Types of Microorganisms, Viruses and Role of Microorganisms in our Life - Biology Guide for Class 8

Information about Microorganisms and Viruses


Types of Microorganisms, Viruses and Role of Microorganisms in our Life


Class 8


Class 8 Biology

Topics Covered

  • Microorganisms
  • Types of Microorganisms
  • Viruses
  • Where microorganism live?
  • Role of Microorganisms in our life

We see a large number of plants and animals around us. Besides these, there are a large number of small organisms which cannot be seen with our unaided eye. However, they can be easily observed through the microscope. These living organisms are invisible to the naked eye but are visible under the microscope. They are called microorganisms and their study is known as microbiology.
Microorganisms include viruses and single-celled organisms like bacteria, yeast, protozoans and algae. Each of these groups of microorganisms includes some harmful organisms (foes) and some useful organisms (friends).
The discovery of microorganisms was possible due to the invention of the microscope. Anton von Leeuwenhoek was the first person to establish the existence of bacteria.
Now, with the help of modern microscopes and other new techniques, we have come to know a lot more about microorganisms. 

Types of Microorganisms

  • Microorganisms are the oldest forms of life on earth.
  • Certain varieties of microorganisms have existed for millions of years. They affect us in many ways. 
  • On the basis of their cell structure, microorganisms can be divided into four groups. These groups are:
    (i) bacteria
    (ii) fungi
    (iii) protozoa
    (iv) algae
Some of these organisms have been shown in the following pictures.


  • Viruses are unique.
  • They can exhibit the characteristics of both living organisms and non-living things.
  • When they are floating in air, or are settled on a door knob, they are non-living like, say, salt and sugar.
  • In fact, they can be crystallised and stored in jars for years.
  • However, when they come in contact with a suitable plant, animal or bacteria, they show the characteristics of living organisms.
  • They infect the cell and quickly multiply inside it.
  • Viruses are, therefore, regarded as being on the borderline between living and non-living entities.

Where do Microorganisms Live?

  • Microorganisms are found in almost all kinds of environment:
    (i) in ice-cold water
    (ii) in hot springs
    (iii) in dry
    (iv) marshy or saline areas.
  • Some of them need oxygen for their growth while others do not.
  • They are found in soil, on the ocean floor, high in the atmosphere and deep inside rocks within the earth's crust.
  • Microorganisms are also found in the human body and in the bodies of other plants and animals.
  • Our mouth, throat, nose and the alimentary canal are all inhabited by a large number of microorganisms. Thus, microorganisms are found everywhere.

Role of Microorganisms in Our Life

  • Microorganisms play an important role in our lives as well as in the overall environment.
  • They help in the decomposition process and in maintaining the biogeochemical cycles (like the carbon and nitrogen cycles).
  • They are useful and beneficial for mankind in many ways. However, some of them are harmful as they spoil our food and cause diseases.

Microbial Population in the Human Body

  • Under normal conditions, our bodies house a large population of microorganisms.
  • Microorganisms, however, kept in balance and are usually harmless.
  • These microorganisms are important for our body; they form an essential system that helps our body.

Some important points

  • • Extremophiles are microorganisms which have adapted themselves so that they can survive, and even thrive, in conditions that are normally fatal to most life forms.
  • Hyperthermophiles are organisms that can thrive even at temperatures between 80°C-122°C, such as those found in hydrothermal systems.
  • Hypoliths live inside rocks in cold deserts.
  • Cryophiles grow better at temperatures of 15°C or lower; common in cold soils and polar ice-cold ocean waters.
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