Study Notes On Biology: MICRO ORGANISMS

Study Notes On Biology: MICRO ORGANISMS

Here we are providing the short notes on Biology which will be help to crack science part in may examinations like SSC, Railway and other competitive exams.


Micro organisms are classified into four major groups. These groups are bacteria, fungi, protozoa and algae.

  • Viruses: They reproduce only inside the cells of the host organisms which may be bacterium, plants or animal.
  • Common cold, influnenza and most coughs are caused by viruses.
  • Serious diseases like polio and chickenpox are also caused by viruses.
  • Micro organisms may be single celled like bacteria, Some algae and protozoa. Multicellular such as algae and fungi.
  • Micro organisms like amoeba can live alone, while fungi and bacteria may live in colonies.

 Advantages of Micro Organisms

  • Making of curd and breed:-milk is turned into curd by bacteria. The bacterium “lactobacillus” promotes the formation of curd.
  • Yeast reproduces rapidly and produces CO2 during respiration. Bubbles of the gas fill the dough and increase its volume.
  • Yeast is used for commercial production of alcohol and wine. For this purpose yeast is grown as natural sugars present in grains like barley, wheat, rice, crushed fruit juice etc.
  • This process of conversion of sugar into alcohol is known as fermentation. Lewis Pasteur discovered fermentation.

 Medicinal Use of Micro Organisms

  • The medicine which kills or stops the growth of diseases causing microorganism is called antibiotics.
  • Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotics. Which are made from fungi and bacteria.
  • Alexander Fleming discovered penicillin.
  • Antibiotics are not effective against cold and flu as these are caused by virus.


  • Edward Jenner discovered the vaccine for small pox.

 Harmful Microorganisms

  • Disease-causing microorganisms are called pathogens.
  • Microbial diseases that can spread from an infected person to a healthy person through air water, food, or physical contact are called communicable diseases. i.e.- cholera, common cold, chicken pox and TB.
  • Female anopheles mosquito which carries the parasite of malaria.
  • Female aedes mosquito acts as carrier of dengu virus.
  • Robert Koch discovered the bacteria (bacillus anthracis) which causes anthrax disease.

 Common Methods of

Preserving Food in our Homes

  • Chemical method: salt and edible oils are the common chemical generally used.
  • Sodium benzoate and sodium metabisulphite are common preservatives. These are also used in the Jams and squashes to check their spoilage.

 Preservation by sugar :

  • Sugar reduces the moisture context which inhibits the growth of bacteria which spoil food.
  • Use of oil and vinegar prevents spoilage of pickles become bacteria cannot live in such an environment.
  • Pasteurized milk : the milk is heated to about 70˚C for 15 to 30 seconds and then suddenly chilled and stored.
  • This process was discovered by Louis Pasteur. It is called

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