"Microorganisms: Friend and Foe" for Class 8 Science (CBSE):-

Extra 30 short questions and answers from the chapter:2

 

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.