Useful microorganisms — Class 8 CBSE Science MCQs with Solutions
Free Class 8 CBSE Science Useful microorganisms MCQs with step-by-step solutions (18 questions). Part of Microorganisms: Friend and Foe. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Useful microorganisms · easy · theory
Which bacterium multiplies in milk and converts it into curd?
A. Lactobacillus ✓ Correct
B. Rhizobium
C. Penicillium
D. Plasmodium
Solution: The bacterium Lactobacillus promotes curd formation by multiplying in milk and turning it into curd.
Q2 — Useful microorganisms · easy · theory
During baking, yeast produces which gas that makes the dough rise?
A. Oxygen
B. Carbon dioxide ✓ Correct
C. Nitrogen
D. Hydrogen
Solution: Yeast releases carbon dioxide during respiration, and these bubbles of gas make the dough rise.
Q3 — Useful microorganisms · easy · theory
The antibiotic penicillin was discovered by which scientist?
A. Louis Pasteur
B. Edward Jenner
C. Alexander Fleming ✓ Correct
D. Robert Koch
Solution: Alexander Fleming discovered penicillin in 1929 from a green mould that stopped the growth of bacteria.
Q4 — Useful microorganisms · easy · theory
Who discovered the vaccine for smallpox?
A. Edward Jenner ✓ Correct
B. Alexander Fleming
C. Louis Pasteur
D. Robert Koch
Solution: Edward Jenner discovered the smallpox vaccine in 1798.
Q5 — Useful microorganisms · easy · theory
Fermentation is the conversion of sugar into which of the following by yeast?
A. Curd
B. Alcohol ✓ Correct
C. Bread
D. Antibiotics
Solution: Fermentation is defined as the conversion of sugar into alcohol by yeast.
Q6 — Useful microorganisms · medium · theory
Which microorganism is used to make bread, pastries and cakes?
A. Lactobacillus
B. Yeast ✓ Correct
C. Amoeba
D. Spirogyra
Solution: Yeast reproduces rapidly and produces carbon dioxide that makes the dough rise, which is the basis of making bread, pastries and cakes.
Q7 — Useful microorganisms · medium · theory
Antibiotics such as penicillin and streptomycin are obtained from which organisms?
A. Viruses and protozoa
B. Bacteria and fungi ✓ Correct
C. Algae and viruses
D. Only green plants
Solution: Antibiotics are made from microorganisms, namely bacteria and fungi.
Q8 — Useful microorganisms · medium · theory
Which of the following is an antibiotic?
A. Sodium benzoate
B. Sodium metabisulphite
C. Streptomycin ✓ Correct
D. Lactobacillus
Solution: Streptomycin is an antibiotic, along with penicillin, tetracycline and erythromycin; sodium benzoate and metabisulphite are preservatives.
Q9 — Useful microorganisms · medium · theory
The polio drops given to children are an example of a/an:
A. Antibiotic
B. Vaccine ✓ Correct
C. Preservative
D. Antibody
Solution: Polio drops given under the Pulse Polio Programme are a vaccine that protects children from polio.
Q10 — Useful microorganisms · medium · theory
Who discovered the process of fermentation?
A. Alexander Fleming
B. Edward Jenner
C. Louis Pasteur ✓ Correct
D. Robert Koch
Solution: Louis Pasteur discovered fermentation in 1857.
Q11 — Useful microorganisms · medium · theory
Microorganisms clean the environment by decomposing organic waste such as vegetable peels into:
A. Plastic
B. Manure ✓ Correct
C. Antibiotics
D. Alcohol
Solution: Microbes decompose organic waste into simple, harmless, usable substances like manure, whose nutrients are reused by plants.
Q12 — Useful microorganisms · medium · theory
On which of these materials can microorganisms NOT act to decompose?
A. Vegetable peels
B. Dead plants
C. Plastic ✓ Correct
D. Animal faeces
Solution: Microbes cannot act on polythene, glass or plastic, though they can decompose organic wastes.
Q13 — Useful microorganisms · medium · theory
Apart from setting curd, bacteria are also used in making which of these foods?
A. Cheese ✓ Correct
B. Bread
C. Wine
D. Vinegar
Solution: Bacteria help make cheese and pickles, whereas bread, wine and vinegar are all produced using yeast.
Q14 — Useful microorganisms · hard · theory
Ravi has a common cold and takes an antibiotic, but it does not cure him. What is the best reason for this?
A. The common cold is caused by a virus, and antibiotics do not work against viruses ✓ Correct
B. The dose of antibiotic he took was too small
C. Antibiotics only work against protozoa
D. The common cold is caused by a fungus that resists antibiotics
Solution: Antibiotics are not effective against cold and flu because these are caused by viruses.
Q15 — Useful microorganisms · hard · theory
A doctor tells a patient to finish the complete course of antibiotics and not stop as soon as he feels better. Why is completing the course important?
A. It makes the medicine taste better each day
B. Stopping early can let surviving microbes make the drug less effective later, so the full course must be taken ✓ Correct
C. It helps the body produce more carbon dioxide
D. It turns the antibiotic into a vaccine
Solution: Wrong or incomplete use of antibiotics lets microbes survive and makes the drug less effective in the future, so the full course must be completed on a doctor's advice.
Q16 — Useful microorganisms · hard · theory
Both antibiotics and vaccines protect us from microbial diseases, but they act differently. How does a vaccine work?
A. It directly kills the disease-causing microbes like an antibiotic does
B. It supplies extra nutrients to fight the disease
C. It introduces dead or weakened microbes so the body makes antibodies that stay and give future protection ✓ Correct
D. It adds preservatives that stop microbes from growing in the body
Solution: A vaccine works by introducing dead or weakened microbes, prompting the body to make antibodies that remain and protect against future infection.
Q17 — Useful microorganisms · hard · theory
Which of the following statements about useful microorganisms is correct?
A. Lactobacillus is used to make bread dough rise
B. Yeast converts milk into curd
C. Yeast produces carbon dioxide that makes dough rise ✓ Correct
D. Penicillin is used to preserve pickles
Solution: Yeast produces carbon dioxide during respiration and this gas makes the dough rise; the other statements wrongly swap the roles of these microbes.
Q18 — Useful microorganisms · hard · theory
A farmer's soil becomes more fertile because certain bacteria live in it. How do these bacteria increase the soil's fertility?
A. By fixing nitrogen from the atmosphere into compounds that plants can use ✓ Correct
B. By producing carbon dioxide in the soil
C. By making antibiotics in the soil
D. By decomposing plastic present in the soil
Solution: Some bacteria are biological nitrogen fixers that fix atmospheric nitrogen into compounds usable by plants, which raises soil fertility.