• Written By Harshitha A
  • Last Modified 31-07-2023

Monera Kingdom Classification


Kingdom Monera: Have you heard about Bacteria or E. coli? These bacteria are seen everywhere, and it is also present in our body. Is it surprising? Yes!! The members of the kingdom Monera are ubiquitous in nature. These are the oldest known microorganisms on earth. 

Organisms belonging to the Monera kingdom are prokaryotes. Characteristics of monera organisms are – They do not contain a true nucleus. The DNA of organisms belonging to the classification of Monera, are not contained within the nucleus. They are generally found in damp environments such as hot springs, snow, deep oceans, or as parasites. They do not have any organelle that are bound to their membranes.

This is the only kingdom that has most of the identified microorganisms. This‌ ‌article covers‌ ‌the definition of the Monera classification, the kingdom and‌ ‌much‌ ‌more.‌ ‌Read‌ ‌on‌ ‌to‌ ‌find‌ ‌out‌ ‌more‌ ‌interesting‌ ‌facts‌ ‌about‌ the Monera kingdom classification.

Biological Classification

Biological classification is the process of grouping organisms into convenient categories based on some easily available characters.
Copeland included the Kingdom Monera in his four-kingdom classification. Later, R H Whittaker added the fourth kingdom for bacteria in his five-kingdom classification. Carl Woese, in 1977 divided the kingdom into Archaebacteria and Eubacteria.

Define Kingdom Monera

The Monera kingdom examples include single-celled prokaryotic organisms. The members of this kingdom do not have a true nucleus without membrane-bound organelles.

Characteristics of Kingdom Monera

The Monera characteristics are as follows:
1. The members of this kingdom are unicellular organisms, i.e., single-celled organisms.
2. All monerans are prokaryotic in nature, i.e., absence of defined nucleus and have 70s ribosomes.
3. The monerans are microscopic, and monerans are the smallest and the most plentiful organisms on earth.
4. Most of them have a rigid cell wall and are made up of non-cellulosic murein.
5. Have various modes of nutrition, which could be autotrophic or heterotrophic.
6. The members of the kingdom reproduce by both asexual and sexual reproduction.

Kingdom Monera Flowchart

The Kingdom is usually divided into two broad sub-kingdoms: Archaebacteria and Eubacteria. The flowchart is given below:

Flowchart of Kingdom Monera

Classification of Kingdom Monera

Monera is divided into Two Major Groups:

  1. Archaebacteria
  2. Eubacteria: It includes bacteria and Cyanobacteria (blue-green algae).
  3. Some other Monerans are: Mycoplasma, Actinomycetes, and Rickettsia.

Archaebacteria or Archaea or Extremophiles

Archaebacteria are olden primitive heterogeneous groups of prokaryotes which live in the extreme condition of the environment such as the absence of oxygen, high temperature, high salt concentration, hot springs, deep oceans, salt marshes. Hence, they are called Extremophiles.
The cell wall is made up of protein and non-cellulosic polysaccharides. The presence of 16s rRNA makes them unique and helps in placing them in a separate domain called Archaea between bacteria and eukaryote.

Types of Archaebacteria

There are three types of Archaebacteria:
1. Methanogens: These are methane-producing bacteria and they are strict anaerobes and produce methane through pathways of anaerobic chemosynthesis. They are present in hydrothermal bends and biogas plants, present in the gut of several ruminant animals such as cows, buffaloes, etc., and they are responsible for the production of methane (biogas) from the dung of these animals.
Example: Methanobacterium and Methanococcus.

2. Halophiles: These are the bacteria that live in extreme salt habitats. 
Example: Halobacterium and Halococcos.

3. Thermoacidophiles: These are the bacteria that live in the hot sulphur springs.
Example: Thermoplasma and Thermococcus.

Archaebacteria can be used for the following:
  1. Experimentation for absorption of solar radiation.
  2. Production of gobar gas or biogas from dung and sewage.
  3. Fermentation of cellulose in ruminants.

Do You Know This!

Thermophilic bacteria

Thermus aquaticus is a species of bacteria that can tolerate high temperatures and hence it is used in the polymerase chain reaction (PCR) – DNA amplification technique.


Eubacteria are ‘true bacteria’ which lack a nucleus and membrane-bound organelles like mitochondria, chloroplasts, etc.
Eubacteria are usually divided into five phylum – Spirochetes, Chlamydia, Gram-positive bacteria, Cyanobacteria and Proteobacteria.
The structural detail of a typical eubacterial cell is given as follows:

A labelled diagram of a typical Eubacterial cell

Bacteria are minute, microscope, unicellular prokaryotic organisms. The study of bacteria is called Bacteriology, a scientist involved in the study of bacteria is called a bacteriologist.
Occurrence: Bacteria are ubiquitously found in freshwater, marine water, boiling water, ice water, sewage, etc.

1. There are approximately \(4000\) species of bacteria, with cosmopolitan occurrence. Bacteria can be regarded as both friends and foes on the basis of interaction with human beings.

2. An average weight human \(\left({~70\,{\text{kg}}} \right)\) has about \(2.5\,{\text{kg}}\) of bacteria in the form of gut microflora to supplement the proper digestion and other metabolic functions.

Respiration in Bacteria

Respiration occurs in the plasma membrane of bacteria. Glucose is broken down into carbon dioxide and water using oxygen in the process called aerobic cellular respiration and other molecules such as nitrate \(\left({{\text{N}}{{\text{O}}_{\text{3}}}} \right)\) in the process called anaerobic cellular respiration.

Reproduction of Bacteria

Bacteria reproduce by both asexual and sexual methods.

Asexual methods: Asexual reproduction takes place by primary fission (Bacteria divide both laterally and longitudinally) and by endospore formation (It is a thick-walled, resistant, dormant structure formed by the bacteria during unfavourable condition).

Sexual methods: Although sexes are not differentiated in bacteria, the following methods of genetic recombination are categorized under sexual reproduction in bacteria, namely:
I. Transformation – It was discovered by F Griffith in \(1928\). In this, the genetic material of one bacterium is transferred to another through a conjugation tube.
II. Conjugation – It was discovered by two scientists, namely Lederberg and Tatum, in the year \(1946\). It is the transfer of genetic material that occurs through sex pili.
III. Transduction – It was discovered by Zinder and Lederberg in the year \(1952\). In this, the transfer of genetic material occurs by bacteriophage.

Economic Importance of Bacteria

Some of the economic importance of Bacteria are as follows:

1. Scavenging – Bacteria decompose the dead bodies of animals and plants and convert them into simple organic compounds. It increases soil fertility. Hence, bacteria are called “The World’s Best Scavenger”.

2. Fermentation – Many industrial products like butter, cheese, etc., are obtained by fermentation using bacteria.

3. Antibiotics – Many bacteria are used in the production of antibiotics. Example: Streptomycin, Erythromycin, etc.

4. Nitrogen Fixation – Bacteria increase soil fertility by fixing the atmospheric nitrogen in the soil. Example: Rhizobium, Nitrobacter, etc.

5. Genetic Engineering – Genetically engineered bacteria yield useful substances like hormones, enzymes, vaccines, vitamins, transgenic animals and plants, biopesticides, etc. Example: E.coli.

6. Mineral Extraction – Mineral ores containing useful metals like gold, copper, iron, nickel, etc., are extracted by bacteria called bioleaching or microbial leaching. Example: Sulfolobolus, Thiobacillus, etc.


Cyanobacteria are photosynthetic prokaryotic microorganisms commonly known as “Blue-Green Algae” or BGA.

Characteristics of Cyanobacteria

The characteristics of Cyanobacteria are as follows:
1. Cyanobacteria are Gram-negative unicellular, colonial blue-green algae and can live in both freshwater and marine habitats and are responsible for ‘blooms’ in polluted water (eutrophication).
2. They have photosynthetic pigments, chlorophyll-a, carotenoids, and phycobilins, and food is stored in the form of cyanophycean starch, lipid globule, and protein granules.
3. Cyanobacteria have a cell wall formed of peptidoglycan, naked DNA, \(70\)s ribosomes, and the absence of membrane-bound organelles like endoplasmic reticulum, mitochondria, Golgi bodies, etc.
4. Cyanobacteria can fix atmospheric nitrogen through a specific structure called heterocyst. These are modified cells in which photosystem-II is absent. Hence, non-cyclic photophosphorylation does not take place. Nitrogen-fixation is performed through the enzyme nitrogenase present in it.

A labelled diagram of Nostoc

Economic Importance of Cyanobacteria

Some of the economic importance of Cyanobacteria are as follows:
1. Cyanobacteria serve as food for fishes and other aquatic animals.
2. Cyanobacteria like Anabaena and Nostoc are used as biofertilizers.
3. Cyanobacteria like Spirulina are used for human consumption as single-cell protein (SCP).
4. Cyanobacteria like Chlorella are used in sewage treatment.

Harmful Role

  1. Cyanobacteria contaminate the water by forming water blooms. These produce toxins in water and cause the death of aquatic animals.
  2. Cyanobacteria grow and develop blooms in the urban water supply pipelines.
  3. Some Cyanobacteria grow on buildings during the rainy season and cause damage to the buildings.

Did You Know This?

Red sea

The Red Sea is named after the colouration provided by red coloured Cyanobacteria i.e., Trichodesmiumerythraeum.

Some Other Monerans


It was discovered by two scientists, namely, Nocard and Roux, in the year \(1898\). These lack cell walls and aerobic non-motile organisms. Due to the absence of cell walls and pleomorphic nature, they do not have a specific shape. The Mycoplasmas are also known as Pleuro-Pneumonia Like Organisms (PPLO). These are the smallest living cells, yet discovered, can survive without oxygen and are typically about \(0.1\) μm in diameter.
Witches broom is the common plant disease caused by the Mycoplasma in Sandalwood trees.

A labelled diagram of Mycoplasma


The members of a heterogeneous group of Gram-positive, are generally anaerobic bacteria noted for a filamentous and branching growth pattern.

Some of the characteristics are as follows:
1. Morphologically, the members of this group resemble fungi because of their elongated cells that branch into filaments or hyphae.
2. During the composting process, mainly thermophilic and thermotolerant Actinomyces are responsible for the decomposition of organic matter at elevated temperatures.
3. Generally, Actinomycetes grow on fresh substrates more slowly than other fungi and bacteria.
4. During the composting process, the Actinomycetes degrade natural substances such as chitin or cellulose.
5. Natural habitats of thermophilic Actinomycetes are corn mills, air conditioning systems, and closed stables. Some Actinomycetes are found responsible for allergic symptoms in the respiratory tract, e.g., Extrinsic Allergic Alveolitis (EAA).

Image of Actinomycetes


These are small, aerobic, and Gram-negative bacteria. These organisms belong to the phylum called Proteobacteria, which are capable of growing at a low level of nutrients and have a long generation time relative to other Gram-negative bacteria.

Rocky Mountain Spotted Fever (RMSF) is a tick-borne human disease caused by Rickettsia rickettsii, an obligate, intracellular bacteria.

Image of Rickettsia


Bacteria is the most commonly heard term and these bacteria are the members of the kingdom and are seen everywhere on this Earth abundantly. Through this article, we got to know how the members of the kingdom Morena are classified, their special characteristics, and much more. Monerans are friendly as well as harmful to our bodies.

Frequently Asked Questions (FAQs) on Kingdom Monera

Q. What are Monerans?
Ans: The Monerans are prokaryotic unicellular microorganisms found in a moist environment.

Q. How are Monerans classified?
Ans: Monerans are classified into Archaebacteria, Eubacteria, and Cyanobacteria.

Q. How does Monera reproduce?
Ans: Monerans reproduce both asexually and sexually. Under asexual reproduction – fission and through endospore formation. In sexual mode – transformation, conjugation, and transduction.

Q. Where is Monera found?
Ans: Monerans are found in freshwater, marine water, boiling water, ice water, sewage, etc.

Q. How does Monera feed?
Ans: Some Monerans feed on dead organisms as they show heterotrophic nutrition. And some Monerans like Cyanobacteria are photosynthetic and produce their own food.

Q. How is Bacteria classified on the basis of mode of nutrition?
On the basis of mode of nutrition, bacteria can be Autotrophic or Heterotrophic in nature. Autotrophic bacteria make their own food. Heterotrophic bacteria are dependent on other materials for their nutrition.

Q. How many types are Heterotrophic organisms classified into?
Heterotrophic organisms are classified into three types – Parasites, Symbionts and Saprotrophs.

Now that you have a detailed article on Kingdom Monera, we hope you study well. If you get stuck somewhere do let us know in the comments sections. We will get back to you at the earliest. Stay tuned to Embibe for latest news and updates on Monera Classification.

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