Aug 09, 2022, 16:45 IST

About Microorganisms

We cannot see them, we cannot hear them but they are with us: There are about 100 trillion microorganisms in and around our bodies. The fact is that without microorganisms we would not survive.

A microorganism is a living organism that is so small that it can only be seen with the aid of microscope. Fungus that grows on the bread can be seen with a magnifying glass.

Bacterial cells are about one hundredth of the size of a human cell and viruses are much more smaller.

While it is true that microorganisms are responsible for a large number of human diseases, they also bring cycle of chemical exchange between organisms and their environment. The decision as to whether bacteria are friend or foe becomes more difficult when both the positive and negative aspects of the relationship between human beings and microorganisms is considered. However, it can be concluded that bacteria can survive without us but we would not be able to live without them.

The study of microorganisms is known as microbiology.

The main microorganisms are protozoa, algae, fungi, bacteria and viruses.

Major Groups of Microorganisms

Bacteria – Lactobacillus and Rhizobium

Fungi – Penicillium and Aspergillus

Protozoa – Amoeba and Paramoeciu

About Virus 

Viruses are microorganisms that are so basic that they are not even classified as living cells. Viruses consists of only genetic material (either DNA or RNA), wrapped around inside a protein covering. They cannot survive by themselves, so they need a host cell that will enable the virus to multiply. HIV Virus  

Where do Micro-organisms live?

They are found in all living beings, plants and animals. Microorganisms can live in the air, on land, and in fresh or salt water environments. However, most microbes need water to survive, therefore, wherever there is water there are microbes.

There is not one place on earth that does not have bacteria or some other microorganism living there.

They can survive at temperatures less than 20ºc temperatures, hotter than boiling water.

Microorganisms and us Friendly Microorganisms 

There are a number of microorganisms that are useful to us.

(i) Lactobacillus for the production of curd (yogurt) from milk. 

(ii) E.coli bacteria are used for the production of drugs such as insulin and antibiotics, after genetically modifying the bacteria.

(iii) Nitrosomonas is used for sewage treatment.

(iv) E.coli produces vitamin k and vitamin B6 and B12 in our digestive tract which are essential nutrients for our body.

(v) Streptomyces bacteria is used in making antibiotics.

(vi) Fungus Penicillium revolutionized medicine with the discovery of penicillin antibiotic obtained from it.

(vii) Microorganisms such as bacteria and fungi act as decomposers in the ecosystem, decomposing dead plants and animals. Through the decay process, elements such as carbon, nitrogen and sulphur are released into the soil, making it more fertile.

(viii) Many vaccines are prepared from microorganisms to protect them from like tuberculosis, polio etc.

(ix) Yeast is used in dough to make porous and spongy bread and cakes.

(x) Yeast is also used to convert natural sugars present in grains into alcohol.


Louis Pasteur discovered the process of fermentation.

The process of converting sugar into alcohol is called fermentation.

Yeast convert the natural sugars present in grains into alcohol.

Wine is also produced by fermentation.

Yeast Cells showing budding

Louis Pasteur


Medicines used to cure a variety of diseases caused by bacteria, protozoans. However, antibiotics are not effective against diseases caused by virus.

Penicillin is the first antibiotic discovered by Alexander Fleming in 1929 from the fungus Penicillium.

Some commonly used antibiotics which are produced from bacteria and fungi are streptomycin, tetracycline and erythromycin.

Alexander Fleming Vaccination

When microbes enter our body, there is production of antibodies to fight against them.

Vaccine is prepared by inactivating the disease causing microbes so that it can produce antibodies but not the disease.

Several diseases like hepatitis, chicken pox, tuberculosis etc can be prevented by vaccination.

Small pox has been completely eradicated from the world.

Harmful Microorganism

Pathogens are disease causing microorganisms. They thrive under unhygienic conditions.

Microorganisms cause diseases like typhoid, cholera, tuberculosis, chicken pox, swine flu etc., which can spread from an infected person through air, water food or physical contact.

These cause plant diseases like rust of wheat and citrus cancer. 

Bacteria and fungi cause food poisoning by producing toxic substances in the food.

RBC infected by Plasmodium

Bacteria and protozoans cause pollution of water and make it unfit for drinking.

Anthrax caused by a bacterium, in a dangerous human and cattle disease.

Foot and mouth disease is caused by a virus in cattles.

Bird flu in causes by virus.

Some insects like housefly and mosquitoes acts as carriers for diseases causing microbes.

Housefly transfers pathogens from contaminated food to uncovered food. Therefore, food should always be kept covered.

Female Anopheles  mosquito is a carrier for malarial parasite Plasmodium.

Female Aedes mosquito acts as a carrier for dengue virus.

Hence, we should not allow water to collect any where to prevent mosquitoes from breeding.

Common human diseases called by viruses include the common cold, influeuza.

Serious disease caused by viruses are chicken pox, Jaundice, AIDs, SARS, Herpes, Swine flu, mumps etc.

Female Anopheles Mosquito infecting a man with Plasmodium

Most of the viral diseases are contagious and spread from person to person.

Some Common Human Diseases caused by Microorganisms

Find detail in the following pdf 

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