World of Micro Organisms : Science Cbse / Ncert Revision Notes


Living organisms invisible to the naked eye are called microorganisms. Microorganisms are omnipresent. Microorganisms are found everywhere, in the air, water, soil, in and on living organisms.

The instrument used to view microorganisms is called a microscope. Microscopes can be of different types based on their complexity. Microorganisms can be classified into four groups – 
Bacteria, Fungi, Algae and Protozoa.

World of MicroOrganisms, Science Cbse / Ncert Revision Notes, Class 8, Useful and harmful MicroOrganisms,

Virus is also a microorganism which is neither considered living nor non-living. Hence, viruses form the boundary between the living and the non-living world.

Microorganisms can survive extreme conditions like hot springs to polar regions. Microorganisms can be unicellular or multicellular. Organisms which are made up of a single cell are unicellular while the organisms made up of many cells are multicellular forms. Most of the protozoans are unicellular in nature while most fungi and some algae are multicellular organisms.

Microorganisms can be useful or harmful to us.

Useful microorganisms

Microorganisms are extensively used in baking industry. Yeast is a microorganism which multiplies rapidly in dough and produces carbon dioxide. This dough, when baked, yields porous and spongy cakes. These are used in baking industry to provide puffiness to bread, cake and other bakery products.

Microorganisms like lactobacilli are used in the preparation of curd. Microorganisms are also used to prepare pickles, cheese and other products

Microorganisms are used in industrial production of wine. Yeast converts the natural sugars present in grains into alcohol. Wine is produced by the process of fermentation. The process of converting sugar into alcohol is called fermentation. Louis Pasteur discovered the process of fermentation. Microorganisms like bacteria act as decomposers to clean up organic waste by decomposing them into usable substances.

Must Read: Food Preservation

Harmful microorganisms

Harmful microorganisms can spoil our food, leather, clothing etc. Harmful microorganisms causing diseases are called as pathogens.

Pathogens select carriers to reach their particular host. Flies, mosquitoes, worms and sometimes even animals act as carriers for pathogens.

Pathogens can mostly cause communicable diseases. Communicable diseases are transmitted from one person to another by different modes of infection.

Modes of infection 

Infection is the transmission of pathogens from diseased individual to healthy individual. Infections are transmitted from animals to humans by eating contaminated or uncooked food.

Microbial infection can be transmitted by direct contact with an infected person or animal, or by consuming meat prepared from an infected animal.

Human diseases like cholera, common cold, chicken pox and tuberculosis spread from an infected person to a healthy person through air, water, food or physical contact.

Female mosquitoes carry pathogens for diseases like malaria and dengue, and spread infection from one person to another by biting.

The foot and mouth disease in cattle is caused by a virus.

Prevention of infection

We can prevent the spread of infection by using a handkerchief while sneezing or coughing.

Penicillin was discovered by Alexander Fleming in 1929. Antibiotics are used to cure a variety of diseases caused by fungi, bacteria and protozoa.

Antibiotics, insecticides and pesticides are sprayed in the field to control many plant diseases. Usage of some bacteria or fungi which produce specific chemicals to prevent the growth of microbes causing disease.

Diseases can be prevented by vaccination. During vaccination inactivated or weakened microbes called as vaccines are introduced into the body. They trigger the production of antibodies. When disease-carrying microbes enter our body, self-protecting proteins called antibodies fight against the invader.
  • Small pox has been completely eradicated from the world by administering vaccine.
  • Several diseases including cholera, tuberculosis and hepatitis, can be prevented by vaccination.

Antibiotics are mixed with the feed of livestock and poultry in order to prevent microbial infection in animals and birds.

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