Biological Classification

Kingdom Monera

You have suffered from a lot of diseases that bacteria cause. But, do you think all bacteria are bad? No! The bacteria have a huge kingdom of their own that consists of a number of varieties of them. Each bacteria has a different role to play. They belong to the kingdom Monera. Here, we will know all about the kingdom Monera. We will look at both their characteristics and divisions in greater detail.

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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 in these organisms is the naked circular DNA. A nuclear envelope is absent. Both, ribosomes and simple chromatophores, are the only subcellular organelles in the cytoplasm.
  • 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 non-motile or move by the beating of simple flagella or by gliding.

Learn more about the Different type of Kingdom Classifications here.

Bacteria Shape

  • Cocci: They are oval or spherical in shape.
  • Bacilli: They are rod-shaped. They may or may not have flagella.
  • Vibrios: These are small and ‘comma or kidney’ like. They have a flagellum at one end and are also motile. Vibrio bacteria has a curve in its cell.
  • Spirillum: They are spiral or coiled like a cork­screw. The spiral forms are usually rigid and bear two or more flagella at one or both the ends e.g., Spirillum, Spirochaetes etc.
  • Filament: Just like fungal mycelia, the body of the bacterium is filamentous. The filaments are very minute in size. Examples include Beggiota, Thiothrix etc.
  • Stalked: The body of bacterium possesses a stalk e.g., Caulobacter.
  • Budded: The body of the bacterium is swollen at places e.g., Rhodomicrobiu

Learn more about Kingdom Fungi here.

Structure of Bacteria

  • 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, anthracite, Diplococcus pneumoniae, Mycobacterium tuberculosis.
  • Cell wall: All bacterial cells .are covered by a strong, rigid cell wall. Therefore, we classify them under plants. Inner to the capsule, the cell wall is present. It is made up of polysaccharides, proteins and lipids. We also find D-glutamic acid and diaminopimelic acid.

Monera

  • Plasma membrane: Each bacterial cell has a plasma membrane. It is situated just internal to the cell wall. It is a thin, elastic and also differentially or selectively permeable membrane.
  • Cytoplasm: The cytoplasm refers to a complex and aqueous fluid or semifluid ground substance (matrix). This material consists of vitamins, salts, enzymes, carbohydrates, soluble proteins, co-enzymes, lipids, mineral and nucleic acids. The organic matter is present in the colloidal state.The cytoplasm is granular due to the presence of a large number of ribosomes.
  • Nucleoid: It has other common names like genophore, naked nucleus or incipient nucleus. There is nuclear material in these, DNA. It is double helical as well as circular. Some kind of typical protein surrounds it. However, these are not histone proteins.
  • Plasmids: In addition to the normal DNA chromosomes, many bacteria (e.g., E.coli) have extrachromosomal genetic elements or DNA. These elements are plasmids. They are small circular double-stranded molecules.
  • Flagella: These are fine, thread-like, protoplasmic appendages. These 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.
  • Pili or Fimbriae: Besides flagella, some tiny or small hair-like outgrowths are present on the bacterial cell surface. These are pili. They comprise of pilin protein. They consequently measure about 0.5-2 mm in length and 3-5mm in diameter.

Learn more about Kingdom Animalia here.

Nutrition in Bacteria

On the basis of mode of nutrition, we can group bacteria into two broad categories. First is autotrophic whereas second is heterotrophic bacteria.

  • Autotrophic bacteria: These bacteria are able to synthesize their own food from inorganic substances, as green plants do. They derive their carbon 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 consequently depend on external organic materials. They require at least one organic compound as a source of carbon for their growth and energy. Such bacteria are heterotrophic bacteria. Heterotrophic bacteria are of three types­: Parasites, Saprotrophs and Symbionts.

Learn more about Kingdom Protista here.

Solved Example For You

Question: Write a short note on cyanobacteria.

Answer: Cyanobacteria, also known as blue-green algae are photosynthetic prokaryotes. They perform oxygenic photosynthesis. Photosynthetic pigments include chlorophyll a, carotenoids and phycobilins. They primarily store the food in form of cyanophycean starch, lipid globules and protein granules. We can trace their origin to around 3 billion years back. They consequently added oxygen to the atmosphere. These bacteria also paved the path for the evolution of aerobic forms, including aerobic bacteria.

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