Skip to main content

Class 8, Science, Chapter-2, Lecture-1, Microorganism (Notes)

MICROORGANISMS: 

The living organisms which cannot be seen with naked eyes are termed as microorganisms or microbes.

  • the oldest form of life on earth are microbes.

Microbes are also called Micro-organisms.

Reason: 
Micro means very Small. 
The size of these organisms is very small and cannot be seen with naked eye.

Classification

  1. Bacteria 
  2. Fungi 
  3. Protozoa 
  4. Algae 
  5. Virus

Characteristics of Microorganisms:

  1. Bacteria:
    • unicellular micro-organisms
    • have cell walls
    • does not have organized nucleus and other structures.
    • are found in air, soil, water, on our bodies and inside our bodies.
    • feed , move, respire and reproduce on their own.
    • Diseases caused by Bacteria: 
      Cholera, Typhoid, Tuberculosis(TB), Diptheria, Whooping cough, Food poisoning etc.
  2. Viruses: 
    • are smallest microbes
    • can develop only inside the cells of the host organisms (animal, plant or bacterium).
    • are much smaller than bacteria
    • do not show much characteristics of a living thing.
    • Diseases caused by Viruses: 
      Common cold, Influenza (Flu), Measles, Polio, Chickenpox, Small pox, AIDS etc.
    • Diseases caused by virus cannot be treated with antibiotics.
    • Viruses do not respire, feed, grow, excrete or move on their own. 
      They can only reproduce and multiply inside the cells of other organisms. 
      Viruses are agents of disease.
  3. Protozoa:
    • are a group of single celled microorganisms which are classified as animals.
    • found in ponds, lakes, dirty water drains, rains, sea water and damp soil.
    • Many protozoa are parasites and cause diseases.
    • Examples of Protozoa: Amoeba, Paramecium, Plasmodium and Entamoeba.
    • Diseases caused by Protozoa: 
      Dysentery (Entamoeba), Malaria (Amoebic).
  4. Algae:
    • is a large group of simple, plant like organisms but they do not have proper roots, stems or leaves.
    • contain chlorophyll and produce food by photosynthesis.
    • Examples of algae: Chlamydomonas, Spirogyra, Blue-green algae, Diatoms and Seaweeds.
    • Some algae are unicellular- chlamydomonas and diatoms.
    • Most algae are multicellular- blue-green algae and spirogyra.
    • The blue-green algae act for nitrogen fixation in the atmosphere.
  5. Fungi:
    • Fungi are a large group of organisms which do not have chlorophyll and do not photosynthesise.
    • Examples: yeast, bread mould (rhizopus), penicillium and aspergillus, mushrooms, puffballs.
    • All fungi except yeast are made up of fine threads called hyphae.
    • Some fungi are parasites while most are saprophytes feeding on remains of dead plants and animals.
    • Diseases caused by Fungi: Ringworm, Athelete’s foot.