Extra 30 short questions and answers from the chapter:2 "Microorganisms: Friend and Foe" for Class 8 Science (CBSE):-

What are microorganisms?

Microorganisms are tiny living organisms that cannot be seen with the naked eye. They include bacteria, fungi, protozoa, algae, and viruses.

 

Name the five major groups of microorganisms.

The five major groups of microorganisms are:

Bacteria

Fungi

Protozoa

Algae

Viruses

 

Which microorganisms are used in making curd?

Lactobacillus bacteria

convert milk into curd by converting lactose into lactic acid.

 

How do microorganisms survive in extreme conditions?

Some microorganisms, like certain bacteria, can form

spores

to survive in extreme heat, cold, or dryness.

 

What are antibiotics? Give an example.

Antibiotics are medicines that kill or stop the growth of disease-causing microorganisms.

Example:

Penicillin

, discovered by Alexander Fleming.

 

What is fermentation? Name a microorganism used in fermentation.

Fermentation is the process of breaking down sugar into alcohol or acids by microorganisms.

Yeast

is used in fermentation to produce alcohol.

 

How do bacteria help in nitrogen fixation?

Bacteria like

Rhizobium

live in the root nodules of leguminous plants and convert atmospheric nitrogen into a usable form for plants.

 

What are pathogens?

Pathogens are

disease-causing microorganisms

such as bacteria, viruses, fungi, and protozoa.

 

What is the role of microorganisms in making medicines?

Microorganisms like

Penicillium

help in making antibiotics, and some bacteria are used to produce vaccines.

 

How do microorganisms help in cleaning the environment?

Microorganisms decompose

dead plants, animals, and waste

, converting them into nutrients for the soil.

 

Name two diseases caused by bacteria and two caused by viruses.

Bacterial diseases:

Typhoid, Tuberculosis

Viral diseases:

Influenza, Polio

What is pasteurization? Who discovered it?

Pasteurization is the process of heating milk to

kill harmful bacteria

and then cooling it rapidly.

Discovered by

Louis Pasteur

.

What are vaccines?

Vaccines contain

weakened or dead microbes

that trigger the immune system to produce antibodies and provide immunity against diseases.

What is food preservation? Name two methods.

Food preservation is

preventing the growth of microorganisms

to keep food fresh for a longer time.

Methods:

Refrigeration, Salting

What is the function of yeast in baking?

Yeast produces

carbon dioxide gas

during fermentation, which makes bread and cakes soft and fluffy.

Why are viruses considered different from other microorganisms?

Viruses are

inactive

outside a host but become active and reproduce inside a living cell.

What

are

nitrogen-fixing bacteria?

Bacteria like

Rhizobium

convert atmospheric nitrogen into a usable form, helping plants grow.

What is the role of fungi in the environment?

Fungi

decompose organic matter

, recycle nutrients, and some (like mushrooms) are used as food.

How do microorganisms help in sewage treatment?

Certain bacteria

break down organic waste

in sewage, making water safer for disposal.

What are the harmful effects of microorganisms?

They cause diseases, spoil food, and damage crops.

 

What is food poisoning? Name a microorganism that causes it.

Food poisoning is caused by

toxins released by bacteria or fungi

in spoiled food.

Example:

Salmonella bacteria

.

How do protozoa cause diseases? Give an example.

Protozoa enter the human body through contaminated food or water and cause diseases.

Example:

Plasmodium causes malaria

.

Name two methods to kill microorganisms in drinking water.

Boiling water

and

adding chlorine (chlorination)

.

How does refrigeration prevent food spoilage?

Low temperatures

slow down the growth of bacteria and fungi

, keeping food fresh.

What are preservatives? Give examples.

Preservatives are

substances added to food to prevent spoilage

.

Examples:

Salt, Sugar, Vinegar

.

How does salting help in food preservation?

Salt

removes moisture

from food, preventing microbial growth.

Used in

pickle and meat preservation

.

Why should we avoid eating stale food?

Stale food may contain

harmful bacteria and toxins

, causing food poisoning.

What is dehydration? How does it help in food preservation?

Dehydration is the process of

removing water from food

to prevent microbial growth.

Used in

drying fruits and vegetables

.

How do microorganisms affect animals?

Microorganisms cause diseases in animals, such as

anthrax in cattle

and

foot-and-mouth disease in livestock

.

What precautions should be taken while handling microorganisms in laboratories?

Use sterilized equipment.

Wear gloves and masks.

Dispose of microbial cultures properly.