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Amarchand Singhvi International School
Subject : Science
Class : VIII
Chapter : Microorganisms: Friend and Foe (Part-2)
Topics : Harmful microorganisms, spoilage of
food and methods of food preservation
Teacher : Ms. Prity Vinjoda
E-Learning Programme
Contents• Where do microbes live?
• Major groups of microorganism
• Bacteria
• Viruses
• Algae
• Fungi
• Protozoa
• Useful microorganisms
• Harmful microorganisms
• Food Preservation
Amarchand Singhvi International School
Harmful Microorganism
Amarchand Singhvi International School
• Some microorganisms which are not good for us are called harmful microorganism.
• Disease causing microorganisms in humans, plants and animals are called pathogens.
Amarchand Singhvi International School
Disease- causing Microorganisms in Humans
- Pathogens are present everywhere.
- Transferred to our body through - air, water and food or by direct contact with infected body.
- There are some insects and animals which act as carrier of disease causing microbes.
- Diseases that are transferred from unhealthy or infected person to healthy person are called communicable disease.
- (Ex. Cholera, common cold, chickenpox and tuberculosis)
Amarchand Singhvi International School
Diseases- causing Microorganisms in Humans
• Some insects and animals act as a carrier of disease-causing microbes.
• MALARIA- caused by the female anopheles mosquito
that act as the carrier of malaria.
• DENGUE - female Aedes mosquito acts as carrier of
dengue virus.
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Diseases- causing Microorganisms in Animals
•Anthrax is a dangerous human and cattle disease caused by a bacterium. • Foot and mouth disease of cattle is caused by a virus.
Diseases- causing Microorganisms in plants • Disease in plants reduces the yield of crops. • Example - citrus canker caused by bacteria, rusting of
wheat by fungi attack, etc.
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SPOILAGE OF FOOD
• Food that is unfit for human consumption is called spoilt food.
Causes of food spoilage
• Growth of bacteria on food
• Improper cooking
• Improper storage
• Temperature variation
Signs of food spoilage • Foul smell
• Slime
• Sour taste
• Discoloration
• Gas formation
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FOOD PRESERVATION METHODS
Spoilage of food can be prevented by preserving food. Some
methods of food preservation are:
1. Salting: Used to preserve meat, fish,
raw mangoes, tamarind and so on.
Salt inhibits bacterial growth.
2. Adding sugar: Used to preserve fruits
by making jams and jellies. Sugar
reduces the moisture and inhibits
bacterial growth.
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FOOD PRESERVATION METHODS contd..
3. Adding oil and vinegar: Used to
preserve mangoes, carrot and so
on by making pickles. Oil and
vinegar create an environment in
which bacteria cannot live.
4. Storing and packing: Used to
preserve dry fruits, fruits and
vegetables. Prevent attack by
microbes.
Amarchand Singhvi International School
FOOD PRESERVATION METHODS
5. Refrigeration: Used to preserve meat, milk, fruits, and
vegetables and so on. Low temperature inhibits the
growth of microbes.
6. Heating and boiling: Used to preserve milk. Boiling
kills microorganisms.
Amarchand Singhvi International School
FOOD PRESERVATION METHODS
7. Adding chemical preservatives: Used to preserve fruits
and vegetables. Chemical preservatives like sodium
benzoate and sodium metabisulphite prevent the attack of
microbes.
8. Pasteurization:Pasteurization is a method
used to preserve milk in
which milk is heated to
about 700 C for 15 to 30
seconds and then suddenly
chilled and stored. This
prevents the growth of microbes.
Note: This presentation is a part of the E-Learning Program of Amarchand
Singhvi International School and is created only for educational purpose.
Compilation & presentation : Ms. Prity Vinjoda
Web support & management : Mr. Deepak Chellani
Technical support : Mr. Shivam Gundecha
E-learning Program Co-ordination:
Mr. Prashant Chaturvedi
Produced by
Mr. Mridul Varma (Principal)
Amarchand Singhvi International School
Parekh Parisar, Ward 7A, Gandhidham – Kutch
Gujarat 370201 India
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