Kingdom Archaebacteria and Kingdom Eubacteria, Biology tutorial

Introduction to Kingdom Archaebacteria:

Archaebacteria is first kingdom in 6 kingdom categorization of living things. Word Archae just means ancient. This kingdom has organisms at simplest level of organization. They are prokaryotes, who were earlier in kingdom Monera but now identified as being hereditarily and structurally distinct, forming own domain, Archaea. Not like bacteria, archaea lack peptidoglycan in the cell walls and contain unusual (ether-linked) lipids in their cell membranes that are not discovered in any other group of organisms. This group of single celled organisms lives under tremendous situations likes no oxygen and very high temperatures. Structure and function of genes in archaea are alike to structure and function of genes in eukaryotes, while those of eubacteria are not.

Diagnostic Features of Archaebacteria:

i) Archaebacteria contain no peptidoglycan in cell walls

ii) The cell wall is composed of glycoproteins and polysaccarides.

iii) The cell wall envelopes have the high resistance to antibiotics and lytic agents because of difference in cell wall composition.

iv) Archaebacteria are approx 1/10th of a micrometer to approx 15 micrometer in size. A few are flagellated and flagella structure is different from flagella of other bacteria.

v) Archaebacteria is non-pathogenic bateria which live in and around organisms.

vi) Archaebacteria is autotrophs and utilizes CO2 in atmosphere as the source of carbon for the procedure known as carbon fixation.

Classification of Archaebacteria:

The archae are presently situated in 4 phyla, they are

i) Eurychaeota e.g Pyrococcus abysi

ii) Crenarchaeota e.g sulfolobus acidocaldarius

iii) Nanoarchaeota e.g Nanoarchaeum equitans

iv) Korarchaeota

Archaebacteria cells possess diameters that range from about 0.0002-0.0004 in (0.5-1.0 micrometer). Volume of cells is only around one-thousandth that of typical eukaryotic cell. They have 3 major shapes

i) Spherical cells called cocci,

ii) Rod shaped cells called bacilli,

ii) Spiral shaped cells that can either be vibrio, spirillum, or spirochete


Archaebacteria, like every prokaryotes, possess no membrane bound organelles. This signifies that archaebacteria are without endoplasmic reticula, Golgi complexes, mitochondria, nuclei, lysosomes, or chloroplasts. Cells have thick cytoplasm which has all molecules and compounds of metabolism and nutrition . Archaebacteria possess the cell wall which has no peptidoglycan. Rigid cell wall supports cell, permitting the archaebacterium to keeps its shape, and protecting cell from bursting when in hypotonic environment. Plasmids may be present in archaebacterial cell. These are small, circular pieces of DNA which can duplicate independent of larger, genomic DNA circle. Plasmids frequently code for s enzymes or for antibiotic resistance.


These organisms dwell in tremendous environmental situations, like very high temperatures, (over 100 °C) and in deficiency of oxygen and light (thus are also called as extremophiles) Particular examples has Near volcanic activity, black smokers, Geysers, and oil wells, Deep oceans, Very cold habitats, highly saline ,acidic, or alkaline water, Marshland,

Archaebacteria Groups:

Archaebacteria are autotrophs and utilize CO2 in atmosphere as the source of carbon for the process called carbon fixation. They use different chemical reactions to survive in the harsh conditions. Based on nature of habitats archae are clustered into three , these are

i) Methanogens

ii) Halophiles

iii) Thermoacidophiles.

Methanogens can decrease carbon dioxide in methane. They can live in absence of oxygen. They make marsh gas which one can observe as bubbles in inactive waters. They are there in gut of cattle and termites. The bacteria are spherical or rod shaped and can be gram positive and negative.

Thermoacidiophiles :- Organisms which can survive in very high temperatures and low pH. They can live at 100° Celsius with the pH of 2. Most of the organisms are anaerobic nature like Pyyrodictium, Sulfolobus, thermoproteus, thermococcus, Pyrococcus,.

Adaptive features:

Archaebacteria don't form spores and few species of haloarchae suffers phenotypic switching. This signifies it can develop numerous various cell types which are resistant to osmotic shock. Therefore, organisms live in low salt concentration aquatic environments.

Introduction to Kingdom Eubacteria:

This is second kingdom in 6 kingdom categorization of living things. They are also called as true bacteria. They are prokaryotes and many of them live as single cells, but they are able to make colonies or link up in chains to create filaments.


The Eubacteria are cosmopolitan, they exist everywhere water, faeces, soils, decaying substances, bodies of plants and animals.

Categorization of Kingdom Eubacteria:

There are 3 main criteria utilized to categorize Eubacteria, they are:

1) Shape:

It is simple to differentiate Eubacteria based on the shape. Bacterial cells possess 3 main shapes:

i) Cocci: round with bumps

ii) Bacilli: rod-shaped with lacerations

iii) Spirilli: spiral-shaped with grooves

In addition, bacteria can be categorized by the growth characteristic patterns (Groupings). Prefix diplo- means that cells are arranged in pairs. Prefix staphylo- signifies that bacterial cells are set in groups like grapes. Prefix strepto- means that bacteria are set in the chain.

2) Kind of cell wall structure:

  • Gram-positive: Gram-positive bacteria possess simple cell walls which are composed of only one layer of peptidoglycan prior to plasma membrane. When stained with violet and red dye, gram-positive bacteria appear purple. On occasion blue, depending on temperature.
  • Gram-negative: Gram-negative bacteria possess more complex cell walls, comprising of one layer of lipopolysaccharide membrane and peptidoglycan layer. Gram-negative bacteria seem red when stained with violet and red dye.
  • Carbon and Energy Sources

a) Photoautotrophs b) Photoheterotrophic c)Autotrophic d) Heterotrophic

3) Structure:

Eubacteria possess prokaryotic chromosomes that have circular DNA molecules known plasmids. They don't possess the nuclear membrane, in its place they possess plasmids, which can be observe in comparatively clear areas in cytoplasm known as nucleoids. The rest of cytoplasm is occupied with ribosomes. Several eubacteria possess particular internal membranes. For instance, cyanobacteria have membranes which have chlorophyll and other chemicals used to perform photosynthesis. Several eubacteria possess cell walls which lie outside of the plasma membranes. These are like cell walls located in plants and fungi, but are composed of peptidoglycan rather than cellulose or chitin. In few eubacteria, this cell wall is enclosed by another layer known as outer membrane. Several eubacteria have yet another coating layer known as a capsule. It is composed of complex sugars and serves to protect cell against environmental dangers, like attack by host immune defenses or dehydration.

Adaptive Features of Kingdom Eubacteria:  

i) Shape Spiral shaped bacteria can move by fluids more simple than can cocci or bacilli bacteria.

ii) Plasmids Bacteria contain plasmids, which can be transmitted from one cell to another. This skill to trade genes with every comer makes bacteria amazingly adaptible; advantageous genes, like those for antibiotic resistance, may be spread extremely rapidly through bacterial populations.

iii) Capsule protects cell against environmental dangers, like attack by host immune defenses or dehydration.

iv) Endospore - These are created when surrounding situations are unfavorable and are for protection thick walled endospores

v) Outer membrane- Enhances potential surface area for photosynthesis

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