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Kingdom Monera: Archaebacteria & Eubacteria | Biology Class 11 - NEET PDF Download

Have you ever found yourself curled up in bed, feeling miserable due to a bacterial infection? It’s nothing but a bad bacteria present in our environment. On the other hand, have you heard about the good bacteria that are often talked about? Like in curd or in our gut that helps in digestion?

All these harmful and helpful bacteria that we just talked about are classified under the Kingdom Monera. And hence, bacteria are the sole members of Monera Kingdom.

So, if we have to study Kingdom Monera, it's really imp. to understand Bacteria first.

Bacteria Everywhere!

These tiny, single-celled organisms are so unique that they have their own biological kingdom that is Kingdom Monera. Bacteria are found in almost every environment on Earth, from soil to water to the human gut. Bacteria are some of the oldest forms of life on Earth. They have been around for billions of years and are believed to have played a crucial role in shaping the planet's atmosphere and environment also.

Classification of Bacteria on the basis of Shape

Bacteria are tiny, single-celled organisms that come in different shapes and sizes. Scientists group bacteria into four categories based on their shape. 

Kingdom Monera: Archaebacteria & Eubacteria | Biology Class 11 - NEET

  • The first category is Coccus (cocci): These bacteria are spherical or oval in shape. These can be micrococcus (single), diplococcus (in pairs), tetracoccus (in fours), streptococcus (in chains), and staphylococcus (in clusters like grapes)
  • The second is the rod-shaped bacteria called Bacillus (bacilli): They can be with or without flagella.
  • The third is the comma-shaped bacteria called Vibrium (vibrio): These are small bacteria with flagella at one end.
  • The fourth is the spiral-shaped bacteria called Spirillum (spirilla): They are rigid forms due to the spiral structure and bear flagella at one or both the ends.

Question for Kingdom Monera: Archaebacteria & Eubacteria
Try yourself:Which category of bacteria is comma-shaped?
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Classification of Kingdom Monera

Now that you've understood Bacteria. It's time to understand how they are classified on the basis of their behaviour. 

Kingdom Monera is classified into two sub-kingdoms: 

Kingdom Monera: Archaebacteria & Eubacteria | Biology Class 11 - NEET

In Archaebacteria we will see the examples: Methanogens, Halophiles and Thermoacidophiles

In Eubacteria we will study: Cyanobacteria, Chemosynthetic Bacteria, Heterotrophic Bacteria and Mycoplasma.

Archaebacteria

These are some of the oldest living organisms on Earth. They have been around for over 3.5 billion years and they are different from other bacteria because of their unique cell wall structure. This feature helps them to survive in extreme conditions that would be deadly to other bacteria.
  • They are a group of most primitive procaryotes which are believed to have evolved immediately after the evolution of the first life. 
  • They have been placed in a separate subkingdom or domain of Archaea by a number of workers (e.g., Woese, 1994). 
  • Archaebacteria are characterized by the absence of peptidoglycan in their wall.
  • Instead, the wall contains protein and noncellulosic polysaccharides. 
  • It has pseudomurein in some methanogens. 
  • The cell membranes are characterized by the presence of a monolayer of branched-chain lipids. 
  • Their 16S rRNA nucleotides are quite different from those of other organisms. 
  • Core histones are present. 
  • DNA replication, transcription and translation are quite similar to those of eukaryotes. Operons are monocistronic.
  • Many archaebacteria even now live under extremely hostile conditions where very few other organisms can dare subsist, e.g., salt pans, salt marshes, hot sulphur springs seawents.
    For Example:
    (i) Some Archaebacteria called halophiles can survive in extremely salty conditions, such as in the Dead Sea or in salt pans.
    (ii) Other Archaebacteria called thermoacidophiles can survive in hot and acidic environments, such as in volcanic hot springs.
    (iii) And yet other Archaebacteria called methanogens can survive in oxygen-free environments and produce methane gas as a byproduct of their metabolism. In fact, methanogens are present in the guts of ruminant animals like cows and buffaloes and are responsible for the production of biogas from their dung.
  • The archaebacteria are of two broad categories, obligate anaerobes and facultative anaerobes. 
  • Obligate anaerobes can live under anaerobic conditions only. 
  • They get killed in the presence of oxygen, e.g., methanogens. 
  • Facultative anaerobes are actually aerobic archaebacteria that can bear anaerobic conditions comfortably. 
  • They are represented by thermoacidophiles and halophiles.
  • Archaebacteria are of three major types-methanogens, halophilic and thermoacedophilic. 
  • Methanogens and halophiles are placed in division euryarchaeota while thermoacidophiles are placed in division creuarchaeota.

Methanogens. The archaebacteria are strict anaerobes. 

  • Nutritionally they are "autotrophs" which obtain both energy and carbon from decomposition products. 
  • They occur in marshy areas where they convert formic acid and carbon dioxide into methane with the help of hydrogen. 
  • This capability is commercially exploited in the production of methane and fuel gas inside gobar gas plants e.g., Methanobacterium, Methanococcus. 
  • Some of the methanogen archaebacteria live as symbionts (e.g., Methanobacterium) inside rumen or first chamber in the stomach of herbivorous animals that chew their cud (ruminants, e.g., cow, buffalo). 
  • These archaebacteria are the ruminants in the fermentation of cellulose.

Halophiles (Halophils). Halophiles are named so because they usually occur in salt-rich substrata (2.5-5.0 M) like salt pans, salt beds and salt marshes e.g., Halobacterium, Halococcus

  • They are aerobic chemoheterotrophs. 
  • Their cell membranes have red carotenoid pigment for protection against harmful solar radiation. 
  • Under anaerobic conditions, halophiles cannot use external materials. 
  • At this time they subsist on ATP synthesized by membrane pigment system from solar radiations.
  • Halophiles are able to live under high salt conditions due to four reasons:
    (1) Presence of special lipids in the cell membranes.
    (2) Occurrence of mucilage covering.
    (3) Absence of sap vacuoles and hence plasmolysis.
    (4) High internal salt content. Halophiles growing in salt pans and salt beds give an offensive smell and undesirable pigmentation to the salt. 

Thermoacidophiles (Thermoacidophils). These archaebacteria have a dual ability to tolerate high temperature as well as high acidity. 

  • They often live in geothermal vents as well as hot sulphur springs where the temperature may be as high as 80°C and pH as low as 2, e.g., Thermoplasma, Thermoproteus
  • Basically, these archaebacteria are chemosynthetic, i.e., they obtain energy for the synthesis of food from oxidizing sulphur. 
  • Under aerobic conditions, they usually oxidize sulphur to sulphuric acid.
  • If the conditions are anaerobic, the thermoacidophiles may reduce sulphur to H₂S. Bicarbonates are also precipitated into the carbonate form by their activity.
  • Thermoacidophiles are able to tolerate high temperature, as well as high acidity due to two reasons
    (1) Branched-chain lipids in the cell membranes.
    (2) Presence of special resistant enzymes capable of operating under acidic conditions. 
  • Archaebacteria are also known as ancient living fossils because they represent one of the earliest forms of life which experimented on the absorption of solar radiations for the first time, lived comfortably under anaerobic conditions and developed techniques to oxidize the chemicals present in the substratum on the availability of oxygen. 

Uses:
(i) Archaebacteria are employed in the production of gobar gas from dung and sewage.
(ii) In ruminants, they cause the fermentation of cellulose.

Eubacteria

Now, coming to the Sub-kingdom Eubacteria. It is also known as true bacteria, are single-celled organisms that belong to the kingdom Monera. They are one of the most diverse groups of organisms on Earth and can be found in virtually every environment, from deep sea vents to the human gut.

On the basis of shape, Eubacteria is classified into four categories: 

Kingdom Monera: Archaebacteria & Eubacteria | Biology Class 11 - NEET

Characteristics of Eubacteria

One fascinating aspect of Eubacteria is their ability to adapt and evolve rapidly. This has allowed them to develop resistance to antibiotics, which can make treating bacterial infections more challenging. Scientists are working to find new ways to combat these bacteria and prevent the spread of antibiotic-resistant strains.

Pili 

  • Bacterial cell wall is covered by numerous hair-like structures called pili. Pili are smaller than the flagella. (Pl. - Pili; Sing. – Pilus).
  • They are of two types – (A) Longer pili, (B) Shorter pili
  • Longer pili is also known as 'F' pili or 'sex' pili. Longer pili occur in only donor (F+ or male) bacteria and help in conjugation. These are absent in recipient bacteria or females.
  • The shorter pili take part in attachment. These are also known as 'infective' pili or fimbriae. These are found only in pathogenic bacteria.

Structure

1. Every pilus is a cylindrical hollow structure and is composed of protein monomers.

2. Each monomer is made up of 'pilin' protein. Pilin is a non-contractile protein.

3. Pili does not play role in motility

Kingdom Monera: Archaebacteria & Eubacteria | Biology Class 11 - NEET

Structure of Eubacteria

  • Though the bacterial structure is very simple, they are very complex in behaviour
  • The bacterial cell has a chemically complex cell envelope.
  • The cell envelope consists of a tightly bound three-layered structure.
    (1) Outermost glycocalyx
    (2) Cell wall
    (3) Cell membrane

Although each layer of the envelope performs distinct function

they act together as a single protective unit.

EubacteriaEubacteria

1. Glycocalyx (Capsule or Slime layer) –

A. Loose and a thin layer are called slime layer and a thick and tough layer is called a capsule. Formation of Glycocalyx is done by the cell membrane.

B. Capsule is made up of polysaccharides and polypeptides while slime layer is made up of polysaccharides.

C. Glycocalyx protects the bacteria from W.B.C. and also helps in colony formation.

2. Cell Wall – The bacterial cell wall is made up of the main peptidoglycan.

3. Cell membrane – Bacterial cell mem. is made up of lipoprotein (unit membrane) like the eukaryotic membrane.

4. Cytoplasm – In bacterial cytoplasm membrane-bound cell organelles viz. Mitochondria, Chloroplast E.R. Lysosome, Golgibody, Microbodies etc. are absent.


Cytoplasmic organelles 

1. Mesosomes 

A. Mesosome was discovered by F. James. The cell membrane of bacteria invaginates (extensions) in the cytoplasm at different places and form mesosomes or chondroid. These extensions are in the form of vesicles, tubules and lamellae.

B. These are functionally mitochondria-like structures. Oxidative enzymes are found in mesosomes.

Functions:

(i) Mainly cell respiration, cell wall secretion.

(ii) Help in DNA replication, cell division.


2. Storage granules/Inclusion bodies 

  • Reserve material in prokaryotic cells is stored in the cytoplasm in the form of inclusion bodies. 
  • These are not bounded by any membrane system and lie free in the cytoplasm.
    A. Glycogen granules – They store carbohydrate
    B. Volutin granules – These are also known as metachromatic granules. The volutin granules are phosphate polymers and function as a storage reservoir for phosphate.

3. Chromatin material (Nucleoid ) 

A. Besides the main DNA (Genophore) another small and ds-circular DNA is also present in the bacterial cell, which is called Plasmid. It is also known as extrachromosomal or extranuclear genetic material. (The term 'plasmid' was given by Lederberg).

B. Plasmids have the ability to replicate independently. 

Plasmids are of many types on the basis of their functions and phenotypic characters.

(1) F or fertility factor (F-plasmid): On the basis of the presence or absence of the 'F' factor, there are two mating types of bacteria. 

(a) F+:Cells, carrying the 'F' factor acts as donors and are called F+ or male.

(b) F–: Cells, lacking the 'F' factor acts as recipients and are called F– or female.

(2) R-Factor: Resistance to antibiotics.

Nutrition in Bacteria

  • Compared to many other organisms, bacteria as a group show the most extensive metabolic diversity.
  • Most of the bacteria are heterotrophic but some are autotrophic. 
  • On the basis of nutrition, bacteria are classified into the following three categories:

(i) Autotrophs:

These bacteria use light or chemical energy for their own food synthesis.

On the basis of the source of energy, autotrophs are of the following two types

A. Photosynthetic autotrophs 

  • These bacteria use light energy for food synthesis.
  • Photosynthetic pigments are present in the cytoplasm for photosynthesis.
  • In these bacteria, photosynthesis is non-oxygenic.
  • They need hydrogen ion for photosynthesis, so hydrogen ion is received from sources like inorganic sulphur compound (H2S, Thiosulphate) or organic compound (Aminoacids, Isopropyl alcohol Fatty acid).

Some photosynthetic bacteria are:-

  • Purple sulphur bacteria – e.g. Chromatium
  • Green sulphur bacteria – e.g. Chlorobium, Thiothrix
  • Purple non-sulphur bacteria – e.g. Rhodospirillum, Rhodopseudomonas

B. Chemosynthetic autotrophs

  • These are nonphotosynthetic autotrophs i.e., photosynthetic pigments are absent.
  • They use chemical energy instead of light energy for food synthesis.
  • Chemical energy is obtained from the oxidation of chemical compounds.
  • These bacteria oxidize chemical compounds and release energy that is used for food synthesis.
  • Nitrifying bacteria – They oxidize nitrogenous compounds and obtain energy.
  • Nitrite bacteria – Converts ammonia into Nitrite; e.g., Nitrosomonas or Nitrococcus
  • Nitrate bacteria – Convert nitrite into nitrates; e.g. Nitrobacter

(ii) Heterotrophs

You will be amazed to know that some or other kinds of bacterias are all around us and are actually the most common type of bacteria in nature! These are none other than our Heterotrophic Bacteria. These little guys again play a really important role in breaking down dead plant and animal matter, which helps keep the ecosystem healthy. They receive their own food from dead organic matter or living organisms.

But heterotrophic bacteria are also really important to us humans. They can help us make things like curd from milk and even produce life-saving antibiotics! Heterotrophic bacteria are also able to fix nitrogen in the roots of legumes, which can help the plant to thrive.

Unfortunately, not all heterotrophic bacteria are friendly. Some can cause serious harm to humans, crops, and animals. You've probably heard of diseases like cholera, typhoid, and tetanus, which are all caused by different types of bacteria. And there's even a disease called citrus canker that affects citrus fruits!

These are of following types
(i) Saprotrophic bacteria – These bacteria obtain food from dead and decaying organic matter.
These are of two types:
(a) Obligate saprotrophic – These bacteria obtain food only from dead organic matter.
These are completely saprotrophs
e.g. Clostridium botulinum
(b) Facultative parasites – These are normally saprophytic in nature, but in the absence of dead organic matter, they can become parasitic.
e.g. Pseudomonas
(ii) Parasitic bacteria – They obtain their food from living organism
These are of two types
(a) Obligate parasite – They always remain parasitic.
e.g. Mycobacterium leprae
(b) Facultative Saprotrophic – They are normally parasitic in nature but in the absence of a living host, they may become saprotrophs
e.g. Mycobacterium tuberculosis

Symbiotic bacteria

These bacteria convert atmospheric nitrogen into nitrogenous compounds like Amino acid, NO3 or Salts of ammonia. e.g. Rhizobium

Respiration in Eubacteria

On the basis of respiration bacteria are of two types:

(i) Aerobic bacteria

These are of two types

(A) Obligate aerobic - These are completely aerobic and die in the absence of O2

eg. Azotobacter

(B) Facultative anaerobic - These are normally aerobic bacteria but can survive in the absence of O2. 

eg. Acetobacter aceti, Clostridium tetani


(ii) Anaerobic bacteria

These are of two types

(A) Obligate anaerobic - These are completely anaerobic bacteria and do not have a capacity for aerobic respiration.

eg. Clostridium botulinum

(B) Facultative aerobic - These are normally anaerobic but also have a capacity for aerobic respiration.

eg. Fermentation bacteria [except Acetobacter aceti]

Reproduction in Eubacteria

Asexual Reproduction

(i) Binary fission –

(a) This is the most common method of bacterial reproduction.

(b) Under favourable conditions first of all DNA replication takes place in the bacterial cells. The bacterial cell divides into two daughter cells due to the formation of the transverse septum in the centre of the cell. Each daughter cell grows into a new bacterium.

(c) Under favourable conditions, the cells of bacteria divide by amitosis which is faster than mitosis and meiosis.

(ii) By Endospore – Endospore formation occurs under unfavourable conditions.

(a) It is a highly resistant structure. It is resistant to high temperatures, radiation, antibiotics and chemicals.

(b) Endospore is a highly resistant structure due to the presence of Ca-dipicolinate in the cortex.

(c) Endospore formation is seen in mostly bacillus-type bacteria.

Genetic Recombination –

Genetic Recombination includes the following methods :

(I) Transformation

(II) Transduction

(III) Conjugation

  • A sort of sexual reproduction by adopting a primitive type of DNA transfer from one bacterium to another.


Cyanobacteria

One type of eubacteria is called cyanobacteria, but you might know them as blue-green algae. These little guys are really interesting because they can make their own food through a process called photosynthesis, just like plants! They have a green pigment called chlorophyll ‘a’ that helps them do this and that’s why they are photosynthetic autotrophs.

Kingdom Monera: Archaebacteria & Eubacteria | Biology Class 11 - NEET

  • Cyanobacteria or blue-green algae are Gram (+) photosynthetic prokaryotes that perform oxygenic photosynthesis. 
  • Photosynthetic pigments include chlorophyll and phycobilins. 
  • Food is stored in the form of cyanophycean starch, lipid globules and carotenoids, protein granules. 
  • Cyanobacteria evolved more than 3 billion years back. 
  • They added oxygen to the atmosphere and paved the path for the evolution of aerobic forms, including aerobic bacteria.

Occurrence

  • Cyanobacteria or blue-green algae are one of the most successful autotrophic organisms on earth which have mastered all types of environments- freshwater, seawater, salt marshes, moist rocks, tree trunks, moist soils, hot springs, frozen waters. 
  • Their abundance can be gauged from the fact that the red sea is named after the colouration provided by red coloured planktonic cyanobacteria known as Trichodesmium erythraeum
  • Cyanobacteria are the most self-contained photosynthetic organisms. 
  • They can, therefore, live under every type of environment and on every type of substrate. 
  • Because of this fact, they are one of the earliest colonizers of barren areas. Many of them have the ability of nitrogen fixation.

Morphology 

  • Cyanobacteria may be unicellular, colonial or filamentous. 
  • Each filament consists of a sheath mucilage and one or more cellular strands called trichomes. 
  • Single trichome filaments may further be of two types, homocystous (= undifferentiated, e.g.. Oscillatoria) and heterocystous (= differentiated, having heterocysts, e.g., Nostoc). 
  • Spirulina has a spirally coiled filament. 
  • Colonies develop in some cases, e.g., Nostoc. 
  • Flagella are absent but gliding movements are known in a number of cyanobacteria. 
  • The name Oscillatoria has been given to a common blue-green alga on the basis of pendulum-like oscillating movements of its anterior region. 

Cell Structure

  • Cyanobacterial cells are larger and more elaborate than bacteria. 
  • Cell structure is typically procaryotic-one envelope organization with peptidoglycan wall, naked DNA, 70S ribosomes and absence of membrane-bound structures like endoplasmic reticulum, mitochondria, Golgi bodies, plastids, lysosomes, sap vacuoles. 
  • The cell wall is four layered with peptidoglycan present in the second layer. 
  • The outer part of the protoplast contains a number of photosynthetic thylakoids or chromatophores. It is called chromoplasm. 
  • The thylakoids lie freely in the cytoplasm. 
  • Their membranes contain chlorophyll a, carotenes and xanthophylls. Chlorophyll b is absent. 
  • Attached to the thylakoid membranes are small granules known as phycobilisomes. 
  • The latter possess accessory photosynthetic pigments known as phycobilins. 
  • The phycobilins are of three types- c-phycocyanin (blue), allophycocyanin (blue) and c-phycoerythrin (red). Differential formation of phycobilins produces a specific colouration that is adapted for absorbing the maximum amount of solar radiation. 
  • Therefore, cyanobacteria are not always blue-green. 
  • They may appear purplish, violet, brownish, etc. 
  • Instead of typical vacuoles or sap vacuoles, s, gas vacuoles or pseudo-vacuoles are found. 
  • Each gas vacuole consists of a number of microscopic units called gas vesicles. Gas vacuoles function as light screens, provide l regulating mechanism and pneumatic strength.

Heterocyst

Kingdom Monera: Archaebacteria & Eubacteria | Biology Class 11 - NEET

  • It is a large-sized, pale-coloured, thick-walled cell that occurs in the terminal, intercalary or lateral position in filamentous cyanobacteria, e.g., Nostoc. 
  • The thick wall is impermeable to oxygen but permeable to nitrogen. 
  • Mucilage sheath absent. 
  • Photosystem II is absent. 
  • Thylakoids lack phycobilisomes. 
  • Therefore, photosynthesis is absent but cyclic photophosphorylation occurs. 
  • Heterocyst is dependent for its nourishment on adjacent vegetative cells. 
  • It has enzyme nitrogenase. 
  • Heterocyst is specialized to perform nitrogen fixation.

Kingdom Monera: Archaebacteria & Eubacteria | Biology Class 11 - NEET

Reproduction in Cyanobacteria

  • Cyanobacteria mostly multiply by asexual methods. 
  • The latter include binary fission, fragmentation with or without formation of small segments called hormogones (hormogonia), hormospores, akinetes, endospores, nannocytes, exospores, etc. 
  • Typical sexual reproduction involving the formation and fusion of gametes is absent but like bacteria, gene recombination can occur by three types of parasexual methods (Kumar, 1985)-conjugation, transformation and transduction.

Importance of Cyanobacteria

1. They are one of the early colonizers of bare and barren areas. They provide suitable conditions for the growth of other organisms even in the most hostile environment. 

2. Blue-green algae function as food to several aquatic animals. Spirulina is regularly collected for human consumption in parts of Africa. Nostoc is similarly used in China. In Rajasthan, Anabaena and Spirulina are collected from Sambar lake and used as fodder and manure. Spirulina is very easily cultivated in tanks and can be used as a palatable protein-rich food supplement for humans and animals.

3. Several cyanobacteria have the ability of nitrogen fixation. The filamentous forms possess special large pale cells or heterocysts for this. Some of the fixed nitrogen comes out as excretion. After the death of cyanobacteria, the substratum becomes rich in nitrogen. Such nitrogen-fixing cyanobacteria are now regularly inoculated in the rice fields. This saves consumption of nitrogen fertilizers.

4. Nitrogen-fixing cyanobacteria are often used for reclaiming usar soils, e.g., Nostoc, Anabaena. These cyanobacteria produce acidic chemicals for counteracting the alkalinity of the soil and nitrogenous compounds which are generally deficient in these soils. 

5. Antibiotics can be manufactured from the extract of Lyngbia

6. Species of Anabaena and Aulosira do not allow mosquito larvae to grow nearby. Such cyanobacteria can be inoculated in village ponds and rice fields to prevent the growth of mosquitoes.

7. Cyanobacteria can grow on the walls and roofs of buildings during the rainy seasons causing discolouration, corrosion and leakage. 

8. They produce water blooms, imparting bad od and colour to water bodies. 

9. Some cyanobacteria produce toxins harmful to most aquatic animals. They may prove equally toxic to human beings drinking or bathing in such water. The important toxins producing cyanobacteria are Microcystis aerugino (= Anacystis cyanea), Aphanizomenon flos-aquae, Anabaena flos-aquae. 

Differences between Cyanobacteria and Bacteria

Kingdom Monera: Archaebacteria & Eubacteria | Biology Class 11 - NEET

Mycoplasma

Mycoplasma are teeny tiny living things that don't have a cell wall. They're so small that they're actually the smallest cells we know of! What's really amazing about them is that they don't even need oxygen to survive. Some types of mycoplasma can make animals and plants sick, which we call pathogenic.

  • Mycoplasmas are unicellular, smallest prokaryotic organisms.
  • The cell membrane is tri-layered and made up of lipoprotein. Both DNA (ds DNA circular mainly) and RNA (ssRNA) is present.
  • They are cell wall-less hence, they exhibit pleomorphism and are thus called as Joker of the plant kingdom.
  • Osmotrophic mode of nutrition (absorption of nutrients by osmosis) is found in Mycoplasma.
  • They are resistant to antibiotics as penicillin that act on the cell wall.
  • Most of the species of Mycoplasma are facultative anaerobes.
  • Species of Mycoplasma are saprophyte or facultative parasites.
  • Asexual Reproduction: Binary fission - Most common method of reproduction in Mycoplasma. 

Plant diseases

(i) Little leaf disease of Brinjal.

(ii) Bunchy top of papaya.

(iii) Witches broom of Groundnut (Legume) / Potato.

(iv) Aster yellow disease of sunflower.

Even though they're small and don't have a cell wall, mycoplasma are still alive and can do a lot of things that other cells can do. However, because they don't have a cell wall, they can be a bit sneaky and cause problems in animals and plants by infecting them.

Old NCERT Syllabus

Motility in Bacteria

  • Bacteria are motile as well as non motile.
  • Bacteria show a range in the number and arrangement of flagella. 

Depending upon the presence or absence of flagella, bacteria are grouped into flagellate and non-flagellate types. The various forms of flagellation are as follows:

(a) Atrichous. Flagella absent.

(b) Monotrichous. A single flagellum occurs at or near one end of the bacterium. 

(c) Amphitrichous. A flagellum at each of the two ends.

(d) Lophotrichous. A group or tuft of flagella is found only at one end.

(e) Cephalotrichous. A tuft or group of flagella occurs at each of the two ends or poles. Many authors use the term amphitrichous for both single flagellum and tuft of flagella at each end.

(f) Peritrichous. A number of flagella are distributed all over the surface.

Kingdom Monera: Archaebacteria & Eubacteria | Biology Class 11 - NEET

A flagellum of bacteria is made up of three parts:

(1) Basal body (2) Hook (3) Filament

Economic Importance of Bacteria

1. Harmful Activities 

(i) Spoilage of Food. Saprotrophic bacteria cause the rotting of vegetables, fruits, meat, bread, souring of milk, cheese, butter and spoilage of jams, jellies and pickles. 

(ii) Food Poisoning. Botulism is caused by the anaerobic bacterium Clostridium botulinum (C. perfringens). The bacterium infects canned food. Common food poisoning is caused by Staphylococcus aureus. The poisoning is accompanied by diarrhea and vomiting. Another is salmonellosis which is generally produced by eating contaminated meat. The bacterium causing this type of poisoning is Salmonella enteritidis and S. typhimurium.

(iii) Deterioration of Domestic Articles. Spirochaete cytophaga deteriorates cotton fibres, leather and wooden articles. 

(iv) Destruction of Penicillin. Bacillus brevis destroys penicillin.

(v) Denitrification of Soils. Thiobacillus denitrificans and Micrococcus denitrificans convert nitrates of the soil into gaseous nitrogen. 

(vi) Desulphurification of Soils. Desulfovibrio desulfuricans changes soil sulphates into H₂S.

(vii) Diseases. Over 90% of human and animal diseases are caused by bacteria and over 40% of plant diseases are due to them. 

2. Beneficial Activities

Role in Agriculture

  • Nature's Scavengers. Along with saprotrophic fungi, saprotrophic bacteria cause the decay and decomposition of dead bodies of plants and animals. In the process, they cleanse the earth and release raw materials for new generations. 
  • Segge Disposal. The organic content of sewage is broken down by bacteria. 
  • Ammonifying Bacteria. Bacillus vulgaris releases ammonia from amino acids.
  • Nitrifying Bacteria. Nitrosomonas and Nitrosococcus oxidize ammonium salts to nitrites. The nitrites are further changed into nitrates by Nitrobacter and Nitrocystis. 
  • Nitrogen Fixing Bacteria. A few free-living bacteria are able to pick dinitrogen from the soil atmosphere and convert it into organic nitrogenous materials like amino acids, e.g., Azotobacter, Beijerinckia, Clostridium pasteurianum.
  • Symbiotic nitrogen-fixing bacteria of the genus Rhizobium occur in the root nodules of a number of legumes.
  • These legumes are used in crop rotation and green manuring. 
  • The plants as well as their seeds are rich in proteins. 
  • Root nodules containing symbiotic nitrogen bacteria also occur in Casuarina and Alnus. 
  • Leaf nodules containing such bacteria are found in Ardisia.
  • Manure. The saprotrophic bacteria convert farm refuse, dung and other organic wastes into manure.
  • Gobar Gas Plants. They employ bacteria for converting animal dung and other organic wastes into manure along with the production of fuel gas.
  • Sulphur Bacteria. Beggiatoa and other sulphur bacteria pick up H₂S released during the putrefaction of proteins to produce sulphates.
  • Ensilage. Ensilage is preserved cattle feed or fodder. It is formed by packing fresh chopped fodder in silos sprinkled with molasses. The fermentation activity of bacteria produces lactic acid which has a preservative action. 

Role in Industry

  • Dairy Industry. Lactic acid bacteria (e.g., Streptococcus lactis) convert milk sugar lactose into lactic acid. 
  • Lactic acid coagulates milk protein casein and converts milk into yogurt, curd and cheese. 
  • Lactic Acid. Lactic acid is commercially got from ammoniated sugar solution through fermentation caused by Lactobacillus delbreuckii. Acid is used in food preservation, tanning and preparation of a number of drugs. 
  • Vinegar. Acetic acid bacteria (Acetobacter aceti) oxidize ethyl alcohol into acetic acid. Ethyl alcohol is from molasses.
  • Butyl Alcohol and Acetone. Clostridium acetabutylicum is able to produce butyl and preparation a number of drugs. alcohol, methyl alcohol and acetone from molasses.
  • Retting of Fibres. Stem and leaf fibres are separated from softer tissues by bacterial action of two types-dew rettings (e.g., Pseudomonas fluorescence) and anaerobic retting(e.g., Clostridium or butyric acid bacteria).
  • Curing. Leaves of tea and tobacco are cured of their bitterness with the help of certain bacteria, e.g., Bacillus megatherium. Beans of coffee and cocoa are similarly cured. 
  • Cleaning of Hides. Hides are cleaned of their fat, hair and other attached tissues by bacterial action. Commercial sponges are cleaned similarly. 
  • Several bacteria synthesize cellulose which can be put to several uses, e.g., Acetobacter, Azotobector. 
  • Antibiotics. A number of antibiotics are obtained from the mycelial bacterium Streptomyces (e.g., Streptomycin, Chloramphenicol, Tetracycline, Oxytetracycline). 
  • A number of antifungal medicines are also produced by this genus, e.g., hamycin, trichomycin, primaricin. 
  • Bacitracin, subtilin, polymyxin, gramicidin are some other antibiotics obtained from bacteria. 
  • Vitamins. Riboflavin was formally prepared from Clostridium butylicum. Cobal amine (B12) is obtained from bacteria like Bacillus megatherium. 
  • Acetic acid bacteria are used in some steps during the preparation of vitamin C.
  • Escherichia coli present in the human intestine produce large quantities of vitamin K and B complex vitamins.
The document Kingdom Monera: Archaebacteria & Eubacteria | Biology Class 11 - NEET is a part of the NEET Course Biology Class 11.
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FAQs on Kingdom Monera: Archaebacteria & Eubacteria - Biology Class 11 - NEET

1. What are the different shapes of bacteria?
Ans. Bacteria can have various shapes, including spherical (cocci), rod-shaped (bacilli), spiral (spirilla), and comma-shaped (vibrios).
2. How are bacteria classified in the Kingdom Monera?
Ans. Bacteria are classified into two major groups in the Kingdom Monera: Archaebacteria and Eubacteria. Archaebacteria are ancient bacteria that inhabit extreme environments, while Eubacteria are more common bacteria found in various habitats.
3. How do bacteria reproduce?
Ans. Bacteria reproduce through a process called binary fission, where a single bacterium divides into two identical daughter cells. This allows bacteria to rapidly multiply and colonize their environment.
4. What is the economic importance of bacteria?
Ans. Bacteria have significant economic importance in various fields. They are used in food production, such as in the fermentation of yogurt and cheese. Bacteria also play a crucial role in nitrogen fixation, aiding in plant growth. Additionally, they are used in the production of antibiotics, enzymes, and bioplastics.
5. What are cyanobacteria and their specialized cells called?
Ans. Cyanobacteria, also known as blue-green algae, are a type of bacteria capable of photosynthesis. They possess specialized cells called heterocysts, which fix atmospheric nitrogen into a form that can be utilized by other organisms, making cyanobacteria important contributors to the nitrogen cycle.
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