Class 8 Chapter 2 MICROORGANISMS : FRIEND AND FOE

MICROORGANISMS : FRIEND AND FOE

Microorganisms

• Microorganisms are microscopic organisms that cannot be seen with the naked eye.

• These organisms are usually unicellular in nature.

Bacteria

• Bacteria are unicellular prokaryotic microorganisms.

• Some bacteria are useful for humans while some can be harmful.

• They are of four major types: Bacillus, Vibrio, Cocci and Spirilla

Probiotics

• Probiotics are live bacteria and yeasts that are good for your health, especially the digestive system.

Fungi

• Fungi are saprophytic or parasitic organisms.

• They are mostly multicellular and not microscopic.

• However, yeast is a unicellular and microscopic organism.

Fermentation

• Fermentation is a metabolic process that converts sugar to acids, gases or alcohol.

• Fermentation is used in the preparation of curd and alcohol.

Protozoa

• Protozoa are single-celled microscopic animals which include flagellates, ciliates, sporozoans and many other forms.

• A few examples of protozoa are amoeba, paramecium, euglena, plasmodium, etc.

Viruses

• Viruses are organisms that possess nucleic acid but lack replicating machinery.

• Thus, a virus cannot survive without a living cell.

• Viruses are also considered to be on the borderline between living and nonliving entities.

• A few examples of viruses are influenza virus, HIV, Rabies virus, poliovirus, tobacco mosaic virus, etc.

Vaccines

A vaccine is a biological preparation that provides active acquired immunity to a disease.

• Vaccines are usually made for viral diseases.

• A few examples of vaccines are Salk vaccine for Polio, Influenza vaccine, Rabies vaccine, etc.

Antibiotics

Antibiotics is an inorganic or organic compound that inhibits and kills microorganisms.

• Antibiotics usually target bacteria.

• Thus, most bacterial diseases are treated with antibiotics.

Pathogens

• A pathogen is any organism that causes disease.

• In this context, pathogens are microorganisms.

• Bacteria, protozoa and viruses can be pathogenic.

Carrier

• A carrier is a person or organism infected with an infectious disease agent but displays no symptoms of it.

• They can spread the infection since they already have the pathogen in their bodies.

Vector

• A vector is an organism, which is a biting insect or tick, that can transmit disease or parasite from one animal or plant to another.

• Common examples are mosquitoes.

• Aedes mosquito spreads dengue virus, Anopheles mosquito spreads the malarial parasite.

Airborne diseases

• Certain diseases can spread by air.

• These diseases are called airborne diseases.

• Influenza is the best example of this type of disease.

Waterborne diseases

• The diseases that spread through water are called waterborne diseases.

• Contaminated water is host to several pathogens.

• Typhoid is the best example of a waterborne disease.

Examples of Diseases

Human diseases	Causative Organism	Mode of Transmission
Tuberculosis	Bacteria	Air
Measles	Virus	Air
Chickenpox	Virus	Air/Contact
Polio	Virus	Air/Contact
Cholera	Bacteria	Water/Food
Typhoid	Bacteria	Water
Hepatitis B	Virus	Water
Malaria	Protozoa	Mosquito bite
Sleeping sickness	Protozoa	Tsetse fly

Plant diseases

• Certain pathogens can cause diseases in plants. Just like humans, plants can be attacked by bacteria or viruses.

• Several micro-organisms cause diseases in plants like rice, potato, wheat, sugarcane, orange, apple and others.

Disease	Pathogen	Mode of Transmission
Citrus canker	Bacteria	Air
Rust of Wheat	Fungi	Air/Seed
Yellow vein mosaic of bhindi	Virus	Insect

Food poisoning

• When food contaminated with pathogens or toxins is consumed, it causes food poisoning.

• The most common symptom is a pain in the stomach.

• In severe cases, food poisoning can also cause death.

Food preservation

• Food preservation is the most vital part of the food industry.

• Certain chemicals inhibit the growth of bacteria and increase the life of the cooked food.

• Certain simple preservation methods can be carried out at our home.

Chemical methods

• Chemical preservatives are used in food preservation by major food industries as they are harmless to humans.

• Sodium meta-bisulphate and sodium benzoate are commonly used chemical preservatives.

Uses of common salt

• Common salt also known as sodium chloride,  is used as a preservative at home.

• Vegetables are pickled using salt as the salt removes water and kills bacteria and fungus cells.

Preservation by Sugar

• Sugar is used for the preservation of jams, jellies and squashes.

• The growth of microbes is restricted by the use of sugar as it reduces the moisture content.

Preservation by oil and Vinegar

• Many food preparations, like pickles,  are preserved by adding either oil or vinegar to them.

• Bacteria cannot grow in such medium.

Pasteurization

• Pasteurization is a process of superheating and cooling beverages to kill pathogenic microbes.

• Pasteurization ensures the taste of the beverage, such as milk does not get destroyed.

Storage and Packing

• Dry fruits and many vegetables are preserved in airtight/air-sealed containers.

• The absence of air prevents the growth of bacteria or fungi.

Nitrogen Cycle

The nitrogen cycle is a biogeochemical cycle by which nitrogen is converted into various chemical forms as it circulates among the atmosphere and terrestrial and marine ecosystems.