Morphology of Bacterial cell

Morphology means systematic study of external characters of bacteria.

Morphology of bacterial cell deals with study of

  • Size of bacteria.
  • Shape of bacteria.
  • Arrangement of bacteria.

Size of bacteria.

  • Size of bacterial cell is less than 3 micrometer.
  • The bacteria are microscopic in nature and are visible only under compound microscope.
  • These bacteria may be spherical,cylindrical or spiral in shape.
  • Size of a spherical shape bacteria can be measures in diameter.
  • Size of a cylindrical bacteria is measured by its length and width.
  • In spiral shape bacteria length is measured but due to spiral form it is not exact.
  • As we know all bacteria are microscopic in nature so their size is also measured under microscope.
  • Size of bacteria is measured  by using calibrated slide and calibrated  occular compound microscope is used.
  • The above method of measuring size is called as micrometry.
  • The size of bacteria can also be measured by electron microscopic micrometry.
  • Units of measurement used in bacteriology are
  1. Micron or micrometer.
  2. Nanometer (nm) or Millimicron.
  3. Angstrom (A°)
  • The conversion are as follows
  • 1 μm = 10-3 mm = 10-4cm = 10-6 meter1 nm = 10-3 μm = 10-6 mm1 A0 = 10-1 nm = 10-4 m =10-7 mm
  • Size of spherical bacteria or cocci ranges from 0.5 to 3.0 μm.
  • Size of cylindrical or rod shape bacteria ranges from 0.15 μm to 2.0 μm in width and 0.5 μ to 20 μ in lenght.
  • The small size of bacteria have large surface area for entry of nutrients, water and exit of waste.

Shape of bacteria

Microscopic observation of bacterial cells

  • Shape of bacteria cell depends on the rigidity of cell wall.
  • There are three shapes of bacteria.

a) Spherical or cocci shape.

If the cells are spherical  or ball shape  then the cells are called as cocci or spherical     shape bacteria.

b) Cylindrical or rod shape.

If the cells are rod or cylindrical in shape it is called bacilli.

c) Spiral shape.

A bacteria which is twisted two or more time along the axis is called a spiral form bacteria.

Arrangement of bacterial cells.

Variety of arrangement of cells is observed in cocci and rod shape bacteria.

a) Arrangement of cocci cells.

Arrangement of cocci shape bacteria.

  • Singly :- If a cocci cell appear individually then simply  it is called cocci.
  • Diplococci :- When two cells are attach to each other even after dividing them in one plane is called as diplococci.
  • Streptococcus:- If cocci cells are arranged in long chain and remain attach to each other even after dividing them in one plan is called as streptococcus.
  • Staphylococcus:-  If the cocci cells arranged in form of a cluster even after dividing them in three plane then these cocci cells are called staphylococcus.

b) Arrangement of rod shape bacteria.

Bacillus cells show very less variety in arrangement of cells as these cells can be divided only in one plane.

  • Single cell :- If only one cell exist it is called as bacilli.
  • Diplobacilli :- If two bacilli cells are attach to each other it is called as diplobacilli.
  • Streptobacilli :- It bacilli cells are arranged in the form of long chain it is called as streptobacilli.

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