Chapter 2 Microorganisms: Friend and Foe

  • Microorganisms are too small and are not visible to naked eyes.
  • Microorganisms are found in air, water and in the bodies of the plants and animals.
  • They may be unicellular or multicellular.
  • Microorganisms includes bacteria, fungi, protozoa and some algae. Viruses are different from the above mentioned living organisms, are considered microbes.
  • Viruses are quite different from the other microorganisms. They reproduce only inside the host organism: bacterium, plant and animal cell.
  • Some microorganisms decompose the organic waste and dead plants and animals into the simple substances and cleans up the environment.
  • Some bacteria present in the soil fixes the nitrogen from the atmosphere and convert into the nitrogenous compounds.
  • Microorganisms can live in all kind of environment ranging from cold climate to hot deserts.
  • Protozoan causes serious disease like malaria and dysentery.
  • Microorganisms grow on our food which may lead to food poisoning.
  • Algae is a type of microorganism which lives in the water and contain chlorophyll.
  • Antibiotics are the medicines which kill or stop the growth of disease causing organism.
  • WBCs (white blood cells) produces a protein called antibiotics which identify and destroy the microbes.
  • Carrier may be defined as the living beings which carry the microorganisms to spread disease.
  • The disease which can spread from an infected person to healthy person through air, water and by physical contact.
  • The process of conversion of sugar into alcohol is called as fermentation.
  • Pasteurization is the process, in which milk is heated to 70◦C for 15 to 20 seconds and then suddenly cooled and stored, then the growth of microbe is prevented in the milk. This process was discovered by Louis Pasteur, so it is known as pasteurization.
  • Preservation is the process in which food can be preserved from the actions of microorganisms.
  • Injecting the dead or weak microbes in healthy body is called as vaccine. It develops immunity.  


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Exercise 1 ( Page No. : 30 )