenetic classification of plant kingdom.

This classification is the complete classification of plant kingdom.

This is the most acceptable classification for books and study.

(a) Cyanophyta:B.G. Alage

(b) Euglenophyta:Euglenoids

(c) Chlorophyta:Green algae

(d) Chrysophyta:Yellowgreen algae

(e) Pyrrophyta:Dinoflagellates & Diatoms

(f) Phaeophyta:Brown algae'

(g) Rhodophyta:Red algae

(h) Schizomycophyta:Bacteria

(i) Myxomycophyta:Slime molds (False fungi)

(j) Eumycophyta:True fungi

9. Karl Menz:

He showed the importance of serology in taxonomy.

Similarities and dissimilarities in stru. of proteins help to know the phylogenetic

relationship of living beings. Living organisms which are phylogenetically close

relatives have more similarities in their proteins.

Organisms which are distantly related have different proteins.

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(1) First tissue was originated in animal kingdom in → Coelentrata

(2) First tissues was originated "in plant kingdom in → Bryophyta

(3) Phylogenetic relationship of plants and animals can be established by animal serum.

Serology indicates that chimpanzee is closest relative of man.

10. Haeckel:

Haeckel gave the three kingdom (Protista, Plantae, Animalia) system of

classification.

Haeckel established the kingdom Protista.

Haeckel grouped those living organisms in Protista which did not have tissues.

Kingdom Protista: Prokaryotes, Protozoa, porifera, Algae & fungi

Five kingdom classification (from 1969 to 1990)

In order to develop phylogenetic classification, R.H. Whittaker (1969), an American

taxonomist, divided all the organisms into five kingdoms. As the viruses are on the border line

of living and nonliving, they have been left out. Whittaker has used five criteria for delimiting

the different kingdoms.

1) Complexity of cell structure, prokaryotic and eukaryotic .

2) Complexity of body structure or structural organization, unicellular and multicellular.

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3) Mode of nutrition which is divergent in multicellular kingdoms photoautotrophy in plantae,

absorptive heterotrophy in fungi and ingestive heterotropy in animalia. Photoautotrophy

totrophic nutrition is also calledholophytic nutrition while ingestive heterotrophy is known as

holozoic nutrition. Absorptive heterotropy issaprobiotic (=saprophytic ) nutrition.

4) Ecological life style like producers (plantae), decomposers (fungi) and consumers

(animalia).

5) Phylogenetic relationships.

Whittaker’s five kingdoms are monera, protista, plantae, fungi and animalia.

Table. Characteristics of five kingdom S.N

O

CHARACTE

RS

MONERA PROTIST

A

FUNGI PLANTAE ANIMALIA

1 Cell type prokaryotic Eukaryotic Eukaryotic Eukaryotic Eukaryotic

2 Cell wall Noncellulosi

c

polysacchari

de+ amino

acid)

Present in

some

(various

types)

Present

(non

cellulosic)

Present

(cellulose)

absent

3 Chloroplast Absent Present in

some

Absent Present Absent

4 Mitochondri

a

Absent Present in

some

Persent Present Present

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5 Nuclear

membrane

Absent Present Present Present Present

6 Tissue or

multicellulari

ty

Absent Absent Present but

limited

Present in

all forms

Present in all

forms

7 Motility Bacterial

flagella,

gliding or

nonmotile

Cilia,flagell

a

amoeboid

or

contractile

fibrils

Cilia,

flagella in

some, none

in most of

the forms

Cilia and

flagella in

lower forms,

absent in

most of the

forms

Cilia and

flagella,contrac

tile fibrils

8 Mode of

nutrition

Autotrophic

chemosynth

etic and

photo

synthetic,

heterotrophic

(saprophytic

and

parasitic)

Phosynthe

sis and

heterotrop

hic

Heteroprop

hic,

saprophytic

and

parasitic

absorptive

Autotrophic

by

photosynthe

sis

Heterotrophic

by ingestion

9 Reproductio

n/ means of

genetic

Conjugation

transduction

Syngamy

and

meiosis,

Fertilization

and

meiosis,

Fertilization

and meiosis

Fertilization

and meiosis

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recombinati

on

transformatio

n or none

conjugatio

n or none

dikaryosis

or none

10 Nervous

system

Absent Primitive

for

conduction

stimuli

Absent Absent Present, often

complex

Three Domains of Life (Six Kingdom Classification) 1990

The three domain system is a biological classification which was introduced by

Carl Woese, a professor in the department of microbiology, university of Illinois,

Urbana Champaign in 1990 that divides cellular life forms into archaea, bacteria

and eukarya domains.

It emphasizes the separation of prokaryotes into two groups, originally called

eubacteria (now bacteria) and archaebacteria (now archaea) because of their

fundamental differences, Woese argued that each of the two arose separately from

an ancestor with poorly developed genetic machinery, often called a progenote.

In fact the threedomain system is loosely based on the traditional five kingdom

system but divides the monera into two ‘’domains’’, leaving the remaining

eukaryotic kingdoms in the third domain.

It is actually a six kingdom classification.

(1) Archaea domain:

The demain contains prokaryotic organisms which have a monolayer core of lipids in the cell

memebrane and distinct nucleotides in their 16S RNA. It contains a single kingdom.

Kingdom archaebacteria

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The kingdom contain early prokaryotes which live in extreme environments,

For Example:

(a) Methanogens metabolize hydrogen and carbon dioxide into methane.

(b) Halophiles live in salt.

(c) Thermoacidophiles – live in acid high temperatures (upto 110 degrees Celsius).

(2) Bacteria domain:

The domain contains prokaryotes which lack membrane covered cell organelles but do have a

sort of micro chambers for separating various activities. There is a single kingdom.

Kingdom eubacteria:

The domain contains diverse type of bacteria having peptidoglycan cell wall, glycogen as food

reserve,naked DNA coiled to form nucleoid, absence of sap vacuoles and presence of 70S

ribosomes. Some common group are bacteria, mycoplasma, ctinomycetes, rickettsiae,

spirochaetes, firmicutes, cyanobacteria.

(3) Eukarya domain. The domain contains eukaryotic organisms which originated by

endosymbiotic association between some archaebacteria and eubacteria. It has four

kingdoms protista, fungi, plantae and animalia.

Viroids (L. Virus point, EIos – diminutive)

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They are the smakkest seif replicating particles which were discovered by Diener

(1971).

They are obligate parasites.

Molecular weight of a viroid is low.

The RNA is tightly folded to form circular or linear structure.

Viroids are known to cuse diseases (some 20) in plants only, e,g,. potato spindle

tuber, chrysanthemum stunt. Animal or human infection is not known.

Viroud does not production is not very clear. Viroids particle can multiply by both

RNA development and DNA dependent replication.

Prions (Prusiner,1983)

They are highly resistant glycoprotein particles which function as infectious agents.

They are formes due to mutation in gene PRNP.

They can also act as catalyst converting normal protein into prion state.

Prions are not affected by proteases, nucleases, temperature up to 800OC, UV

radiations and formaldehyde.

Prions accumulate in nervous tissue and bring its degeneration. Common diseases

caused by them are scrapie of sheep, mad cow disease, cruetzfeldtjakob disease

(CJD) and kuru.

KINGDOM MONERA

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(1) Bacteria are the sole members of the Kingdom

Monera.

(2) Bacteria are grouped under four categories based on their shape: the spherical Coccus,

the rodshaped Bacillus, the commashaped Vibrium and thespiral Spirillum.

(3) Compared to many other orgarusrns, bacteria as a group show the most extensive

metabolic diversity.

(4) They may be photosynthetic autotrophic or chemosynthetic autotrophic. Some of the

bacteria are autotrophic, i.e., they synthesise their own food from inorganic substrates.

(5) The vast majority of bacteria are heterotrophs, i.e.; they do not synthesise their own food

but depend on other organisms or on dead organic matter for food.

Characteristics of monera

Monera (Monos single) includes prokaryotes and shows the following characters:

They are typically unicellular organisms (but one group is mycelial).

The genetic material is naked circular DNA, not enclosed by nuclear

envelope.Ribosomes and simple chromatophores are the only subcellular

organelles in the cytoplasm.

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The ribosomes are 70 S.

Mitochondria, plastids, golgi apparatus, lysosomes, endoplasmic reticulum,

centrosome, etc., are lacking.

Sap vacuoles do not occur. Instead, gas vacuole may be present.

The predominant mode of nutrition is absorptive but some groups are

photosynthetic (holophytic) and chemosynthetic.

The organisms are nonmotile or move by beating of simple flagella or by gliding.

Flagella, if present, are composed of many, intertwined chains of a protein flagellin.

They are not enclosed by any membrane and grow at the tip.

Moneran cells are microscopic (1 to few microns' in length).

Most organisms bear a rigid cell wall (Peptidogl yean).

Reproduction is primarily asexual by binary fission' or budding.

Mitotic apparatus is not formed during cell division.

Monera is a kingdom of prokaryotes. Therefore, it is also known as procaryota.

It includes the most primitive form of life which developed from an early stock

known as progenote.

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Being the earliest forms of life, monerans are adapted to all types of habitats.

Bacteria shape

Cocci: They are oval or spherical in shape. They are called micrococcus when

occur singly as in Micrococcus, diplococcus when found in

pairs as in Diplococcus pneumoniae, tetracoccus in fours, streptococcus when

found in chains as in Streptococcus lactis staphylococcus when occurring in grape

like clusters as in Staphylococcus aureus and Sarcine, when found in cubical

packets of 8 or 64 , as in Sarcina.

Bacilli: They are rodshaped bacteria with or without flagella. They may occur singly

(bacillus), in pairs (diplobacillus) or in chain (streptobacillus).

Vibrios: These are small and 'comma or kidney' like. They have a flagellum at one

end and are motile, vibrio bacteria has curve in its cell e.g., Vibrio cholerae.

Spirillum: They are spiral or coiled like a corkscrew. The spirillar forms are usually

rigid and bear two or more flagella at one or both the ends e.g., Spirillum,

Spirochaetes etc.

Filament: The body of bacterium is filamentous like a fungal mycelia. The filaments

are very small e.g., Beggiota, Thiothrix etc.

Stalked: The body of bacterium possesses a stalk e.g., Caulobacter.

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Budded: The body of bacterium is swollen at places e.g., Rhodomicrobiu

Structure of bacteria

(1) Capsule: In a large number of bacteria, a slimy capsule is present

outside the cell wall. It is composed of polysaccharides and the nitrogenous substances

(amino acids) are also present in addition. This slime layer becomes thick, called, capsule.

The bacteria, which form a capsule, are' called capsulated or virulent bacteria. The capsule 'is

usually found in parasitic forms e.g., Bacillus, anihracis, Diplococcus pneumoniae,

Mycobacterium tuberculosis.

(2) Cell wall: All bacterial cells .are covered by a strong, rigid cell wall. Therefore, they are

classified under plants. Inner to the capsule cell wall is present. It 'is made up of

polysaccharides, proteins and lipids.In the cell wall of bacteria there are two important sugar

derivatives i.e., NAG and NAM (Nacetyl glucosamine and Nacetyl muramic acid) and

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besides L or D alanine, Dglutamic acid and diaminopimelic acid are also found.

(3) Plasma membrane: Eachbacterial cell has plasma membrane situated just internal to the

cell wall. It is a thin, elastic and differentially or selectively r permeable membrane. It is

composed of large amounts of phospholipids, proteins and some amounts of polysaccharides

but lacks sterols. It is characterised by possessing respiratory enzymes.

(4) Cytoplasm: The cytoplasm is a complex aqueous

fluid or semifluid ground substance (matrix) consisting of carbohydrates, soluble proteins,

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enzymes, coenzymes, vitamins, lipids, mineral. salts and nucleic acids. The organic matter is

in the colloidal state.The cytoplasm is granular due to presence of a large number of

ribosomes. Ribosomes in bacteria are found' in the form of polyribosome.Membranous

organelles such as mitochondria, endoplasmic reticulum, golgi bodies, lysosomes and

vacuoles are absent. In some photosynthetic bacteria the plasma membrane gives rise to

large vesicular thylakoids which are rich in bacteriochlorophylls and proteins.

(5) Nucleoid: It is also known as genophore, naked nucleus, incipient nucleus. There is

nuclear material DNA which is double helical and circular. It is surrounded by some typical

protein (polyamine) but not histone proteins. Histones (basic proteins) are altogether absent itt

bacteria. This incipient nucleus or primitive nucleus is named as nucleoid or genophore.

(6) Plasmid: In addition to the normal DNA chromosomes many bacteria (e.g., E.coli) have

extra chromosomal genetic elements or DNA. These elements are called plasmids. Plasmids

are small circular double stranded DNA molecules. The plasmid DNA replicates

independently maintaining independent identity and may carry some important genes.

Plasmid terms was given by Lederberg (1952). Some plasmids are integrating into the

bacterial DNA chromosome called episomes.

(7) Flagella: These are fine, threadlike, protoplasmic appendages which

extend through the cell wall and the slime layer of the flagellated bacterial cells. These help in

bacteria to swim about in the liquid medium.Bacterial flagella are the most primitive of all

motile organs. Each is composed of a Single thin fibril as against the 9+2 fibrillar structure of

eukaryotic cells. The flagellum is composed entirely of flagellin protein.

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(8) Pili or Fimbriae: Besides flagella, some tiny or small hairlike outgrowths are present on

bacterial cell surface. These arecalled pili and are made up of pilin protein. They measure

about O.52mm in length and 35mm in diameter. These are of 8 types I, II, III, IV, V, VI, VII,

and F types. I to F are called sex pili. These are present in all most all gram ve bacteria and

few gram +ve bacteria. Fimbriae take part in attachment like holding the bacteria to solid

surfaces.The function of pili is not in motility but they help in the attachment of the bacterial

cells. Some sex pili acts as conjugation canals through which DNA of one cell passes into the

other cell.

Staining of bacteria

(1) Simple staining: The coloration of bacteria

by applying a single solution of stain to a fixed smear is termed simple staining. The ells

usually stain uniformly.

(2) Gram staining: This technique was introduced by Hans Christian Gram in 1884. It is a

specific technique which is used to classify bacteria into two groups Gram +ve and Gram ve.

The bacteria are stained with weakly alkaline solution of crystal violet. The stained slide of

bacteria is then treated with 0.5 percent iodine solution. This is followed by washing with

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water or acetone or 95% ethyl alcohol. The bacteria which retain the purple stain are called as

Gram +ve. Those which become decoloutised are called as Gram ve.

Differences Between Gram +ve Bacteria and Gram ve Bacteria S.No. Gram +ve Bacteria Gram ve Bacteria

1. They remain coloured blue or purple

with gram stin even washing with

absolute alcohol or acetone.

The bacteria di not retain the stain when

washed with absolute alcohol.

2. The wall is single layered. Outer

membrane is absent.

The wall is two layered. Outer membrane

is present.

3. The thickness of the wall is 2080nm. It is 812nm.

4. The lipid content of the wall is quite low. The lipid content of the wall is 2030%.

5. The wall is straight. The wall is wavy and comes in contact with

plasmalemma only at a few places.

6. Merein or mucopeptude content is

7080%

It is 1020%.

7. Basal body of the flagellum has two

rings of swellings.

Four rings of swellings occur in the basal

body.

8. Mesosomes are more promiment. Mesosomes are less prominent.

9. The bacteria are more susceptible to

antibiotics.

They are more resistant to antibiotics.

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10. Fewer pathogenic bacteria belong to

Gram+ve group.

Most of the pathogenic bacteria are Gram*

ve.

11. Porins are absent. Porins or hydrophilic channels occur in

outer membrane of cell wall.

12. Cell wall contains teichoic acids. Teichoic acids are absent.

Nutrition in bacteria

On the basis of mode of nutrition, bacteria are grouped into two broad categories. First is

autotrophic and second is heterotrophic bacteria.

Autotrophic bacteria: These bacteria are able to synthesize their own food from

inorganic substances, as green plants do. Their carbon is derived from carbon

dioxide. The hydrogen needed to reduce carbon to organic form comes from

sources such as atmospheric H2, H2S or NH3.

Heterotrophic bacteria: Most of the bacteria cannot synthesize their own organic

food. They are dependent on externalorganic materials and require atleast one

organic compound as a source of carbon of their growth and energy. Such bacteria

are called heterotrophic bacteria. Heterotrophic bacteria are of three

typesParasites, Saprotrophs and Symbionts.

Arhaebacteria

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They are a group of most primitive prokaryotes which are believed to have evolved immediately after theevolution of the first life.

They have been placed in a separate subkingdom or domain of archae by a

number of workers (e.g., woese, 1994).

Archaebacteria are characterised by absence of peptidoglucan in their wall. Instesd

the wall contains protein and noncellulosic polysaccharised.

It has pseudomurein in some methanogens.

Mycoplasma (PPLO)

Mycoplasmas ar mollicutes are the simplest and the smallest of the free living

prokaryotes.

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They discovered in pleural fluid of cattle suffering from pleuropneumonia (nocard

and roux, 1898).

The organisms are often called MLOs(pleuropneumonia like organisms).

The size ranges from 0.10.15um. a cell wall is absent. Plasma membrane forms

the outer boundary of the cell.

Due to the absence of cell wall the organisms can change their shape and are

pleomorphic.

Cyanobacteria

(Blue green algae, Cyanophyceae, Myxophyceae)

Cyanobacteria or blue – green algae are gram (=) photosynthetic prokaryotes which

perform oxygenic photosynthesis.

Photosynthetic pigments include chlorophyll a, carotenoids and phycobilins.

Food is stored in the form of cyanophycean starch, lipid globules and protein

granules.

Cyanobacteria evolved more than 3 billion years back.

They added oxygen to the atmosphere and paved the path for evolution of aerobic

forms, including aerobic bacteria.

Difference Between Bacteria and Cyanobacteria S.No

.

Bacteria Cyanbacteria

1. The cells are comparatively smaller. The cells are comlarativey larger.

2. The cell wll is 12 layered. The cell wall is four layered.

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3. Plasmodemata and pores do not occur

in cell walls.

They are often present.

4. They exhibit lesser structural

elaboration.

They show higher degree of morphological

complexity as well as structural elaboration.

5. Bacteria are both autotrophic and

heterotrophic.

Cyanobacteria contain chlorophyll a as

found in eucaryotic autotrophs.

6. Autotrophic bacteria possess

bacteriochlorophyll.

Cyanobacteria contain chlorophyll a s

found in eukaryotic autotrophs.

7. Photosynthesis is anoxygenic. Photosynthetic is oxygenic.

8. Photoautotrophic bacteria do not contain

phycobilins.

They possess accessory water soluble

photosynthetic pigments known as

phycobilins.

9. Flagella may be present. Flagella are absent.

10. Carbohydrate reserve food is glycogen. Carbohydrate reserve food is a special

starch known as cyanophycean starch.

KINGDOM PROTISTA

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All Singlecelled eukaryotes are placed under Protista,

but the boundaries of this kingdom are not well defined.

Members of Protista are primarily aquatic.

This kingdom forms a link with the others dealing with plants, animals and fungi.

Being eukaryotes, the protistan cell body contains a well defined nucleus and other

membranebound organelles.

Some have flagella or cilia.

Protists reproduce asexually and sexually by, process involving cell fusion and zygote

formation.

It may be photosynthetic, holotrophic, saprotrophic, parasitic and symbionts. Some have

mixotrophic nutrition (holotrophic + saprobic).

The photosynthetic, floating protists are collectively called phytoplankton.

The freefloating, holozoic protozoans are collectively termed zooplankton.

Unicellular protists have been broadly divided in to three major groups:

(a) Photosynthetic Protists: Example: Dinoflagellates, Diatoms, Euglenoids

(b) Consumer Protists: Example: Slime moulds or Myxomycetes

(c) Protozoan Protists: Example: Zooflagellata, Sarcodina, Sporozoa, Ciliata

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Life cycles in Protists

“The sequence of events between any given phase in one generation and that similar phase

in the next succeeding generation constitute a life cycle.”

Two types of life cycle are found in protists:

(a) Life Cycle Showing Zygotic Meiosis:

It occurs in some dinoflagellates (Example: ceratium, gymnodinium; von stosch,

1973) and cellular slime moulds.

The zygote is 2n that divides by meiosis (also called zygotic meiosis) and

produces vegetative cells with 1n chromosome number.

These cells divide repeatedly by mitosis and all the resulting daughter cells

maintain the 1n number of chromosomes.

Some of the vegetative cells produce gametes.

When these gametes combine in fertilization, a zygote is formed and the life

cycle is completed.

(b) Life Cycle Showing Gametic Meiosis:

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This is found in the majority of protozoan protists, diatoms and acellular slime

moulds.

The organism spends most of its life cycle in the 2n condition.

The gametes are only 1n (haploid) that are produced by meiosis (also called

gemetic meiosis).

The gametes fuse to form zygote that grows to form the diploid individual.

Major Groups of Protists

Chrysophytes:

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This group includes diatoms and golden algae (desmids).

They are found in fresh water as well as in marine environments.

They are microscopic and float passively in water currents (plankton).

In diatoms the cell walls form two thin overlapping shells, which fit together as in a

soap box.

The walls are embedded with silica and thus the walls are indestructible. Thus,

diatoms have left behind large amount of cell wall deposits in their habitat; this

accumulation over billions of years is referred to as 'diatomaceous earth'.

Being gritty this soil is used in polishing, filtration of oils and syrups.

Diatoms are the chief 'producers' in the oceans.

Silicon is present in the frustule of diatoms.

Auxospones are formed by diatoms.

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Noctiluca dinoflagellate is called 'night light'.

Diatoms are emploid as a source of water glass or sodium

silicate.

Ganobacteria term was coined by IBCN (1978).

Dianoflagellates

These organisms are mostly marine and photosynthetic.

They appear yellow, green, brown, blue or red depending on the main pigments

present in their cells.

The cell wall has stiff cellulose plates on the outer surface.

Most of them have two flagella; one lies longitudinally and the other transversely in

a furrow between the wall plates.

Very often, red dianoflagellates (Example:Gonyaulax) undergo such rapid

multiplication that they make the sea appear red (red tides).

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Toxins released by such large numbers may even kill other marine animals such as

fishes.

Dinoflagellates reproduce asexually through cell division or by the formation of

zoospores and cysts.

The cell division starts from posterior end. During cell division, centromeres and

spindle are not seen. The spindle is replaced by cytoplasmic microtubules.

During mitosis, the chromosomes break up into pairs of chromatids. The nuclear

envelops and nucleolus persists during, division.

If sexual reproduction occurs, it is isogamous or anisogamous.

Two cells conjugate by a conjugation canal where the two amoeboid gametes fuse

to form a diploid zygote.

Life cycle involves zygotic meiosis (Example: Ceratium, Gymnodinium etc.) or

gametic meiosis (Example:Noctiluca).

Dinoflagellates, due to spinning caused by activity of

transverse flagellum (in cingulum/annulus) and longitudinal

flagellum (in sulcus), represent whorling whips.

Dinoflagellates with bioluminescence/phosphorescence due to

light producing protein luciferin are called fire algae. e.g.

Noctiluca, Pyrocystis, Pyrodinium etc.

Leeuwenhock (1674, 1675, 1681) was first to observe and

sketch protozoan protists including Vorticella and Giardia.

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Acellular organisms do not contain cellular structure e.g.,

viruses or not considered as cells but as complete organisms

e.g., protists.

Wallless multicellular protoplasm of acellular slime moulds

having branched veins and with process of cyclosis are

calledphaneroplasmodium.

Dinoflagellates symbionts in other protists and invertebrates

are called zooxanthellae.

Some dinoflagellates produce blooms or red tides. e.g.

Gonyaulax, Gymnodinium etc.

Euglenoids

Majority of them are fresh water organisms found in stagnant water.

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 a long one. The two flagella join with each other

at a swelling called paraflagellar body. An orange red coloured eyespot or stigma

is located at the base of flagellum attached to the membrane of reservoir at the

level of paraflagellar body.

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Both paraflagellar body; and eye spot act as photoreceptors and direct the

organism towards the optimum light.

Though they are photosynthetic in the presence of sunlight, when deprived of

sunlight they behave like heterotrophs by predating on other smaller organisms.

Interestingly, the pigments of euglenoids are identical to those present in higher

plants. Example: Euglena. They contain red pigment astaxanthin.

Nutrition is holophytic (photoautotrophic), saprobic (e.g., Rhabdomonas) or holozoic

(e.g., Peranema). Even holophytic forms can pick up organic compounds from the

outside medium. Such a mode of nutrition is called mixotrophic.

Euglena is a connecting link between animals and plants. Nutrition in Euglena is

mixotrophic, when light is available it is photosynthetic, in darkness it is saprophytic

absorbing food from surrounding water.

Slime Moulds

Slime moulds 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. The spores possess true walls. The spores are

dispersed by air currents.

They are extremely resistant and survive for many years, even under adverse

conditions.

Slime moulds are of two types:

(1) Acellular (Plasmodila) Slime moulds:

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Acellular slime moulds commonly grow as slimy masses on damp places rich in

dead and decaying r organic matter.

The somatic phase is diploid and consists of a free, living organic matter

multinucleated protoplasm called plasmodium.

The plasmodium slowly streams or glides over decaying organic matter putting out

blunt finger like pseudopodia showing amoeboid movement.

They also absorb dissolved organic substances from the substratum showing

saprotrophic nutrition.

Under unfavourable conditions the plasmodium contracts and gets surrounded by

thick horny wall. It is called sclerotium.

Each plasmodium reproduces asexually by the formation of several, small, sessile

or stalked, brightly coloured sporangia.

The multinucleated protoplasm of sporangium is cleaved to produce a large number

of small uninucleate spores.

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(2) Cellular Slime moulds

The cellular slime moulds occurs in the form of, haploid uninucleated, naked

(without cell wall) cell covered by plasma membrane.

These cells are called myxamoebae. The myxamoebae move freely with the help of

amoeboid movement and phagotrophic or holozoic nutrition.

They grow and divide to form a large population of individuals.

Under unfavourable condition a myxamoeba secrete a rigid cellulose wall to form

the microcyst. Microcyst formation is a means of perennation.

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Slime moulds possess animal like as well as fungi like

character.

Euglenoids possess plant like as well as animal like characters.

De Bary (1887) classified slime moulds as a animal and called

them 'Mycetozoa'.

Macbrid coind the term 'Myxomycetes' (Slime moulds).

Protozoans

All protozoans are heterotrophs and live as predators or parasites. They are believed to be

primitive relatives of animals.

There are four major groups of protozoan

Group 1. Flagellated Protozoans

Characters:

(i) They possess flagella for locomotion.

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(ii) They may be free living aquatics, parasites, commensals or symbionts.

(iii) Zooflagellates are generally uninucleate, occasionally multinucleate.

(iv) The body is covered by a firm pellicle.

(v) Nutrition is holozoic, saproboic and parasitic

(vi) Asexual reproduction is by binary fission.

Examples:

Trypanosome gambiense – The parasite of sleeping sickness. It was first

observed by Forde in 1901. Fruce discovered that the parasite of sleeping

sickness is transmitted by tsetse fly. It causes Gambian sleeping sickness. The

disease, also called Gambain trypanosomiasis, is found in western and central

parts of Africa.

Trypansoma rhodesiense It causes Rhodesian sickness. The disease is also

called Rhodesian trypanosomiasis. The parasite is transmitted by the bites of

tsetse fly (glossina palpalis and glossina morsitans). Initially parasite is present

in the blood of man but later on it enters the cerebrospinal fluid.

Trypanosome cruzi It causes South American trypanosomiasis (also called

Chagas disease). The symptoms of the disease are fever, diarrhea, anaemia

and enlargement of lymphoid glands.

Group 2. Amoebid protozoans

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Characters:

(i) They develop pseudopodia which are temporary protoplasmic outgrowths. They are of four

types lobopodia (broad and blunt), filppodia (slender, unsupported, independent), axpodia

(slender with axial support) and reticulopodia (slender, reticulate).

(ii) pseudopodia are used for locomotion and engulfing food articles.

(iii) Sarcodines are mostly free living, found in fresh water, sea water and on damp soil. Only

a few are parasitic.

(iv) The body may be covered with plasmalemma or a shell.

Examples: Amoebe, pelomyxa, entamoeba, radiolarians, foraminiferans, heliozoans.

Amoeba proteus The Proteus Animalcule. Amoeba was discovered by Russel

Von Rosenhoff in 1755. H.I. Hirschfied (1962) has given a detailed account of

the biology of amoeba. It is found in fresh water. Types of pseudopodia are

lobopodia.

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Pelomyxa It is also known as giant amoeba. The size is about 2.5 mm long.

Pelomyxa occurs in fresh water. Nutrition is holozoic. The chief food article is

diatoms.

Entamoeba histolytica – Lamble (1859) discovered Entamoeba histolytica.

Losch (1875) discovered its pathogenic nature. The life cycle of Entamoeba

histolytica is monogenetic (single host life cycle). It resides in the upper part of

the human large intestine and causes the disease known as amoebic dysentery

or amoebiasis.

Group 3. Sporozoans

Characters:

(i) All sporozoans are endoparsites.

(ii) Some sporozoans such as Eimeria cause severl diseases like coccidiosis in the birds.

(iii) Locomotory organelles (cilia, flagella,pseudopodia,etc.)are absent.

(iv) Nutrition is parasitic (absorptive). Phagotrophy is rare.

(v) The body is covered with an elastic pellicle or cuticle.

(vi) Contractile vacuoles are absent.

(vii) Asexual reproduction occurs through syngamy.

(ix) Life cycle consists of two distinct asexual and sexual phases. They may be passed in one

(monogenetic) or two different hosts (digenetic).

Examples:

Plasmodium, monocystis, eimeria.

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Monocystis: Monocystis live as endoparasite in the coelomic epithelial cells and

seminal vesicles of earthworm. The fertility of the earthworm is not greatly

impaired, since most of the seminal vesicles are not haemorrhage.

Group 4. Ciliated Protozoans

Characters:

(i) Ciliates are protozoan protists which develop a number of cilia during a part or whole of the

life cycle.

(ii) Cilia are used for locomotion and driving food.

(iii) There is a high degree of morphological and physiological specialization.

(iv) Most ciliates are free living individuals in fresh and marine waters. A few are parasitic.

(v) The body is covered by a pellicle.

(vi) Nutrition is holozoic except in the parasitic forms.

(vii) there are definite regions for ingestion and egestion. The region of ingestion consists of

an oral groove, cytostome (mouth) and gullet.

Examples:

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Paramecium, vorticella, opalina, balantidium.

Paramecium The slipper organism or slipper Animalcule. Paramecium is a free

living ciliate which is found in fresh water. Most widely distributed species are

paramecium caudatum and paramecium Aurelia. Nutrition is microphageal.

Bacteria are its chief feed. Paramecium is a surface feeder. Pellicle maintains

the shape. The cilia of the extreme posterior end longer and form a bunch called

caudal tuft.

Kingdom Fungi

The science dealing with the study of fungi is called as mycology.

The knowledge of fungi to mankind dates back to prehistoric times.

Clausius, 1601 may be regarded as one of the earliest writers to describe fungi.

Bauhin (1623) also included the account of known fungal forms in his book Pinax Theatric

Botanica.

The fast systematic account of fungi came from Pier Antonio Micheli (1729) who wrote 'Nova

Plantarum Genera'. He is described by some workers as founder or mycology.

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Characteristics of Fungi

Thallus organization:

The plant body of true fungi (Eumycota), the plant body is a thallus.

It may be nonmycelial or mycelial. The nonmycelial forms are unicellular;

however, they may form apseudomycelium by budding. In mycelial forms, the plant

body is made up of thread like structures called hyphae (sing. hypha).

The mycelium may be aseptate (nonseptate) or septate. When nonseptate and

multinucleate, the mycelium is described as coenocytic.

In lower fungi the mycelium is nonseptate e.g., Phycomycetae. In higher forms it is

septate e.g., Ascomycotina, Basidiomycotina and Deuteromycotina.

In some forms the plant body is unicelled at one stage and mycelial at the other.

Their organization is sometimes described as dimorphic.

Specialised formation:

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In higher forms the mycelium gets organised into loosely or compactly woven

structure which looks like a tissue called plectenchyma. It is of two types:

(i) Prosenchyma: It comprises loosely woven hyphae lying almost parallel to each other.

(ii) Pseudoparenchyma: If the hyphae are closely interwoven, looking like parenchyma

in a crosssection, it is called as pseudoparenchyma.

In addition to above, the fungal mycelium may form some specialized structures as

under:

(a) Rhizomorphs: It’s a 'rootlike' or 'stringlike' elongated structure of closely packed

and interwoven hyphae. The rhizomorphs may have a compact growing point.

(b) Sclerotia: Here the hyphae gets interwoven forming pseudoparenchyma with

external hyphae becoming thickened to save the inner ones from desiccation. They

persist for several years.

(c) Stroma: It is thick mattress of compact hyphae associated with the fruiting bodies.

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Fungus : The term was used by Gaspard Bauhin (1560–1624).

Father of Mycology : Pier Antonio Micheli. In 1729 he wrote 'Nova Genera

Plantarum' in which 900 fungi were described.

Father of Systematic Mycology : E.M. Fries (1794–1878). He wrote 'Systema

Mycologicum' in three volume.

Father of Modern Mycology and Plant Pathology : H.A. de Bary.

Father of Indian Mycology and Plant Pathology: E.J. Butler.

Smallest Fungus : Yeast with a size of 3–15 mm × 2–10 mm.

Largest Fungus : Lignocolous Shelf Fungus/Bracket Fungus Ganoderma

applanatum (fruiting body 60 cm across). Glant Puffball/Clavatia is 90–120 cm

across. It possesses anticancer properties.

Cell organization:

The cell wall of fungi is mainly made up of chitin and cellulose.

While chitin is a polymer of Nacetyl glucosamine, the celulose is polymer of

dglucose.

Precisely, the cell wall may be made up of celluloseglucan (Oomycetes), chitin

chitosan (Zygomycetes) mannanglucan (Ascomycotina), chitinmannan

(Basidiomycotina) or chitinglucan (some Ascomycotina, Basidiomycotina and

Deuteromycotina).

Besides, the cell wall may be made up of celluloseglycogen, cellulosechitin or

polygalactosaminegalactan.

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Nutrition:

The fungi are

achlorophyllous organisms and hence they cannot prepare their food. They live as

heterotrophs i.e., asparasites and saprophytes. Some forms live symbioticallywith other green

forms.

(i) Parasites: They obtain their food from a living host. A parasite may be obligate or

facultative. The obligate parasites thrive on a living host throughout their life. The facultative

parasites are in fact saprophytes which have secondarily become parasitic. While the above

classification is based on the mode of nutrition, however, on the basis of their place of

occurrence on the host, the parasites can be classified as ectoparasite, endoparasite

andhemiendoparasite (or hemiectoparasite).

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(ii) Saprophytes: They derive their food from dead and decaying organic matter. The

saprophytes may be obligate orfacultative. An obligate saprophyte remains saprophytic

throughout its life. On the other hand, a facultative saprophyte is infact a parasite which has

secondarily become saprophytic.

(iii) Symbionts: Some fungal forms grow in symbiotic association with the green or bluegreen

algae and constitute the lichen. Here the algal component is photosynthetic and the fungal is

reproductive. A few fungal forms grow in association with the roots of higher plants. This

association is called as mycorrhiza. They are two types – Ectotrophic mycorrhiza and

Endotrophic mycorrhiza e.g., (VAM).

Millardet discovered fungicide Bordeaux mixture. Which is solution of copper

sulphate and calcium hydroxide (CaSO4 + Ca(OH)2).

Pseudogamy : Fusion between unrelated cells.

Pedogamy : Fusion between mature and immature cells.

Adelphogamy : Fusion between mother and daughter cells or sister cells.

Nonciliated spores called 'aplanospores'.

Bipolar heterothallism found in Mucor and Rhizopous.

Reserve food material of fungi is glycogen and oil bodies.

Reproduction:

The fungi may reproduce vegetatively, asexually as well as sexually:

(i) Vegetative reproduction

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(a) Fragmentation: Some forms

belonging to Ascomycotina and Basidiomycotina multiply by breakage of the mycelium.

(b) Budding: Some unicelled forms multiply by budding. A bud arises as a papilla on the

parent cell and then after its enlargement separates into a completely independent

entity.

(c) Fission: A few unicelled forms like yeasts and slime molds multiply by this process.

(d) Oidia: In some mycelial forms the thallus breaks into its component cells. Each cell

then rounds up into a structure called oidium (pl. oidia). They may germinate

immediately to form the new mycelium.

(e) Chlamydospores: Some fungi produce chlamydospores which are thick walled cells.

They are intercalary in position. They are capable of forming a new plant on approach

of favourable conditions.

(ii) Asexual reproduction

(a) Sporangiospores: These are thinwalled, nonmotile spores formed in a sporangium.

They may be unior multinucleate. On account of their structure, they are also called as

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aplanospores.

(b) Zoospores: They are thinwalled, motile spores formed in a

zoosporangium.Example: In Pilobulus a sticky mass containing many spores is

discharged as a single unit.

(c) Conidia: In some fungi the spores are not formed inside a sporangium. They areborn

freely on the tips of special branches called conidiophores. The spores thus formed are

called as conidia. On the basis of development, two types of conidia are recognised

namely thallospores and blastospores or true conidia.

(iii) Sexual reproduction:

With the exception of Deuteromycotina (Fungi imperfecti), the sexual reproduction is found in

all groups of fungi. During sexual reproduction the compatible nuclei show a specific

behaviour which is responsible for the onset of three distinct mycelial phases. The three

phases of nuclear behaviour are as under:

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Plasmogamy : Fusion of two protoplasts.

Karyogamy : Fusion of two nuclei.

Meiosis : The reduction division.

These three events are responsible for the arrival of the following three mycelial phases:

Haplophase : As a result of meiosis the haploid (n) or haplophase mycelium is formed.

Dikaryotic phase : The plasmogamy results in the formation of dikaryotic mycelium (n +

n).

Diplophase : As a result of karyogamy the diplophase mycelium (2n) is formed.

Clamp connection

In Basidiomycotina, the dikaryotic cells divide by clamp connections. They were first observed

by Hoffman, (1856) who named it as 'Schnallenzellen' (bucklejoints).

Heterothallism

Blakeslee, (1904) while working with Mucor sp. observed that in some species sexual union

was possible between two hyphae of the same mycelium, in others it occured between two

hyphae derived from 'different' spores. He called the former phenomenon as homothallism

and the latter as heterothallism.

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A fungus which requires only one single host for complition of its life cycle is

called 'autoecious'.

Phycomycetes are called algal fungi or lower fungi.

Fungi inhabiting wood are known as epixylic.

Aspergillus secretes toxin during storage conditions of crop plants. The hyphae of

this fungus are septate and uninucleate.

Ascomycetes are our worst fungus enemies.

Neurospora (an ascomycete) is known as Drosophila of plant kingdom.

Peziza and Helvella are coprophilous fungi (grow on dung).

Classification of fungi

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Phycomycetes

Members of phycomycetes are found in aquatic habitats and on decaying wood in

moist and damp places or as obligate parasites on plants.

The mycelium is aseptate and coenocytic,Asexual reproduction takes place by

zoospores (motile) or by aplanospores (nonmotile).

These spores are endogeneously produced in sporangium.

Zygospores are formed by fusion of two gametes. These gametes are similar in

morphology (isogamous) or dissimilar (anisogamous or oogamous). Examples:

Mucor, Rhizopus and Albugo (the parasitic fungi on mustard).

Rhizopus/Mucor

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They are cosmopolitan and saprophytic fungus, living on dead organic matter.

Rhizopus stolnifer occur very frequently on moist bread, hence commonly called

black bread mold.

Mucor is called dung mold.

Both are called black mold or pin mold because of black coloured pin head like

sporangia.

Besides, it appears in the form of white cottony growth on moist fresh, organic

matter, jams, jellies, cheese, pickles, etc.

Albugo

Albugo is a member of phycomycetes.

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It is an obligate parasite and grows in the

intercellular spaces of host tissues. It is parasitic mainly on the members of families

Cruciferae, Compositae, Amaranthaceae and Convolvulaceae, The disease caused

by this fungus is known as white rust or white blisters.

The most common and well known species is Albugo candida which attacks the

embers of the mustard family (Cruciferae). It is commonly found on

Capsella bursa pastoris (Shepherd's purse), and occasionally on radish, mustard,

cabbage, cauliflower, etc.

The reserve food is oil and Glycogen.

Ascomycetes

Commonly known as sacfungi, the ascomycetes are 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.

The asexual spores are conidia produced exogenously on the special mycelium

called conidiophores.

Sexual spores are called ascospores which are produced endogenously in sac like

asci (singular ascus). These asci are arranged in different types of fruiting bodies

called ascocarps.

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Some examples are Aspergillus, Claviceps and Neurospora. Neurospora is used

extensively in biochemical and genetic work. Many members like morels and

buffles are edible and areconsidered delicacies.

Yeast:

Yeast was first described by Antony Von Leeuwenhoek in 1680.

Yeast are nonmycelial or unicellular, which is very small and either spherical or oval

in shape.

However, under favourable conditions they grow rapidly and form false mycelium or

pseudomycelium.

Individual cells are colourless but the colonies may appear white, red, brown,

creamy or yellow:

The single cell is about 10mm in diameter. It is enclosed in a delicate membrane

which is not made up of fungal cellulose but is a mixture of two polysaccharides

known as mannan and glycogen.

Reproduction: Yeast reproduces by vegetative or asexual and sexual methods.

(1) Vegetative reproduction: 'Yeast reproduce vegetatively either by budding or by

fission.

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(2) Sexual reproduction: Sexual reproduction in yeasts takes place during unfavourable

conditions, particularly when there is less amount of food.The sex organs are not

formed in yeasts 'and the sexual fusion occurs between the two haploid vegetative cells

or two ascospores which behave as gametes. The two fusing gametes are haploid and

may be isogamous or anisogamous. Such kind of sexual reproduction is called gametic

copulation. It is the best example of hologamy i.e., the entire vegetative thallus is

transformed into reproductive body. The sexual fusion leads to the formation of diploid

zygote. The zygote behaves as an ascus and forms 4 8 haploid ascospores. These

liberate and function as vegetative cells.

Basidiomycetes

Commonly known forms of basidiomycetes are mushrooms, bracket fungi or

puffballs.

They grow in soil, on logs and tree stumps and in living plant bodies as parasites,

e.g., rusts and smuts.

The mycelium is branched and septate.

The asexual spores are generally not found, but vegetative reproduction by fragmentation is common.

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The sex organs are absent, but 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 take place in the basidium producing four basidiospores.

The basidiospores are exogenously produced on the basidium.

The basidia are arranged in fruiting bodies called basidiocarps.

Some common members are Agaricus (mushroom), 'Ustilago (smut) and Puccinia

(rust fungus).

Deuteromycetes

Commonly known as imperfect fungi because 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. Examples: Alternaria,

Colleiotrichum and Trichoderma.

Kingdom Plantae and Animalia

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Kingdom Plantae

Kingdom plantae includes green, brown and red algae, liwerworts, mosses, ferns and seed

plants with or without flowers. They have the following characters.

(1) Multicellular organisms with walled and frequently vacuolate eukaryotic cells.

(2) They contain photosynthetic pigment in plastids.

(3) Principal mode of nutrition is photosynthesis but number of plants have become

absorptive.

(4) Primarily nonmotile, living anchored to a substrate.

(5) Structural differentiation leading towards organs of photosynthesis, anchorage and support

and in higher forms towards specialised photosynthetic, vascular and covering tissues.

(6) Reproduction is primarily asexual or sexual. The reproductive organs are multicellular.

(7) A multicellular embryo is formed during development from the zygote. Algae lack embryo

stage. Life cycle consists of alternating haploid gametophyte and diploid sporophyte

generation. This phenomenon is called alternation of generation.

Classification of plantae

August Wilhelm Eichler (1883) a Vinnese botanist, divided plant kingdom into two

subkingdoms mainly on the basis of presence or absence of seeds.

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(1) Cryptogamae (Gr. Cryptos = hidden; gamos = marriage): Lower plants in which sex

organs are hidden and seeds and flowers absent. It includes Thallophytes, Bryophytes,

pteridophytes.

(2) Phanerogamae (Gr. Phaneros = visible; gamos = marriage): Higher plants in which sex

organs are evident; seeds present. It includes Gymnosperms and Angiosperms.

Thallophyta

Comprises the simplest plants which possess undifferentiated or thallus like forms.

Reproductive organs single celled no jacketed called gametangia.

Embryo stage, vascular and mechanical tissues are all absent.

Differentiation of true roots, stems and leaves is also absent.

Asexual reproduction by accessory spores is very common. Presently, it includes

only Algae.

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Bryophytes

These are nonvascular terrestrial plants of moist habitats in which a multicellular diploid

sporophyte lives as a parasite on an independent multicellular haploid gametophyte that

develops multicellular jacketed sex organs.

Vascular plants – tracheophyta

They are those plants which posses conductiong or vascular tissues, xylem and

phloem. Xylem transports water and minerals while phloem conducts organic food.

Vascular plants comprise more than 275,000 living species.

They are most visible green plants around us, so much so that the term ‘plants’

generally means vascular plants.

Pteridophytes pteridophyta

Pteridophytes are seedless vascular or bryptogamic plants that have sporophytic plant body,

inconspicuous gametophytes contining small sessile antheridia and partially embedded

archegonia with 4 rowed neck.

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Seed plants spermatophyte

They comprise over 250,000 vascular plants.

After sexual reproduction,the plants produce seeds for dispersal and multiplication.

The seeds are dormant and can easily pass through unfavourable conditions.

The plant body belongs to sporophytic generation.

The sporophytic plant body is differentiated into true stem, lves and roots.

Plants show heterospory or two types of meiospores, microspores and

megaspores.

Gymnosperms

Gymnosperms are those seed plants in which the seeds remain exposed over the surface of

the megasporophylls because the latter are not folded to form pistils.

Angiosperms

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Angiosperms are those seed plants in which seeds are formed inside fruits and the

sporophylls are organized into flowers.

In Linnaeus' time a Two Kingdom system of classification with Plantae and Animalia kingdoms was developed that

included all plants and animals respectively. This system did not distinguish between the eukaryotes and

prokaryotes, unicellular and multicellular organisms and photosynthetic (green algae) and nonphotosynthetic (fungi)

organisms.

Kingdom Animalia

This kingdom is characterised by heterotrophic eukaryotic organisms

that are multicellular and their cells lack cell walls.

They directly or indirectly depend on plants for food. They digest their food in an internal

cavity and store food reserves as glycogen or fat.

Their mode of nutrition is holozoic by ingestion of food.

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They follow a definite growth pattern and grow into adults that have a definite shape and

size.

Higher forms show elaborate sensory and neuromotor mechanism.

The sexual reproduction is by copulation of male and female followed by embryological

development.

Anaima: Animals without red blood e.g., sponges, cnidaria, mollusca, arthropoda,

echinodermata, etc.

Enaima: Animals with red blood e.g., vertebrate

Vivipara: Animals which give birth to young ones are included in this subgroup e.g.,

man, dogs, cows, etc.

Ovipara: Animals which lay eggs are included in this subgroup e.g., frogs, toads,

lizards, snakes, birds, etc.

Anamniotes: Vertebrates without embryonic membranes e.g., fishes, amphibians.

Amniotes: Vertebrates with embryonic membranes (chorion, amnion, allantois, yolk

sac) e.g., reptiles, birds, mammals.

Acraniata or Protochordata: Chordates without cranium (brain box). It includes

urochordata and cephalochordata.

Chordates: Animals with notochord dorsal tubular nerve cord, paired pharyngeal gill

slits.

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All urochordates, cephalochordates and vertebrates are called chordates.

Craniata or Vertebrate: Chordates with cranium.

It Includes cyclostomes, pisces, amphibians, reptiles, birds and mammals.

Nonchordates: Animals without notochord (a rod like elastic structure which

supports the body). Phylum Porifera to phylum Hemichordata are called

nonchordates.

Invertebrates: Animals without vertebral coloumn (backbone). All the nonchordates,

urochordates and cephalochordates are callectively called invertebrates.

Viruses, Viroids and Lichens

The viruses are noncellular organisms that are characterised by having an inert

crystalline structure outside the living cell. Once they infect a cell they take over the

machinery of the host cell to replicate themselves, killing the host.

The name virus that means venom or poisonous fluid was given by Pasteur. D.J.

Ivanowsky (1892) recognised certain microbes as causal organism of the mosaic

disease of tobacco. These were found to be smaller than bacteria because they

passed through bacteriaproof filters.

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M.W. Beijerinek (1898) demonstrated that the extract of the infected plants of

tobacco could cause infection in healthy plants and called the fluid as Contagium

vivum fluidum (infectious living fluid).

W.M. Stanley (1935) showed that viruses could be crystallised and crystals consist

largely of proteins. They are inert outside their specific host cell.

Viruses are obligate parasites.

In addition to proteins viruses also contain genetic material, that could be either

RNA or DNA.

No virus contains both RNA and DNA.

A virus is a nucleoprotein and the genetic material is infectious. In general, viruses

'that infect plants have single stranded RNA and viruses that infect animals have

either single or double stranded RNA or double stranded DNA. Bacterial viruses or

bacteriophages (viruses that infect the bacteria) are usually double stranded DNA

viruses.

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The protein coat called capsid made of small subunits called capsomeres, protects

the nucleic acid. These capsomeres are arranged in helical or polyhedral geometric

forms.

Viruses cause diseases like mumps, small pox, herpes and influenza. AIDS in

humans is also caused by a virus. In plants, the symptoms can be mosaic

formation, leaf rolling and curling, yellowing and vein clearing, dwarfing and stunted

growth.

Viroids: In 1971 T.O. Diener discovered a new infectious agent that was smaller

than viruses and caused potato spindle tuber disease. It was found to be a free

RNA; it lacked the protein coat that is found in viruses, hence the name viroid. The

RNA of the viroid 'was of low molecular weight.

Lichens: Lichens are symbiotic associations i.e, mutually useful associations,

between algae and fungi. The algal component is known as phycobiont and fungal

component as mycobiont, which are autotrophic and heterotrophic, respectively.

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.

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Biologicalclassification

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