Micro Organism – 2 Science For Class 8th

Is Micro-Organisms Good For Us ?

Microorganisms play a very important role in our lives

Based on their behavior ,These can be classified into two classes :

  • Friendly Microorganism
  • Harmful Microorganism

Friendly Microorganism

  • The microorganisms which are useful to us are friendly microorganism
  • In Preparation of Curd, Bread,Cake etc.
  • In the production of alcohol
  • in cleansing the environment
  • In agriculture for increasing productivity and soil fertility

Making of curd and  bread 

  • The Bacterium ,Lacto Bacillus promotes the formation of curd from milk
  • The bacterium Renin is used in cheese production
  • Yeast is used in the production of bakery products(Bread ,Cake,Dosa etc.)
  • Yeast is a beneficial fungi
  • Yeast causes fermentation of dough and causing and liberates carbon dioxide making the food items porous and fluffy

Commercial use of microorganisms

  • Alcohol from Starch
  • Wine from fruit juices

Fermentation –

The enzymatic breakdown of large organic molecules into smaller ones in the absence of air is called fermentation

Alcohol is obtained from sugar by fermentation with yeast

Yeast contains the enzymes zymaze and invertase

Sugar–Zymase–> Glucose + Fructose

Glucoze –Invertase —> Ethyl Alcohol + Carbon Dioxide


Image result for fermentation equation

Medicinal use of microorganisms

  • Antibiotics are specially manufactured by growing specific microorganisms under controlled conditions
  • Antibiotics are used in the treatment of infections in humans as well as in animals
  • Antibiotics should be  taken only on the advise of doctor
  • Antibiotics should not be taken when not needed as it may kill useful bacteria


  • Another way to prevent disease is by immunization
  • A small dose of weakened or killed disease causing microbes needed to immunize the body against a particular disease is called vaccine
  • Vaccine should be kept/stored at low temperature

How does vaccine work

  • When a disease causing microbe enters our body , the body produces antibodies to fight the invader.
  • These antibodies destroy the weakened microbes and remain in the blood to fight any further attack by such – disease causing microbes
  • Children are more sensitive to to diseases.
  • to protect them from any such harmful microbes ,appropriate vaccine must be given at suitable age.
  • Such vaccines are easily available in hospitals and health centers

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Increasing soil fertility 

  • blue green algae can fix the atmospheric nitrogen as nitrogen compounds in the soil
  • symbiotic bacteria living in the root nodules of the leguminous plants absorb atmospheric nitrogen and convert it into nitrogenous compounds
  • as a result they enrich the soil with nitrogen

Cleansing the Environment

  • Many microorganism decompose the dead organic waste of plants and animals into simpler and harmful substances
  • Such simpler substances get into soil and used by other plants
  • Anaerobic bacteria degrade the animal dung into bio gas and the leftover slurry can be used as a manure
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