World of Microorganisms

1.1  World of Microorganisms

1. Classification of microorganisms

  • Bacteria
  • Fungi
  • Protozoa
  • Virus
  • Algae


  Bacteria Fungi Protozoa Virus Algae
Size 0.2 µm - 10 µm  10 µm - 100 µm 5 µm - 250 µm 0.02 µm - 0.4 µm

1 µm - 100 µm

Shape Coccus, bacillus, spirilla, vibrio Spherical, filamentous Spherical, spindle-shaped, irregular shaped Sphetica;, helix, polyhedral, complex Spherical, oval-shaped, filamentous
Nutrition Autotrophic, saprophytic, parasitic

Saprophytes, parasitic

Saprophytic, parasitic - Autotrophic
Habitat Air, water, soil, food, bodies of other organisms Places with decaying matter, faeces, animal skin and food Aquatic habitats, damp place, bodies of living organisms Live in living host cells, form crystals outside a living cell Aquatic habitats, damp place
Method of reproduction

Asexual: binary fission

Sexual: conjugation

Asexual: budding, spore formation

Sexual: conjugation

Asexual: binary fission

Sexual: conjugation


Asexual: binary fission, spore formation

Sexual: conjugation

Example Bacillus sp., Vibro sp. Mushroom, yeast Paramecium sp., Ameoba sp. Influenza A virus

Chlamydomonus sp. 

Spirogyra sp.

3. Factors that affect the growth of microorganisms
Factors Explaination

Damp conditions promote the growth and reproduction of microorganisms.

In dry condition, some bacteria will form cyst or spores. 


Microorganisms with chlorophyll prefer light condition.

Fungi and few bacteria prefer dark condition.

Exposure to UV light can kill microorganisms.


Most microorganisms prefer 35 °C - 40 °C.

Low temperature in refrigerator reduce growth rate of microorganisms.

High temperature can kill microorganisms.

pH value

Optimum pH for most microorganisms is pH 7.

Some microorganism can live in environment with slightly acidic or alkaline.

Nutrients The growth rate of microorganisms depends on amount of nutrients.