Microorganisms : Friend and Foe

Microorganisms are the living organisms, which are not visible through naked eyes. Microorganisms are divided into four groups; bacteria, fungi, protozoa and some algae. Viruses are also microscopic microbes and they reproduce inside the host cell. Microorganism can survive in hot springs, on the ocean floor, high in the atmosphere and deep inside rocks within the Earth's crust. They can also live inside animal body as well as on the body of other microorganisms.

Some microorganisms play an important role in our daily life. They are used for various purposes such as preparation of curd, bread and cake. The bacteria responsible for the formation of curd are Lactobacillus. Yeast converts sugar into alcohol by the process called fermentation. They are used to manufacture antibiotics, vaccines etc. Some of the vaccines are DPT, polio vaccine etc. Several diseases, including cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination.



The bacterium Rhizobium is involved in the fixation of nitrogen in leguminous plants. Nitrogen fixation is performed in which nitrogen is taken from its natural, relatively inert molecular form (N2) in the atmosphere and converted into nitrogen compounds. Microorganisms also play a role in increasing soil fertility. Microorganisms act as scavengers. Some microorganisms are harmful to us. Disease causing microorganisms are called pathogens.

  • Diseases caused by bacteria: Tuberculosis, cholera, typhoid etc.
  • Diseases caused by protozoa: Malaria etc.
  • Diseases caused by viruses: Measles, chicken pox, polio, Hepatitis B etc.
Communicable diseases are transmitted from an infected person to another person. Some microbial diseases require carriers (vectors) for their transmission. Some vectors are: Housefly, Anopheles mosquito that carries the parasite of malaria. In animals, microorganisms cause anthrax, foot and mouth disease etc. In plants, bacteria cause citrus canker, fungi cause rust of wheat, and virus causes yellow vein mosaic of bhindi. As microorganisms spoil our food and can cause food poisoning, various methods are used to preserve the food and prevent them from the attack of microorganisms.

The methods to preserve food are:
  • Chemical methods: Use of salts, sugar, edible oil, nitrogen, vinegar, sodium benzoate, sodium metabisulphite etc
  • Heat and cold treatments: keeping food in refrigerators, pasteurisation of milk etc
  • Storage and packing: Use of airtight packets to pack fruits and vegetables
Packaging materials commonly used for foods may be classified as flexible, semi-rigid and rigid.

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