Microorganisms: Friend & Foe MCQ | Class 8 Science Ch 2 Quiz

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Class 8 Science Chapter 2 Objective Questions

This online MCQ test for Class 8 Science Chapter 2 (Microorganisms: Friend and Foe) helps assess preparation and revise key concepts frequently asked in exams. It covers uses and harms of microbes, food preservation, diseases, vaccination, fermentation, and nitrogen fixation.

In this test, the objective questions relate to:

• Microbial groups and characteristics
• Beneficial uses (curd, bread, antibiotics, fermentation)
• Diseases and transmission
• Vaccination and immunity
• Food spoilage and preservation
• Nitrogen fixation and soil fertility

Answer all 25 questions and review the score at the end to analyze preparation. Good luck!

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Which group of organisms includes unicellular fungi used in baking?

Molds Yeast Mushrooms Lichens

Yeast are unicellular fungi that ferment sugars and are used in baking to raise dough.

Which microbe requires a living host cell to reproduce?

Bacteria Virus Protozoa Algae

Viruses are obligate intracellular parasites and replicate only inside living cells.

Curd formation from milk is primarily due to the activity of:

Rhizobium Lactobacillus Penicillium Plasmodium

Lactobacillus converts lactose to lactic acid, causing milk proteins to coagulate into curd.

Bread dough rises because yeast produces:

Oxygen Ethanol Carbon dioxide Nitrogen

During fermentation, yeast releases carbon dioxide that becomes trapped in dough, making it rise.

The process of converting sugar into alcohol by microorganisms is called:

Pasteurization Fermentation Nitrogen fixation Decomposition

Fermentation is an anaerobic process in which yeast converts sugars to ethanol and carbon dioxide.

Which pair forms a symbiotic association in lichens?

Fungus and alga Bacterium and virus Protozoan and alga Fungus and bacterium

In lichens, algae photosynthesize and provide food, while fungi offer protection and moisture retention.

Rhizobium bacteria are beneficial because they:

Cause food spoilage Fix atmospheric nitrogen Produce antibiotics Pasteurize milk

Rhizobium live in root nodules of legumes, converting atmospheric nitrogen into usable forms.

Which disease is caused by a protozoan?

Influenza Malaria Tuberculosis Measles

Malaria is caused by Plasmodium, a protozoan parasite transmitted by Anopheles mosquitoes.

Which of the following is used to make antibiotics like penicillin?

Lactobacillus Penicillium Rhizobium Saccharomyces

The fungus Penicillium produces penicillin, a widely used antibiotic.

The process of heating milk to kill harmful microbes and then cooling it rapidly is called:

Sterilization Pasteurization Fermentation Clarification

Pasteurization involves controlled heating and rapid cooling to reduce pathogenic microbes in milk.

Which is a viral disease?

Typhoid Hepatitis A Cholera Anthrax

Hepatitis A is caused by Hepatitis A virus; typhoid and cholera are bacterial, anthrax is bacterial.

Which of the following is correctly matched for food spoilage indication?

Curd turning blue Bread developing green patches Milk freezing at 0°C Rice turning hard after cooking

Green patches on bread are fungal growths (molds), indicating spoilage.

The primary role of preservatives like sodium benzoate is to:

Increase sweetness Enhance color Inhibit microbial growth Improve texture

Chemical preservatives slow or prevent growth of spoilage and pathogenic microbes in food.

Which method is best to preserve fruits by reducing water availability to microbes?

Salting Sugaring Refrigeration Smoking

High sugar concentration binds water, lowering water activity and inhibiting microbial growth.

Which statement about vaccines is correct?

They cure diseases immediately They provide passive immunity They stimulate antibody formation They are effective only in adults

Vaccines contain antigens that trigger the immune system to produce protective antibodies.

Which microbe is commonly used in the production of alcohols and wines?

Aspergillus Lactobacillus Saccharomyces cerevisiae Clostridium

Brewer’s yeast (S. cerevisiae) ferments sugars to produce ethanol in alcoholic beverages.

Which disease is correctly paired with its mode of transmission?

Cholera – contaminated water Rabies – houseflies Tetanus – air Dengue – contaminated food

Cholera spreads through water contaminated with Vibrio cholerae; rabies via animal bites, tetanus via wounds, dengue via mosquito bites.

Blue-green algae (cyanobacteria) help in agriculture by:

Killing soil insects Improving soil aeration Fixing atmospheric nitrogen Decomposing plastics

Cyanobacteria like Anabaena in paddy fields fix nitrogen, enhancing soil fertility.

Which option best describes probiotics?

Antiviral drugs Beneficial live microbes in food Food colorants Chemical preservatives

Probiotics are live beneficial microorganisms added to foods like yogurt to support gut health.

Which practice is not a method of food preservation?

Dehydration Canning Irradiation Ferromagnetism

Dehydration, canning, and irradiation are preservation methods; ferromagnetism is a physical property of materials.

Which statement about decomposition is true?

It converts alcohol to sugar It is performed mainly by microorganisms It increases food shelf life It requires high levels of oxygen only

Decomposition is carried out by bacteria and fungi that break down dead organic matter.

Which disease is caused by bacteria?

Measles AIDS Tuberculosis Ringworm

Tuberculosis is caused by Mycobacterium tuberculosis; measles and AIDS are viral, ringworm is fungal.

Which is the safest practice to avoid foodborne infections at home?

Thaw meat on the kitchen counter Cook food to safe temperatures Re-freeze thawed raw meat Store hot food at room temperature

Adequate cooking kills harmful microbes and reduces the risk of foodborne illness.

Which product is correctly matched with its microbial origin?

Citric acid – Aspergillus niger Vitamin C – Penicillium notatum Insulin – Lactobacillus bulgaricus Ethanol – Rhizobium

Industrial citric acid is commonly produced by fermentation using the fungus Aspergillus niger.

Which practice helps prevent antimicrobial resistance?

Stopping antibiotics when symptoms decrease Sharing leftover antibiotics Completing the full antibiotic course Using antibiotics for viral colds

Completing the prescribed course helps eliminate pathogens fully and reduces resistance development.

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