[Biology] Kingdom-Monera

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INTRODUCTION

  • Kingdom Monera is comprised of the simplest organisms of earth.
  • These organisms are unicellular and microscopic with a prokaryotic cellular organization.
  • Monera consists of
    • Bacteria
    • Mycoplasma
    • actinomycetes
    • cyanobacteria
    • rickettsia

SALIENT FEATURES OF MONERA

  • The members of kingdom Monera mainly include microscopic, unicellular prokaryotes.
  • Prokaryotes are simple organisms that lack a true nucleus and majority of the membrane-bound organelles such as endoplasmic reticulum, Golgi apparatus, lysosomes etc.
  • DNA of prokaryotes is present in the form of a loose assembly inside the cytoplasm and is termed as nucleoid.
  • Their DNA is arranged in the form of a single chromosome.
  • They reproduce mainly by asexual means especially binary fission
  • Unlike animal cells, prokaryotes have cell walls which is mostly composed of peptidoglycan and provide rigidity to their cells.

BACTERIA

  • Bacteria were the first organisms to survive on planet earth after life originated around 3.5 billion years ago.
  • They are unicellular organisms, structurally simple and carry out all of their activities within one cell.
  • They are microscopic and range in size from 0.1 to 10 microns.
  • Unlike other complex cells, bacteria are prokaryotic and do not possess any membrane-bounded nucleus or other intracellular organelles.
  • Their genetic material is structured into a single circular chromosome containing deoxyribonucleic acid (DNA)
  • They multiply by asexual means through conjugation and binary fission.
  • Genetic exchange in bacteria occurs through conjugation, transduction, and transformation.

Bacteria

ACTINOMYCETES

  • The Actinomycetes are a group of Gram-positive bacteria which form branched filamentous hyphae
  • Their hyphae resemble the fungal hyphae.
  • Their hyphal diameter is around 1µm, whereas in fungi it is 5 to 10 µm
  • These are usually rod shaped having a filamentous and branched structure.
  • Most of the species are aerobic, but few of them are also anaerobic and facultative aerobes.
  • Structurally their Cell wall is similar to bacteria.
  • The growth of Actinomycetes is slower as compared to bacteria and fungi and thus they are called as “slow growers”
  • The growth of actinomycetes is efficient in alkaline pH.
  • Actinomycetes are most abundant in soil and marine habitat.
  • These are most usually non-motile and non-capsulated.

Actinomycetes Images, Stock Photos & Vectors | Shutterstock

MYCOPLASMAS

  • Mycoplasmas are ubiquitous intracellular gram negative type bacteria.
  • Majority of mycoplasma organisms are motile, and they use their gliding motility for movement instead of pili or flagella.
  • They are the smallest organism which are capable of self-replication. Their size ranges from 0.2 to 2 µm in diameter
  • They lack the genes which are responsible for the formation of cell wall.
  • Instead of a cell wall, they contain a three-layered membrane, containing sterol, which is taken up from the environment.
  • Most of mycoplasmas are facultative anaerobic, but some are completely anaerobic.

CYANOBACTERIA

  • Cyanobacteria are more commonly known as Blue-Green Algae
  • Blue-green algae are the most primitive organisms. They are not considered as “true-algae”. They resemble bacteria in structure and therefore were placed in kingdom Monera.
  • Cyanobacteria are basically phototrophic bacteria.
  • They are single-celled organisms and thus contain a simple structure.
  • Cyanobacteria reproduce asexually, either through binary fission or multiple fission, in unicellular and colonial forms or by fragmentation and spore formation in filamentous species. Under favorable conditions, cyanobacteria can reproduce at explosive rates, forming dense concentrations called blooms
  • Nucleus of cyanobacteria lacks any boundary or nucleolus.
  • The nucleoplasm is scattered throughout the cells.

I) Cyanobacteria - Is Cyanobacteria Good or Bad?

Rickettsia

  • Rickettsia are one of closest living relatives to bacteria.
  • Rickettsia species are small, Gram-negative bacilli
  • They consist of the Genera Rickettsiae, Ehrlichia, Orientia, and Coxiella
  • They usually act as obligate intracellular parasites of eukaryotic cells
  • Rickettsia can be transmitted by arthropod vectors to humans, causing disease
  • The vectors could be ticks, fleas or lice
  • They cause diseases in humans such as typhus, rickettsia pox, Boutonneuse fever, African tick bite fever, Rocky Mountain spotted fever etc.
  • Rickettsia can be classified into three main groups, on the basis of serology and DNA sequencing:
    • Spotted fever
    • Typhus
    • Scrub typhus.

REFERENCES

  • Arihant’s handbook of biology. Biological classification. Page no: 7-23.
  • NCERT biology; textbook for class 11. Biological classification. Page no: 16-28.
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