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Biology

Microorganisms Practice Questions

19 free Microorganisms practice questions for the General Science. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.

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Question 1 of 19 Medium

Which of the following best describes microorganisms?

  1. A Only plants that grow in water
  2. B Large animals living in soil
  3. C Non-living particles found in rocks
  4. D Organisms seen only under a microscope

Correct answer: Organisms seen only under a microscope

Microorganisms are living organisms that are too small to be seen clearly with the naked eye. They are usually observed with the help of a microscope.

Question 2 of 19 Medium

Which group of microorganisms is commonly used in making curd from milk?

  1. A Viruses
  2. B Bacteria
  3. C Protozoa
  4. D Algae

Correct answer: Bacteria

Certain bacteria, especially Lactobacillus, convert milk into curd by producing lactic acid. This acid causes milk proteins to coagulate and form curd.

Question 3 of 19 Medium

Which microorganism is used in the fermentation of dough for making bread?

  1. A Amoeba
  2. B Plasmodium
  3. C Spirogyra
  4. D Yeast

Correct answer: Yeast

Yeast ferments sugar in the dough and releases carbon dioxide gas. The gas makes the dough rise and gives bread its soft texture.

Question 4 of 19 Medium

Which of the following is a bacterial disease?

  1. A Malaria
  2. B Measles
  3. C Cholera
  4. D Chickenpox

Correct answer: Cholera

Cholera is caused by the bacterium Vibrio cholerae. Malaria is caused by a protozoan, while measles and chickenpox are viral diseases.

Question 5 of 19 Medium

The disease malaria is caused by which type of microorganism?

  1. A Bacterium
  2. B Protozoan
  3. C Fungus
  4. D Virus

Correct answer: Protozoan

Malaria is caused by the protozoan parasite Plasmodium. It is transmitted to humans through the bite of infected female Anopheles mosquitoes.

Question 6 of 19 Medium

Which microorganism is commonly used in the production of antibiotics such as penicillin?

  1. A Amoeba
  2. B Lactobacillus
  3. C Plasmodium
  4. D Penicillium

Correct answer: Penicillium

Penicillin was first obtained from the fungus Penicillium. Antibiotics are substances that kill or inhibit the growth of disease-causing microorganisms.

Question 7 of 19 Medium

Which of the following microorganisms can fix atmospheric nitrogen in soil?

  1. A Yeast
  2. B Amoeba
  3. C Influenza virus
  4. D Rhizobium

Correct answer: Rhizobium

Rhizobium bacteria live in root nodules of leguminous plants and fix atmospheric nitrogen. This enriches the soil and helps plants grow better.

Question 8 of 19 Medium

Which process uses microorganisms to convert sugar into alcohol and carbon dioxide?

  1. A Photosynthesis
  2. B Fermentation
  3. C Transpiration
  4. D Pollination

Correct answer: Fermentation

Fermentation is a process in which microorganisms like yeast break down sugars without oxygen. It produces alcohol and carbon dioxide in many food and beverage preparations.

Question 9 of 19 Medium

Which of the following is an example of a fungus?

  1. A Amoeba
  2. B Euglena
  3. C Bacteriophage
  4. D Mushroom

Correct answer: Mushroom

Mushroom is a fungus and belongs to a group of organisms that absorb nutrients from organic matter. Amoeba and Euglena are protists, while bacteriophage is a virus.

Question 10 of 19 Medium

Which microorganism is responsible for causing food poisoning in many cases?

  1. A Nitrogen-fixing Rhizobium
  2. B Disease-causing bacteria
  3. C Yeast used in baking
  4. D Lactobacillus in curd

Correct answer: Disease-causing bacteria

Food poisoning is often caused by harmful, disease-causing bacteria (such as Salmonella or E. coli) or the toxins they produce in contaminated food. Rhizobium, yeast, and Lactobacillus are all beneficial microorganisms used in nitrogen fixation, baking, and curd-making respectively, not in causing food poisoning.

Question 11 of 19 Medium

What is the main purpose of pasteurization of milk?

  1. A To increase the fat content of milk
  2. B To kill harmful microorganisms
  3. C To convert milk into curd
  4. D To remove all minerals from milk

Correct answer: To kill harmful microorganisms

Pasteurization involves heating milk to a specific temperature for a short time and then cooling it quickly. This kills many harmful microorganisms without greatly changing the milk's quality.

Question 12 of 19 Medium

Which of the following diseases is prevented by vaccination?

  1. A Night blindness
  2. B Scurvy
  3. C Rickets
  4. D Smallpox

Correct answer: Smallpox

Vaccination helps the body develop immunity against specific infectious diseases such as smallpox. Night blindness, scurvy, and rickets are mainly deficiency diseases.

Question 13 of 19 Medium

Which microorganism can multiply only inside a living host cell?

  1. A Bacterium
  2. B Fungus
  3. C Virus
  4. D Alga

Correct answer: Virus

Viruses cannot reproduce independently and need a living host cell to multiply. Outside a host cell, they remain inactive.

Question 14 of 19 Medium

Which of the following is a useful role of microorganisms in nature?

  1. A They always cause diseases
  2. B They decompose dead plants and animals
  3. C They stop all plant growth
  4. D They remove oxygen from the atmosphere permanently

Correct answer: They decompose dead plants and animals

Many microorganisms act as decomposers by breaking down dead plants and animals. This process recycles nutrients back into the soil and ecosystem.

Question 15 of 19 Medium

Which microorganism is commonly found in stagnant water and can be seen as a protozoan under a microscope?

  1. A Mushroom
  2. B Rhizobium
  3. C Bread mould
  4. D Amoeba

Correct answer: Amoeba

Amoeba is a unicellular protozoan often found in freshwater or moist environments. It moves and feeds using temporary projections called pseudopodia.

Question 16 of 19 Medium

Which of the following is an algal microorganism?

  1. A Lactobacillus
  2. B Penicillium
  3. C Plasmodium
  4. D Spirogyra

Correct answer: Spirogyra

Spirogyra is a filamentous green alga commonly found in freshwater. It contains chlorophyll and can prepare its own food by photosynthesis.

Question 17 of 19 Medium

Why should leftover food be stored in a refrigerator?

  1. A Refrigeration kills all microorganisms
  2. B Refrigeration removes all nutrients from food
  3. C Low temperature increases bacterial reproduction
  4. D Low temperature slows the growth of microorganisms

Correct answer: Low temperature slows the growth of microorganisms

Refrigeration only slows down the growth and multiplication of microorganisms; it does not kill them, remove nutrients from food, or increase bacterial reproduction. This slowdown helps delay spoilage and keeps food safe for longer.

Question 18 of 19 Medium

Which of the following is commonly used as a food preservative?

  1. A Pure oxygen
  2. B Fresh water
  3. C Chlorophyll
  4. D Common salt

Correct answer: Common salt

Common salt is used to preserve foods such as pickles and fish by reducing water availability for microorganisms. This slows microbial growth and prevents spoilage.

Question 19 of 19 Medium

Which statement about microorganisms is correct?

  1. A All microorganisms are harmful to humans
  2. B Microorganisms are found only in air
  3. C Microorganisms can be both useful and harmful
  4. D Microorganisms cannot live in soil or water

Correct answer: Microorganisms can be both useful and harmful

Microorganisms can be both useful and harmful. Some help in food production, decomposition, and medicine, while others cause diseases and food spoilage.

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