definition-a microorganism is a living organisms that is very can only be seen with the aid of a microscope. Example bacteria, virus, mycoplasma etc.

Presence of micro-organisms-
1.Microorganisms are present every where in air,soil,water food stuffs sewage waste as well as inside animal bodies.
they can survive in hot springs, saline water, ice-cold water and marsh land.
2. They are also present in dead and decay organic matter.
3.Some microbes live as parasites either outside or inside the body of other organisms and cause diseases.



1.These are single celled ,prokaryotic organisms.
2.Bacteria are present every where in air,water,food stuff so they are called cosmopolitan.
Shape of bacteria-
1.Round shape- cocci
2.Rod shape- bacilli
3.Spiral shape-  spirillum
4.Comma shape- vibrio


1.These are multicellular(yeast-unicellular), heterotrophic organisms ,lack chlorophyll.
2.These are generally found in colonies.
3.Cell wall of fungi is made up of chitin.
4.They are parasites or saprophytes.
5.example– Aspergillus, penicillium
Important point
The first antibiotic to be isolated was penicillin from penicillium notatum by Alexander Fleming in 1929.


1.These are unicellular eukaryotic micro-organisms.
2.Usually found in moist and aquatic habitats.
3.They are reproduce by binary fission or multiple fission.
4.Mode of nutrition is mainly holozoic( heterotopic).
5.Euglena shows mixotrophic nutrition ,it is both autotrophic and heterotrophic in nature.
Ex amoeba ,paramecium, euglena


1.These are unicellular or multicellular eukaryotic organisms.
2.They contain chlorophyll pigment and carry out photosynthesis.
3.Cell wall of algae is mainly made up of cellulose.
4.They usually grow and cover the surface of water body and move on the mercy of water current.
5.They are the major producers of aquatic ecosystem.
Example– chlamydomonas ,spirogyra , chlorella

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1.These are ultra microscopic organisms, which require cells of host organisms to reproduce.
2.Structure of virus consist of nucleic acid and a protein coat.
3.Nucleic acid can either be DNA or RNA.
4.Virus as considered as connecting link between living and nonliving.

Microorganism-as friends

1.Formation of curd-
milk —curd

a.curd contains several microbes. Out of these, Lactobacillus promotes the formation of curd.

b.When the curd is added to lukewarm milk,the bacteria, multiplies faster and results in conversion of whole milk into curd.

2.In beverages- alcoholic beverages are major fermented foods in the diet of humans.
The yeast also enrich the beverages with B-vitamins.
The process of conversion of sugar into alcohol is called fermentation. Louis Pasteur discovered fermentation in 1857.
3.In industry- yeast is grown on natural sugars present in fruit juices and grains like barley and rice. Yeast brings about conversion of sugars into alcohol and carbon di oxide.
4. Increase soil fertility-the microbes used to increase soil fertility are referred as bio-fertilizers.
soil microorganisms are one of the most important elements of a healthy soil. Example- Nostoc , anabaena
5.In agriculture- some bacteria and blue green algae convert atmospheric nitrogen into compounds of nitrogen and so called as biological nitrogen fixers.


6.Use in medicine

microbes used for the production of both antibiotics and vaccines.
Antibiotics –antibiotics are produced by a number of micro-organisms and inhibit the growth of other microorganisms even at very low concentrations.
-antibiotics are not effective against cold and flu as these are caused by viruses.
1.Antibiotics obtained from bacteria-streptomycin, Aureomycin, and chloromycetin.
2.Antibiotics obtained from fungi-penicillin and Griseofulvin.
Use of antibiotic-
these antibiotics are used to cure a variety of diseases in humans, plants and animal.


a vaccine is a biological preparation that improves immunity to a particular disease. often made from weakened or killed forms of the microbes or its toxins.
2.Edward Jenner discovered the first vaccine against small pox.
3.Example- vaccines for diphtheria, measles,mumps,rubella,and polio.

-vaccination is given to children/infants to strengthen or activate the defense mechanism of the body against a disease and to protect the body from the disease causing microbes, because the immunity of an infant is low and so is more susceptible to any infection.

Microorganisms-as foe

1.Disease causing micro-organism-

2.Food spoilage-

Microorganisms like bacteria and fungi are responsible for food poisioning,these microbes when grow on food substances produce toxin. These make the food poisonous causing vomiting,illness,and even death . therefore, there is a need to preserve food from being spoiled.

Food preservation

The process of treating and handling food with an aim to stop or slow down its spoilage while maintaining its nutritional value, texture and flavour.
Methods of food preservation-
1.Heat and cold treatment-low and high temperature inhibit the growth of microorganisms.
Pasteurization– it is used to store milk and liquid food products.
-in this the food is heated up to 60 degree centigrade for 30 minutes or 70 degree centigrade for 15-30 second and then is suddenly chilled and store. This methods was developed by scientist Louis Pasteur.
Low temperature storage– metabolic activities of microorganisms can be arrested at low temperature( -10 to -18 degree Celsius.)

2.Chemical Method : The commonly used preservatives are sodium benzoate , sodium metabisulphite and potassium metabisulphite.
3.Preservation by common salt : Concentrated solutions of common salt can kill microorganisms due to dehydration
4.Preservation by sugar- sugar reduce the moisture content which inhibits the growth of bacteria. Jams,jellies,and squashes are preserved by sugar.
5.Preservation of oil and vinegar- use of oil and vinegar prevents spoilage of pickle because bacteria can not live in this environment.
6.Preservation by radiation-this method is new and cheaper .in this method .in this method air tight food substances pass through a radiation beam.
7.Storage and packing-dry fruits and vegetables are sold in sealed air tight packet to prevent the attack of microbes.