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CBSE Class 8 Biology Notes for Chapter 2 Microorganisms

Living organisms that we cannot see with our eyes alone are called microorganisms or microbes. They are classified into four major groups: bacteria, fungi, protozoa and some algae.
Viruses are also microorganisms but they reproduce only inside the host organism.

  • Microorganisms are used in the preparation of curd, bread and cake.
  • They are also used in the production of alcohol by fermentation. Fermentation is the process of conversion of sugar into alcohol
  • They also clean up the environment by breaking down organic matter.
  • They are used to increase the soil fertility.
  • They are used in medicines as antibiotics and as antibodies in vaccines.

Disease causing microorganisms are called pathogens. Some common diseases caused by microorganisms are:
Tuberculosis: Bacteria
Measles: Virus
Chicken Pox: Virus
Polio: Virus
Cholera: Bacteria
Typhoid: Bacteria
Hepatitis B: Virus
Malaria: Mosquito
(i) Chemical method: By using preservatives
(ii) By common salt
(iii) By sugar
(iv) In oil and vinegar
(v) Heat and cold treatment: Pasteurization
(vi) Storage and packing
Certain bacteria present in the soil take nitrogen from the air and convert it into nitrogenous compounds. Certain bacteria convert nitrogenous compounds present in the soil into nitrogen gas which is then released into the atmosphere.

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